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Full text of "Rand McNally Biology encyclopedia"

RAND M9NALLY 





Plants • Animals • Genetics • Behavior 



RAND M9N ALLY 



Biology 

Encyclopedia 




WTHDRAWN 



Ito longer the property of the 
Boston Public Library. 
Safe of this material benefits the Library 



RAN DMQNALLY& COMPANY 
Chicago • New York • San Francisco 





Contents 



LIFE ON EARTH 

The Living Planet 8 

The Building Blocks of Life 10 

All Kinds of Cells 12 

Animal Life 14 

Plant Life 20 

Fungi 24 

Bacteria 26 

Viruses 28 

ANIMAL BIOLOGY 

The Body Framework 30 

Muscles and Movement 32 

Blood - a Transport System 34 

The Body Pump 36 

Your Lymph System 37 

Food, Teeth and Diet 38 

Food Pathways 40 

Getting Rid of Wastes 4 1 



Energy from Food 42 

The Breath of Life 44 

A Communications Network 46 

The Control Center 48 

Chemical Messengers 49 

Seeing the World 50 

Sound and Hearing 52 

Skin, Fur and Feathers 54 

New Generations 56 

New Human Life 58 

How a Baby Develops 60 

How Long do they Live? 61 

PLANT BIOLOGY 

Looking Inside Plants 62 

Pipelines in Plants 64 

How Plants Breathe 65 

Making Food With Light 66 
Pollen Packs 

- Cones and Flowers 68 

Pollen on the Move 70 

Pollen Messengers 72 




AUTHORS 
Edward Ashpole 
Susan Jones 
David Lambert 



EDITOR 
Barbara Taylor 

COVER 
Denise Gardner 



Illll 




Making Seeds 
Spreading Seeds 
How Plants Grow 
New Plants from Old 
Algae, Mosses and Ferns 



SURVIVAL IN NATURE 
Finding Food 
Staying Alive 
Living Together 
Partners and Rivals 
Animal Homes and Young 
Friends and Relatives 
The Changing Seasons 
Amazing Journeys 
Desert Survival 
Life at the Top 
On the Grasslands 
In the Forests 
A Watery Home 
Protecting Nature 



EVOLUTION AND GENETICS 
Evolution - the History 
of an Idea 

Evidence for Evolution 
Fossils - the Key to the Past 
The Fossil Record and 
Catastrophes 
Mendel and the 
Laws of Heredity 
Life's Data Bank 
Making Proteins 
to Control Life 
The Origin of Life 
Is There Life on 
Other Planets? 
The Biotechnology 
Revolution 



118 
120 



122 



124 




The Living Planet 



Top: Slender loris 
Middle: Corn cockle 
Bottom: Leaf-cutter ants 



From space our planet looks as if it is covered by 
a thin, bluish film. This is called the biosphere 
and it is what makes the earth different from all 
the other planets in our solar system. The 
biosphere includes all the places where life exists 
and it is much tougher than it looks. It was 
formed by life and it protects life. The soil in 
which plants grow, the oxygen we breathe and 
the protective layer of ozone (which shields all 
life on earth from deadly radiation from the sun) 
have all been produced by living things. 

Within the biosphere, the chemical ingred- 
ients of life are used over and over again. They 
are taken out of the air or water by living things, 
built into living matter and returned to the 
atmosphere again when the bodies of plants and 
animals decay. They may also be locked up for 
some time in rocks or substances such as coal or 
oil. These substances may be released to the 
atmosphere again by natural chemical reactions 
or by people burning coal or oil. 



Chemical elements such as carbon, oxygen, 
hydrogen and nitrogen have been recycled 
through the biosphere since the dawn of life 
more than 3.5 billion years ago. Some of the 
chemical elements in your body might have been 
part of a dinosaur or a fish millions of years ago. 
Without the bacteria and fungi that break down 
dead plants and animals, all the ingredients of 
life would remain locked up in dead creatures 
and the life cycles would come to a halt. 

The Water Cycle 

Water is vital to life. It is needed for all life 
processes and the hydrogen in water is one of 
the basic ingredients plants use to make their 
own food. The amount of water in the biosphere 
remains roughly the same because the water that 
escapes into the atmosphere from oceans, lakes 
and rivers falls back again as rain or snow. The 
whole cycle is powered by the sun, which 
provides the heat that makes water evaporate. 



8 



THE CARBON AND OXYGEN CYCLES 

atmosphere. Carbon and oxygen also return to the atmosphere 
These two cycles are linked together. Plants take in carbon when the bodies of plants and animals are broken down by 
dioxide from the air to make new plant material and release bacteria and fungi and the chemical processes of decay. Some 
oxygen in the process. This is called photosynthesis (see pages dead plants become compressed into a rock called coal. When 
66-67). Animals take in the carbon when they eat the plants. Both people burn coal they use up oxygen and release carbon dioxide, 
plants and animals take in oxygen to help them release energy Some carbon and oxygen from dead creatures and from the 
from food. This is called respiration (see pages 42-43). Carbon atmosphere becomes locked up in other rocks. This is released by 
dioxide is produced as a waste product and released to the chemical decay. 

Animal Soil respiration 

respiration 



i Hot springs 

Plant respiration ■ ^ Volcanoes release 




The Carbon Cycle 

Carbon is the basis of all life on earth. It is 
recycled about once every 300 years. The main 
cycle is from carbon dioxide in the air to living 
matter and back to carbon dioxide again. This 
happens on land and in the sea. A large amount 
of carbon has become part of rocks and 
substances such as coal or oil. This carbon has 
taken much longer to return to the atmosphere 
than the carbon in living things. It is only 
returned when we burn these substances. 

The Oxygen Cycle 

Oxygen is recycled through the atmosphere 
about once every 2,000 years. Most of the 
oxygen in the atmosphere today comes from 
plants. They produce oxygen during the process 
they use to make their food from hydrogen and 
carbon dioxide (see pages 66-67). Advanced 
forms of life could not evolve on earth until 
simple plants had put enough oxygen into the 
atmosphere. A billion years ago only about one 
percent of the atmosphere was oxygen com- 
pared with about 20 percent today. 



The Nitrogen Cycle 

Although nitrogen is about 80 percent of the 
atmosphere, it cannot be used by most living 
things until it has been combined with hydrogen 
or oxygen. This job is carried out by bacteria. 
Animals take in chemicals that contain nitrogen 
when they eat the plants. The nitrogen is 
returned to the soil or the atmosphere when the 
bodies of plants and animals decay. 



Industrial processes 
convert nitrogen 



Nitrogen converted 
in atmosphere by 
lightning 



41k 



Bacteria in i 
take in nitrogen 
and convert it to Ammonia 1 
a form the plant 

can use. Nitrate 



•Bacteria 
process 
nitrogen 



9 



The Building Blocks of Life 



What do you have in common with a fish, a tree, 
a mushroom or even a virus? At first sight, many 
forms of life on earth seem to have nothing in 
common except the fact that they are alive. 
There is such an enormous diversity of living 
things and they have adapted in a great variety 
of ways to their surroundings. Yet underneath 
all these differences lies a remarkable similarity. 

All life on earth is made from the same 
chemical building blocks, which are called 
organic molecules. These are made mainly of 
carbon, nitrogen, hydrogen and oxygen. The 
organic molecule (DNA) is even used by all 
living things to code the instructions that control 
the way they live, grow and die. Could life be 
different on other planets? Perhaps it could. But 
there are good reasons for thinking that the 
basic chemistry of life may be the same. 



In 1665 an English scientist named Robert 
Hooke discovered what living matter is made of. 
He looked at a piece of cork under a microscope 
and saw hundreds of little boxes. He called these 
boxes cells. All living things are made of one or 
more cells (apart from viruses - see pages 
28-29). The human body is made up of about 
one hundred trillion cells. 

A cell is the smallest unit capable of life. 
Substances constantly stream into a cell. Chemi- 
cal processes take place. Energy is released from 
food to fuel all of life's activities. The instruc- 
tions for making more cells are copied. Yet 
although all these chemical processes are going 
on, a balance is maintained between input and 
output so that overall conditions stay the same. 
This is life. As the great French biologist Jacque 
Monod said "Life is a process." 



AN ANIMAL CELL 

A cutaway drawing of a typical animal cell (about 10,000 times 
larger than life) to show the structures found in most animal cells. 

Endoplasmic reticulum 

The name means "an ' 
inside formed network". 
Along its folded 
membranes are tiny 
structures called 
ribosomes, where 
proteins are made (see 
page 119). 



Cell membrane 
f\ thin wall that holds the 
cell together and con- 
trols what passes in and/ 
out of the cell. 




Golgi body 
A stack of 
saucer-shaped 
channels that 
store the 
proteins made 
on the 
ribosomes. 

Cenlrosomes 
They contain a 
pair of centrioles 
which play an 
important part in 
cell division (see 
pages 116-117). 

10 



Mitochondria 

The power stations of the cell. They 
contain enzymes that trigger the 
conversion of nutrients into energy 
(see page 42). There may be as many 
as 800 in one cell. 



Lysosomes 

The self-destruct mech- 
anism of a cell. Lyso- 
somes contain enzymes 
that break down dam- 
aged parts of the cell or 
any other structures that 
have to be destroyed - 
when the cell dies for 
example. 



Nucleolus 
These small dense 
structures are pro- 
bably concerned 
with the produc- 
tion of ribosomes. 



Nucleus 

The cell's brain. It con- 
tains all the coded infor- 
mation needed to build 
up a new animal on 
thread-like structures 
called chromosomes. The 
coded information also 
controls all the processes 
that go on inside a cell 
(see pages 115-118). A 
cell cannot usually sur- 
vive without a nucleus. 



Animal and Plant Cells 

Although each cell is usually specialized to carry 
out a particular job, all cells have certain 
features in common. You can see these features 
in the diagrams below. If you compare the 
animal cell with the plant cell you will see that 
they are made of more or less the same parts. 
But there are some differences. 

Both plant and animal cells are enclosed in a 
protective membrane but plant cells also have a 
wall made of cellulose. A mature plant cell 
usually has a thin lining of cytoplasm and a large 
central cavity, called a vacuole, which is filled 
with cell sap. Animal cells consist almost 
entirely of cytoplasm and if they have any 
vacuoles, they are usually temporary and small. 
Many plant cells also have structures called 
chloroplasts (see page 66), which they use to 
trap the sun's energy to make their own food. 
Animal cells never have chloroplasts as they do 
not make their own food. 



A PLANT CELL 

A cutaway drawing of a typical plant cell. The structures which 
are the same as those in an animal cell are described on page 1 . 



Chromoplasts 

These contain various pig- 
ments. Green ones, called 
chloroplasts, contain the 
chlorophyll plants use to cap- 
ture the sun's energy and make 
food from air and water (see 
page 66-67). 



Mitochondria 




Above: This was the first drawing of cells ever made. The cells 
come from the corky layer near the surface of a piece of tree bark. 
They were observed by the English inventor and scientist, Robert 
Hooke, under a microscope which he made himself. Hooke 
published his drawing in Micrographia in 1665. 



Cell wall 

This is made of many layers of 
cellulose fibers. Cellulose is a rubbery 
material that helps to make plant 
cells tough. It is never found in 
animal cells. 



Endoplasmic 
reticulum 
with ribosot 
dotted along 
membranes. 



Starch grains 
These hold the 
plant's reserve 
supplies of food. 




uole 

filled with sap, 
stores salts and 
sugars. It also helps 
ell keep its shape 
pressing the proto- 
(all the cell con- 
against the cell 



Plasmodesmata 

The outside part of the cell that links 
one cell to another. 





This microscopic one-celled organism is called Paramecium. It 
looks like a tiny speck to the naked eye. It is not the same as the 
single cells of many-celled animals because it is independent. It 
does not need other cells to survive. The surface of Paramecium is 
covered with tiny hair-like cilia, which beat together to move the 
animal through the water. The cilia also sweep tiny organisms, 
such as bacteria, into the gullet where they enter the cell to be 
digested. The star-shaped structures control water balance. 



All Kinds of 
Cells 

Cells come in a tremendous variety of shapes 
and sizes. For example, our red blood cells are 
only .0003 of an inch across while some of our 
nerve cells are 3 feet (a meter) long. Plants and 
animals that are made of many cells contain 
several different kinds. The human body con- 
tains many different kinds of cells, each with a 
particular job to do. The cells share the work 
rather like people share the work in a factory or 
office. Together they keep the factory or office 
working efficiently, and in the same way the cells 
work together to keep the body of a plant or 
animal working efficiently. This improves its 
chances of survival. 




12 



Phloem Xylem 



How Cells Work Together 

In a plant or animal made of many cells, large 
numbers of cells of the same type are packed 
and held together to form tissues. For example, 
the human brain is made of nerve tissues 
composed of ten thousand million nerve cells 
connected to each other. In a complex plant or 
animal, different tissues are joined together to 
form organs, such as the heart or liver in 
humans, and leaves or flowers in plants. Some 
organs have just one job to do. The only job the 
heart does is to pump blood around the body. 
Other organs, such as the liver, have many tasks 
to carry out. 

Organs and Systems 

Some organs may work together to carry out 
particular tasks. These organs belong to a 
system. For example, in the human body, organs 
such as the intestine, the liver, pancreas and gall 
bladder make up the digestive system. Its task is 
to break down (digest) food so the nutrients can 
be absorbed into the body to provide us with 
energy. 

Tissues, organs and systems appear very 
different in animals and plants. Yet the cells that 
they are made of contain the same basic 
structures - although no animal cell has chloro- 
plasts for photosynthesis and no plant has nerve 
cells. 



Above: A section through a pine needle as it would look under a 
microscope. You can see some of the different tissues which make 
up this plant organ. In the center of the leaf (at the top of the 
page) are the pipelines which carry food and water around the 
plant. The food pipes are called phloem and the water pipes are 
called xylem (see page 64). The two small circles near the edge of 
the leaf are resin ducts. On the very edge of the leaf are some 
openings called stomata (see page 65) which control the flow of air 
and water vapor in and out of the leaf. 



Below: This diagram shows some of the main organs in the human 
body. An organ is a complex structure which has a particular task 
to carry out. It is made of a combination of tissues. Most tissues 
contain two or three types of cells mixed together. 




Lung 
Heart 



r Liver 

■ Stomach 

Intestine 



13 



Animal Life 



More than a million kinds of animals have been 
discovered on the earth so far. They range in 
size from microscopic one-celled animals to the 
gigantic blue whale, which grows up to nearly 
100 feet (30 meters) long. The blue whale is the 
largest animal ever to inhabit the earth. 

Unlike green plants, animals cannot make 
their own food. They have to take it in 
ready-made by eating plants or other animals. 
Because of their need to find food, they have 
developed ways of moving around and respond- 
ing to their surroundings. 

Like plants, some microscopic living things 
can make their own food, but they also take in 
ready-made food, like animals. They are neither 
animals nor plants and are sometimes grouped 
in a separate kingdom, called protista. 

With or Without Backbones 

Animals can be divided into two categories: 
those with backbones (vertebrates) and those 



without backbones (invertebrates). The verte- 
brates include the largest and more intelligent 
animals, such as dolphins, elephants and human 
beings. The invertebrates are mostly very small 
creatures such as worms, snails and insects. But 
they outnumber the vertebrates by millions. 

Animals Without Backbones 

The simplest animals are one-celled organisms 
called protozoa - the name means "first ani- 
mals." There are thousands of different pro- 
tozoa living almost everywhere, even inside or 
outside other animals. Protozoa are not the 
same as the cells that make up many-celled 
animals because they can survive on their own. 
They have no nerves or senses but they react to 
their surroundings as other animals do. 
Sponges are groups of single cells that live as 

Tube sponges from the Caribbean. Sponges draw water in and 
out through their many pores and filter out any food it contains. 



one animal. But if a sponge is broken up, the 
cells can come together again and new sponges 
will grow. Other many-celled animals could not 
survive being split up in this way. 
The simplest many-celled animals are the sea 
anemones, jellyfish, corals and their relatives. 
They all live in water, mostly in the sea, and 
their ancestors can be traced back more than 500 
million years. Biologists call them coelenterates - 
the name' means "hollow gut." They are rather 
like a sack into which they gather food with their 
tentacles. 

A coelenterate is made of many different 
cells, which work together to keep the animal 
alive. It has body cells, reproductive cells, cells 
for stinging, cells that contract like muscles and 
a network of nerve cells. The coelenterates are 
the simplest animals to have nerve cells. 

The simplest kind of worms are the flatworms. 
There are several thousand different kinds and 
they live in fresh water, seawater and inside 
other animals. A flatworm has a gut, which is a 
simple food sack with only one opening. 

Roundworms are an advance on flatworms. 
Most roundworms live freely in water or in soil, 

Right: Most adult coelenterates are attached to the seabed, like 
this living coral colony. Corals produce a hard, chalky skeleton 
for support and protection. This remains when the animal dies 
and new corals grow on top. After many generations, coral reefs 
or islands form. 

Below: Earthworms push their way through soil, eating it as they 
go. The soil passes through the worm and any nutrients are taken 
out. Waste products are pushed out at the other end to form 
wormcasts. Earthworm tunnels help to mix up the soil layers and 
provide spaces for air to collect and water to drain away. 




Tentacles Mouth 




The inside of a sea anem- 
one. The tentacles wave in 
the water to keep food 
particles flowing past. If a 
small animal touches the 
tentacles, stinging threads 
shoot out and paralyze it. 
(A jellyfish stings in this 
way.) The animal is then 
taken into the body cavity 
and digested in the parti- 
tions. The disk is used to 
grip on to rocks. 



where they break down organic matter and 
release nutrients for plants to use. But some 
roundworms are serious parasites of plants and 
other animals. A roundworm has a mouth and a 
gut with an opening at the tail end (an anus) for 
getting rid of waste products. 

The most advanced worms are the annelids or 
segmented worms, such as the earthworm. Their 
bodies are made up of round sections called 
segments and all their internal structures, such 
as blood vessels and nerve fibers, are repeated in 
each segment. 




15 




Above: A crustacean called a swimming crab. It uses its large 
pincers for picking up food. Crabs range in size from the tiny pea 
crabs (with shells only a quarter of an inch across) to the giant 
spider crab of Japan, which can measure 12 feet across its 
outstretched legs. 




Above: An insect called a large tortoiseshell butterfly. Butterflies 
usually have feelers (antennae) with knobs on the end. Their 
relatives the moths usually have thread-like or feathery antennae. 
The wings of butterflies and moths are covered with colored or 
shiny scales. If you touch the wings the scales may rub off. 

Below: A bird-eating spider, which is an arachnid. It can kill a 
small bird with its poisonous bite. Most spiders eat insects and 
only a few kinds (such as the black widow spider) are poisonous to 
humans. All spiders produce silk, which they spin from organs at 
the end of the abdomen called spinnerets. Most spiders use the 
silk as a safety line to help them move around. Some use the silk to 
make webs, which they use to trap insects. 



Animals With Outside Skeletons 

Animals with outside skeletons (exoskeletons) 
and many joints are the largest group of animals 
on earth. Biologists call them arthropods - 
arthros means "joint" and podos means "foot." 
The arthropods owe their great success to their 
small size and strong exoskeleton, which is made 
of chitin (animal plastic). Most biologists think 
all the arthropods evolved from worm-like 
creatures a few hundred million years ago. Some 
of the arthropods alive today, such as centipedes 
and millipedes, look similar to worms. 

Most of the arthropods living in the sea, such 
as crabs and prawns, are crustaceans. A few 
crustaceans, such as the woodlouse, live on land, 
but they need a damp home. The most success- 
ful arthropods are the insects - more than three 
quarters of all animal species are insects. Many 
insects, such as bees, are useful to people but 
others, such as moths and termites, are pests. 
Some insects, such as mosquitoes, can carry 
disease. 

The spiders and their relatives are called 
arachnids - arachnes means "spider." You can 
always tell an arachnid from an insect. Arach- 
nids have 8 legs and a body in 2 parts. Insects 
have 6 legs and a body in 3 parts. Most insects 
can fly and have feelers called antennae. Arach- 
nids never have antennae. Most spiders are 
harmless and are useful to us because they eat 
insect pests. But there are a few dangerous 
spiders in hot climates and some of the spiders' 
relatives are harmful. Mites and ticks suck blood 
and can cause disease. 



From Snails to Squids 

Mussels, oysters, whelks, snails, octopuses, and 
squid all belong to the second largest group of 
invertebrates, the mollusks. Some are only a 
tenth of an inch across while the giant squid, the 
largest of all invertebrates, can grow up to 66 
feet (20 meters) long. Some mollusks (such as 
the snail) live in one shell, others (such as 
oysters and mussels) have two shells held 
together with a powerful "hinge." 

The most advanced mollusks are the cephalo- 
pods - the name means "head and mouth." The 
cephalopods include the most intelligent of all 
invertebrates, the squid and octopuses. The 
cuttlefish is also a member of this group. You 
may know its skeleton, an internal shell shaped 
like a leaf, which is given to parakeets as a 
source of vitamins. 

Animals Apart 

The starfish, sea urchins and their relatives are 
unlike any other animals. Biologists call them 
echinoderms - the name means "spiky skin." 
There is evidence that they are related to the 
ancestors of the vertebrates, which lived in the 
seas some 500 million years ago.y: 

Echinoderms have a completely different 
shape and structure from other animals. Their 
bodies are divided into five identical parts and 
they have a skeleton of plates inside their 
bodies. Echinoderms have no head or brain but 
they do have a system of nerves running through 
their bodies. They have no blood, so food and 
oxygen are carried to all parts of their bodies by 
water. 



Below: This echinoderm 
starfish called a sunstar. 




Above: Most starfish, 
such as this cushion 
star, have five arms. 
They can grow new 
limbs if they lose 
them. 




Above: The edible common whelk, which is a mollusk. It crawls 
around on its muscular foot and has a well developed head with 
eyes and tentacles. 




Above: The common octopus can change color to match different 
backgrounds. Octopuses have eyes that are remarkably like ours, 
although they are quite unrelated to humans. 

Below: A yellow-fringed sea slug (really a snail without a shell) 
feeding off sea anemones. It breathes through gill-like structures 
on its back. 




Animals With Backbones 

Fish, the first animals with true backbones, 
evolved in the seas about 450 million years ago. 
There are three main groups of fish today - the 
bony fish (such as cod and herring), the 
cartilaginous fish (such as sharks) and fish with 
lungs. The lungfish can breathe in air and 
underwater. This helps them survive when the 
water they live in dries up from time to time. 

The amphibians were the first vertebrates to 
walk on land. Even now, they still need to go 
back to the water to breed and have to keep 
their skin moist. Amphibians, such as frogs, are 
cold blooded, which means their bodies are at 
the same temperature as their surroundings. In 
cold weather, they have to hibernate to survive. 

The reptiles were the first true land verte- 
brates because they do not have to go back to 
the water to breed. They evolved from the 
amphibians about 300 million years ago and 
some of them, the dinosaurs, were amazingly 
successful. Today's reptiles are an insignificant 
bunch compared to those of dinosaur days. They 
include lizards, snakes, tortoises, turtles and the 
largest living reptile, the crocodile. Reptiles are 
also cold blooded and must hibernate in cold 
conditions. Many fresh-water turtles spend win- 
ter in the warm mud at the bottom of a pond. 



The skeletons of four vertebrates. Each is designed for . 
different way of moving. 




ird (flying) 




Above: A gray shark, a fish with a skeleton made of cartilage and 
a skin covered in sharp spines. 

Bottom right: The arrow poison frog secretes a powerful poison 
from its skin. 

Bottom left: A lizard called a green iguana. Like all reptiles, it has 
a scaly skin, so it does not lose water easily. 




Above: A common dormouse (a placental mammal) at its summer 
nest in a bramble bush. 

Bottom left: The platypus is an unusual Australian mammal. It 
uses its sensitive bill to hunt for small animals in rivers. 
Bottom right: A newly-born kangaroo (only an inch and a half 
long) feeding from a teat in its mother's pouch. 




Birds evolved from reptiles about 150 million 
years ago. You can still see the reptile in birds in 
their scaly legs. By developing feathers birds 
have been able to conquer the air. No other 
animal can fly half way around the world and 
back. But to fly like a bird uses a lot of energy. 
Birds have large hearts to keep their flying 
muscles well supplied with food and oxygen. 
Their body temperature is higher than ours 
because they burn up food faster to release 
energy more quickly. We would die from fever if 
our temperature reached that of birds. 

Like the birds, mammals also evolved from 
the reptiles. They did not become a major group 
of animals on earth until the dinosaurs died out 
about 65 million years ago. 

There are three main kinds of mammal. 
Placental mammals (such as humans) where the 
young stay inside their mother's womb until they 
are fully formed, marsupials (such as kangaroos) 
which bear their young at an early stage of 
development, and monotr ernes which are un- 
usual mammals that lay eggs. The only living 
monotremes are the platypus and spiny anteater 
of Australasia. All mammals are warm blooded 
(which means their body temperature remains 
constant) and they have fur or hair. Mammals 
also have better developed brains and are more 
intelligent than other animals. 





Plant Life 



Algae called diatoms are an important part of the plankton in the 
oceans. Their silica shells are often shaped into the most amazing 
patterns. 



Green plants connect life on earth to its energy 
source, the sun. They capture energy from 
sunlight using chlorophyll, which is the sub- 
stance that gives most plants their green color. 
They use the energy to make food in a complex 
chemical process called photosynthesis - the 
word means "making things with light. " 

Animals cannot make their own food so they 
have to eat plants, or eat animals that have eaten 
plants. (We only eat steak because cows eat 
grass.) The process of photosynthesis releases 
oxygen into the atmosphere. So plants not only 
feed us, but they enable us to breathe as well. 

Algae 

The simplest plants are the algae. They have no 
roots, stems or leaves and most of them are 
made of just one cell. Plants similar to today's 
single-celled algae evolved in water more than 
two and a half billion years ago. 

Algae in the oceans carry out most of the 
photosynthesis on earth. This is not really 
surprising because oceans cover nearly 70 per- 
cent of the earth's surface. The algae float in the 
surface waters and form part of what biologists 
call plankton. Plankton is the basis of all 
nutrition in the sea. It even feeds some of the 
great whales. 



Algae exist in water or damp places almost 
everywhere. A single-celled alga called Chlamy- 
domonas sometimes turns the surface of ponds 
and streams green. Seaweeds, a common feature 
of seashores all over the world, are also algae. 
They are made of many cells. Some of them can 
grow up to 50 feet (15 meters) long. Did you 
realize that the green powdery film you often see 
on trees and old wooden fences is caused by an 
alga called Pleurococcusl This is one of the few 
algae that can survive away from water. 



Many seaweeds contain red or 
brown pigments to help them 
capture the particular 
wavelengths of light energy from 
the sun that reach them 
underwater. 




Bladder wrack 



20 



Moving on to Land 

Plants began to colonize the land about 500 
million years ago. But they had problems to 
overcome. Water plants are supported by the 
water all around them. The gases they need for 
breathing and photosynthesis are dissolved in 
the water in a form easily taken in. Their seeds 
are carried away by the flow of the water. 

But land plants have to hold themselves 
upright against the earth's gravity. They have to 
take in water and gases from the air and soil and 
transport food and water around inside their 
bodies. Their seeds have to be carried away by 
the wind or animals. And they must avoid being 
dried out by the sun and wind. 

The simplest land plants are the liverworts, 
which have this name because they are supposed 
to be shaped like a liver. They are very common 
in damp places. 





4 



Above: Liverworts have no leaves, stems or roots. They consist of 
a plant body fixed to the ground by thread-like cells, called 
rhizoids. 

Below: The leaves of sphagnum mosses have large empty spaces, 
which hold large amounts of water. 




Right: A few ferns, such as this one from 
Tahiti, grow to the size of trees. Their 
"trunks" are the remains of old dead 
fronds (leaves). 




Above: The European hard fern carries its spores on special 
fronds that stand upright in the center of the plant. 



Mosses have stems and leaves but no actual 
roots. Most mosses are only about an inch high. 
Like liverworts, they are fixed to the ground by 
hair-like structures called rhizoids. Their rhi- 
zoids can break up rock or stone surfaces and 
help soil to form. Other plants may then be able 
to grow in this soil. 

Ferns have leaves called fronds, which usually 
grow from underground stems called rhizomes. 
Roots anchor the plant in the soil. Ferns were 
the dominant life form on earth between 400 and 
300 million years ago, when the first animals 
were appearing on the land. Much of the coal 
mined today is the preserved remains of the 
great fern forests of that time. Ferns and their 
relatives were the first plants to develop a system 
of tubes for transporting food and water around 
inside their bodies. These tubes are like our 
arteries and veins. 



21 



Mature female cones of 
the sitka spruce, which is 
widely planted for its 
timber. 



Left: A giant redwood tree. One of these trees is the largest living 
thing on earth. The trees can grow more than 300 feet high and 
some have lived for four thousand years. The bark of the trees is 
thick and spongy. This helps them to withstand the heat of forest 
fires. 



Plants With Cones 

A remarkable group of plants called the gymno- 
sperms evolved after the ferns. These were the 
first plants to produce real seeds - the word 
gymnosperm means "naked seed." Most of the 
gymnosperms are conifers, which were the main 
plant group on earth 250 million years ago. 

Conifers are still very common today and 
include trees such as the pines and redwoods. 
They have needle-like leaves (which they keep 
year-round) and their seeds grow in protective 
cones. The scales of the cones open in spring so 
that reproductive cells (pollen) from the male 
cones can fertilize the reproductive cells in the 
female cones. The scales close again while the 
seeds develop but open again to release the ripe 
seeds. These are carried away by the wind or by 
animals that eat them. 

Flowering Plants 

The flowering plants evolved some 150 million 
years ago and are the most successful group of 
plants on the earth today. They have outstripped 



Black mulberry 




Horse chestnut 



Above left: Birds and other animals eat fruits but the seeds inside 
pass through their bodies unharmed and may grow into new 
plants. 

Above right: This beautiful bee orchid (Orchis apifera) attracts 
male bees by looking and smelling like a female bee. The bees may 
pick up some of the orchid's pollen and carry it to another flower 
(see page 73). 



all other plants in their spectacular variety and, 
above all, they have perfected the production of 
seeds. Biologists call them angiosperms , which 
means "container seeds." 

The special characteristics of flowering plants, 
their flowers, fruits and nuts, are ways of 
improving the process of reproduction. Many 
flowers have bright colors, scents or shapes to 
attract the right animals, especially insects, to 
carry their pollen from flower to flower. Putting 
the seeds inside fruits and nuts works in a similar 
way to persuade birds and mammals to visit 
them and carry the seeds away. The evolution of 
animals and flowering plants has been closely 
linked, with each helping the other to survive. 
The search for fruit in the trees may have 
influenced the evolution of the ape-like, distant 
ancestors of man. 

Some flowering plants rely on the wind to 
carry their pollen and seeds. Their flowers, such 
as tree catkins or grass flowers, are not colorful 
or scented and their seeds are light and may 
have special structures to help them float on the 
wind. 



Flowering plants have evolved a variety of 
roots, stems and leaves, and some have taken on 
special jobs. Large taproots (such as carrots), 
swollen stems (such as potatoes) and fleshy 
leaves (such as onions) all store food for the 
plants as well as carrying out their other tasks. 
For instance, some of the leaves of roses have 
developed into thorns to protect the plant. Many 
leaves of flowering plants are good to eat. None 
of the grazing animals could have evolved 
without the grasses they feed on. 



Phloem tubes 



Xylem tubes 




lowering plants have perfected a 
system of tubes for carrying food 
and water around the plant. You 
can see them in this cutaway view 
of a tree trunk. 



23 



Fungi 



The fungi are an ancient and separate kind of 
life. They are not plants because they have no 
chlorophyll and cannot make their own food. 
They are also built differently from plants. Fungi 
have no stems, leaves or roots and no cell walls 
of cellulose. The nearest relatives of the fungi 
are the bacteria. The fungi probably evolved 
from this simple lifeform a few hundred million 
years ago. 

Fungi get their food directly from living or 
dead plants and animals. They cause many 
serious diseases in plants (such as mildews on 
food crops) and a few diseases in animals. The 
most common disease we get from fungi is 



athlete's foot, which causes the skin between our 
toes to crack. 

Millions of people owe their lives to the most 
common kind of fungus, the molds. In 1928 
Alexander Fleming discovered by chance that a 
mold produced a substance that killed certain 
bacteria. The name of the mold was Penicillium 
notatum and the substance it produced was 
called penicillin. It was the first antibiotic 
prepared for medical use. Since that time, 
biologists have found that other fungi produce 
their own kind of antibiotics and doctors now 
have a large range of antibiotics to treat 
different bacterial diseases. 



The poisonous fly agaric toadstool usually grows on birch tree 
roots. It has a special give-and-take relationship with the tree. 
(This is a form of symbiosis - see page 88.) The fly agaric obtains 
sugars from the tree and in return provides the tree with nutrients 
it cannot easily get from the soil. Both partners benefit from living 
together in this w£ 



The fruiting bodies of some 
fungi are very unusual 
shapes. The underside of 
this ear fungus has folds 
and ridges, which look like 
the inside of an ear. The 
spores are produced on this 
surface. This fungus grows 
on the branches of decidu- 
ous trees, especially elder. 




24 



There are about 90,000 species of fungi 
ranging from microscopic single cells, such as 
yeasts, to large mushrooms and toadstools. 
Yeasts are very important to people because 
they break down sugars, making alcohol and 
carbon dioxide gas in the process. They are used 
to make wine and beer and the carbon dioxide 
they produce makes bread rise. 

The above-ground parts of mushrooms and 
toadstools are the structures of reproduction. 
They carry out the same job as the microscopic 
pinheads of the molds - they hold billions of 
spores, which are blown away by the wind. The 
body of the mushroom or toadstool is a mass of 
fine threads under the ground. 



Lichens 

Some fungi have overcome the problem of not 
being able to make their own food in an unusual 
way. They have evolved a close relationship with 
algae, which live within the fungus. 

The fungus provides the algae with protection 
and water. The algae use sunlight to make food 
for themselves and the fungus. This group of 
fungi are called lichens. The shape of the lichen 
depends on the shape of the fungus. Some 
lichens look like flat patches of color while 
others are leafy and stubbly. A close rela- 
tionship between two different life-forms in 
which both partners benefit is called symbiosis 
(it means "living together") - see pages 88-89. 



Fruiting body 
forming 



Capv 



Annulus 




Myceli' 



Above: The body of a fungus is called a mycelium. It is made up of 
a mass of fine threads called hyphae. The hyphae produce 
enzymes, which break down the food into a form the fungus can 
absorb. Sometimes the hyphae weave together to form mush- 
rooms and toadstools above ground. These structures carry the 
spores of the fungus and often appear in autumn. 



Right: Us nea subfloridana, 
a branching lichen, which 
forms tangled clumps on 
tree trunks and branches. 
Spores are produced in 
white patches on the stems. 
Young lichen of this species 
are usually upright. 



Xanthoria parietina, a leafy 
lichen, which is common on 
rocks and old walls, es- 
pecially near the sea. Spores 
are formed in the darker 
patches in the center of the 
lichen. 




Below: A water droplet splashing on to this earthstar, Geastrum Below: Map lichens growing on a rock. Individual plants have 
triplex, has released a cloud of billions of spores. black edges, which join together like the lines drawn on maps. 




25 



Bacteria 



Bacteria are everywhere - in the air we breathe, 
on and inside our bodies, in soil, fresh water and 
the sea. They can even live on iron, sulfur and 
other non-living materials. It is estimated that all 
the bacteria in the world would weigh 20 times 
more than the weight of all other living things 
put together. 

Bacteria are single cells and the smallest form 
of life on earth. A microscope with high 
magnification is needed to study individual 
bacteria. A drop of water may contain thou- 
sands of bacteria, while there may be a million in 
a drop of sour milk. 

Bacteria have a distinct structure and are 
unlike other single cells. They have a rigid outer 
shell (cell wall) made of chitin, which is covered 
by slime and mucus. (Chitin is the very strong 
material used by insects and other arthropods 
for their exoskeletons.) Inside the chitin shell is 
an inner cell membrane enclosing the usual 
structures found in cells. This includes the 
special chemicals that carry the genetic infor- 
mation of the bacteria. But this genetic material 
is not enclosed in a nucleus as it is in plant and 
animal cells. 




26 




Round bacteria Rod-shaped Bacteria with fine threads 
linked in chains. bacteria to help them move. 




AFTER 6 HOURS AFTER 9 HOURS 

Above: Bacteria can reproduce very rapidly. In good conditions, 
they can divide every 30 minutes. At this rate, a single bacterium 
would leave 280,000,000,000,000 descendants at the end of 24 
hours. 

Below left: A microscopic view of chains of the bacterium 
Ruminococcus jiavefaciens in the grass cells in the stomach of a 
cow. The bacteria break down the cellulose of the grass cells into 
sugar. Some of the sugar is used by the bacteria but the rest is 
absorbed by the cow. 

Below right: Rod-shaped bacteria Lactobacillus bulgaricus as they 
appear under a high-power microscope. 




Above: Louis Pasteur at his clinic. He was one of the first 
scientists to prove that some diseases were caused by particular 
microbes. This idea is called the germ theory of disease and in the 
1860s and 1870s it seemed a revolutionary idea. Before this theory 
was accepted, all sorts of strange ideas (such as supernatural 
influences and the character of the sick person) had been used to 
explain diseases. 



Right: During the 20th century, people have controlled many 
harmful bacteria with drugs and antibiotics. 



Bacteria and Disease 

The first person to see bacteria was a Dutchman, 
Anton van Leeuwenhoek. In 1683 he saw what 
he described as "animacules" or "little eels" in a 
drop of rainwater under a simple microscope. 
However, almost a hundred years passed before 
Leeuwenhoek's work led to some practical 
ideas. In 1762 an Austrian doctor, Anton von 
Plenciz, suggested that bacteria cause diseases 
and that different diseases are caused by 
different bacteria. But Plenciz was not shown to 
be correct until the middle of the last century. 

Robert Koch of Germany (1843-1910) was 
able to link certain bacteria to the diseases they 
cause. He found the bacillus (a rod shaped 
bacterium) that causes tuberculosis, which was a 
major killer before the age of antibiotics. 

Louis Pasteur of France (1822-1895) showed 
that decay and infection were caused by micro- 
scopic living things, including bacteria. Pasteur's 




research led to vaccines against bacteria. He 
showed that vaccines of dead bacteria could be 
used to stimulate the body's natural defenses 
against bacteria. He was also asked to solve the 
problem of wine being soured by bacteria. He 
found that bacteria could be killed by heating 
the wine to a temperature below the boiling 
point. This work led to the widespread use of the 
process known as pasteurization, which protects 
people from harmful bacteria in milk and other 
foods. 

Fortunately most bacteria are harmless. Only 
a few dangerous ones cause diseases. And many 
bacteria live with us and are essential for our 
health. We could not live without the vast 
quantities of bacteria within our system which 
help us to digest our food. Bacteria also feed on 
dead plants and animals and play a vital role in 
breaking down their bodies and making the 
chemicals in them available for new life. 



27 




Above: A potato plant with leaf roll virus. This makes the leaves 
so dry that they rattle if the plant is shaken. 




Above: A virus causes the white streaks in these pink tulips. It 
reduces the amount of pigments in the petals.' 




Viruses 

At the end of the last century, biologists 
discovered that fluids from sick animals could be 
used to cause diseases in healthy animals, 
although they contained no bacteria or any other 
cells. The mysterious agents of disease turned 
out to be viruses. They could not be seen until 
the development of powerful electron micro- 
scopes. 

Viruses are built differently from all living 
things. They are the only life-forms that are not 
made of one or more cells. They consist mainly 
of nucleic acids (genetic materials) with a 
coating of large protein molecules. The nucleic 
acid molecules contain the building plans for a 
new virus. In this respect, viruses are exactly like 
all living things. Every organism has its own 
plans coded in nucleic acid molecules that are 
copied and handed on from generation to 
generation. 

But, unlike living things, viruses cannot make 
copies of their plans and produce new viruses on 
their own. They have to invade a living cell and 
use this cell's "machinery" in order to reproduce 
themselves. 

Yet viruses are particular. They do not invade 
any cell. Each kind of virus only invades certain 
types of cells in particular animals or plants. For 
example, cold viruses invade the cells of the 
nose or throat in human beings but will not 
affect those cells in your cat or dog. Even 
bacteria have their own viruses. 

Left: This is what a virus called a bacteriophage looks like under 
the electron microscope. Bacteriophages attack bacteria. They 
attach themselves to the bacteria with their tail section. Then they 
inject their nucleic acids (which are stored in the head section) 
into the bacteria. 



A VIRUS INVASION 




1. Virus injects its 2. Nucleic acids 3. Cell bursts open 
nucleic acids into a are copied and and new viruses 

cell. new viruses made, set free. 



28 



Viruses and Disease 

Viruses cause many diseases in plants and 
animals. They include influenza, mumps, 
measles, polio, rabies, foot-and-mouth disease 
in cattle and myxomatosis in rabbits. The big 
problem with viruses is that they cannot be 
knocked out by drugs as bacteria can. But if a 
plant or animal suffers from a viral infection, its 
body develops a natural defense against that 
disease and this protects it against further 
attacks. 

An injection of dead or subdued viruses (a 
vaccination) stimulates these natural defense 
systems in the same way. So vaccinations can 
protect people against serious attacks by viruses. 
This is the only way to fight these diseases unless 
medical scientists learn how to block the way 
viruses work inside cells and prevent them 
taking over cells to produce more viruses. But 
this is difficult because it has to be done without 
affecting the workings of the cell under attack. 

Not all viruses cause disease and even those 
that do sometimes lie dormant and have no 
effect at all. Almost all tissues of animals and 
plants contain viruses and many seem to cause 
no trouble. There is still much scientists do not 
understand about viruses and they are a major 
subject for modern research. 

Below left: Polio viruses seen through a very strong microscope. 
Polio attacks the brain and spinal cord. 

Below right: An Iranian boy being vaccinated against tuberculo- 
sis. Edward Jenner, an English doctor, began the use of vaccine 
injections to protect people against viral diseases. Mass vaccina- 
tion campaigns have stopped many people from catching some of 
the worst infectious diseases. 




Above: The most common viral disease, the common cold, is 
caused by too many varieties of the virus for medical scientists to 
prepare a vaccine. When people catch colds, it usually takes 
about three days for the body's natural defenses to overcome the 
invading viruses. 




29 




The Body Framework 



Animals have to support and protect their soft 
tissues and organs. Some soft-bodied animals, 
such as jellyfish, are supported by the water they 
float in. Others, such as worms, keep their shape 
because of the pressure of the fluids inside them. 
But most animals support their bodies with a 
framework called a skeleton. 

All vertebrates have skeletons inside their 
bodies. This "inside skeleton' 1 can be made of 
bone or cartilage. Some fish, such as sharks, 
have skeletons of cartilage throughout their 
lives. The skeletons of all vertebrate embryos 
(including those of humans) are made mostly of 
cartilage to begin with. This is gradually re- 
placed by bone during growth and development 
but the process is not completed in humans until 
the age of about 25. The skeleton in some parts 
of our bodies (such as the end of our nose and 
our earlobes) remains as cartilage throughout 
our life. 



What are Bones Made of? 

Bones are made of two different types of 
material - hard minerals, containing calcium and 
phosphorus, and flexible living protein, called 
collagen. This makes bones strong but at the 
same time bendable enough not to snap easily. 
Cracks in the hard bone minerals cannot travel 
easily through the flexible collagen. As people 
get older, the rubbery collagen is replaced by 
hard minerals so the bones become more brittle 
and break easily. 

Blood vessels and nerves are contained in tiny 
canals that run through bones. The blood carries 
food, oxygen and waste products to and from 
living cells in the bone. At the center of many 
bones (such as your leg bones) is a hollow with 
soft tissue, called marrow, inside. Red marrow, 
which is found only in mammals, produces blood 
cells - it produces red blood cells at the rate of 
about 2.5 million cells every second. 





Left: A giant bone from a dinosaur called Camarasaurus being 
uncovered at the Dinosaur National Monument, Utah. 
Below: Your skeleton is a framework which supports your body 
and protects the delicate organs inside. You have over 200 bones 
in your skeleton. Your largest bone is the thigh bone and your 
smallest bones are in the middle ear. 



Skull (Cranium) 



Shoulder blade_ 
(Scapula) 



Backbone 
(Vertebrae) 



""Collar bone (Clavicle) 

_ Breast bone 
(Sternum) 
— Ribs 

Upper arm bone 
(Humerus) 



da 



Thigh bone 
(Femur) 



Hip bone 
(Pelvis) 



Knee cap 
\ (Patella) 



Foot bones 
(Metatarsals) 



Toe bones 
(Phalanges) 



Shin bone 
(Tibia) 



Ankle bones 
(Tarsals) 




Above: X-ray of a bone from a pelican, showing the many air 
passages. Hollow bones help to cut down a bird's weight so it 
needs less energy to fly. 

Right: X-ray of human shoulder joint. 
Bottom right: X-ray of human pelvis. 

Both these X-rays reveal ball and socket joints, which allow 
movement in many directions. 



LOOKING AT JOINTS 

The place where two bones meet is called a joint. Some 
joints, such as those between the bones in your skull, have 
grown together so tightly that they are fixed. But most 
joints are movable. In a movable joint, muscles and tough 
straps called ligaments hold the bones together. The ends of 
the bones are coated with a smooth protein called cartilage. 
The joint is surrounded by a thin, slippery membrane. This 
produces a special fluid, which lubricates the joint. Without 
cartilage and fluid, your bones would grind against each 
other when you moved. If you force a joint beyond the 
limits of the ligaments, they may tear. This is a sprain. If 
the bones slip out of place, they are said to be dislocated. 





Above: The empty exoskeleton of a dragonfly nymph. 



Outside Skeletons 

The skeletons that some animals (such as 
insects) wear outside their bodies are made 
mainly of chitin. This material is tough, hard and 
waterproof and provides good protection. 
Muscles attached inside the skeleton allow the 
animals to move. But there is one major 
disadvantage to an outside skeleton, which is 
that it cannot stretch as the animal grows. It has 
to be shed from time to time and replaced by a 
larger skeleton. While this is happening the 
animal is not protected from attack. 




Muscles 

and Movement 

Most animals move from place to place to find 
food, water, a mate or to escape from danger. 
Even one-celled animals respond to changes in 
their environment by making simple movements 
backward and forward. They are able to do this 
because parts of the cell have the power to 
contract (shorten). More complex animals, such 
as fish, birds and mammals, act in the same way 
but have highly developed muscles which help 
them to carry out more precise movements, such 
as running, swimming and flying. Did you 
realize that almost all the meat we eat is muscle? 

Animals with outside skeletons, such as 
insects, have their muscles attached to the inside 
of their skeletons. But they work in a similar 
way to your muscles. Animals with inside 
skeletons have muscles attached to the outside 
of the bones that make up their skeleton. You 
have over 600 muscles, many of which are 
arranged in layers over your skeleton. 

Some of your muscles (such as those in your 
arms and legs) work when you want them to. 
They are called voluntary muscles. But other 
muscles (such as those in your stomach) work 
automatically, without your being aware of 
them. They are called involuntary muscles. A 
ring of involuntary muscle (called a sphincter) 
opens or closes the entrance or exit to a hollow 
organ, such as the stomach. A third type of 
muscle, called cardiac muscle, is what a heart is 





Above: A honeybee in flight. Insect flight muscles are attached to 
the thorax (the middle part of the body) rather than to the wings 
themselves. By contracting and relaxing these muscles, they can 
move their wings rapidly. 




Above: Powerful muscles in the back legs of this edible frog thrust 
it into the air. The smaller front legs help the frog to steer when it 
is swimming and absorb the shock of landing after a jump on 
land. 

Below: The cheetah's long legs and flexible spine make it the 
fastest animal over short distances. It has a top speed of over 68 
miles per hour (110 kilometers per hour) and can reach about 43 
miles per hour (70 kilometers per hour) in just two seconds. But 
cheetahs cannot keep up such high speeds for long because their 
body temperature rises dangerously high and would damage the 
brain. They use up so much energy when they chase animals that 
they may have to rest for up to 15 minutes after a fast sprint. 




Above: The fibers in a voluntary muscle are made up of strands 
called myofibrils. And each myofibril is made up of two kinds of 
tiny interlocking filaments. When these filaments overlap, the 
muscle fibers become shorter and the muscle contracts. The 
filaments are held in place by chemical links. When they move 
apart, the muscle relaxes. Each muscle fiber can either contract 
completely or not at all. But not all the fibers in a muscle have to 
contract at once, so the pulling power of a muscle can vary. 

Below: A striated (striped) muscle from a mammal under a 
microscope. The stripes are caused by the two different proteins, 
actin and myosin, which make up the filaments in the myofibrils. 




. ^w^^^. Biceps 

-^contracted 




made of. It works automatically and will 
continue to make the heart beat even after it has 
been removed. 

Inside a Muscle 

A muscle is made of bundles of long, thin cells 
called muscle fibers. The bundles are held 
together by and enclosed within connective 
tissues. You can see how the fibers of voluntary 
muscle are arranged in the diagram to the left. It 
is called striped muscle because of its appearance 
under the microscope. Involuntary muscle has 
no stripes, so it is called smooth muscle. Cardiac 
muscle is in between the two. It has some stripes 
but fewer of them and the fibers are branched. 

How Does a Muscle Work? 

Voluntary muscles contract (get shorter) when 
they receive electrical impulses from nerves and 
relax (get longer) when they do not. This means 
they can only pull, they cannot push. So most 
muscles work in pairs, one pulling one way, the 
other pulling the opposite way. They are called 
antagonistic muscles, which means they work 
against each other. 

Muscles convert food and oxygen to pulling 
power. But this produces harmful waste prod- 
ucts, such as lactic acid. If these waste products 
build up, it stops nerve impulses reaching the 
muscles and they "feel tired." The drug curare 
has the same effect. South American indians 
used to cover their arrow-heads with it for 
hunting - some still do. If the prey is not killed 
by the arrow, it will be paralyzed by the curare. 



33 




blood cell 



Above: Your blood is made of red and white blood cells and 
platelets floating in a liquid called plasma. One drop of blood 
contains about 5,000,000 red cells and 5,000 white cells. The body 
of an average-sized adult contains about 8-10 pints (5-6 liters) of 
blood. 

Right: Section through an artery (top) and a vein. Arteries have 
thick elastic walls because blood pulses through them at high 
pressure. 




Blood — a Transport System 



Blood is far more than a red liquid that carries 
oxygen. It is a transport system for food, waste 
products and hormones (see page 49). It carries 
a chemical repair kit in case of injury, and 
defenses to protect animals against infections 
and poisons. In mammals and birds it helps to 
keep the body at a constant temperature. 

What is Your Blood Made of? 

Your blood is made of a mixture of cells floating 
in a straw-colored liquid called plasma. Plasma 
is 90 percent water and contains dissolved 
nutrients, vitamins, minerals, proteins and 
wastes. Red blood cells carry oxygen from the 
lungs to all parts of the body. They can do this 
because they contain a complex protein mole- 
cule called hemoglobin. This takes in oxygen 
where there is a high concentration, such as in 
the lungs. It then becomes oxyhemoglobin, 
which is bright red. Where the concentration of 
oxygen is low (where cells are using up oxygen in 
their life processes) oxyhemoglobin releases its 
oxygen to become hemoglobin again. 

You have an incredible number of red blood 
cells. A teaspoon of blood contains about 25 



million cells. They live for about four months 
and are finally broken up in the liver or spleen. 
New blood cells have to be made in your bone 
marrow because mature red cells have no 
nucleus and cannot reproduce themselves. 
About one percent of your red blood cells are 
replaced every day. 

The other inhabitants of the blood are the 
white cells. There is only one white cell for every 
500 to 1000 red cells. They are made in the bone 
marrow, lymph nodes and spleen. One kind of 
white cell, called a granulocyte, helps to fight 
infections by eating harmful bacteria. It also 
removes wastes and dead cells. Another kind of 
white cell, called a lymphocyte, detects anything 
alien in the blood or lymph (see page 37) and 
causes antibodies to be produced to destroy or 
neutralize the invaders. This is what happens 
when an organ is transplanted from another 
person's body. Powerful drugs have to be taken 
to stop the antibodies destroying the organ. 

Blood platelets are tiny fragments of large cells 
in your bone marrow. Their purpose is to clump 
together to help form blood clots, which stop 
wounds bleeding and seal them against bacteria. 



34 



Pipelines for Blood 

Blood travels around your body in tubes called 
blood vessels. It is pumped by the heart to all 
parts of the body along thousands of miles of 
blood vessels. Red blood cells travel around the 
body in less than a minute. All vessels carrying 
blood from the heart are called arteries. All 
vessels carrying blood to the heart are called 
veins. Arteries and veins are linked by a network 
of microscopic vessels called capillaries, which 
pass between the cells of all the tissues in your 
body. 

Arteries are tough, muscular vessels. They 
have to be thick-walled to withstand the pres- 
sure of blood coming straight from the heart. In 
veins, the blood flows slower and at a lower 
pressure than in arteries, so the walls of veins 
are thinner and have valves to stop the blood 
flowing backward. Blood in veins has given up 
its oxygen and lost its red color. You can see this 
if you look at the veins in your wrist. 

Capillaries are very narrow vessels with thin 
walls only one cell thick. They are only just wide 
enough for red blood cells to pass along, so 
blood flows very slowly through them. This 
(together with the thin walls) helps substances 
such as food and oxygen to pass into the tissue 
fluid, and waste products to pass back into the 
capillaries. The tissue fluid carries the sub- 
stances into the individual cells. In this way, the 
capillaries deliver to and collect from all parts of 
the body. 



Right: This diagram shows the main blood vessels in the human 
body. Arteries (shown in red) carry food and oxygen from the 
heart to the organs and limbs. Veins (shown in blue) carry the 
blood back to the heart. Blood circulates continuously around the 
body, driven by the pumping of the heart. 



Subch 
Arteries 
To Shoulders 
And Arms 



Vena Cavae 
(the main veins) 




STOPPING LEAKS 

1. When blood vessels are damaged, 
tiny platelets gather around the wound. 
They give off an enzyme that helps sticky 
threads of fibrin to develop. 



2. The threads form a web that traps 
red blood cells and platelets. This thick- 
ens to form a scab, which stops bleeding 
and keeps bacteria out. 



3. New skin grows beneath the scab. 
People suffering from hemophilia do not 
have one of the substances needed for 
blood clotting, and could die from even 
small cuts. 




Righi 

Ventricle | nfenor 

Vena Cava 



The Body Pump 



The human heart is a very strong and specialized 
muscle about the size of a person's fist. The job 
of the heart is to pump enough blood at a high 
enough pressure so that it travels throughout the 
body and returns to the heart. The whole circuit 
takes about 45 seconds.y 

The heart has four chambers - the two at the 
top are called atria (singular atrium) and the two 
at the bottom are called ventricles. The atrium 
and ventricle on the right side pump blood to the 
lungs to get rid of waste carbon dioxide and pick 
up fresh oxygen. The atrium and ventricle on the 
left side pump oxygen-rich blood to all parts of 
the body. As the heart pumps, four valves open 
and close to prevent the blood from flowing 
backward. 

How Does the Heart Work? 

Blood returning from its journey around the 
body flows into the vena cava, which leads into 
the right atrium. Then it passes through a valve 
into the right ventricle. The right ventricle then 
contracts, pumping the blood through a second 
valve into the pulmonary artery, which leads to 



BLOOD OUT TO 
^ LOWER I 



the lungs. Here carbon dioxide is released from 
the blood and oxygen taken up. 

The blood flows back to the left atrium of the 
heart through the pulmonary veins. From the 
left atrium, it passes through a third valve into 
the left ventricle. This then contracts and 
oxygen-rich blood is pumped out at high 
pressure through a fourth valve into the aorta - 
the main artery of the body. Both atria contract 
at the same time, as do both ventricles. The 
complete cycle usually takes less than one 
second. 

The heart beat is a characteristic of heart 
muscle, with nerves helping to maintain a steady 
beat at the right pace. The heart of an average 
adult beats about 70 times a minute. Athletes 
develop more powerful hearts through years of 
exercise. They can pump more blood with every 
beat so their heart beat is usually slower. Many 
top athletes have heart rates below 50. The heart 
rate of birds is much higher than that of human 
beings because birds need a lot of energy to fly. 
A sparrow has a heart rate of about 500 beats a 
minute. 



HEARTS AND CIRCULATION 



THE LYMPH SYSTEM 



AH vertebrates and some invertebrates have a transport 
system of blood vessels containing blood, which is moved 
around the body either by muscles contracting in the vessel 
walls or by the pumping action of a heart. A heart is really 
an expanded blood vessel with a thick muscular wall. In 
fish, the heart has two chambers, in many reptiles and 
amphibians it has three chambers and in mammals and 
birds it has four chambers. In a four-chambered heart, 
oxygen-rich blood can be separated from oxygen-poor 
blood for more efficient use. 



Diagram of 

insect 

circulation 




Above: Insect blood is contained in an open space called a 
sinus, rather than in blood vessels. It is kept moving by the 
heart, which sucks in blood through little holes in its sides 
and pumps it out through a hole at the front. Insect blood is 
a colorless fluid, which carries food and waste substances, 
but not oxygen (see page 43). 




Above: A fish heart has only one atrium and one ventricle. 
It pumps oxygen-poor blood from the body to the gills, 
where it takes up oxygen. Oxygen-rich blood then flows to 
various parts of the body where oxygen is needed, before 
eventually returning to the heart. 
Lungs 

Diagram of 
reptile 
circulation 




Above: In most reptiles, the heart has two atria but the 
ventricle is only partly divided. When the ventricle pumps 
blood, some goes to the lungs and the rest goes to all the 
other cells in the body. Oxygen-poor blood seems to go 
mainly to the lungs and oxygen-rich blood goes mainly to 
the tissues. 




Left: The main lymph vessels 
(shown in red) and lymph 
nodes (shown in blue) in a 
human. 



Below: Lymph nodes range in 
size from that of a pinhead to 
that of a broad bean. Many 
nodes are grouped in the floor 
and roof of the mouth (tonsils 
and adenoids) and in the neck, 
armpits and groin. When the 
nodes are fighting an infection, 
they become enlarged and ten- 
der. Then you may have a sore 
throat or infected tonsils. 



Artery 



Section through a 
lymph node 



Lymph nodule 




Your Lymph System 

Along with your blood system, there is another 
transport system in the body, the lymph net- 
work. Inside the lymph vessels is a colorless fluid 
called lymph, which is similar to blood without 
the red cells. It comes from excess fluids that 
leak out of your capillaries into the spaces 
between your cells. Lymph fluid flows eventually 
into your bloodstream when the lymph vessels 
join major veins which lead directly to the heart. 

The lymph system has no pump. Exercise and 
pressure move lymph forward and valves stop 
any backflow. Lymph vessels also collect fats 
directly from the small intestine (the ileum) and 
transport them to your cells. At various points 
along the lymph vessels are lymph nodes. They 
filter out and destroy bacteria in the lymph and 
make white blood cells called lymphocytes. 

Lymphocytes produce antibodies, which seek 
out alien bodies, such as viruses or bacteria, and 
make them harmless. They detect invaders by 
their various proteins, which are different from 
the proteins of the body itself. You are able to 
produce up to a million different antibodies. 



37 



Food, Teeth and Diet 

Food does two main things for an animal. It 
provides energy for the work the cells do, and 
raw materials for building, repairing and con- 
trolling body tissues. All animals feed on either 
plants or other animals or a mixture of both - as 
you do. They are equipped with the teeth (or 
mouthparts) and digestive systems to cope with 
their particular diet. 

A few animals get all the nutrients they need 
from only one type of food. Koalas eat nothing 
bu{/the leaves of certain eucalyptus trees, a diet 
that would poison other animals. Animals with 
specialized diets have specialized digestive sys- 
tems. Even cows, sheep and other grazing 
animals need specialized digestive systems to get 
enough nourishment from the large amounts of 
cellulose (a tough material) in grass and other 
plants. They have a large cecum and appendix 
which contain vast numbers of bacteria that 
digest cellulose for them. (A cecum is a 
blindly-ending piece of gut at the junction of the 
small and large intestines. The appendix is an 
extension of this.) 

Teeth are a good indication of what an animal 
eats. Plant-eaters, especially grazing animals, 
have flat teeth with ridges on the surface for 
grinding up their rough diet. Meat-eaters have 
long, sharp teeth to kill and tear the flesh of their 
prey. Human beings have very unspecialized 
teeth, which would indicate to a biologist from 
another planet that they eat a wide variety of 
foods. But we need a balanced diet to keep us 
healthy. 




The teeth on the radula ( a tongue-like structure) of a snail under 
a high-power microscope. The radula is used to rasp tissue from 
plants. 




(molars) incisors 

Above: The skull of a sheep, showing the teeth of a typical 
plant-eater. Sheep have no canine teeth and there is a toothless 
gap between their front teeth (the incisors) and their back teeth 
(the molars). Sheep have loose joints between the lower jaw and 
the skull so they can move their lower jaw from side to side when 
they chew. This helps the grinding action of the cheek teeth. 



Rectum Small intestine Rumen 




Above: The digestive system of a cow. The intestine can be as long 
as 12 feet (40 meters). This slows down digestion so that tough 
plant material can be broken down before it reaches the end of the 
gut. A cow's stomach has four chambers, the first of which is 
called the rumen. The cow eats grass and swallows it into the 
rumen without chewing it first. After a while, it coughs up 
(regurgitates) the food and chews it in the mouth. This helps 
digestion and is called chewing the cud. 




Above: The digestive system of a honeybee. The gut is divided into 
three parts, the fore-gut, the mid-gut and the hind-gut. Food is 
pushed through the gut by peristalsis (see page 40). 



38 




Carnassial teeth 



Molars 



Above: Meat-eaters have dagger-like canines to kill their prey and 
tear its flesh. Their sharp cheek teeth slide past each other to slice 
off flesh and crack bones. The back teeth {molars) have more 
flattened surfaces and meet together to crush the food into smaller 
particles. The jaws are very powerful and the lower jaw only 
moves up and down. This helps to prevent the jaw from being 
dislocated. 



Oesophagus 




Above: The digestive system of a lion. Most digestion takes place 
in the small intestine, where enzymes complete the breakdown of 
food begun in the mouth and stomach. When digestion is 
completed, the finger-like villi that line the walls of the small 
intestine, pick up nutrients. The nutrients pass through the thin 
walls of the villi into the blood and are carried around the body to 
all the cells that need energy. 



Ename 
Pulp 



, Dentine 
Blood vessels 




Left: The structure of a 
human molar tooth. The 
outer layer of enamel is 
the hardest substance in 
the body. The molars are 
used for grinding food. 
An adult usually has 
twelve of these teeth at 
the back of the mouth. 



Different Kinds of Food 

Scientists classify foods as proteins, carbohy- 
drates, fats, vitamins, minerals and roughage. 
Water is also a major part of food - you are 
about 60 percent water. 

Proteins are essential for the growth and 
repair of animal tissues. They are formed from 
about twenty basic units called amino acids. 
These link together to form chains, which fold 
up in many ways to form a huge variety of 
protein molecules. The main sources of protein 
in your diet are meat, fish, eggs and dairy 
products. Beans and peas are also a g^od and 
cheap source of protein. 

Carbohydrates usually provide the body's 
main energy requirements. They include sugars 
and starch. 

Fats are essential to the life of every cell. They 
supply twice as much energy as other foods and 
some are used in the formation of cell mem- 
branes. Some fat may be used immediately and 
the rest is stored as body fat. The main sources 
of fat are milk, vegetable oil, eggs and meat fat. 

Tiny quantities of vitamins are needed to keep 
the chemical processes in an animal's body 
working efficiently. For example, you need 
vitamin D for strong bones and teeth and 
vitamin A to see in dim light. People have to 
take in their vitamins ready-made. We cannot 
make vitamin C in our bodies. We get it through 
eating fruits and vegetables. But cats, which do 
not get vitamin C in this way, can make their 
own. 

Minerals carry out vital roles in an animal's 
body. For example, you need iron for red blood 
cells, calcium, magnesium and phosphorus for 
bones and teeth and sodium and potassium for 
your nerves and muscles. 




Part of an X-ray of a human mouth taken by a dentist. The white 
patches are fillings in the molar teeth. You can see the pulp cavity 
in the middle of these teeth. 



39 



Food Pathways 



Before food can be used by your cells, it has to 
be broken down into a form the blood can carry. 
This process is called digestion. 

In the mouth, your teeth bite and chew the 
food into small pieces. Salivary glands under the 
tongue produce saliva, which helps to bind the 
food particles together and make the food easier 
to swallow. Saliva contains the first digestive 
enzyme, which starts to break down starch. 
(Enzymes speed up chemical reactions in the 
body but are not changed themselves in the 
reaction. So they can be used over and over 
again. Each enzyme works only in a particular 
reaction.) As you swallow, a flap of skin called 
the epiglottis blocks off the windpipe so the food 
goes down the right hole. It reaches the stomach 
in about six seconds. 

The stomach mixes up the food and adds 
digestive juices, which include the enzyme 
pepsin. This starts to digest proteins. A normal 
meal may remain in the stomach for two to four 
hours before it is pushed into the duodenum, the 
first part of the small intestine. 



In the duodenum, food is mixed with bile from 
the liver, which is stored in the gall bladder. Bile 
breaks up fats so that enzymes can work on 
them. Juices from the pancreas are also poured 
into the duodenum. These contain a range of 
enzymes, such as trypsin and amylase, which 
help to complete the breakdown of all types of 
food. By the time the food gets to the ileum, 
most of it has been digested. It passes through 
the walls of the ileum into the blood. (Fats go 
into lymph vessels and enter the blood later.) 

Your blood carries the digested food to your 
liver for more processing before taking it to all 
the body's tissues. Undigested food (mainly 
fiber) and water pass into the large intestine. 
Although there are no enzymes in the large 
intestine, the bacteria that live there break down 
some of the remaining matter as they feed. Most 
of the water passes into your blood through the 
walls of the first part of the large intestine - the 
colon. More solid waste is stored further along 
in the rectum and pushed out of the body as 
feces. 




40 



Getting Rid of Wastes 

Animal cells and tissues constantly produce 
chemical wastes that will poison them if they are 
not removed. This removal process is called 
excretion and the main organs of excretion are 
the kidneys. (The lungs, liver and sweat glands 
in the skin also help the body to remove waste 
substances.) 

Your kidneys are at the back of your 
abdomen, roughly on a level with your waist. 
They work by filtering substances out of the 
blood and then taking back the substances the 
body needs, such as water and salts. Blood flows 
to the kidneys through renal arteries, and filtered 
blood returns to the body via the renal veins, 
which join the vena cava. 

The fluid and waste substances filtered out by 
the kidneys, which is called urine, passes down 
two tubes called ureters into your bladder. The 
bladder is a muscular bag with a tight band of 
muscle, called a sphincter, holding it shut. When 
you relax the sphincter, the muscles in the wall 
of your bladder contract and the urine flows into 
a tube called a urethra and out of your body. 



Right: One of the millions of filtering units in a human kidney. 
The pressure of blood in the glomerulus forces the fluid part of the 
blood through the walls of the capillaries into the space inside the 
capsule. The fluid that goes through contains urea, glucose, water 
and salt. (Urea is a waste substance produced during the 
breakdown of amino acids - the units proteins are made of. ) The 
fluid goes into the tubule, where all the glucose and amino acids, 
and almost all the water and salts, are taken back into the 
capillaries wrapped around the tubule. The rest of the fluid, 
which consists mainly of water, salts and urea, passes into the 
ureter as urine. 

Below: A microscopic view of a glomerulus , part of a filtering unit 
in a mammal's kidney. 





Fatty capsule 
around kidney. 



Urethra 

Above: The human excretory system. The kidney to the right of 
the picture has been cross-sectioned to reveal the darker outer 
part (the cortex) and the lighter inner part (the medulla). The 
cortex contains a network of fine blood vessels that branch from 
the renal artery. Each one of these ends as a little bunch of 
capillaries called the glomerulus, where blood is filtered. 

Unfiltered blood I 
from renal artery J 



Bowman's capsule 




Filtered blood 
carried away by 
renal vein 



Urine passes 
to ureter 



41 




Energy, carbon dioxide and 
water are produced as a result 
of the chemical reactions in the 
mitochondrion. 



Respiration - the "burning" of food to release energy - takes 
place inside cells. Many of the chemical reactions that are 
involved take place inside structures called mitochondria, which 
are the cell's power stations. A special chemical called ADP picks 
up energy from the mitochondria to become ATP. In this form, it 
acts as a power supply for the rest of the cell. As its energy is used 
up, it becomes ADP again and goes back to the mitochondria for 
recharging. 



Energy from Food 



All animals "burn" food inside their cells to 
provide the energy they need to keep their 
bodies working. This process is called respiration 
and involves combining food with oxygen in a 
series of chemical reactions, which are con- 
trolled by enzymes. Energy is released from the 
food, while carbon dioxide and water are 
produced as by-products. 

Animals obtain oxygen in a variety of ways. 
Microscopic single-celled animals have no prob- 
lem because they are so small. They have a large 
surface area compared to the volume of their 
bodies and all the oxygen they need passes 
through their cell membrane. Some many-celled 
animals get their oxygen in a similar way. 
Tadpoles do so in their early stages of develop- 
ment and an adult frog absorbs enough oxygen 
through its skin to keep it alive at the bottom of 
a pond during a winter's hibernation. 

Insects have a system of tubes called tracheae 
(singular trachea) to allow oxygen to reach all 
their body tissues. Air enters an insect's body 
through holes called spiracles, which are opened 
or closed by valves. Each spiracle leads to a 
tracheal tube, which branches and becomes 
thinner and thinner until it ends up as a network 
of tiny tubes called tracheoles. These contain the 
membranes through which oxygen passes into an 
insect's cells. 



The ends of the tracheoles are filled with fluid 
that keeps the membranes moist. This helps 
oxygen to pass through because gases must 
dissolve in fluid before they can enter cells. Most 
insects do not push air through the tracheae. But 
large and active insects, such as the locust, use 
muscles in their abdomen to pump air hrough. 
This allows them to release a lot of energy from 
their food. 

Large animals cannot get their oxygen like 
insects because it would take too long for the 
oxygen to reach all their tissues. Instead they 
transport oxygen in their blood and have special 
organs such as gills and lungs to absorb oxygen. 

Gills are the breathing organs of most animals 
that live underwater. Gills have a large surface 
area and a lot of blood vessels beneath thin 
protective membranes. Oxygen passes through 
the membranes and the walls of the blood 
vessels into the bloodstream. Carbon dioxide 
passes out in the opposite direction. 

Most fish have gills to take in oxygen from the 
water. They take in water through their mouths 
and force it over their gills. (Not all animals with 
gills do this. The lobster bales water past its 
gills.) A few fish also have lungs - they are called 
lungfish. Their lungs are a backup system, 
which helps them to get oxygen when the rivers 
they live in dry up. 



Gill filaments 




Operculum Gill bar 



A fish uses its gills for breathing and needs to keep a continuous 
stream of water flowing over them. Some fish pump water over 
their gills. Bony fish do this by opening and closing the operculum 
(a muscular flap of skin that covers the gills) and opening and 
closing the mouth. Cartilagenous fish, such as the dogfish, have 
flaplike branchial valves instead of an operculum. These open and 
close to draw water over the gills in the same way. Fast-swimming 
fish swim with their mouths open, which forces water over the 
gills. 



HOW A DOGFISH BREATHES IN 

Valves move out 



Spiracle 




Floor of mouth 
drawn down 



HOW A DOGFISH BREATHES OUT 



Gill pouch 



Valves open 



Closed 
mouth 

Floor of mouth 
pushed up 




Below: These pond dwellers obtain the oxygen they need in a 
variety of ways. Some water snails come to the surface to fill their 
lungs. Backswimmers and water beetles also collect air from the 
surface but store it as bubbles under their wing cases. Drone fly 
larvae and water scorpions draw in air from the surface through 
long breathing tubes - just as people do when they use a snorkel. 
Mosquito larvae also have a breathing tube at the back end of 
their body. The end of the tube is open so air can get in. Look out 
for these larvae hanging from the surface of the water in ponds 
during the summer. The only truly underwater creature in this 
picture is the mayfly nymph, which has gills to take oxygen from 
the water. The gills look like three long tails. 



Above: Two diagrams to show how a dogfish draws water past its 
gills. To breathe in, it opens its mouth and pulls the floor of the 
mouth and pharynx down. This draws water into the mouth. The 
flaplike valves covering the gills move outward to draw water past 
the gills. To breathe out, the dogfish closes its mouth and pushes 
up the floor of the mouth and pharynx. The valves open and water 
is sucked out over the gills where oxygen is absorbed from the 
water and carbon dioxide is given out. 



Left: The feathery gills of this lugworm show up along the side of 
its body. The lugworm burrows in mud and sand on the seabed, 
where there is very little oxygen. The hemoglobin in its blood is 
able to pick up oxygen even when it is present in very small 



Tracheole Tracheal 
Muscle tube 

I I 



Right: A small part of the 
breathing tubes (tracheae) 
of an insect. Holes called 
spiracles lead into two main 
tracheae along each side of 
the body. Smaller tubes cal- 
led tracheoles, branch out 
from these to reach all the 
tissues of the body. Gases 
are exchanged at the end of 
each tracheole. 





The Breath of Life 

Oxygen enters your body in the air you breathe 
into your lungs. There it moves into the 
bloodstream and is carried to all your body cells 
where it is used in the chemical reactions that 
release energy from food. The waste gas 
produced in this process, carbon dioxide, moves 
from the blood into the air in your lungs and 
leaves the body as you breathe out. 

You usually breathe automatically at a rate of 
about 16 breaths a minute - try timing yourself. 
If you hold your breath, the amount of carbon 
dioxide in the blood builds up. This is detected 
by the brain and if the amount gets dangerously 
high, it sends out signals which make you 
breathe. This is one of the many feedback 
systems that work to keep your body running 
smoothly. 

Where are Your Lungs? 

Your lungs fill most of the chest cavity, which is 
an airtight box formed by the ribs, sternum, 
backbone and diaphragm. Each lung is sur- 
rounded by two thin sheets of tissue called the 
pleural membranes. The inner one covers the 
lungs and the outer one lines the inside of the 
chest cavity. Between the two is a narrow space 
containing a fluid. This makes the membranes 
slippery so they slide over each other smoothly 
as you breathe in and out. 




Right: This diagram shows 
the right lung in the human 
chest. The lungs fill most of 
the chest cavity and have 
branching tubes and mil- 
lions of air sacs inside them. 
This increases the area over 
which oxygen can be 
absorbed. 




Oxygen-poor blood 
(bluel 



Left: A group of alveoli 
covered with a network 
of blood capillaries. 
There are about 300 
million alveoli altogether 
in your lungs. 



From body 




Right: One alveolus, 
showing how gases are 
exchanged. 



Above: Each alveolus has a wall only one cell thick. Oxygen from 
the air passes into the blood vessels and carbon dioxide moves 
from the blood into the alveolus. 

Left: Lung tissue under the microscope, showing some of the 
alveoli (air sacs) with blood vessels around them. 



44 



How You Breathe 

Breathing is controlled by the movements of 
muscles in your chest, which suck air in and 
force it out. When you breathe in, your rib cage 
is pulled upward by your chest muscles. At the 
same time, the diaphragm is lowered. These two 
movements expand the space in your lungs, 
making the air pressure inside your body lower 
than it is outside. Air rushes in to fill the space. 
These actions happen in reverse when you 
breathe out. Most people have room for about 7 
to 9 pints (4 to 5 liters) of air in their lungs but 
they only exchange about a pint (half a liter) of 
air on each breath. 

Pathways for Air 

When the lungs are expanded, air is sucked 
through your nose or mouth and down the 
windpipe (trachea). The trachea branches into 
two tubes called bronchi (singular bronchus), 
one entering each lung. Within each lung, the 
bronchus splits into many branches like a tree. 
The branches are called bronchioles. 

Each bronchiole leads into a bunch of tiny 
sacs called alveoli (singular alveolus). There are 
about 350 million alveoli in a pair of lungs. They 
are surrounded by a network of blood capillaries 
and have very thin membranes (just one cell 
thick) so that oxygen, carbon dioxide and water 
can pass easily through them. 

The trachea and bronchi are reinforced with 
rings of cartilage. This prevents them from 
collapsing when you breathe out. They are also 
lined with goblet cells which produce a slippery 




BREATHING IN BREATHING OUT 




liquid called mucus. This helps to trap dust 
particles and germs that have escaped being 
caught in the nose passages. Tiny hairs called 
cilia gently waft the mucus away from your lungs 
towards your nose and throat so it can be 
swallowed or coughed and sneezed out. 

How Much Oxygen? 

The energy released when food is "burned" in 
our cells is measured in calories - a measure of 
the energy the food contains. The average 
person at rest uses 1.2 calories a minute and this 
consumes about 15 cubic inches (250 cubic 
centimeters) of oxygen. An active man will use 
up about 3,000 calories a day. A woman uses 
slightly less. A person may use thirty times more 
oxygen during exercise. 

How Birds Breathe 

Birds have a very efficient system of respiration 
to provide the extra energy they need for flight. 
They have special air sacs as well as lungs. When 
a bird breathes in, its blood gets oxygen once as 
air passes through the lungs into the air sacs. As 
in other animals, only some of the oxygen in this 
air passes into the blood. Then, as the bird 
breathes out, the air travels back through the 
lungs and is used again. So one breath provides 
two helpings of oxygen. The air in the air sacs 
also makes the bird lighter (which helps it to fly) 
and helps to cool its body. 

Bird blood cells carry a large amount of 
oxygen and very large arteries supply blood to 
the flight muscles. The hearts of birds beat faster 
to pump blood around the body as quickly as 
possible. Small, active birds may eat a third of 
their body weight each day to provide enough 
energy to meet their high energy needs. 



45 



A Communications 
Network 



All animals react to their surroundings and in 
most animals these reactions depend on electri- 
cal signals (nerve impulses) sent around the body 
by nerve cells. Nerve cells are usually linked 
together to form a communications network, 
which collects information and sends out instruc- 
tions to control the way an animal's body works. 

Invertebrates, such as hydra, have the sim- 
plest sort of nervous system. It is made up of a 
net of nerve cells, which reaches all over its 
body. More complex invertebrates, such as 
worms, have bunches of nerves called ganglia as 
well as a nerve net. The ganglia are like simple 
brains. Of all the invertebrates, the octopuses 
and squid have a nervous system and brain most 
similar to ours. They even have a cranium of 
cartilage to protect their brain, just as the 
human brain is protected by the bones of the 
skull. 

All vertebrates have complex nervous sys- 
tems. The brain and the spinal cord (inside the 
backbone) together are called the central ner- 
vous system. From the central nervous system, 
bundles of nerve cells branch out to all parts of 
the body. One of the most remarkable events in 
the history of life is the evolution of very large 
brains, especially in people. 

Nerves and How they Work 

The basic unit of all nervous systems is the nerve 
cell. A typical nerve cell has a cell body with 
short branches called dendrites all around it and 
a much longer branch, called an axon, extending 
from one side. Axons can be up to three feet (a 
meter) long - you have some that reach from 
your toes to your spinal cord. 

What people call a "nerve" is really a bundle 
of axons surrounded by a protective sheath of 
fatty material called myelin. This stops nerve 
impulses escaping and helps them to travel 
faster. The thickest myelin-covered nerves can 
send impulses at 450 feet (150 meters) per 
second. Uncovered nerves can manage a speed 
of only three feet (one meter) a second. Nerves 
are rather like the telephone wires between your 
phone and the telephone company switchboard. 




This is a simplified diagram of 
your nervous system, showing 
how nerves reach to all parts of 
the body. Each nerve is made up 
of a bundle of nerve fibers. Each 
fiber is part of a nerve cell. The 
brain and the spinal cord are 
called the central nervous system. 




Above: The cell body of a motor nerve cell from the spinal cord 

under a high-power microscope. 

Below: The nervous systems of three invertebrates. 



Ganglion 



In an insect, there are several 
ganglia, which are small, solid 
masses of nervous tissue. 




An octopus has a 
well-developed ner- 
vous system. 



46 



Instant Action 

Most of the movements of animals, especially in 
emergencies, are automatic. They have to be to 
prevent injury or even death. For instance, if 
you put your hand on something hot, it will be 
pulled away immediately. In such emergencies, 
the message from the sensory nerves in the skin 
does not travel to the brain for instructions. 
Instead, nerves in your spinal cord instruct the 
muscles to move your hand. This is called an 
automatic reflex action. All animals are armed 
with a wide range of reflex actions, such as 
coughing and sneezing. The way the pupils in 
your eyes contract in bright light is also a reflex 
action. 

Animals can also be trained to carry out 
automatic reflex actions. These are called con- 
ditioned reflexes. For example, in a series of 
experiments, the Russian doctor Ivan Pavlov 
rang a bell before he gave food to a dog. An 
automatic reflex makes dogs produce saliva 
when they see food. After a while the dog 
produced saliva when it heard the bell, even 
though there was no food in sight. 



Cell body 

of nerve cell Dendrites 



In the circle below is an 
enlarged view of the gap 
between one nerve cell and 
the next. This is called a 
synapse. Chemicals released 
from one nerve cell cross 
the synapse and trigger an 
electrical impulse in the 
next nerve cell. 




Passing Messages On 

Impulses pass from one nerve cell to another 
across tiny gaps called synapses. Some large 
nerve cells may be linked to as many as a 
thousand other nerve cells by synapses. The 
electrical impulse has to be changed into a 
chemical message, which "jumps across" the 
gap. The chemical message triggers an electrical 
impulse in the next nerve cell. There may be as 
many as a hundred different chemicals able to 
pass on messages in the central nervous system 
of a complex animal. The large number of 
chemicals helps to prevent communications 
from getting confused. 

Nerve impulses are all the same but the 
number of impulses that travel along the nerves 
can vary and may reach up to a thousand 
impulses a second. The way the brain acts on 
information from the nerve impulses depends on 
where they have come from. Nerves carrying 
impulses from receptor cells in the skin to the 
spinal cord or the brain are called sensory 
nerves. Nerves carrying impulses out from the 
brain or spinal cord to the rest of the body are 
called motor nerves. These nerves cause muscles 
to move. 



Spinal 




Above: The pathway followed by nerve impulses in a reflex 
action. This is an automatic response that does not involve the 
brain. Impulses travel to the spinal cord along sensory ner>es and 
back out to muscles along motor nerves. 

Below and left: Diagram to show how human nerve cells link 
together to carry nerve impulses. The impulses are passed from 
one nerve cell to another across tiny gaps called synapses. 



THE HUMAN BRAIN 

Your brain is in three 
main parts - the 
brain stem (medulla), 
the hind brain (cere- 
bellum) and the fore 
brain (cerebrum). 

BACK 



The cerebellum helps 
you to balance and 
coordinate your 
movements. 




The cerebrum is the 
largest part of the 
brain. The most ad- 
vanced thinking takes 
place here. 



FRONT 



The brain is very sensitive to lack of oxygen 
and brain cells are easily damaged if the 
supply of oxygen is cut off - for instance if 
the heart stops beating for 3 - 5 minutes. 



Pituitary 
Thalamus gland 

The medulla controls 
essential functions 
such as heart rate and 
breathing. 



The hypothalamus is part of your 
nervous system and helps to. keep 
conditions inside your body con- 
stant. It also controls the release 
of many hormones from the pitu- 
itary gland (see page 49). 



The Control Center 



A brain is rather like a computer. It takes in 
information, processes it and sends out the 
results of its processing as instructions to control 
and coordinate all the other organs in your 
body. Your brain contains about 10,000 million 
nerve cells and is far more complex and versatile 
than any computer. No computer can do 
anything until it has been programmed by a 
human brain. People use up to twenty percent of 
their total energy to supply enough fuel for their 
massive brain. 

The brain of any animal has to keep body 
processes running automatically and at the same 
time respond to the environment, which may be 
constantly changing. 

Animal brains receive an uninterrupted flow 
of signals from their sensory nerves. This 
information is continuously coordinated and 
signals go out to all parts of the body. As a 
general rule, large animals have large brains. 
They need large brains to control their big 
bodies. And the development of an animal's 
brain reflects its needs and way of life. For 
example, a dog has a large area of its brain to 
deal with smells. A dolphin's brain is well 
developed to process the sounds it relies on to 
navigate underwater. 



The Two Halves of the Brain 

The large, folded part of your brain, the 
cerebrum, is in two halves, which are called the 
left and right hemispheres. The nerves cross 
over as they enter your brain so that the left 
hemisphere controls the right side of your body 
and the right hemisphere controls the left side. 
Each hemisphere has specialized areas. Most 
people depend more on the left hemisphere of 
their brain than the right. This is why most 
people are right-handed. 

In right-handed people, the left hemisphere is 
responsible for speech, reading, writing and 
logical thinking. The right hemisphere is more 
important in appreciating music, artistic ability, 
creativity and the emotions. Scientists have been 
able to plot the areas of the brain responsible for 
many functions and feelings by applying an 
electrode to the exposed brain during oper- 
ations. It is surprising that the brain, which has 
by far the most nerve cells of any organ in the 
body, cannot sense pain. 

Very little is known about some areas of the 
brain, such as those that control memory. 
Memory can probably be improved by regular 
use, as the connections between the nerve cells 
become like well-worn paths in your brain. 



48 



Smell, Taste and Touch 

Receptor cells at the back of your nose are 
sensitive to chemicals dissolved in the mucus of 
your nose. Impulses then travel to certain areas 
of the brain, giving us sensations of smell. 
Human beings can distinguish about 3,000 
different smells. 

Taste works in a similar way. The sensory cells 
(taste buds) are in your tongue. A combination 
of our senses of taste and smell helps us to taste 
food. 

In people and many other animals all parts of 
the skin are sensitive to touch. Different kinds of 
receptors in the skin each respond mainly to a 
particular stimulus, such as heat, cold or pain. 



Right below: The position of the main endocrine glands in the 
human body and some of the main hormones they produce. The 
testes and ovaries are included for simplicity although they do not 



occur in the same body. 



Chemical Messengers 



Along with a nervous system, many animals 
have a second control system based on chemical 
substances called hormones. In humans, they 
are produced mainly by special glands, called 
endocrine glands, and poured directly into the 
bloodstream. They reach their targets as blood 
flows through the body. 

Hormones control major processes in the 
body including growth, water balance, repro- 
duction and your reaction to an emergency. All 
hormones are broken down when they reach the 
liver. Hormones cannot control body processes 
efficiently unless they are maintained at the right 
level in the blood. This level is controlled by the 
hypothalamus and pituitary gland, using a 
balancing system called feedback. 

Right above:, The hypothalamus and the pituitary gland control 
hormone levels in the blood by a balancing system known as 
feedback. For example, the pituitary controls the amount of 
thyroxine in the blood by producing a thyroid-stimulating 
hormone (TSH). The pituitary detects high or low levels of 
thyroxine in the blood and releases less or more TSH to keep the 
level constant. But sometimes the body's needs for thyroxine rise 
above or fall below the constant level. (More thyroxine is needed 
to increase heat production in cold weather for instance.) This 
information is fed through the hypothalamus (part of the brain). 
The hypothalamus controls the amount of TSH produced by the 
pituitary by producing a substance called a releasing factor (RF). 
You can see how this works if you follow the arrows. 



NERVES OF THE SKIN 




Nerve fibers round Touch receptors Nerve endings 
base of hair sensitive to pain 

Some of the different sensory receptors in the skin, which 
each respond mainly to a particular stimulus, such as heat, 
cold, pain or touch. The numbers of these receptors vary 
over the body surface. For example, the fingertips have 
many touch receptors. 



A FEEDBACK SYSTEM 




Ovaries 
(progesterone, 
oestrogen) 

Testes 

(testosterone) 



4 • 



49 



Seeing the World 

Eyes provide a way for nerve endings to be 
stimulated by light waves. And in this way, the 
human eye and the eyes of all but the simplest of 
animals can gather a vast amount of information 
about the outside world. 

The Human Eye 

The human eye is often compared to a camera. 
Both have lenses to bring objects into focus on a 
light sensitive area. Both have openings that 
control the amount of light entering. The eye, 
however, is more complicated than any camera. 

The human eye is enclosed by three layers. 
We can see part of the outer layer, the sclera, as 
the white of the eye. It is formed of tough 
material and protects the eye. The middle layer, 
the choroid, is made of tissues with many blood 
vessels to nourish the eye. The inner layer, the 
retina, is formed of nerve endings from the optic 
nerve, which have spread out to line the inside 
of the eye. 

The colored part of your eye is called the iris. 



It gets its color from pigments it contains. Blue 
eyes, however, have no pigment. Babies often 
start life with blue eyes, which change color 
when they start producing pigment. The pupil is 
the hole through the colored iris. Around the 
pupil is a sphincter muscle. When it contracts, 
your pupil gets smaller. Other muscles, called 
radial muscles, reach from the pupil to the outer 
rim of the iris. When they contract, they pull the 
iris back and the pupil becomes larger. This lets 
more light into the eye. 

The lens focuses light waves onto the light- 
sensitive cells of the retina - you can see how 
this works in the diagram below. Light stimu- 
lates the cells of the retina to send impulses 
through the optic nerve to the brain. And it is in 
the brain that "seeing" really takes place. The 
vast complexity of the brain translates nerve 
impulses into our view of the world around us. 
For instance, the image of everything we see is 
focused upside down on the retina but the brain 
turns the images right side up. 



THE HUMAN EYE 



In the diagram to the left you can see inside the human eye. The 
light waves entering the eye are bent (refracted) by the lens so 
they meet on the back of the eye, which is called the retina. (The 
image is upside down because the rays of light cross over behind 
the lens.) The retina contains millions of sensory cells, which are 
switched on by the light and send nerve impulses to the brain. The 
brain interprets the impulses so that you can > 
Eyelashes 




Human figure 
wrong way up 




Ciliary muscle 
Vitreous humor 



The center of the eye and the part between the cornea and the lens 
Bone sockets are filled with clear fluids called humors. These help to keep the 
shape of the eye and play a part in focusing. 
The choroid stops light being reflected back out of the eye. Blood 
vessels in this layer carry food and oxygen to the eye. 
Circle: The light sensitive cells of the retina are shaped like rods 
and cones and are called by those names. The cones respond to 
bright light and color. The rods respond to dim light but not to 
color. This is why it is difficult to see colors as the light fades. 



50 



How the Lens Works 

If your vision is perfect, you can focus on 
anything from infinity to book-reading distance. 
Focusing is carried out by the lens, which bends 
(refracts) the light rays so they meet on the 
retina at the back of the eye. 

Light from a nearby object has to be bent 
more than light from a distant object. This is 
possible because the lens is pliable and muscles 
pull it into a different shape. If you are looking 
at a nearby object, the muscles relax, which 
makes the lens rounder. If you are looking at a 
distant object, the muscles contract, which 
makes the lens flatter. 

Failure of the eyes to focus is a common fault, 
especially as we grow older. This can usually be 
corrected by wearing glasses, which make sure 
the light rays are bent at the right angle when 
they enter the eye. As long as this happens, they 
will meet exactly on the back of the retina and 
we can see clearly. Only one other group of 
animals, the squid and octopuses, have eyes 
similar to those of humans and other verte- 
brates. 



FARSIGHTEDNESS 

r^BHxj^^ Farsighted people 

mU Wj^ focus on 

HPIk things a long way 

Bf J _ off but not close 

HL^'"~ I up. The rays focus 

W r 

^^^^ Farsightedness 

^nBHlfek corrected 

Hk by wearing lenses 

Mtk Hk that make the liyht 

I ... "''"')) ra > s Den d inward 

^H^JL- I (converge) before 

WB HJr ■ thev enter the 

NEARSIGHTEDNESS 

• Nearsighted people can focus on 
things close up but not a long way off. 
| 
The rays focus in front of the retina. 




Below left: Owls, like most birds of prey, have their eyes at the 
front of the head. This helps them to see ahead very clearly and 
find prey more easily. They have to turn their heads to keep track 
of objects and can almost turn them in a full circle. 




Lenses make light rays bend 
outward (diverge) before they 
enter the eye. 






Above: Most birds have eyes at 
the side of the head so they can 
watch for danger without turn- 
ing the head. 



Left: The head of a horsefly 
showing the large compound 
eyes which are made up of 
many tiny eyes called omma- 
tidia. Each ommatidium forms 
a picture of the world im- 
mediately in front of it. Insects 
have very large eyes and are 
good at detecting movement. 



Right: Look carefully at 
this picture. Do you see a 
vase or two people facing 
each other? Your brain 
sees the picture in both 
ways and cannot choose 
between them. 

Below: The cube on the 
left looks larger because 
the brain uses clues from 
the background to work 
out the size and position of 
objects. It is fooled by the 
background lines. 



Are all these cubes 
the same size? 




The cube on the left looks larger 
but they are all the same size. 



51 



Sound and Hearing 

Sound waves are vibrations in the air. These 
vibrations are caught by the outer part of your 
ear - the only part you can see. The other two 
parts of your ear (the middle and inner ear) are 
hidden inside your head where they are pro- 
tected by the bones of the skull. The outer ear 
funnels vibrations down the ear hole to your 
eardrum. This vibrates at the same rate as the 
sound waves hitting it and tiny bones on the 
other side of the eardrum pick up the vibrations. 
They carry them across to the inner ear where 
they trigger nerve impulses, which travel to the 
brain. The brain interprets the impulses as 
sound. 

The ears of many other animals work on the 
same principle. Whales and dolphins have 
probably the most advanced hearing of all. 
Some of them, such as the killer whale, may 
"see" underwater by sound waves as well as we 
see by light waves. 

Your Outer Ear 

Sound waves collected by your outer ear pass 
down the ear canal. The hairs and wax along this 
canal trap dust and other particles so they do not 
damage the eardrum. The eardrum is a thin 
sheet of skin slightly over an inch (3 centimeters) 
inside the canal. 

Your Middle Ear 

Three tiny, delicate bones form a chain carrying 
sound vibrations across the cavity of the middle 
ear. Because of their shapes, these bones are 
called the hammer, anvil and the stirrup. The 
base of the stirrup covers the oval window, a 
thin sheet of skin at the entrance to the inner 
ear. The oval window vibrates when the stirrup 
vibrates. 

Vibrations of the eardrum become more than 
twenty times greater within the middle ear. This 
is due to the structure of the three bones and the 
fact that the oval window is much smaller than 
the eardrum. The middle ear is connected to the 
throat by a narrow tube, 1.5 inches (four 
centimeters) long, which opens automatically 
when you swallow or yawn. This helps to keep 
the pressure equal inside and outside the 
eardrum. 

52 




Above: The head of a killer whale. Whales have very acute 
hearing and communicate with each other by making a variety of 
sounds. They also produce ultrasonic pulses which bounce back 
from objects in the water and on the seabed. This helps the whale 
to find food and navigate through the ocean depths. 
Below: Frogs have well-developed and highly sensitive ears. They 
pick up sounds by means of a large ear drum - you can see this 
just behind the eye in this common frog. 





Auditory nerve 
(to the brain) 



Semicircular 
canals 




Receptors 



Nerve fibers 



Above: The organ in the inner ear that helps you to balance. Each 
semicircular canal contains a swollen area called the ampulla. 
This contains receptor cells. As you tilt your head, fluid presses on 
the sensory hairs of the receptor cells and triggers electrical nerve 
impulses. These are sent to the cerebellum of your brain. When 
you spin around and around and then stop, the fluid in your 
semicircular canals continues to swirl for a while as though you 
were still moving. This confuses your brain and makes you feel 
dizzy. 



Noise over 
80 decibels 
is dangerous 



HOW NOISY IS IT? 

Normal breathing 
Whisper 

Conversation 
Busy traffic 

Vacuum cleaner 
Underground train 
Decibels Rock group at 4ft 

(approx) Jet fighter taking off 

i i i i i i — r — i — i — i — i i i r~ 

!0 20 30 40 50 60 70 80 90 100110120 130 



Eustachian tube 
(to the throat) 



Above: A section through the human ear showing the three main 
parts. The outer ear collects sounds from the air and the middle 
ear carries the vibrations across to the inner ear. In the inner ear, 
the vibrations trigger off nerve impulses, which travel to the 
brain. 



Your Inner Ear 

The inner ear is deep within the skull, behind 
and slightly below your eyeball. It is full of fluid 
and contains two elaborate structures, one for 
hearing (the cochlea) and the other for balance. 

Sound vibrations from the oval window travel 
through the fluid-filled tube called the cochlea, 
which is coiled like the shell of a snail. They 
cause the movement of tiny, hair-like nerve 
endings - about 25,000 in each ear. Receptor 
cells convert the movements to electrical signals 
(nerve impulses), which travel to the brain. The 
brain interprets these impulses as sounds. Bigger 
vibrations cause the sensory cells to send more 
impulses to the brain and we hear louder 
sounds. With two ears, animals can tell where a 
sound is coming from because one ear will 
usually receive a stronger signal than the other. 

The other structure of the inner ear helps you 
to keep your balance. It consists of three 
semicircular canals and two tiny sacs, called the 
utricle and the saccule. The whole structure is 
filled with fluid called endolymph. The sacs tell 
you what position your head is in and the canals 
tell you what direction it is moving in. 



53 



Skin, Fur, 
and Feathers 

Skin protects an animal's body from the outside 
world and provides a barrier against infection. It 
is a waterproof covering, which prevents animals 
from drying out. In mammals and birds, it helps 
to maintain a constant body temperature. The 
skin also has vast numbers of sensory cells and 
nerve endings within it so it is sensitive to touch, 
pressure, pain and temperature. In some mam- 
mals, such as the porcupine, the hairs in the skin 
are thickened up into sharp spines, which help to 
protect the animal from attack. And in animals 
like the rhinoceros, the horns are made of lots of 
hairs fused together. 

Your Skin 

Your skin is made of two main layers - the top 
part is called the epidermis and the thick layer 
underneath is called the dermis. The epidermis 
consists of three layers of cells arranged like the 
bricks in a wall. New cells are constantly being 
formed in the bottom layer, the malpighian 
layer. In the middle is the granular layer. The 
lower cells of this layer are living but they merge 
into an outer layer of dead cells, called the 
cornified layer. Cells are constantly being shed 
or worn away from this layer. 

The cornified layer in humans can be many 
cells deep. But in invertebrates, such as insects, 
the whole epidermis is only one cell thick. This 
thin layer usually produces the insect's cuticle 
(its exoskeleton). The cuticle prevents water 
being lost and gives protection against injury. 
But it is only useful on a small body. The cuticle 
of an insect the size of a dog or a sheep would be 
too heavy for the animal's muscles to move. 

Underneath your epidermis lies the dermis. It 
is made of connective tissues and flexible 
collagen fibers. The dermis has many blood 
capillaries and sensory cells as well as sweat 
glands and hair follicles. 

A hair follicle is a deep, narrow hole in the 
skin. Cells grow continuously at the base of the 
follicle and push the older cells up the follicle. 
As they do so, they absorb keratin (a tough 
fibrous protein) and die. This forms the hair. 
Sebaceous glands open into the follicle, provid- 
ing oil for hair and skin. Below the dermis lies 
adipose tissue in which fat is stored. 




Blood capillary 



Adipose tissue 



Diagram showing the main structures in human skin. Your skin is 
the largest organ in your body. The skin of an average adult 
weighs 8 to 10 pounds (3.5 to 4.5 kilograms) and covers an area of 
about 22 square feet (2 square meters). 



Warming Up and Cooling Down 

The most complex job of your skin is tempera- 
ture control. The brain keeps a constant check 
on the temperature of the blood. If it goes above 
or below 98.6 degrees fahrenheit (36.8 degrees 
celsius), the brain sends nerve signals to the 
arteries feeding blood to the capillaries of the 
skin. These arteries open wider so that more 
blood reaches the surface of the skin, which may 
become reddish. Heat can then escape from the 
skin surface. 

When the body gets too cold, the same 
capillaries narrow, which cuts down the amount 
of blood reaching the skin surface and keeps 
heat in the body. 

The blood vessels, sweat glands and hairs in your skin all work 
together to warm you up or cool you down so that your body 
temperature stays roughly the same. 



COLD DAY 

Follicle closes 
to stop warm air 
escaping. 




HOT DAY 

Heat escapes from 
blood through skin. 
Follicle opens 
and warm air escapes. 



Fur and feathers help mammals and birds to 
maintain a constant body temperature. Minute 
muscle fibers are attached to the individual hair 
follicles. Mammals can therefore pull up their 
fur, which creates air spaces. This traps heat 
because air is a poor conductor of heat. Birds 
fluff up their feathers in the same way and this 
helps to keep them warm for the same reason. 

We show signs of this reaction when we get 
goose pimples, which occur when tiny muscles 
attached to our hair follicles contract to make 
our body hairs stand on end. This response was 
probably inherited from our distant ancestors, 
who had plenty of hair. It is not much use to us 
today, so we rely more on the fatty tissues below 
the skin and clothes to keep us warm. 

Shivering is another automatic response we 
have to cold. It moves our muscles, which 
"burns" food and releases energy to keep us 
warm. 

The Role of Sweat Glands 

Your skin also helps to get rid of waste products, 
such as urea and salts. It does this via sweat 
glands - there are two to three million of them in 
your skin. A sweat gland consists of a coiled 
tube leading to the surface of the skin. The tube 
gathers fluid from blood capillaries and sur- 
rounding cells and releases it from the skin 
surface. This also helps to cool you down. 

Many other mammals have few sweat glands 
and birds have none. They have to lose heat in 
other ways. Birds do this by opening their beak, 
while dogs sit with their wet tongues hanging out 
on hot days. The sweat glands on a dog are 
mainly on the pads of the feet. 

Below: No two people in the world have the same fingerprints. 
Even the fingerprints of identical twins are different. This is why 
fingerprints help the police to identify criminals. 




Above: Close-up of a pheasant's feather. Feathers are strong and 
tough but very light. The central shaft or quill of a feather is 
hollow. It has many barbs either side, which are linked by tiny 
hooks called barbules. 




Left: Close-up of the scales on a 
butterfly's wing. The scales are in 
fact flattened hairs and they pro- 
vide the colors on the wings. 
Butterflies and moths belong to a 
group of insects called Lepidoptera, 
which means "scaly winged." 




Right: The amazing spir- 
al horns of the markhor 
(a wild goat) measure as 
much as five feet in 
length. Horns are made 
of a tightly packed fiber 
called keratin. 




Branch 
grows 



Tentacles 
and 
mouth 
develop. 



Ready to 

break 

away 



Above: Hydra is a many-celled animal (a coelenterate) that lives 
in fresh water. It usually reproduces asexually by budding. A new 
hydra grows out from the side of the parent and eventually drops 
off to lead a separate life. 

Below: A trypanosome dividing into two - look for the two nuclei. 
Trypanosomes are parasitic protozoa that cause diseases in 
people, horses and cattle. 




Below: Obelia is an animal that lives in the sea in colonies attached 
to rocks. It develops two types of branches called polyps. The 
feeding polyps capture food with their tentacles. The reproductive 
polyps produce male and female medusa, which look like tiny 
jellyfish. These swim off into the water and, when they are 
mature, the male releases sperm and the female releases eggs. 
When a sperm fertilizes an egg, it develops into a swimming larva 
called a planula. This settles onto a rock and grows into a new 
obelia colony. 



New Generations 



Animals have to produce new individuals like 
themselves for their species to survive. There 
are two kinds of reproduction, sexual and 
asexual ("a" means without). Most animals 
reproduce sexually but some, particularly the 
simplest animals, reproduce asexually as well. 

Asexual reproduction involves only one 
parent and produces new individuals which are 
exact copies of that parent. No sex cells are 
involved. Although it is a rapid method of 
reproduction, the animals do not change from 
one generation to the next so they cannot adapt 
to changes in their surroundings. Two of the 
most common methods of asexual reproduction 
are when one single-celled animal divides into 
two and when a new individual grows out from 
its parent in a process called budding. 

Sexual reproduction involves two parents and 
produces new individuals which are different 
from their parents. This allows animals to 
change from one generation to another so they 
are more likely to survive if conditions around 
them change. 




Feeding polyp 



•JUT! > , 




mm 



Male medusa 



Reproductive \\ //^M^ 
polyp, 



Young polyp- 



/ 



56 



m 




Frog 
spawn 



Tadpole- about 
6 weeks old 



M 

:0 



Adult 

Common frog 



Left: Recently laid frog spawn floating on the surface of a pond. 
Above: The female common frog lays her jelly-covered eggs 
(spawn) in the spring. As they emerge into the water, the male 
releases his sperm onto them. The sperm swim through the jelly 
and fertilize the eggs. The tadpoles hatch after about 10 days. 
They take about three to four months to develop into young frogs. 




Left: The tough, leathery shell 
of a reptile's egg keeps moist- 
ure in and helps to stop the egg 
drying out. The double layer of 
membranes shields the embryo 
from external shocks and 
changes in temperature. A 
third membrane, the allantois, 
collects wastes excreted by the 
embryo. Food is provided by a 
yolk sac and fed to the embryo 
through blood vessels. 



THE LIFE CYCLE OF A BLTTERFLY 

This swallowtail butterfly starts life as an egg. It hatches into a 
caterpillar, which feeds on leaves. It changes its skin several times 
as it grows. Then it attaches itself to a leaf or twig and turns into a 
pupa. Inside this protective coating, it changes into a butterfly. 
Finally, the pupa splits open and an adult butterfly pushes its way 
out. The butterfly pumps blood into its wings to make them 
unfold and waits for its wings to dry before flying away. 




w 



In sexual reproduction, two sex cells have to 
fuse together. One of these cells comes from a 
female animal and is called an egg cell or ovum 
(plural ova). The other sex cell comes from a 
male animal and is called a sperm cell. The sex 
cells are known as gametes and the fusing of two 
gametes is called fertilization. The. result of 
fertilization is a cell called a zygote, from which 
a new individual can develop. The zygote 
contains a mixture of the genetic instructions 
from two individuals in the dna molecules in its 
nucleus. (You can find out more about genetic 
instructions later in the book.) They control the 
characteristics of an animal, including its 
appearance and the chemical processes that go 
on inside its body. 

In some animals, including fish and amphi- 
bians such as frogs, fertilization takes place 
outside the body. The female lays her eggs and 
the male fertilizes them by placing sperm on 
them afterward. In birds, the eggs are fertilized 
inside the body of the female. The male passes 
sperm into the egg tubes and fertilizes the eggs 
before they are laid. The chick does not develop 
much before the egg is laid, however. 

The eggs are also fertilized inside the female's 
body in mammals and the young develop there 
as well. Some, such as kangaroos, are born in a 
very immature state but others, such as zebras, 
are able to run about soon after they are born. 
All mammals feed their young with milk 
produced in glands on the mother's body. They 
look after their young following birth more than 
any other animals do. 

57 



New Human Life 

Human beings reproduce sexually. It takes just 
one sperm cell to combine with one ovum in a 
woman's body to produce a new cell, which 
grows and develops into a baby in the woman's 
womb (uterus). 

The male and female reproductive systems 
start working fully at puberty. This is about 11 
years in females and 13 in males but the age 
varies a lot between individuals. 

As both sexes develop, they grow pubic hair 
and hair under the arms. In females, the breasts 
develop, the hips widen, the reproductive 
organs grow and develop and the menstrual cycle 
(monthly periods) begins. In males, the beard 
starts to grow, the larynx (Adam's apple) 
enlarges and the voice deepens, the shoulders 
and chest broaden, the reproductive organs 
develop and sperm are produced. The body 
changes at puberty enable a mature ovum and 
sperm cell to come together and to prepare the 
female's body for a baby. 

The Male Reproductive System 

The main organs of the male reproductive 
system are the testes, which produce sperm, and 
the penis, which releases the sperm. 

The testes hang outside the body in a loose 
bag of skin called the scrotum. This helps to 
keep them cool. The temperature inside the 
body is too warm for sperm production to be 
very efficient. Inside each testicle are up to a 
thousand tiny coiled tubes where sperm are 
produced. They are stored in a long, coiled tube 
called the epididymis, which is about 20 feet (6 
meters) long. It lies alongside each testicle. 

During sexual excitement, the mature sperm 
move from the epididymis into the urethra, 
which is the outlet tube for the bladder. Along 
the way, fluids from the prostate gland are 
added to the sperm. Another gland (Cowper's 
gland) sterilizes the urethra for the passage of 
the sperm. The fluids protect the sperm from 
bacteria and provide nutrients. The mixture of 
fluids and sperm is called semen. The semen is 
discharged (ejaculated) into the woman's vagina 
during sexual intercourse. At this time the penis 
becomes larger and stiff (erect) because a lot of 
blood flows into it. One ejaculation contains 
hundreds of millions of sperm. 

58 




Above: Human sperm cells as they appear under a high -power 
electron microscope. Sperm are among the smallest cells in the 
body. The oval head contains 23 chromosomes, which may 
combine with the 23 chromosomes in a female ovum to form a 
fertilized egg cell. The tail of the sperm cell swings from side to 
side to push it along. The energy for this movement is stored in 
the thickest part of the tail. 




Above left: The human female reproductive system (from the 
front). 

Above right: The human male reproductive system (from the 
side). 

Below: A diagram showing the main stages in the human 
menstrual cycle (monthly period). The number of days given for 
each stage are only approximate as the timing of the cycle varies 
slightly from woman to woman. At the start of the cycle the lining 
of the uterus is shed, which causes bleeding (the period). A new 
lining then builds up. Sometime between days 10-18, an egg is 
released into one of the fallopian tubes (ovulation) and begins its 
journey toward the uterus. The lining of the uterus thickens, 
ready to receive a fertilized egg. If the egg is not fertilized, the 
lining is shed and a new cycle begins. 





2. The head of one 
sperm gets through 
into the jelly. 




3. The head of the 
sperm passes into 
the egg and the 
nuclei join. 



Capillary 
network in 
placenta 




Blood with 
oxygen 



Diagram showing the 
relationship between 
the blood of the fetus 
the blood of the 
mother. The two 
bloodstreams come 
close together but 
they never mix. 



The Female Reproductive System 

The main organs of the female reproductive 
system are the two ovaries and the uterus. 
Thousands of immature eggs (ova) are stored in 
the ovaries from birth. Every month from 
puberty to the age of about 45, an ovum matures 
in one of the ovaries and is released. This is 
called ovulation and the time ovulation stops is 
called the menopause. The ovum is drawn down 
a tube called the fallopian tube (oviduct) to the 
uterus. On the way it may be fertilized by one of 
the sperm that swim up to the fallopian tubes 
after sexual intercourse. 

Every month, from puberty to menopause, 
the lining of the uterus thickens to prepare for 
the arrival of a fertilized ovum. If the ovum is 
not fertilized, it is pushed out of the body, 
together with the inner part of the uterus lining 
and some blood, in the monthly period. The 
muscular contractions of the uterus walls some- 
times cause pain and cramps at this time. 

If the ovum is fertilized, it sinks into the 
uterus lining and in about two weeks a special 



Left: Diagram showing the process of fertilization, which takes 
place in a fallopian tube. The sperm cells are attracted to the 
ovum by chemicals it produces. The head of one sperm cell 
manages to pass through the membrane of the ovum. Changes in 
the membrane prevent any other sperm cells from entering. The 
nucleus of the sperm cell fuses with the nucleus of the ovum to 
form a fertilized egg cell. 



Right: How a baby grows in- 
side its mother. About 6 weeks 
after fertilization, the baby's 
muscles, hands and feet begin 
to form. By about 10 weeks, all 
the main parts of the body are 
formed, although they are not 
yet fully developed. The baby 
is now only about 2.5 inches (6 
centimeters) long. At 22 weeks, 
the mother can feel the baby 
moving. About two months 
before birth, the baby comes to 
rest in a head-down position 
ready to be born. 



5 weeks 

0.4 in. (10mm) 



8 weeks 

1.6 in. (40 mr 




22 weeks 



34 weeks^^ 




organ called the placenta has formed. This is a 
barrier separating the mother's blood from the 
blood of the developing baby (the embryo). It 
allows food and oxygen to pass from the 
mother's blood to the blood of the embryo and 
wastes from the embryo to pass in the opposite 
direction. The baby is attached to the placenta 
by the umbilical cord. 

During its growth, the baby lives in a fluid- 
filled bag called the amniotic sac, which helps to 
protect it from injury. A few weeks before the 
baby is born, 'it is positioned head-down over a 
ring of muscle called the cervix, the exit from the 
uterus. The time from fertilization to birth is 
usually about nine months. 

At birth, the muscles of the uterus contract to 
push the baby out. The cervix, which is usually 
only about the size of a pinhole, enlarges to let 
the baby through. The amniotic sac breaks, 
releasing a gush of fluid down the vagina. More 
muscular contractions push the baby down the 
vagina into the outside world. 

59 





Above: Babies have to learn to recognize things. At first, their 
mother's eyes interest them more than the rest of her head. But 
by the time the baby is three months old, it has learned to 
recognize the rest of its mother's face. Later still, a small child 
learns to recognize every feature of her face. 
Below: These children are playing house. They have used toys and 
everyday objects to represent many different things. Play helps 
children to develop their imagination. It also gives them a chance 
to escape into a fantasy world when they can't understand things, 
and play helps them to learn about themselves. 



How a Baby Develops 



A newborn baby can carry out some simple 
actions, such as gripping objects and sucking its 
mother's breast. At first it spends a lot of time 
asleep, except when it is hungry. After about a 
month, it can hold up its head if it is supported 
and after about six weeks, it can turn its head 
and smile. After about seven or eight weeks, it 
can roll over and reach for things. 

A baby explores its surroundings to discover 
more about its world. Before it can crawl, it will 
touch its mother's face and any other objects it 
can reach. It will even put things in its mouth to 
get the feel of them. Gradually it learns to eat 
mashed up food, crawl and eventually toddle. 
All the time its understanding grows as it 
experiences new events and situations and learns 
from them. 

There are many different ways of learning. 
One is by trial and error and another is by 
imitating (copying) other people. Babies begin 
to imitate when they are a few months old. By 
the time they are two years old, they are 
beginning to think. An important step in this 
process is the use of symbols and signs (such as 
drawings and words) to represent things they 
cannot see in front of them. 

The development of thinking takes a long 
time but gradually children come to understand 
ideas such as number, length and weight, and by 
the time they reach adolescence they are able to 
reason and work out problems in a logical way. 




MP! 



Tortoise 
150 



LIFE SPANS 










This chart shows the longest recorded life 
spans for a variety of different animals. 


Human 
115 






Elephant 
70 






Carp 
50 

Hippo | 
in 








Cat 
30 

Dog 
20 I 
Rabbit Ht H 
Bee U 1 

Fly M0USe ^ 1 


Hi 

■HI 

t 








Above: This photograph shows the contrast between the skin ; 
muscles in an old person and in a young person. 



How Long do they Live? 



Scientists do not really understand why animals 
die. The cells in their bodies may just come to 
the end of their natural life, or there may be 
some kind of "body clock" which switches life 
off after a certain time. 

In spite of the great advances in medical 
science, human beings today do not live much 
longer than those of past generations. Ages of 
150 years are sometimes claimed, but in coun- 
tries where reliable documents are available no 
one seems to live much beyond a hundred years. 
This still makes humans the longest-living 
mammals. 

Reptiles, such as tortoises and turtles, do 
better. One tortoise lived at the barracks at Port 
Louis on the island of Mauritius for at least 150 
years. It may be that these creatures escape 
aging to some extent because (unlike birds and 
mammals) they continue to grow throughout 
life. Plants also grow throughout life and some 
can live for several hundreds or even thousands 
of years. A bristlecone pine tree in the United 



States is known to be 4,900 years old. 

Many biologists believe that uncorrected 
errors in the chemical processes of life (such as 
faults in the production of enzymes) may be 
connected with aging. As the cells, tissues and 
organs deteriorate, they slowly age. Our im- 
mune system, which detects and destroys the 
faulty products of cells, becomes less efficient 
with age. Another factor is that the cells of our 
brain and nervous system die throughout life 
and cannot be replaced. A very old person has 
lost a considerable amount of brain cells. 

One of the first research projects on aging was 
carried out by Dr. Clive McCay of Cornell 
University. He discovered that by underfeeding 
rats and mice he could lengthen their lives by 
about 50 percent. He showed that the right 
amount of food for the proper growth of rats and 
mice was not the same as the right amount of 
food for a long life. Studies have also shown that 
different parts of the human body age at differ- 
ent rates. But much work remains to be done. 



61 



Looking Inside Plants 

Plants grow in an amazing variety of shapes and 
sizes, from microscopic green specks to giant 
trees. But no matter how different they look 
\\ from the outside, most familiar plants have the 

same features inside. 




Above: A leaf has a waterproof outer skin (the cuticle) and a tough 
inner skin (the epidermis). Under the epidermis is the palisade 
layer. This is the greenest part of the leaf, where food is made. A 
network of pipelines carries food and water through the leaf. 




Packing tissue 



Above: Stems connect the roots to the leaves. Under the epidermis 
is a ring of pipelines carrying food and water. The rest of the stem 
is made up of packing cells and fibers. In some plants, such as 
grasses and lilies, the pipelines are not in a ring but scattered 
throughout the stem. 



More About Leaves 

You can usually recognize a plant from the 
shape of its leaves but sometimes a plant has 
more than one type of leaf. For example, the 
floating leaves of water crowfoot are rounded 
but the underwater leaves are feathery. 

The branching pattern on the surface of a leaf 
is part of the network of pipelines that carry 
food and water around the plant. The pipelines 
are sometimes called veins and the main vein is 
called the midrib. The veins show up most 
clearly as the skeleton that remains on a dead 
leaf after the soft parts have been eaten away. 

Some leaves have special features to help 
them survive in difficult climates. Furry leaves 
keep out the cold and thick fleshy leaves help to 
prevent the plant from drying out under a hot 
sun. Cactus spines and pine needles also help to 
prevent the plant from losing water. They are 
modified leaves. In tropical jungles, where it 



rains every day, some of the plants have leaves 
that end in long points (drip tips) so that the rain 
runs off. Some of the plants that live high up on 
the branches of the jungle trees have their leaves 
arranged in a cup shape to catch water. The 
leaves on a pineapple are arranged like this. 

Plants also arrange their leaves so they get as 
much light as possible. You can see this for 
yourself if you look at a plant such as a begonia 
from above. Each leaf is placed so that it is not 
covered by another one and there are no gaps 
where you can see the soil below. Nobody 
knows exactly how plants do this. 

Leaves are usually attached to stems by stalks. 
Where each stalk ends in one leaf, such as on a 
beech tree, the leaf is called a simple leaf. Where 
the leaf is divided so that each stalk looks as if it 
has several leaves (as on a horse chestnut tree) 
the leaf is known as a compound leaf. Some 
leaves have no stalks at all. 




Pipelines in Plants 




Above: Xylem tubes in a plant stem, 
showing the spiral thickening in the 
walls of the vessels. 




Flowering plants have two kinds of pipelines in 
their leaves, stems and roots. One carries water 
and dissolved minerals. The other carries food. 

Water Pipes 

The pipelines that carry water are made up of 
rows of cells joined end to end with no walls 
between them. These cells are called vessels and 
they are dead structures. The vessels and the 
packing tissue around them are called xylem. 

Water enters the plant through tiny fragile 
hairs just behind the tip of each root and travels 
across a few cells to join the main xylem in the 
middle of the root. From here it rises up the 
stem partly by being pushed from below and 
partly by being pulled from above. This flow of 
water is called the transpiration stream and the 
evaporation of water from the leaves is called 
transpiration. 

Transpiration supplies all the water that plants 
need to make food and helps the cells to keep 
their shape, which stops the plant from wilting. 
Water evaporating from the leaves also helps to 
cool the plant down. Some trees lose their leaves 
in winter to cut down the amount of water they 
lose. It is often difficult for large trees to get 
enough water if the ground is frozen. 

Food Pipes 

Food is made in the leaves and travels around 
the plant in pipelines made of rows of living cells 
joined end to end. They are called sieve tubes 
because the end walls of the cells are full of 
holes. The sieve tubes and the packing tissue 
that supports them are called phloem. Food can 
travel up or down the stem in the phloem to 
reach any cells that need energy, such as those in 
growing regions. Sometimes food can travel up 
and down the plant at the same time but 
scientists are not sure how this is done. 



STOMA CLOSED 



STOMA OPEN 



Plant with 
leaves and 
roots intact 



Colored water 



Daffodil 
Stem sph 
into two 






Chloroplasts 



Above: Stomata are tiny holes in the leaf that open and close to 
control the flow of gas and water vapor. The stoma opens as the 
guard cells bulge outward. When the stoma closes, the strong, 
elastic walls of the guard cells keep it tightly shut. 



Left: Experiments to show how water is taken up by plants. 
Obtain a plant with its leaves and roots intact. Wash the soil off 
the roots and stand the plant in ajar of water containing a colored 
dye, such as ink, for 24 hours. Then cut the stem with a knife to 
see how far the dye has moved. If you use impatiens, which has a 
transparent stem, you will be able to see where the dye is. You 
could also try making colored flowers. Split the stem and put one 
half in water and the other in water containing a colored dye - as 
shown in the diagram to the left. 



Colored water 



How Plants Breathe 



All plants need to breathe, that is take in oxygen 
from the air and give out carbon dioxide. They 
use the oxygen to convert food into energy, 
which they use to drive their life processes. This 
is called respiration and it involves a series of 
chemical reactions inside the plant cells. Res- 
piration takes place in animal cells as well but 
plants do not make breathing movements like 
animals. Gases simply pass in and out of the leaf 
or stem through tiny holes called stomata, which 
open and close to control the flow of gas. Woody 
stems have small raised pores called lenticels 
instead of stomata. 

There is a network of air spaces between the 
cells of a leaf so that the gases do not have to 
travel far between the cells inside and the air 
outside. Before the gases can enter or leave a 
plant cell, they have to dissolve in the layer of 
moisture surrounding the cells. 

Roots obtain the gases they need by absorbing 
oxygen that has dissolved in water in the soil. 
The cell walls are so thin that gases can get 
through them easily. Plants that live in water 
take in gases that have dissolved in the water 
that surrounds them. 



How Stomata Work 

If you look very carefully with a strong magnify- 
ing lens at the underside of a leaf, you may be 
able to see some circular shapes. Each one of 
these marks the site of a stoma (plural stomata), 
the tiny hole that automatically controls the flow 
of air and water vapor in and out of a leaf. 

The opening of each stoma is surrounded by 
two sausage-shaped cells called guard cells. 
When there is a lot of water in the leaf, the 
guard cells absorb water and swell up. They 
bulge outward and separate, leaving a hole 
between them through which water vapor or 
gases can enter or leave. The stomata open 
when the plant is most active - usually when it is 
busy taking in and giving out gases while it is 
making food (see pages 66-67). 

When the leaf loses water, the guard cells lose 
it too. As they shrink, the strong elastic walls 
between them pull the cells together and the 
stomata close. 

There are more stomata on the underside of a 
leaf than on the upper surface. The upper 
surface is protected by a waterproof skin to 
prevent too much water being lost. 



65 




Granum Stroma 



Above: A view inside one of the chloroplasts in a leaf. Numerous 
sheet-like membranes called lamellae run from one end of the 
chloroplast to the other. In some areas, the lamellae are closer 
together and are arranged neatly on top of each other, rather like 
a stack of coins. Each group of lamellae is called a granum (plural 
grana). The grana hold chlorophyll molecules in the best possible 
position for trapping light energy from the sun. The grana and 
the rest of the lamellae are surrounded by a watery substance 
called the stroma. Light energy seems to be captured mainly in the 
grana, while carbohydrates are built up in the stroma. 



Below: The diagrams below are a simplified summary of the 
chemical reactions during photosynthesis, the process by which 
plants make food. 



Making Food With 
Light 

Green plants are the only living things that can 
make their own food. They convert the sun's 
light energy into chemical energy, which they 
use to combine carbon dioxide and water to 
make sugar and oxygen. This process is called 
photosynthesis, which means "making things 
with light." 

Plants make food mainly in their leaves, 
where a colored substance (a pigment) called 
chlorophyll traps the sun's energy. Chlorophyll 
is bright green and this is why so many plants are 
green. Plants that don't look green, such as 
many seaweeds, still contain chlorophyll but 
they also have other pigments, which mask the 
green color. 

The recipe plants use to make food needs 
simple ingredients, just water and carbon diox- 
ide. Land plants take in carbon dioxide from the 
air and water from the soil. Water travels up to 
the leaves in the xylem vessels and air enters 



THE SUGAR FACTORY 



Chlorophyll 
molecule giving 
off energy 



Sun's rays 
Chloroplast 



Chlorophyll 
molecule 

/ 




I. In the chloroplasts, chemical mole- 
cules called chlorophyll capture energy 
from sunlight. 



Chloroplast 



2. Some of the energy splits molecules of 
water into hydrogen and oxygen. 



3. The oxygen is not needed and finds its 
way out of the leaf. 



Energy 
carrier 



Hydrogen 
V ner 



f d T 0i W Carbohydrate 

Carbon dioxide 



4. Back in the chloroplast, hydrogen 
and energy are picked up by special 
carrier molecules. 



S. Meanwhile, molecules of the gas 
carbon dioxide enter the leaf from the 



6. The energy joins the hydrogen and 
carbon dioxide to make sugar - food for 
the plant. 



66 



through tiny holes in the leaves and stems called 
stomata. (You can find out more about xylem 
and stomata on pages 64-65.) Water plants take 
in water and dissolved carbon dioxide all over 
their surfaces. 

The basic food that plants make is a sort of 
sugar called a carbohydrate. It is rich in the 
energy trapped from sunlight. Some carbohy- 
drates may be broken down by the plant 
immediately to release the energy needed for 
life processes. It is carried around the plant in 
the phloem tubes (see page 64) to all the cells 
that need energy. Some carbohydrates are 
stored for future use. Many plants store car- 
bohydrates in special structures called bulbs and 
tubers. Potatoes are tubers and they are packed 
with starch. 

Carbohydrates can also be converted into 
more complex substances such as the proteins in 
chlorophyll and enzymes. To make proteins, 
plants need extra chemical elements such as 
nitrogen, sulfur and phosphorus, which they 
take in as mineral salts. 




Some of the starch grains in a potato tuber, seen under a 
microscope. You can test for starch in a potato or plant leaf with a 
drop of iodine. You need to crush or boil the plant tissue first to 
break down the cell walls and allow the iodine to get inside the 
cells. Any starch will turn inky black. 



Plants that Eat Animals 

Some plants have an appetite for live animals, 
especially insects. The extra food probably helps 
them to survive in poor soils. Meat-eating plants 
trick their victims into deadly traps. They use 
digestive juices to turn the bodies of their prey 
into liquids they can absorb. 




Robber Plants 

Some plants have no chlorophyll and so cannot 
make their own food. They steal their food from 
other plants instead. They may eventually kill 
the plants they feed from. These plants are 
called parasites - you can find out more about 
parasites on page 89. 



Left: Sundew plants trap 
insects in sticky red hairs 
that cover their leaves. 
The struggles of the in- 
sect make the hairs curl 
over it and stick it firmly 
to the leaf. It takes a day 
or two for a sundew to 
eat an insect. 



Right: This ghostly 
orchid steals its food 
from trees with the help 
of a fungus. It soaks up 
food from the thread- 
like hyphae of a fungus 
that grow around the 
tree roots. The tangle of 
roots and hyphae in the 
soil give the orchid its 
name - bird's nest 




67 




Cone scales are modified 
leaves. 



Cross section through a 
female cone to show the 
seeds hidden beneath the 
woody scales. If you pick 
up a cone, you may be 
able to find some seeds 
flattened against the 
scales. 



Lawson cypress 




Above: Cones come in a variety of shapes and sizes. Some, such as 
juniper, even look like berries. These are all female cones. 
Below: Pollen grains from common juniper (left) and Scoteh pine 
(right). Two air sacs on the Scotch pine pollen grain help it to drift 
vind. 




Pollen Packs — 
Cones and Flowers 

Many new plants grow from seeds, which are 
produced in special structures called cones and 
flowers. Before a seed can develop, a male sex 
cell has to join with a female sex cell. These cells 
often come from different plants. Male sex cells 
are in the yellow dust called pollen, which is 
produced only by gymnosperms (plants with 
cones and their relatives) and angiosperms 
(plants with flowers). Female sex cells are called 
egg cells and they are inside a structure called an 
ovule, which is hidden inside a flower or cone. 

In flowering plants the ovule is protected by 
the wall of a hollow structure called an ovary. 
But in gymnosperms, such as conifer trees, the 
ovule is naked and unprotected. Pollen travels 
from one flower or cone to another but the 
ovules stay where they are. 

A Closer Look at Cones 

Cones are always either male or female. A 
typical conifer, such as a cedar tree, produces 
female cones at the tips of the branches and 
male cones further down the shoot. 

Female cones are small and soft to begin with 
and may take two or three years to develop into 
cones with woody scales. Tucked inside the 
scales, the naked ovules develop into seeds if 
they receive pollen from a male cone. When the 
seeds are fully grown, the scales open to release 
the seeds and the cone falls the ground. Small 
male cones are produced each spring and make 
pollen in sacs attached to a cluster of scales. 




Stigma and 
style 




Carpel 
Ovule 

Receptacle 
Sepa 

Above: Section through a buttercup flower to show the various 
structures inside. 

Right: Tree flowers are often arranged in long bunches called 
catkins. 

A Closer Look at Flowers 

Flowers are probably the most amazing struc- 
tures in the plant world. Despite the huge 
variety of shapes, sizes and colors, they are all 
made of the same parts. 

All flowers are basically four rings of specially 
modified leaves attached to a stalk. The bottom 
ring is made of sepals and is called the calyx, 
which means bud scales. Above the calyx is a 
ring of petals known as the corolla, which means 
crown. Above the petals is a ring of wand-like 
stamens called the androecium, which means 
male parts. Pollen is produced on the tips of the 
stamens, which are called anthers. Above the 
androecium, right in the middle of the flower, 
are the carpels. All the carpels together are 
known as the gynoecium, which means female 
parts. Each carpel has a sticky tip called a stigma 
on top of a stalk called a style. Below the style is 
a hollow structure called an ovary, which 
contains the egg cell inside an ovule. 

There are all sorts of variations on this basic 
plan. For example, some of the different parts of 
a flower may be joined together or some parts 
may be missing, as in unisex flowers. Flowers of 
the other sex may be on the same plant (as in 
hazel) or different plants (as in holly). 



Ripe female flowers 
look like cones 



Common alder 



Ripe catkins 
(male flowers) 




Above: A rich variety of flowers can be found in Alpine meadows. 
Below: The pollen grains of four flowering plants seen under a 
high-power electron microscope. From left to right: bindweed, 
timothy grass, lettuce, and yellow water lily. 




69 



Pollen on the Move 

Pollen grains have to make their way to a stigma 
(one of the female parts of a flower) if a new 
seed is to develop. The transfer of pollen from 
an anther to a stigma is called pollination. The 
pollen of some flowers travels on the wind. 
Other flowers rely on insects or other animals to 
pick up their pollen and carry it from flower to 
flower. 

Some plants can make seeds with pollen from 
the same plant or even from the same flower. 
This is called self-pollination. Garden peas 
always make seeds this way. Other plants, such 
as willow-herb (fireweed) only make seeds with 
their own pollen if they do not receive pollen 
from another plant. 

Most plants do not self-pollinate because 
stronger, more varied plants are produced if two 
different plants breed together. Self-pollination 
is prevented in several different ways. For 
example, the stigma and anthers may ripen at 
different times or in different flowers, or the 
stigma may have a special chemical system to 
spot unwanted pollen grains and stop them 
growing. Some plants, such as dandelions, can 
make seeds without any pollen. This is called 
apomixis. 




Male and female 
holly flowers grow 
on different trees. 
This is an extreme 
way of avoiding 
self-pollination. 

Only female holly 
trees have berries. 
Primroses are polli- 
nated by bees. Bees 
pick up pollen from 
the anthers of one 
plant and may carry 
it to the stigma of 
another plant. 



Stigma 




Some primrose flowers have 
their anthers high up and 
their stigmas low down, 
while others have their stig- 
mas high up and their 
anthers low down. This 
helps to prevent pollen 
grains from reaching the 
stigma on the same plant. 




stick together. — r-^rheTcToutsid*: 




Above: These birch tree catkins are made up of lots of male 
flowers growing together on a long stalk. The flowers on the 
catkins open in spring before the leaves emerge from the buds on 
the tree. This means the pollen stands more chance of being blown 
away by the wind. One birch catkin can produce over five million 
pollen grains. 

Below: The annual meadowgrass has a tall spike of flowers held 
above the leaves. The anthers dangle loosely outside the male 
flowers so the wind will blow their pollen away. The feathery 
stigmas catch the pollen from other flowers. 




Blown by the Wind 

Many flowers are wind-pollinated, for example 
many trees, grasses and some common weeds 
such as stinging nettle. Launching pollen on the 
wind is a risky business for a plant because it is a 
matter of chance whether the pollen reaches its 
destination. So the plant needs to produce a lot 
of pollen to make sure some of it stands a chance 
of landing on the stigma of another plant. For 
example, one male plant of dog's mercury (a 
small plant that grows in European woods) can 
produce about 1.3 billion pollen grains! 

Apart from producing lots of pollen, the 
shape of wind-pollinated flowers and the way the 
different parts of the flowers are arranged helps 
their pollen to be blown away by the wind and 
the pollen of other flowers to be trapped on their 
stigmas. They do not need the large colorful 
petals, scent or nectar (a sweet food) that other 
flowers use to attract insects and other animals 
to carry their pollen. (Turn to pages 72 and 73 to 
find out about flowers that are pollinated by 
animals.) 

Instead, wind-pollinated flowers are usually 
small and grouped in a long flower stalk called 
an inflorescence. In some plants, such as grasses, 
the inflorescence is held high above the leaves 
but in others, such as tree catkins, it dangles 
below them. The anthers are large and hang 
outside the flower on long stalks called filaments. 
Even a slight breeze can shake the flower so that 
pollen is released. 

The pollen grains themselves are small and 
light, with a smooth, streamlined surface, which 
helps them to travel easily on the air currents. 
There are records of pollen traveling as far as 
3,000 miles (5,000 kilometers) - far enough to 
cross the United States at its widest point. To 
catch the pollen arriving from other flowers, the 
stigmas hang outside the flower and are large, 
branched and often feathery. You may have 
seen the long tassels on a corn stalk. 



Hay Fever 

People who suffer from hay fever are allergic to 
pollen in the air. In the spring and summer, 
when plants are producing clouds of pollen, 
these people sneeze and their eyes and noses run 
almost as if they had a cold. Sometimes they also 
have difficulty breathing. Tablets or injections 
may help to relieve the symptoms. 



71 



Pollen Messengers 

Many flowers rely on animal messengers, es- 
pecially insects, to carry their pollen from one 
flower to another. This sort of flower is easy to 
recognize. The petals are usually large and 
brightly colored. They may be scented and 
produce a sweet food called nectar for their 
pollen carriers to eat. The anthers are firmly 
fixed on top of strong filaments and are held in 
just the right place for pollen to brush off onto 
an animal visiting the flower. The pollen grains 
may even be rough and sticky to cling to an 
animal's body. (In many orchids, the pollen 
grains stick together in clumps so that they can 
be carried in a sort of parcel.) The stigmas are 
held where a visiting animal cannot avoid 
touching them. 

Insect Visitors 

Insects are often attracted to a flower by its 
color. Yellow, blue and white are particularly 
popular. Markings on the petals may act much 
like the guiding lights on an airfield, showing the 
insect where to land and which direction to 
move in. Some of these colors and markings are 
invisible to us because we cannot see ultraviolet 
light. 

An interesting smell also attracts insect visi- 
tors. The sweet scent of flowers such as lavender 
and honeysuckle advertises nectar, which is the 
favorite food of many insects. Honeybees turn 
nectar into honey. It would take one bee eight 
years to make a pound of honey. 

Not all plants smell pleasant - some smell 
revolting. Many flies feed on rotting meat and 
some flowers can reproduce the smell perfectly 
to trick insects into visiting them. The Stapelia 
flower not only smells like decaying flesh but 
looks like it as well. It has red petals that look 
like meat and hairs around the edge that look 
like fur. The disguise is so good that female flies 
lay their eggs on the flowers, just as they do on a 
real carcass. 

An insect does not need any special skills to 
be a pollen messenger. Clambering about inside 
a flower is often enough to get dusted in pollen. 
Some insects actually eat some of the pollen. 
Bees collect pollen and feed it to their develop- 
ing young. But there is usually enough pollen 
left over to be carried to other flowers. One 




Above: Honeybees scrape off the pollen dust that clings to their 
bodies and pack it into pollen baskets made of stiff bristles on 
their thighs. They use the pollen to feed their young and only a 
small amount of it pollinates flowers. But bees do pollinate flowers 
as they search for their favorite food, nectar. Watch a bee as it 
collects nectar and try to see which flowers it visits most often. 




72 




Rafflesia is the largest flower in the world and measures about 
three feet (one meter) across. It attracts flies to its huge petals 
which look and smell like rotting meat. As they clamber about on 
the flower, the flies deliver and collect pollen. Only the flower 
grows above ground. The rest of the plant is a network of threads 
that grows inside the roots of a vine. 

Left: The arum lily lures flies into its flower chamber with 
warmth and a powerful smell. The flies climb past the unripe 
anthers and onto the stigmas, where some of the pollen they are 
carrying rubs off. They are trapped for about three days until the 
downward-pointing hairs shrivel. Then the anthers open to dust 
the insects with pollen and they climb out of their prison. 

species of myrtle produces two sorts of pollen - 
one that pollinates flowers and one that is 
particularly tasty and more likely to be eaten by 
insects. 

Plants that do not have much pollen to spare 
guide insects to just the right place. Often the 
weight of the insect on the petals is enough to 
trigger a flick of the anther so that pollen is 
smeared onto its head, back or abdomen. You 
can see this happening if you watch a bee 
landing on an Antirrhinum (snapdragon) flower. 
As the bee pushes the petal down, the anther 
jerks forward and showers pollen onto its back. 

Special Insect Flowers 

Some flowers have developed unusual ways of 
making sure their pollen always goes to the right 
sort of flower so that no pollen is wasted. These 
flowers are tailor-made to suit a particular 
insect. 

Some orchid flowers look, smell and feel very 
much like a particular species of female insect. 
Different species of orchid look like different 
insects - you can see one that looks like a bee on 
page 23. A male insect of the same species is 
attracted to the flower and tries to mate with it. 




Orchid flowers have special "pollen parcels" called pollinia 
instead of anthers. The pollinia consist of clusters of pollen grains 
stuck firmly together in a club-shaped structure. At the base of 
each pollinia is a sticky pad which can glue it to the head of an 
insect that visits the flower. The bee in the picture above has two 
pollinia stuck to its head. These may fertilize the unpollinated 
orchid flower it is about to land on. The bee may also pick up 
more pollinia from this flower before it leaves. 

As he does so, a parcel of pollen sticks to him. 
He then flies from flower to flower and as he 
tries to mate with each of them he collects and 
delivers pollen. 

The only insect that can get pollen from the 
South American yucca plant is a moth with a 
tongue that curves in just the right way to pick 
up pollen. The moth packs the pollen into a ball 
and flies off with it to another flower. She lays 
her eggs through the wall of the ovary in this 
flower and then climbs up to the stigma and fixes 
the pollen ball there. Seeds can then develop in 
the ovary along with the moth caterpillars. So 
the yucca provides a nursery for the moth and 
the moth pollinates the yucca. 

Bird and Bat Messengers 

In tropical countries, some flowers are polli- 
nated by birds. They produce a particularly rich 
nectar for their special visitors. A few tropical 
flowers are also pollinated by bats. Bats are 
color-blind so the flowers are often rather dull 
colors. They open in the evening as the bats start 
to fly and attract them with an interesting smell. 
As the bat laps up nectar with its long tongue, 
pollen dust is showered onto its body. 



73 




A common poppy- 
flower, with two 
seed capsules in 
the background. 
Each poppy flower 
can produce hun- 
dreds of seeds. 



Making Seeds 



When the pollen carried by the wind or an 
animal messenger lands on the stigma of a 
flower, it has to make its way to the ovule before 
a seed can develop. It soaks up sugary liquid 
from the stigma and a tube grows out of the 
pollen grain, down the style and into the ovary. 
It enters the ovule through a tiny hole called the 
micropyle. 

Inside the ovule, the tip of the pollen tube 
breaks open. It releases a nucleus that joins with 
the nucleus of the egg cell. This process is called 
fertilization and the new cell that is formed is the 
start of a seed. Many pollen tubes may start to 
grow down the style but only one will fertilize 
each egg cell. In flowering plants, a second 
nucleus comes out of the pollen tube and joins 
with another female nucleus in the ovule. This 
may then grow to become a food supply (called 
endosperm) for the developing seed. 

The petals, stamens, style and stigma are no 
longer needed. They wither away and usually 
drop off. The sepals sometimes stay and may 
develop to protect the seeds. The hard green 
lump at one end of an orange is the remains of 
the sepals. 




Left: Cross section of the 
ovary of a daffodil. The 
ovules grow in rows 
around the center of the 
ovary. Each ovule can 
develop into a seed if it is 
fertilized by pollen. Try 
slicing open the ovaries 
of different flowers to see 
how the ovules are 
arranged. 



Below: A simplified diagram of a single carpel in an ovary after 
fertilization. A pollen tube grows down to the ovary from a pollen 
grain that lands on the stigma. It usually enters the ovule through 
a small hole called the micropyle. The tip of the pollen tube breaks 
open and releases two male nuclei. One of these fuses with the 
female nucleus in the ovule to become the first cell of a new seed. 




74 



Plumule 
Radicle 



Suspenso 




Integuments 
will develop 
into seed coat. 



Above: A simplified diagram of a seed forming in one of the 
carpels inside an ovary. You can see the miniature plant 
developing in the middle. It has a shoot (plumule), a root (radicle) 
and two seed leaves, which are called cotyledons. The cotyledons 
contain enough food to feed the plant until it can make its own 
food. 

Left: Cross section of a corn Kernel to show the developing 
embryo. 



From Seed to Fruit 

The seed ripens with food sent to it from the 
leaves. It develops a miniature shoot (called a 
plumule) and a miniature root (called a radicle) 
and one or two seed leaves called cotyledons. 
The cotyledons may be a rich food supply for the 
new plant. Grasses, cereals and narrow-leaved 
plants such as tulips have one cotyledon and are 
called monocotyledons. All other flowering 
plants have two cotyledons and are called 
dicotyledons. 

The seed grows a waterproof coat (called a 
testa), which helps to protect it from pests and 
diseases. If you split open a broad bean you can 
see the miniature plant inside. The two large 
lobes are the cotyledons and between them are 
the tiny root and shoot. At one end is a scar 
(called a hilum) where the seed was joined to the 
bean pod (ovary wall). You may also be able to 
find the hole where the pollen tube entered. A 
bean seed has no endosperm, just large 
cotyledons. You can see endosperm in the seed 
of a grain plant, such as corn. 

When the seed is fully grown, it becomes hard 
as it dries out, ready to survive in difficult 
conditions. By this time the ovary wall has 
developed into a fruit. Some fruits, such as 
plums and cherries, have one large seed but 
other fruits, such as grapes and tomatoes, 



contain several small seeds. A blackberry is 
several small fruits joined together in a structure 
called a drupe. Each pip is a seed. In a straw- 
berry, however, each pip is a whole fruit. The 
red, fleshy part is the swollen center of the 
flower. Apples and pears are fleshy flower stalks 
that grow around the ovary and join the ovary 
wall. Many structures called vegetables (such as 
squash and green peppers) are really fruits 
because they contain seeds. 

When do Plants Make Seeds? 

Plants do not make seeds all the time. Some, 
such as the poppy, make seeds at the end of one 
growing season and then die. They are called 
annuals and survive the winter cold or a dry 
season only as seeds. Other plants, such as the 
carrot, grow for two years before they flower, 
produce seeds and die. They are called bien- 
nials. In their first year, biennials store food 
underground to help them survive the following 
winter or dry season. Plants that grow for 
several years are called perennials. Some peren- 
nials, such as many trees, make flowers and 
seeds every year. But others only do so from 
time to time. Most trees can live for hundreds of 
years. Plants that reproduce by runners, such as 
strawberries, can live indefinitely. 



75 




Above: The fruits of a cut-leaved cranesbill plant. On the left of 
the picture are some unripe fruits. When the fruits are ripe, they 
explode and curl up, as you can see to the right of the picture. 
This throws the seeds away from the parent plant. 




Above: A squirting cucumber plant with flowers and unripe 
fruits. When these are ripe, they will burst open to shoot the seeds 
out. They may travel for several yards before they fall to the 
ground. If they land in a suitable place, they may grow into new 
plants. 

Right: The Indian balsam plant has capsules which suddenly twist 
open to throw out the seeds quite violently. A slight touch is 
enough to trigger a mini-explosion that shoots the seeds away 
from the fruit. You can see how this happens in the diagram 
below (to the right). 



Below left: A vetch pod suddenly splits and throws out the seeds. 




Spreading Seeds 

If a seed sprouts too near its parent, it may not 
get enough light, water and minerals to grow. So 
once a plant has made seeds, it must spread 
them to make sure they have a good start in life. 
Seeds travel away from the parent plant in four 
ways. They may be thrown out by the plant itself 
or be carried away by the wind, water or passing 
animals. If a fruit splits open when it is ripe and 
shoots its seeds out, it is called a dehiscent fruit. 
If the seeds are released by some other means, it 
is called an indehiscent fruit. 

Catapults and Guns 

Some plants sow their own seeds with the help of 
springs and catapults. When gorse pods are ripe, 
the two halves suddenly twist apart, flinging the 
seeds in all directions. Many fruits shoot out 
their seeds if something touches them. For 
pennycress, the weight of a raindrop is enough 
to eject the seeds. One of the strangest fruits is 
the squirting cucumber. It squirts all its seeds 
out in a stream through a sort of plug hole. The 
seeds may land several yards away. 

Wind Transport 

The wind can carry seeds for many miles - an 
average journey for a dandelion seed is about 6 
miles (10 kilometers). Orchid seeds are so small 
they drift like dust in the air. Many seeds have 




some sort of wings to help them glide or spin 
through the air. Most conifer seeds are spread 
this way as are the familiar spinning "keys" of 
sycamore and maple. Scabious and thrift seeds 
develop little frills and float on the wind like 
shuttlecocks. Tumbleweed plants scatter their 
own seeds by uprooting themselves and rolling 
along in the wind. 

Water Transport 

Not many seeds travel by water. Those that do 
are mostly from water plants. They have a 
waterproof skin and some sort of float. In the 
Indian lotus plant, the whole woody seed head 
breaks off and floats like a raft. 

Animal Transport 

Many plants depend on animals to spread their 
seeds. Some fruits and seeds have hooks to stick 
to the coat of a passing animal. They may be 
carried long distances before they are brushed 
off by the undergrowth. Other fruits have bright 
colors and sometimes have a shiny surface to 
attract animals to eat them. The seeds have 
tough walls so they pass through the animal 
unharmed and come out in the droppings. If a 
seed lands in a suitable place, it may grow into a 
new plant - with the help of natural fertilizer in 
the droppings. Nuts may be spread by animals 
that store them for the winter. The animals often 
collect more than they need and the left-overs 
can grow in the spring. 



Below: A female blackbird eating hawthorn berries. Birds eat 
juicy berries and either spit out the seeds or pass them out with 
their droppings. The seeds can then grow into new plants. Some 
seeds have to pass through an animal's system before they sprout. 




SEEDS ON YOUR FEET 

Animals often pick up seeds on their feet and carry them 
away from the parent plant. How many seeds do you pick 
up on a muddy walk? Try the experiment below to And out. 




1 . Scrape the mud off your boots or shoes into a tray or 
flowerpot of sterilized compost. You can sterilize the 
compost by baking it in the oven. This kills any living seeds 
in it. 




2. Water the tray and cover it with glass or plastic. (This 
will stop any seeds from the air getting in.) Keep it moist 



3. Watch to see how many seeds sprout in the tray. They 
can only have come from the mud you brought home on 
your shoes. 



Below: Some seeds, such as the dandelion (left) are blown away by 
the wind. Others, such as sanicle (right) have hooks or barbs 
which catch in the fur of passing animals. 



A seed of sanicle attached to 
the fur of an animal with its 
tiny hooks. 





A dandelion with the seeds 
blowing away. 



77 



How Plants Grow 



Seeds are survival kits against cold and dry 
conditions. They do not usually grow as soon as 
they land on the soil but remain dormant for 
days, months or even years. They begin to grow 
only when they have enough warmth, water and 
oxygen. This process is called germination. 

A seed begins to germinate by taking in water. 
It swells up and the seed coat splits. The root 
appears first and grows down into the soil. Then 
the shoot begins to grow upward. In flowering 
plants, roots grow down and shoots grow up - no 
matter which way up the seed is planted. The 
stored food in the cotyledons or endosperm 
helps the seed to grow until the new plant 
develops leaves to make its own food. 

In plants such as the broad bean, the 
cotyledons always stay underground. This sort 
of germination is called hypogeal, which means 
"under the soil." In plants such as the sunflower, 
the cotyledons are pushed above the ground and 
become the first green leaves. This sort of 
germination is called epigeal, which means 
"above the soil." 




78 




Above: Part of an onion root under a high-power microscope. In 
the tip of the root (behind the root cap) the cells are dividing over 
and over again so that the root grows longer. This region is called 
a meristem (growing tip). You can see the nuclei (dark circles) in 
the center of the cells. The root cap protects the meristem as it 
pushes through the soil. 



Left: A coconut seedling germinating. The seedling cannot make 
its own food until the first green leaves develop. Until then it 
depends on food stored inside the seed. 



The growth of roots and shoots is controlled by chemical 
messengers called auxins. Auxins are similar to the hormones that 
control animal growth. In a shoot, auxins are produced at the tip 
and travel downward to make the cells behind the tip grow. Light 
destroys the auxin so the shoot grows more on the side away from 
the light. This makes the shoot curve toward the light. In a root, 
auxin slows the growth of cells. It gathers in the cells on the lower 
side of the root. The cells on the upper side grow more so the root 
curves downward. These movements of the shoot and root are 
called tropisms and they help the plant to get the light and water it 
needs to grow. 




Growing Longer and Thicker 

Plants, unlike animals, continue to grow 
throughout their lives. Growth takes place in 
certain regions of the plant called meristems. In 
a young plant the meristems are at the tip of the 
roots and shoots. The cells continually divide 
and expand to push the shoot up and the root 
down. 

Plants that do not survive from year to year 
above the ground grow mostly by increasing in 
length like this. But woody plants, such as trees 
and shrubs, get thicker as well as longer. As this 
takes place after they have increased in length, it 
is called secondary thickening. 

The meristem that produces this outward 
growth is called vascular cambium. In a young 
woody plant, this consists of small groups of cells 
between the xylem and phloem in each vascular 
bundle of a root or shoot. These link up to form 
a ring of cambium separating the xylem from the 
phloem. Then the cambium cells produce a thick 
ring of new xylem tissue (wood) on the inside 
and a thin ring of new phloem tissue on the 
outside. Another meristem, called cork cam- 
bium, is formed just under the surface of the 
stem. This produces the thick-walled cork cells 
in bark. 




Above: The ancient eastern tradition of bonsai has produced this 
miniature Pinus thunbergii tree. Bonsai trees grow from normal 
trees but do not get enough food and water to grow to a normal 
size. Their shoots are pruned and their roots trimmed so they 
remain as dwarfs. It takes great skill to produce a bonsai tree and 
may take many years to create a tree like this. Some bonsai trees 
are hundreds of years old. 




Wild daffodils growing in the 
country. 



Left: Cross section of daffodil 
bulb to show the swollen leaf 
bases wrapped around a short 
underground stem. 
Food made in the leaves is sent 
down to the leaf bases to be 
stored during the summer. 
New bulbs develop from side 
buds that grow out from the 
main stem. 



Below: Cuckoo pint stores food 
in a swollen underground stem 
called a conn. Strong roots pull 
the corm back down into the 
soil. 




New Plants from Old 

Some flowering plants can produce a new plant 
from a small part of themselves as well as (or 
instead of) reproducing by seeds. A small 
section of the plant, such as part of a stem or 
leaf, can replace the missing parts and develop 
into a new individual. This is known as vegetative 
reproduction. 

People take advantage of this to reproduce 
their house or garden plants. They cut off a 
healthy young shoot and plant it in some fresh 
soil. If roots grow, the cutting may become 
established as a new plant. New begonias and 
African violets can even be grown from the 
leaves. 

Many plants survive from year to year by 
means of vegetative reproduction. They form 
storage organs, such as bulbs, in which they 
store the food they make during the summer. 
The storage organ remains in the ground over 
the winter after the rest of the plant has died. A 
new plant grows out of it the following year, 
using the energy in the stored food. This allows 
woodland plants that grow from bulbs to 
develop leaves and flowers early in the year 
before the leaves on the trees cut out the 
sunlight they need to make food. 

A bulb has buds (just like any stem) so a new 
bulb may sprout from the side of the old one 



Bryophyllum produces tiny plantlets along its leaves. 

during the growing season. Gardeners often dig 
up the new bulbs and plant them separately, 
ready for the following year. 

Other storage organs may also be a way of 
reproducing as well as helping the plant to 
survive the winter. Some plants, such as irises, 
store food in swollen underground stems called 
rhizomes. Rhizomes can become quite large, as 
the old stems last for several years. Plants, such 
as the potato have slender rhizomes with swollen 
tips, called tubers. The actual potato is a tuber. 
If you look at a potato you can see it is a stem 
because it has traces of the leaves and buds - 
these are the "eyes." Each eye can grow into a 
new plant using the food stored in the potato. 

Buttercups and strawberry plants produce 
long, spindly stems, called runners, above the 
ground. At the end of the runner, a new plant 
begins to grow and take root, using the food 
passed along from the parent plant. When the 
plant is big enough to make its own food, the 
runner withers and dies, leaving the new plant 
growing by itself. 

A blackberry bush is really many blackberry 
plants made by the stems arching over and 
taking root where they touch the soil. Unlike the 
strawberry, the stems that produce new plants 
do not die but continue to grow, making the 
bush more and more tangled. Gardeners some- 
times produce new bushes by bending over a 
young branch on a shrub and pushing it into the 
soil so that roots will grow. 



Left: The under- 
ground stem (rhi- 
zome) of an iris, 
which is full of stored 
food. The bud at the 
tip of the rhizome 
turns up and pro- 
duces leaves and flow- 
ers above ground. 

! nr : Ground lev 



HI 




^^^^ Blackberry 
stolon 




New 



Above: Potatoes are the 
swollen tips of under- 
ground stems. They are 
called tubers and store 
food made in the leaves. 



New plants sprout 
from strawberry 
runners. 



/■;v 



Above: When black- 
berry stems arch over 
and touch the ground, a 
new plant develops. The 
stems are called stolons, I 



81 



Algae, Mosses 
and Ferns 

Algae, mosses and ferns do not have flowers and 
so cannot make seeds. Instead they produce 
spores, which develop inside a structure called a 
fruiting body. Spores are small and light and 
float on the air or sometimes on water. If they 
land in a suitable place they may grow into new 
plants. 

Algae 

Algae alive today include the seaweeds and 
microscopic forms that turn pondwater green. 
Some algae can reproduce simply by splitting 
into two. Others grow from fragments of the 
parent plant or sprout from the end of long 
runners produced by the parent plant. Some 
algae grow from spores produced when two cells 
join together. Many algae can reproduce in 
more than one way. 

Mosses 

The leafy moss plant grows from a spore that has 
landed in a suitable spot. The tips of the shoots 
grow special sex cells - female egg cells on some 
shoots, male cells on others. A male cell swims 
to an egg cell and fertilizes it. The egg cell does 
not grow into a moss plant but makes spores 
instead. From the fertilized egg cell a stalk grows 

Below: The life cycle of a common moss, such as Funaria. The 
leafy plant produces male and female cells, which join together to 
grow into a case containing spores. This remains attached to the 
leafy plant. Spores are released into the air and grow into a new 
leafy moss plant if they land on a suitable patch of ground. 

Spores 




case Female egg cell released from 

grows on stalk in structure on structure on 

on leafy plant. leafy moss plant, leafy moss plant. 




Above: Part of two strands of an alga called Spirogyra as it 
appears under the microscope. Spirogyra can produce a special 
sort of spore when the contents of one cell pass through a tube to 
join with the contents of a cell in a different strand. The spore is 
protected by a thick coat and can survive difficult conditions. 




Above: A diatom is a single-celled alga with a silica case made of 
two halves. When the cell divides, the two halves of the case pull 
apart and each half quickly makes a new case to fit inside the old 
one. When the cases get very small, sex cells are produced and 
they fuse to form a new diatom. 




82 



Spores 
are 

released. 

Prothallus 

develops. 



The prothallus 
produces male and 
female cells, which 
join to form a new 
fern plant. 

Above: The life cycle of the common fern, Dryopteris. It 
reproduces in two stages, like the moss on page 82. Look for the 
brown spore cases under fern fronds. 

Below: The fronds of male fern unfolding in spring. This fern 
grows in woods, mountainsides and home gardens. The stem is 
underground. 





upward with a capsule full of spores at the top. 
When the capsule is ripe, it releases the spores. 

Ferns 

Ferns, like mosses, develop in two stages. In 
mosses the main plant is the one that produces 
male and female cells. In ferns the main plant is 
the one that produces spores. Fern spores 
develop in brown spore cases called sporangia 
under some of the leaves {fronds). The sporan- 
gia usually occur in round or long, thin clusters 
called sori (singular sorus) but in some ferns 
they are evenly distributed over part or all of the 
underside of the frond. 

When the spores are ripe, the sori split open 
in dry air and the spores are flicked clear of the 
plant. They look like dust to the naked eye but 
under the microscope it is possible to see 
patterns such as spines, pores and ridges on the 
surface of the spores. The spores need damp 
conditions to germinate. They grow into a thin, 
heart-shaped leaf called a prothallus (plural 
prothalli) on the surface of the ground. Most 
prothalli are less than half an inch (one 
centimeter) long. 

Minute roots and microscopic sex organs grow 
underneath the prothallus. Sex cells develop 
inside the sex organs. In the dark and the damp, 
the male cells swim to the female cells and 
fertilize them. The new cell grows into a fern 
plant, which lives on the prothallus until it is 
established. It grows so slowly that it may take a 
year before a new fern plant appears. 



Below: This liverwort is best known as a weed in greenhouses 
where it grows on the soil in flowerpots. Liverworts reproduce by 
spores in a similar way to their relatives, the mosses. New plants 
can also grow from buds sprouting from the parent plant. 




83 



A FOUR-LINK FOOD CHAIN 




eats leaf. caterpillar. 



Above: The sun's energy is trapped by plants, which are in turn 
eaten by animals. This is called a food chain. Food chains link 
together to form food webs because most animals have several 
kinds of food. 




Above: White rhinoceroses have ridged teeth and broad mouths 
for cropping grass. They graze on the savanna plains of Africa. 
Below: A sea anemone feeding on a prawn. Sea anemones have 
stinging cells to paralyze their prey. 



Finding Food 

Living things obtain the food they need in a 
variety of different ways. Green plants make 
their own food from chemicals they take in from 
the air, soil and water. Animals, however, 
cannot make food. They have to take it in 
ready-made by eating plants or other animals. 

Plant-eaters are known as herbivores. They 
include animals such as horses, sheep and 
rabbits that graze on grass, as well as less 
familiar animals, such as shellfish called limpets, 
which feed on the seaweed growing on rocks. 

Herbivores are eaten in turn by meat-eating 
animals, which are called carnivores. These 
include the lions, wolves and other big carni- 
vores, which can kill herbivores the size of a 
horse. Small carnivores such as sea snails drill 
holes through the shells of shellfish and suck out 
the soft insides. Carnivores may also eat other 
carnivores. For example, killer whales hunt 
seals, which feed on fish. Some animals, called 
omnivores, eat both plants and animals. 

The dead bodies of plants and animals and the 
waste substances they produce also provide food 
for other creatures. For instance, vultures tear 
flesh from dead animals, certain beetles feed on 
dung and earthworms extract nutrients from 
rotting leaves. Soil contains tiny organisms 
called decay bacteria which break down dead 
plant and animal material into simple chemicals. 
These chemicals are sucked up by the roots of 
plants. 



Thus, every creature in the natural world is 
linked with another which either eats it or is 
eaten by it, forming a food chain. Many of these 
food chains are connected, as most animals feed 
on more than one kind of plant or other animal. 
So the chains themselves link up to form a food 
web - the web of life. 

Hunting Tactics 

Many hunters have special features that help 
them to find food. Owls have huge eyes and very 
sensitive ears that help them to detect their prey 
at night. A flying bat squeaks and listens for the 
echoes bounced back off flying moths. This 
helps the bat to home in on the moths and snap 
them up. 

Some hunters chase their prey over long 
distances. A pack of wolves may pursue a 
caribou for miles. When it tires they run in for 
the kill. Big cats, such as lions, prefer to creep 
up stealthily and make a short, sharp rush to 
finish the animal off. Certain other creatures set 
traps or lures and wait for prey to come to them. 
An insect called an ant lion digs a little pit in 
sand and feeds on the ants that tumble in. The 
deep-sea angler fish grows what looks like a 
fishing line baited with wriggling worms. When 
fish swim up to seize the "worms" the angler fish 
swallows them up. 

Teeth, beaks or claws are the main weapons 
for many hunters, but a few make use of tools. 
Egyptian vultures drop lumps of rock on ostrich 
eggs to break open the shells and sea otters 
crack open clams by bashing them with stones. 

Below: Some animals feed on dead and decaying matter. Dung 
beetles shape dung into a ball and then usually work in pairs to 
push the ball along until they find a suitable place to bury it. The 
female lays one or more eggs in the ball of dung and the larvae 
feed on it as they grow. 





Above: The feathery tentacles of the fanworm wave in the sea 
currents to trap tiny particles of food. Fanworms live in 
protective tubes made of small stones or sand grains stuck 
together. They build up the tubes as they grow. 



Below: An egg-eating snake can unhinge its jaws so that they 
stretch wide enough to allow it to swallow a whole egg. This may 
take up to 15 minutes for a large egg. Sharp bones in the snake's 
throat crush the egg shell. The snake swallows the contents of the 
egg and spits out the crushed shell. 




Staying Alive 

Many animals and plants have special character- 
istics to help them avoid ending up as another 
animal's dinner. 

Running Away 

Long-legged grazing or browsing animals can 
outrun most of their enemies. A herd of 
antelopes can outgallop a lion, if the antelopes 
have a start. Rabbits can run faster than most 
dogs. If speedy creatures get caught, it is 
probably because they are either old, very 
young, ill or taken by surprise. 

Escaping somewhere out of reach of enemies 
is another way to stay alive. Agile monkeys and 
mountain goats can outclimb leopards. Scared 
terrapins plunge into a nearby pond. Frightened 
rabbits dash down burrows. 




Above: A grass snake sometimes pretends to be dead when it is 
attacked. This may fool its attacker into leaving it alone. 
Below: Armadillos are small "armor-plated" mammals that roll 
up into a ball when attacked. Their "armor" protects them. 




Armor and Thick Skin 

Slow movers defend themselves in other ways. 
Turtles and crabs hide their soft bodies inside 
hard outer shells. In the same way that thick 
bark protects trees from the teeth of browsing 
mammals such as deer, animals such as 
elephants grow very thick skin which even a 
lion's teeth find hard to bite through. 

Clever Camouflage 

Camouflage is another life-saver. Camouflaged 
animals have shapes or colors like those of their 
surroundings. For instance, a flounder looks like 
the patch of sand it lies on. Many newborn deer 
are brown with pale spots. When they lie down 
in a wood, they look just like a patch of bracken 
lit by sunlight. 




ADOve: The wobbegong is an Australian shark, which is 
camouflaged by a fringe around its head. 

Below: Some plants have swollen leaves that look like pebbles. 
This disguise probably helps them to escape being eaten. 





Certain creatures do not just match the colors of 
their surroundings, they match the shapes of 
objects around them as well. You can easily 
mistake a looper caterpillar for a short, brown 
twig, while some butterflies look just like real 
dead leaves. But all these camouflaged animals 
stay safe and hidden only while they keep quite 
still. The moment they move, they may be 
discovered and eaten. 

Weapons and Poisons 

Not all animals freeze, run, hide or rely on 
armor to protect them when they are 
threatened. Some have formidable weapons of 
defense. Sea urchins look like small pincushions 
bristling with long, sharp pins. Larger animals 
such as hedgehogs and porcupines also have 
protective spines. A hedgehog curls up into a 
spiny ball when attacked but a porcupine will 
back into its enemy and drive its long, sharp 
quills into its attacker's legs or face. Spines also 
help to protect plants from grazing animals. 

Claws, hooves, horns and teeth are among the 
best weapons of defense. Africa's rhinoceroses 
and buffalo put down their great horned heads 
and charge an enemy. An ostrich can kill a 
person with a powerful kick from one of its 
clawed feet. Even a cornered rat can give a 
painful bite. 

Some plants and animals protect themselves 
with poisons. These may just make them taste so 



unpleasant that animals avoid eating them. Or 
they may be strong poisons that can kill their 
attackers. Bees can kill other insects with their 
poisoned stings and many frogs, toads and 
salamanders have deadly poisons in their skin. 
Such poisonous or unpleasant-tasting animals 
are mostly brightly colored as a warning to 
would-be predators to keep away. 

Yet other creatures just pretend that they are 
dangerous. Harmless milk snakes look almost 
identical to deadly coral snakes. Some moths 
open their wings suddenly to reveal what look 
like two big, frightening eyes. The frilled lizard 
spreads its neck frill to make its head appear 
large and terrifying. 



Below: The bright colors on the wings of this tiger moth make it 
easy for enemies to see. But birds soon learn that this brightly 
colored insect tastes unpleasant. 





Above: A sweetlip fish lets a little wrasse swim inside its mouth to 
feed off parasites. Both fish benefit from this arrangement. 
Below: Sea anemones live on the outside of this whelk shell while a 
hermit crab has made its home inside. The crab is protected by 
the anemones' stings and the anemones eat any food the crab 
leaves. 




Living Together 

Certain living creatures form partnerships where 
animals or plants of different kinds live on, in or 
with one another. In some cases this helps both 
partners but sometimes the relationship is 
entirely one-sided. 

Some ferns, mosses and other plants sprout on 
the branches of jungle trees. (You can see one of 
these branches in the picture above.) This allows 
the plants to get more light than if they grew on 
the dark jungle floor. Falling leaves are caught 
on the branches where they rot and provide 
nourishment. Damp air and rain supply plenty 
of moisture. Plants that grow like this are known 
as epiphytes. They do no real harm to the tree 
but do not help it either. 

A partnership where both partners benefit is 
known as symbiosis. Symbiosis sometimes works 
with partners of very unequal sizes. A cow has 
millions of microscopic bacteria inside its food 
canal (see page 38). The bacteria help to break 
down grass into simple chemicals the cow can 
digest, while the cow gives the bacteria food and 
shelter. 

Certain fungi are close partners of conifers 
and various other trees and shrubs. Fungal 
threads grow around and inside the tree roots. 
The fungi take water and minerals from the soil 
and pass them on to the tree roots. The tree 



88 




Caterpillars in the butterfly family Lycaenidae often live in a form 
of symbiosis (see page 88) with some species of ant. The ants 
protect the caterpillar inside their nest and the caterpillar may 
even eat some of the ant larvae. In return, the caterpillars 
produce a sweet "honey" for the ants to eat. 



roots provide sugars in return. This special kind 
of partnership between the roots of a green plant 
and a fungus is called a mycorrhiza. 

Some plant and animal partners cannot exist 
without each other. They include the flowering 
plants and insects. Insects such as bees and 
butterflies get food from flowers. But as they fly 
from flower to flower they also spread pollen, 
which fertilizes the flowers' seeds. So without 
flowers the insects would starve and without 
insects the flowers could not produce new 
plants. 

There are several famous partnerships be- 
tween different animals. One involves the 
oxpecker bird and a rhinoceros. The oxpecker 
perches on the back of the rhinoceros where it 
eats flies and ticks and keeps a lookout and gives 
an early warning of danger. Another animal 
partnership involves clownfish, which live 
among the poisonous tentacles of a certain kind 
of sea anemone in the sea around coral reefs. 
The anemone does not kill the clownfish because 
the fish coat their bodies with a special sort of 
liquid. So the clownfish gain protection from the 
anemone and in return they may lure other 
creatures close enough for the anemone to 
catch. Both the clownfish and the anemone gain 
from the partnership. 



Parasites - All Take and No Give 

Parasites are plants or animals that live on or in 
other kinds of plant or animal, which are called 
their hosts. A parasite takes food from its host 
but gives nothing back in return. 

The largest flower in the world belongs to a 
parasitic plant called Rafflesia (see page 73). 
Rafflesia's other parts are just slim threads that 
suck food from the roots and stems of forest 
plants. Some plants, such as mistletoe, are only 
half parasites. Mistletoe produces some of its 
own food but also steals some from the trees it 
grows on. 

Microscopic parasites cause countless illnesses 
in plants and animals. Viruses give us colds, 
measles, mumps and other problems (see pages 
28-29). Certain fungi cause ringworm, a human 
skin disease, and other fungi produce rust 
diseases that damage grain crops. 



Right: A lamprey's ever- 
open mouth is a sucker 
armed with horny teeth. 
The lamprey fastens its 
sucker onto a fish and 
uses tiny teeth on its 
tongue to rasp away at 
the fish's flesh. Then the 
lamprey sucks its vic- 
tim's blood. 




Below: This photograph shows the pink stems of a parasitic plant 
called dodder growing on a gorse bush. Each young dodder plant 
puts out suckers that grip another plant. Then the dodder's roots 
die and it sucks nourishment from its unlucky host. 




89 



Partners and Rivals 

Male and female animals must meet and mate 
before they can breed. Each kind of creature has 
special signals, which help it to attract a partner 
of the same kind. These signals usually involve 
the creature's appearance, the sounds it makes 
or special scents it produces. 

Sight Signals 

Many male animals are bigger or showier than 
females of their own kind. Visual (sight) signals 
help these males attract a mate. For instance, 
male birds of paradise have much lovelier 
plumage than their females. They perform 
acrobatic dances in front of the females. Other 
kinds of males show off in special ways. Mallard 
drakes bob their heads. Male newts vibrate their 
tails. Male Siamese fighting fishes stiffen their 
splendid fins and waggle their bodies in front of 
female fighters. A male red-eared terrapin 
flutters its front legs against the sides of a 
female's head. Sight signals work even in 
darkness. Some female insects, such as fireflies, 
glow brightly at night to attract males. 

Sound Signals 

Grasshoppers and crickets use sounds as their 
mating signals. Males rub one part of the body 
against another. This makes a buzzing or 
chirruping sound. Males of different species sing 
different ''songs" to attract females of their own 
kind. It is the same with birds, frogs and toads. 
The low croak of a male common toad attracts 
only female common toads. 





Above: A small male frog can make a loud sound by blowing up 
his vocal sac. Male frogs call at mating time to attract a mate. 




Above: A male moth's feathery feelers (antennae) detect tiny 
particles of scent given off by females of his own kind. He follows 
the scent trail until he finds the female. Some male moths can find 
females several miles away. 

Below left: Peacocks try to attract peahens by spreading their 
great fan of feathers and shaking them in a spectacular display as 
they parade in front of the hens. 

Below right: Fireflies attract each other with flashes of light. 
Different species signal with different patterns of flashes. This 
helps each individual to recognize others of its own kind. 





Above: A male and female spoonbill preening each other. 
Preening is one of the acts of courtship that helps to bring a pair 
of birds together. After courtship and mating, both birds will 
work together to build a nest and raise a family. 



Below: These male impala are fighting for a herd of females. They 
clash their heads and horns together in a fierce sounding battle. 
But after a while, the weaker animal will back off and walk away. 
Neither animal usually gets seriously hurt. The male that wins the 
fight will mate with the females. 



Scent Signals 

For most insects and mammals, scent is the 
signal that brings males and females together. 
Usually a special scent produced by the female 
attracts the male. When a female dog is ready to 
mate, she gives off a strong scent that attracts 
male dogs from some distance away. 

Fighting for a Mate 

Some male animals have to fight other males to 
win their mates. Rival deer stags fight with their 
sharp, pointed antlers. They may lock their 
antlers together in a test of strength. Male fur 
seals slash at one another with their teeth. The 
winning stag or seal will mate with many 
females. But fighting males seldom hurt each 
other badly. Instead the weaker individual gives 
up and creeps away. 

A male animal may defend a special area 
called a territory in the breeding season. (Some 
animals defend territories all year round.) He 
may even threaten a female entering his terri- 
tory, especially if she looks like a male, as 
female robins do. The female has to make a 
special "give in" sign to stop the male's attack. 

Courtship 

When animals have found a mate, they may 
behave in a special way, which helps to stop the 
male attacking his mate and keeps the pair 
together while they raise their young. For 
example, a male bird may bring food to a 
female, who pretends to be a baby bird. She 
crouches down, flutters her wings and lets her 
beak gape wide. Male and female birds may also 
preen the feathers of their mate. 



91 



Animal Homes and Young 



Many animals do not make permanent homes. 
Some, such as fish, just sleep wherever they 
happen to be at the time. Others use natural 
shelters such as trees, caves or rocks. Antelope 
will rest under a tree, bats will roost in a cave. 

However, a large number of animals build 
nests and shelters or dig burrows in which to 
sleep, hide from their enemies or raise their 
young. The borers and burrowers dig holes in 
wood, rock, sand or earth. Other creatures build 
complex nests of many different materials with 
astonishing care. Some, such as bower birds, will 
build huge, elaborate constructions that they 
add to year by year. Fish called gouramis build 
nests of bubbles floating on the water. Wasps 

Four kinds of animal homes. The potter wasp molds a tiny 
pot-shaped nest of sand grains stuck together with saliva. She lays 
one egg inside. The foam-nesting frog lays her eggs in a ball of 
froth hanging from a branch. The tadpoles drop into the water 
below when they hatch. Young prairie dogs are born in the safety 
of underground burrows. Weaver birds twist strips of plant 
material together into complex nests which hang from trees. 




make nests of paper, while ants and termites 
mostly work with mud. A female rabbit digs a 
hole and lines it with her own fur. Harvest mice 
weave grass stems into a hollow ball and crows 
build large untidy nests out of twigs. 

Care of the Young 

Most fish, amphibians and animals without 
backbones lay eggs and then leave them to 
chance. Such parents have to lay many eggs for 
very few of them survive. But certain creatures 
take great care of their young. They need not 
produce so many eggs or babies because they 
each have a much better chance of surviving 
than if they were left on their own. 




Above: Baby kangaroos spend the first months of their life inside 
their mother's pouch. A newborn kangaroo is naked and no 
bigger than a person's thumb. Yet it manages to climb to the 
pouch where it can suckle its mother's milk in safety. 



92 



Baby animals often start life in the safety of a 
nest. Nests help to keep young birds and 
mammals warm and usually help to hide babies 
from enemies. Yet seabirds such as terns lay 
their eggs in just a small scrape in the sand of an 
open seashore. They breed in groups of 
thousands though, so parents can gang up to 
attack and drive away intruders. 

With most birds, both parents tend the young. 
An ostrich cock and hen take turns to guard a 
nest containing many eggs laid by several ostrich 
hens. With many birds, though, only hens sit on 
the eggs. A few female insects look after their 
young. And female scorpions carry babies on 
their back. With mammals, too, mothers per- 
form most of the work. A mother cat will lick 
her newborn kittens clean. A mother dolphin 



swims her newborn baby to the water surface for 
its first breath of air. All baby mammals suck 
milk from their mothers. 

Occasionally, only fathers care for the young. 
The male sea horse (a small fish) guards eggs in a 
brood pouch in his body. A male Darwin's frog 
gulps up eggs laid by a female. The eggs develop 
into froglets in a special pouch. When they are 
ready, they hop out of their father's open 
mouth. 

Some babies can fend for themselves as soon 
as they are born or hatch out of eggs. Newly 
hatched crocodiles will swim quickly away from 
danger. Such reptiles act largely by instinct and 
need little help from parents. Mammals, how- 
ever, cannot look after themselves at first and 
some are cared for by their mothers for years. 




1. Female cuckoo removes 2. Baby cuckoo throws out 
some eggs already in the nest other eggs in nest, 
and lays her own. 





Above: The male midwife toad wraps a string of eggs around his 
back legs. He carries them with him wherever he goes and dips 
them in water from time to time to keep them moist. After six 
weeks, he sits in water and waits while the tadpoles hatch and 
swim away. 



Chimpanzee 



3. Cuckoo is fed by its foster 
parents. 



4. Young cuckoo ready to 
leave the nest. 



Cuckoos lay their eggs in the nests of 
other birds. They play no part in rearing 
their own young. When the young 
cuckoo hatches out, it throws out any 
other eggs in the nest by heaving them 
over the side. Then it can eat all the food 
its foster parents provide. It is usually 
several times larger than they are by the 
time it is ready to leave the nest. 

Right: A young chimpanzee watching its 
mother Ashing for termites. The young 
chimp will soon learn to feed in the same 
way. Intelligent animals learn by copy- 
ing their parents. 




Termite mound 





Honeycomb 



> ) 



Above: This close-up view shows part of a honeycomb inside a 
nest of honeybees. Worker bees produce the wax that the comb is 
made of. They shape the wax into hundreds of cells. Each cell is a 
tiny, six-sided room. The shape of the cells allows a lot of cells to 
fit together in a small space. Cells serve as nurseries or food 
stores. The queen lays an egg in each nursery cell and workers fill 
the food store cells with pollen or honey to feed the growing 
larvae. Larvae that will develop into queens go in special royal 
cells. 



Friends and Relatives 



Queen 
termite 



Left: A termite's nest cut 
open to show the struc- 
tures inside. Termites 
are ant-like insects. They 
can control the tempera- 
ture inside their nest. 



Below: Termites built 
this huge nest by cement- 
ing earth together with 
saliva. Some termite 
mounds are much taller 
than a person. 



Some animals find it more useful to live in a 
group rather than "going it alone." Many 
creatures living together find safety in numbers. 
There are more eyes and ears to watch out and 
listen for danger. An enemy that would attack a 
lone animal might well be confused by the sheer 
numbers in a moving herd of antelope, a flock of 
starlings or a shoal of herring. There might 
actually be danger for the predator too. A falcon 
could be injured by flying into the middle of a 
flock of sharp-beaked starlings, so falcons tend 
to leave large flocks alone. 




Insect Cities 

Insects such as ants, bees, wasps and termites 
live in insect cities. A single ant colony or 
beehive may be home to several thousand 
insects. The colony thrives because all its 
citizens work together although each individual 
has special duties to carry out. 

In an ant colony, males mate with queens and 
queens lay eggs. Most of the eggs hatch into 
female workers. Small workers feed larvae that 
hatch out from the queen's eggs. Larger worker 
ants find food and bring it back to the colony. 
The largest workers, called soldiers, defend 
their colony. 

Honeybees work together in a similar way. A 
bee that finds some food returns to the colony 
and performs a kind of dance. The pattern of the 



94 




Above: Apes and monkeys, such as these langurs, spend a great 
deal of time grooming each other. The grooming removes dry 
skin, dirt and parasites. This process not only keeps the animals 
clean but also strengthens the bonds between group members. 



dance shows the direction other bees should 
take to reach the food. How often the bee 
waggles its body tells them how far away the 
food is. 

Inside each ant colony or beehive, the ants or 
bees are always passing food to each other. This 
helps to make the insects feel they belong 
together. The food also tends to give all 
members of one colony or hive the same scent. 
Outsiders have other scents. This helps the 
guard bees and ants to recognize intruders. 

Knowing Your Place 

Inside a group of mammals such as apes or 
monkeys, individuals give each other food or 
help to clean each other. This give-and-take 
helps to keep the members of a group together. 
But they are not all equal. Some hold a higher 
rank than others - this is called a pecking order. 
Chickens have a pecking order as well and this is 
where the name came from. The most aggressive 
individual holds the highest rank. This animal 
will nip or peck any of the rest and none of them 
fight back. The animal holding the second 
highest rank nips or pecks all but the top ranking 
animal. And so on down the pecking order. 

But rank is not always fixed. A female 
monkey and her offspring take the rank of the 
male she mates with. Any individuals that fall ill 
may drop several places in the pecking order. 




Above: Diagram of a troop of baboons. The adult males (green 
and gray) protect the females (tan) and their young (orange and 
blue), who stay in the center of the group. The young baboons can 
play there in relative safety. The troop is led by a dominant male. 

Below: A crowded breeding colony of fur seals. The big bull on 
the right is master of this stretch of beach. The smaller seals are 
his females. 




95 



The Changing Seasons 



In some parts of the world, each year consists of 
four seasons - spring, summer, autumn and 
winter. Plants and animals make the most of the 
warmer seasons and manage to survive the 
colder ones in a variety of ways. 

In spring, new leaves grow from the bare 
branches of trees such as oaks and beeches. 
Seeds sprout, insects hatch and birds build nests 
and lay their eggs. Mammals such as rabbits, 
mice and foxes have their babies. These young 
animals start life when food is just becoming 
plentiful. 

In summer, plants grow thick and fast and 
many produce flowers. Insects visit the flowers 
to feed on pollen and nectar. Young mice and 
rabbits munch tender grasses while foxes and 
owls catch some of the mice and rabbits to feed 
to their own young. 

Autumn brings many changes. Many plants 
produce seeds and some trees lose their leaves. 
Mammals such as bears and hedgehogs try to eat 
enough food to last them through the winter. 
Lizards, snakes and frogs hide underground as 
the days grow chilly. 

In winter, the days are short and cold. Frost 
kills many soft-stemmed plants and insects that 
cannot hide away from the cold. Hedgehogs and 
bears sleep through the winter but rabbits, 
weasels and foxes stay awake and have to search 
for food. 

Right: In autumn, the leaves of deciduous trees turn yellow, red 
and orange and begin to fall off the trees. This helps the trees to 
survive the winter by reducing water loss. 

Below: The short-tailed weasel in its winter coat. In northern 
lands, weasels and stoats turn white in winter. Because they 
match the snow around them, their enemies cannot see them 
easily. 



Mushroo 



Spore print 




Above: Fungi usually produce fruiting bodies, such as mush- 
rooms and toadstools, in late summer or autumn. These fruiting 
bodies give off many thousands of spores, which can grow into 
new fungi. Try leaving a mushroom on a piece of paper overnight. 
The spores that fall off make a ray-like pattern. 





Above and left: The red arrows 
on these maps show the migra- 
tion routes of the arctic tern 
(above) and the monarch but- 
terfly (left). 




Above: Once in their lifetime, adult eels cross the Atlantic Ocean. 
They spawn in the Sargasso Sea - the ringed area of the map. 
Then they die. But ocean currents take their young back across 
the ocean to the United States or Europe. 



Amazing Journeys 

Certain birds, mammals and other animals are 
tremendous travelers. Each year they journey 
many hundreds or even thousands of miles, 
often going without food or water for several 
days. This is called migration. Animals migrate 
mostly to escape the cold or find new feeding 
grounds. Each spring, some warblers, ducks, 
geese, swans and wading birds fly north. They 
raise their young in the long, warm summer days 
of northern lands when food is plentiful. In 
autumn, when food becomes scarce, the tem- 
perature drops and the days grow shorter, the 
migrants and their young fly south to a warmer 
climate. 

Birds are not the only airborne migrants. Bats 
fly long distances overland as well. Some 
butterflies can also travel long distances. 
Monarch butterflies that breed in Canada fly 
south for the winter and millions of these 
creatures spend the winter clustered on tall trees 
in Mexico. Deer called caribou spend summer 
grazing in Arctic North America. As summer 
fades, they trek far south to sheltered forests. In 
spring they wander north again, feeding on the 
fresh green shoots that sprout. 

Migrations go on even in the sea. Some sea 
turtles will swim half way across the Atlantic 
ocean from Brazil to lay their eggs on Ascension 
island in the South Atlantic. Gray whales feed in 
Arctic waters but swim south all the way to 
Mexico to breed. No other mammals in the 
world regularly travel so far. 

Below: Some caribou migrate south for up to 800 miles (1300 
kilometers) each autumn. Next spring they return north. 





Above: The narras melon from southern Africa sucks up water 
with roots that grow far longer than its stems. The roots can grow 
up to 40 feet (12 meters) in their search for moisture. 
Below: The desert cricket supports its weight on feet like tiny 
branches, which give it a good grip on the loose sand. This also 
keeps most of the cricket's body away from the hot desert surface. 




Right: The body of a sidewinder snake hardly touches the ground 
as it throws itself across the hot desert sand. 

Below: A barrel cactus swells up after rain as its pleats till up with 
moisture. But after months of drought, its pleats have lost much 
of their stored water, so the plant looks thinner. 




Desert Survival 

Desert plants and animals manage to survive in 
the driest lands on earth. Many also manage to 
endure tremendous heat. 

Some desert plants produce long roots that 
suck up moisture from deep down, while other 
plants have shorter roots that stretch over a 
wider area to catch the rain that occasionally 
soaks the surface of the ground. Most long-lived 
desert plants store water in juicy tubers, bulbs or 
stems. Cacti have waxy stems to stop water 
leaking out and some also have pleated stems 
that expand like an accordion to take up as much 
water as possible when it does rain. Many desert 
plants survive as seeds buried in the sand. As 
soon as there is any rain, they suddenly sprout 
and produce flowers and seeds. 

Animals cope with the heat and drought in 
various ways. Some lizards feed in the cool of 
the mornings and evenings and burrow into the 
sand to escape the midday heat. Reptiles that 
move around at midday are able to avoid being 
burned by the desert surface. One lizard lifts 
each foot off the ground in turn and another 
rears on its back legs to stay in the shade behind 
a narrow plant. 

Desert animals obtain moisture by eating 
juicy plants or other animals. Most creatures 
need to eat each day but camels can survive for 
days without food or drink. They store food as 
fat inside their humps. Camels do not sweat until 
their body temperature rises very high indeed. 
In this way they lose little moisture from their 
bodies. 




98 



Life at the Top 



The upper slopes of high mountains are cold, 
dry and windy. The air is thin and the soil is 
poor. High mountains are among the harshest 
places anywhere on earth. 

Although the cold wind kills off most trees, 
other plants survive. Many form low clumps that 
hug the ground to avoid the wind, while some 
have hairy leaves that help to trap warmth and 
moisture. Africa's giant lobelias rise high above 
the ground, but a thick, corky stem and clusters 
of dead leaves protect their living tissues from 
the intense cold. 

Birds and mammals also manage to survive 
among the mountain peaks. Crows and eagles 
soar high on rising air currents. Mountain goats 
and sheep leap nimbly from rock to rock. Their 




springy limbs are tipped with hooves that are 
specially adapted to cope with slippery rock 
surfaces. A hollow below each hoof allows it to 
grip the rock like a suction pad and a small 
"claw" behind the hoof gives extra balance. 
Thick coats help to keep these large mammals 
warm but many move downhill to find food 
when snow buries the plants. 

Small mountain mammals burrow to escape 
the winter cold. In winter, pikas feed on heaps 
of hay they have collected and stored. One 
species of pika lives on Mount Everest at heights 
of up to 18,000 feet. These little relatives of 
rabbits stay active all year round but other 
rodents, such as alpine marmots, hibernate. 
They spend nearly half the year sleeping. 




Above: Flowers of the purple saxifrage, which grows as a low 
cushion and clings closely to the mountain soil. The low creeping 
stems and small leaves help to prevent loss of water in the 
windswept places in which it grows. Larger plants would be 
blown over by the wind or lose all their water by evaporation in 
the strong winds high on mountains. 



Left: An ibex perches on a rocky crag in the mountains. Among 
the steep cliffs, this mountaineer is safe from almost all enemies 
but human hunters. Seven species of wild goat are called ibex. 
They live in the rugged mountains of Africa and Eurasia. Their 
hoofs have sharp edges, which dig into rock crevices as they 
climb. They also have hollow soles to their feet, which grip the 
rocks like suction pads. This allows them to leap up incredibly 
steep rock faces. 



99 



On the Grasslands 

Large parts of the world look like seas of grass. 
Grasses grow in lands too dry for large areas of 
trees. 

Tropical Grasslands 

Tall grasses and scattered trees cover the world's 
hot dry grasslands, which are called savannas. 
Africa's savannas are home to large grazing 
mammals, such as antelope and zebra. Huge 
herds crop the grass as they wander over the 
plains. Even though the animals eat the tops of 
the grass, it goes on growing from the base, so 
grazing does not kill it. 

A variety of different animals can live side by 
side because they each need a slightly different 
kind of food. For instance, zebras munch long, 
tough grasses, gazelles graze on young grass 
shoots, antelopes called lesser kudus browse on 
bushes and giraffes eat leaves growing high on 
the scattered trees. Grazers also give the grass a 
rest by moving on from time to time. In 
Southern Tanzania elephants, buffaloes and 
hippopotamuses all eat and trample tall marsh 
grass at the end of the rainy season. Then they 
move away to find fresh feeding grounds. This 
gives the marsh grass time to grow new, tender 
shoots. These shoots in turn attract such grazing 
antelopes as hartebeest and eland. 

Fierce carnivores such as lions and cheetahs 

Below: African grazing and browsing animals at a savanna 
waterhole. A lot of different grazing animals can survive together 
because they feed on different sorts of grasses and leaves. 



attack the large savanna grazers. Cheetahs can 
outsprint the fastest antelope unless it twists and 
turns, and packs of hyenas and hunting dogs can 
run down and kill animals as large as wildebeest 
and zebra. Leopards usually hunt alone. They 
often prefer to lie on a branch overhanging a 
path and pounce on creatures passing under- 
neath. After the carnivores have eaten, scaven- 
gers move in to share the feast. Jackals, vultures 
and marabou storks gobble up whatever lions, 
leopards and hyenas leave. 

Prairies and Steppes 

The North American grasslands and Asian 
steppes are called temperate grasslands. Here 
the grass is shorter then on the African savanna 
and there are fewer trees. Huge herds of large 
grazing animals, such as bison and wild horses, 
once lived here but most have been killed off by 
human hunters. 

The most common steppe and prairie animals 
today are smaller creatures such as birds and 
rodents, which feed off the grasses or seeds of 
flowering plants. In North America, large plump 
rodents known as prairie dogs dig burrows that 
form underground "towns." Burrowing owls 
and rattlesnakes move in to share these homes. 
The owls kill and eat prairie dogs while the 
snakes eat the prairie dogs and the owls' eggs. 

Below: Lions gnaw the flesh from the carcass of a grazing animal 
that they have killed. Lionesses work together to stalk and tackle 
their prey. 



In the Forests 

Forests and woods can be found in many parts of 
the world and in many different climates. Some 
trees can exist in extreme cold, whereas others 
thrive in an atmosphere which is rather like a 
hot, steamy bathroom. The plants or animals of 
any forest depend on where the forest is. 
Tropical forests, temperate forests and cold 
forests each have their special type of wildlife. 

The largest area of forest is in the northern 
hemisphere and stretches from North America, 
across Northern Europe to Asia. The trees here 
are mostly evergreen conifers with needle-like 
leaves, which do not lose their moisture in 
winter. Plant-eaters here include squirrels and 
deer while lynx, wolves and bears are among the 
largest predators. 

South of the conifer belt, are patches of 
broadleaved woodland where deciduous trees 
such as oaks and beeches thrive. These trees lose 
their leaves in autumn. The fallen leaves form a 
rich carpet of compost - food for many small 
insects and nourishment for an undergrowth of 
bushes and flowering plants. 

Close to the equator, tropical rainforests grow 
in a climate that is hot and rainy. There are no 
extremes of temperature, so most of the trees 
are evergreen and broad-leaved. There is a huge 
variety of trees in these forests. A European 
woodland may have 12 kinds of trees, whereas 



hundreds of different kinds grow in a tropical 
forest, supporting a large animal population in 
all its different levels. 

The forest floor is home to plant-eaters such 
as rodents, forest antelopes and Indian 
elephants. But most creatures live high among 
the trees. Apes and monkeys swing through the 
branches, parrots and toucans feed on treetop 
fruits, butterflies flit among the treetop flowers 
and frogs and snakes hide among the leaves. 



Below: These four pictures show 
four stages in the growth of a red 
deer's antlers. 




Below: The layers of plants in a tropical rain forest. The taller 
trees shut out much of the light from the forest floor but ferns and 
mosses thrive in the damp gloom. 



Below: Woodpeckers chisel into decaying tree trunks to search for 
insects and other small animals. They have a long, sticky tongue 
to lick up insects. 




A Watery Home 



Each quiet pool or bubbling river is home to a 
variety of plants and animals. Different parts of 
a pond or river attract different forms of plant 
life. Marsh marigolds and reeds sprout from the 
muddy rims of shallow ponds and marshes. In 
deeper water, the long stems of water lilies lift 
their leaves to the surface. The richest part of a 
pond or river is around the edge where most of 
the plants grow. Here countless tiny crusta- 
ceans, insect larvae, mollusks and worms live 
and feed off the plants. These animals form food 
for newts and many water insects. 

Further out in the water, water snails, tad- 
poles and some fish graze on mossy algae 
growing on underwater plants and stones. Fierce 
hunters such as dragonfly larvae, water beetles 
and fisher spiders seize tadpoles and small fish 
such as sticklebacks. Caddis fly larvae may 
escape unseen. These insects hide their bodies 
with a covering of sand grains, tiny stones or bits 
of plants. And few animals could catch the agile 
pond skaters as they skim across the surface of 
the water on their long legs. Trout and perch 
prowl on the watch for fish smaller than 
themselves. Large pike will snap up trout and 



Right: The larvae of most kinds of caddis fly make tube-like 
homes for themselves out of small stones, pieces of water plants 
and other debris. Each species makes its home in a particular 
pattern. They usually carry their homes around with them, which 
helps to protect them from enemies. Adult caddis flies are- 
moth-like insects with long wings covered in hairs. 
Below: A remarkable variety of freshwater fish live in tropical 
pools or streams. The piranha fish of South America has 
razor-sharp teeth. A shoal of these fish can reduce a horse to a 
skeleton within minutes. 



Fighting fish (S.E.Asia) Swordtails 






Above: The North American fisher spider climbs down water 
plants to feed but must come to the surface to breathe. 





?7| 




r 



Above: The nautilus is a relative of the octopus. It swims one way 
by squirting out water in the opposite direction. 



Bottle-nosed 
dolphin 



perch. Between them, herons, otters, mink and 
bears can tackle fish of almost any size. 

In the sea, as in fresh water or on land, plants 
are eaten by small animals which in turn are 
eaten by larger ones. A drop of sea water teems 
with thousands of tiny drifting plants and 
animals called plankton. The plants are known 
as phytoplankton. Feeding on them are animals 
called zooplankton. These may include young 
jelly fishes, crabs, sea worms and other animals 
without backbones. All these form food for 
small fishes hunting near the surface of the sea. 
Even the world's largest whales feed on little 
shrimp-like creatures called krill. 

Small fish in their turn fall prey to larger ones. 
Millions of sardines and anchovies are gobbled 
up by predators such as mackerel, which are 
themselves eaten by sharks and tunas. Killer 
whales eat fish but will also tackle whales far 
larger than themselves. Whales and seals are 
mammals. They can swim as well as fish but they 
have to come to the surface to breathe. Some 
species can remain underwater for more than an 
hour. 

Way down in the ocean depths live strange sea 
creatures that never see daylight. These fish feed 
on one another and on dead and dying animals 
that drift down from the sunlit surface. Most 
deep-sea fish have huge jaws to snap up any food 
that comes their way. 



Left: The bottle-nosed dophin is a mammal (like you) and 
breathes air through a blowhole on the top of its head. It has a 
smooth, streamlined body, which helps it to swim fast through the 
water. It moves its strong tail up and down to push it along. (Fish 
move their tails from side to side.) 

Below: Some of the animals that live on a coral reef, which is built 
up from the skeletons of tiny animals related to the sea anemones. 
Most coral reefs grow in warm, clear, sunlit tropical seas. 




, Ra, 



nbow parrot fish 



Zebr 
angel fish 




7 



Protecting Nature 

Wild plants and animals are in danger almost 
everywhere and people are one of their greatest 
enemies. For instance, hunters have killed so 
many whales and rhinoceroses that some species 
could vanish forever. Collectors have dug up so 
many venus fly traps that these insect-eating 
plants have become quite rare. 



Poisons and Pollution 

Many harmless creatures have suffered from the 
chemical poisons (pesticides) sprayed on insect 




104 



pests. Spilt chemicals are another threat to 
wildlife. When an oil tanker is wrecked, huge 
amounts of oil may leak into the sea. The oil 
destroys the waterproofing on the feathers of 
seabirds so that they drown. They may also die 
from swallowing the oil as they try to use their 
beaks to clean up their feathers. Untreated 
sewage and industrial wastes poured into rivers 
reduce the oxygen content of the water and 
poison it so it is unfit for fish and other water 
creatures. 




Above: The lady's slipper orchid is a rare plant. 
Some of the places where orchids grow have to be 
guarded by conservationists to stop orchid collectors 
digging up the plants. 



Left: The giant panda is a rare animal that lives on 
remote mountainsides in southwestern China. It may 
be in danger of extinction if the bamboo forests it 
lives in are destroyed. 



Below: A plane spraying insecticide. Pesticide that 
kills insects may collect in the bodies of insect-eating 
animals. Birds that eat the poisoned animals might 
die. 




Destroying Wild Places 

The greatest threat to wildlife is probably the 
disappearance of wild places. Each year, timber 
workers around the world chop down forests 
equal to the size of Indiana, engineers drain 
marshes, builders cover heaths and fields with 
roads and cities and farmers dig up hedges. Such 
destruction could kill off a million kinds of 
plants and animals before the year 2000. 

Saving Wildlife 

Luckily much is being done to save the world's 
endangered wildlife. Some governments forbid 
hunters to kill rare animals such as the white 
rhinoceros or the blue whale. A ban on hunting 
blue whales may have come just in time to save 
the largest animals that have ever lived on the 
earth. Some governments also forbid traders to 
buy or sell rare animals. If collectors cannot sell 
the wild animals they catch, they tend to leave 
those animals alone. 

Chemists have discovered safer pesticides 
than those used in the 1950s. Scientists can also 
now produce chemicals that kill specific plant or 
animal pests without harming other wildlife. 
Some of the chemicals they use are made by 
plants or animals themselves. 

Oil companies, factories and cities can do 
much to prevent poisons leaking into seas or 
rivers. For example, sewage treatment has 
helped to clean up Lake Erie, making it a safe 
home for fish and wildlife for the first time in 
many years. But sewage and factory wastes will 
continue to poison rivers in countries too poor to 
pay for cleaning up their waterways. 

Many nations have set aside national parks 
and nature reserves as safe homes for wild plants 
and animals. Game wardens work to keep out 
poachers. But even nature reserves may not save 
the rarest creatures. Instead biologists try to 
breed them in special zoos or parks. This sort of 
process has saved the Hawaiian ne-ne goose and 
the graceful Arabian oryx. For many other 
endangered species captive breeding may be 
their only hope of survival. 



Right: A conservation group at work in a British woodland. They 
are clearing scrub and coppicing some of the smaller trees. 
Coppicing involves cutting the trees down to a stump to encourage 
many thin shoots to grow. This lets light into the wood and allows 
flowers and shrubs to grow beneath the trees, providing homes 
for wildlife. 




Above: A boat belonging to the Greenpeace conservation group, 
which tries to prevent people catching whales or dumping 
poisonous wastes at sea. Group members go out from the large 
ship in small boats and try to make it impossible for the killing or 
dumping to take place. 




Above: A scientist removing wading birds from a trap on the 
coast of the Camargue, in southern France. The birds are ringed 
and measured and the details recorded. Scientists have to learn as 
much as possible about plants and animals so that they can plan to 
conserve them. 




105 




Evolution — the History of an Idea 



The idea that living things have changed during 
the history of life on earth is more than two 
thousand years old. In Roman times, the 
philosopher and poet Lucretius reviewed this 
subject in his book on human knowledge. But 
the religious dominance in Europe during the 
next 16 centuries ensured that the explanation of 
the Bible, in the book of Genesis, was accepted 
with few questions. 

In the 17th and 18th centuries, explorers 
began to bring back many new plants and 
animals to Europe from far-off lands. And 
naturalists, such as John Ray and Carolus 
Linnaeus, were discovering order in the complex 
variety of plants and animals. They found that 
all plants and animals could be arranged in 
groups (classified) according to the features they 
had in common. Fossils and the huge bones of 
prehistoric animals were also being discovered. 
But most people of the time grasped at a 
religious explanation for these discoveries. The 
fossils and bones were thought to be the remains 
of animals that had perished in the great flood 
described in the Bible. 

However, the naturalists and the men who 



were beginning to study the rocks of the earth 
(the geologists) found that certain kinds of 
fossils were found in certain rocks. They also 
discovered that layer upon layer of rocks had 
been formed in past ages. This led to the idea 
that the earth and the life it supported might be 
very ancient indeed - much older than the date 
of 4004 B.C. worked out by Archbishop Ussher 
in the mid-17th century from writings in the 
Bible. Thinking men began to ask questions and 
look at living things and the rocks and fossils of 
the earth for answers, rather than accepting the 
traditional doctrines developed two thousand 
years previously. 

Erasmus Darwin, the physician grandfather of 
Charles Darwin, suggested two hundred years 
ago that living things might acquire "new powers 
and larger limbs" because of their needs and 
actions. At about the same time, the French 
naturalist George Buffon, wrote a monumental 
series of books on natural history in which he 
maintained that living things have changed and 
advanced during the history of life on earth. But 
neither of these two scholars (nor anyone else) 
could explain how these changes came about. 



106 




Jean Baptiste Lamarck (1744- 
1829) This French naturalist was 
one of the first to suggest a way in 
which evolution might work. He 
suggested that characteristics 
which plants and animals gained 
in their own lifetime could be 
passed on to their offspring. Dis- 
coveries in genetics have shown 
his ideas to be wrong. 



Alfred Russel Wallace (1823- 
1913) An English naturalist 
who worked in the jungles of 
Indonesia and came up with 
the same explanation as 
Charles Darwin for how evolu- 
tion might work. In 1857 Wal- 
lace wrote to Darwin outlining 
his ideas and this forced Dar- 
win to publish. 





Charles Darwin ( 1809-1882) 

This painting shows Darwin in 1840, four years after he returned 
from his famous voyage on H.M.S. Beagle. 



The First Theories of Evolution 

In 1809, the great French biologist Jean Baptiste 
Lamarck published his "Zoological Philos- 
ophy," which included his theory of evolution. 
He believed that animals and plants could 
acquire new characteristics during their own 
lifetimes in order to cope with their environ- 
ment. For example, giraffes had evolved long 
necks because generations of giraffes stretched 
their necks to reach the juicy young leaves high 
up in trees. This seemed a very reasonable 
theory and many people accepted it at the time, 
although Lamarck was later shown to be wrong. 
However, he did give an essential lead to the 
man who was the first to explain how evolution 
could have taken place. This man was Charles 
Darwin. 

As a young man, Darwin spent five years 
sailing around the world as a naturalist on h.m.s. 
Beagle. His discoveries and observations during 
the voyage helped him to think of a scientific 
explanation for how evolution might have 
happened, but he did not publish his theory 
immediately. He worked quietly at his home in 
Kent, England, for the next twenty years, 
carefully gathering evidence to support his 
theory. Then one day, a letter arrived from a 
fellow biologist, Alfred Wallace, who was 
collecting animals and plants in the tropics. The 
letter was a dreadful shock to Darwin. Quite 



independently, Wallace had come up with the 
same theory of how evolution might work. 

To solve the difficulty, the ideas of the two 
biologists were read out at the same time at a 
meeting of the Linnaean Society in London in 
1858. The following year Darwin published his 
book The Origin of Species, which contained a 
detailed explanation of his theory. 

Briefly, the theory that Darwin and Wallace 
offered went like this: All species produce far 
more offspring than can possibly survive to 
reproduce. Their numbers are controlled by 
factors in the environment, such as food supply, 
living space and links with other species. But 
which individuals are most likely to survive? 

No two living things are exactly alike and the 
individuals with the best chance of surviving will 
be those best suited to their particular environ- 
ment and way of life. They will pass on their 
characteristics (which are controlled by their 
genetic instructions) to the next generations (see 
pages 114-119). If the environment changes, 
those animals and plants best suited to the new 
environment are most likely to survive and 
reproduce. Over very long periods of time, one 
species could change into another. 

Darwin called his idea natural selection and 
believed it explained how the enormous diver- 
sity of life on earth had evolved. Darwin's ideas 
still form the basis of evolutionary biology. 



107 



Evidence for Evolution 



The scientific theory of evolution suggests a slow 
process that takes place over millions of years. It 
is therefore not possible to watch one species 
changing into another. Most of the evidence 
supporting the theory of evolution has been 
collected since Darwin's time. It comes from the 
appearance, internal structure, biochemistry 
and behavior of living species as well as the 
relationships between living species and their 
fossil relatives. You can find out more on the 
next six pages. 

The Case of the Speckled Moths 

The best known example of natural selection in 
action is that of the speckled moths. These 
moths are fairly common in Britain. They are 
eaten by several species of birds, which take 
them from the tree trunks where they rest during 
the day. 

In the early 19th century (before the industrial 
revolution) most of the moths were whitish. 
They blended well with the pale-colored lichens 
on the tree trunks, so birds found them difficult 
to spot. A lot of whitish moths survived to 
reproduce and pass on their genes. 

But by the end of the 19th century, pollution 
from factories had killed off most of the lichens 
and blackened the tree trunks in industrial 
areas. The blackish moths (which were present 
in small numbers in the original population) 




Above: Observations of living species can provide clues to how 
species might have formed in the past. These four species of 
Hawaiian honeycreeper do not compete with each other because 
their beaks are adapted to different diets. They probably evolved 
from a finch-like ancestor that reached Hawaii from the North 
American mainland. Eventually they became so different they 
could no longer interbreed and were different species. 



matched the blackened tree trunks and were 
more likely to survive attacks by birds. So the 
numbers of blackish moths gradually built up. 
The characteristics of the population changed to 
survive the change in the environment. Today, 
however, since the environment has been 
cleaned up and the trees are less polluted, the 
whitish moth is replacing the blackish form 
again. 

Natural changes to the environment are not 
usually as rapid or clear-cut as changes caused 
by people. So it is often difficult for scientists to 
work out how the environment might be 
affecting the evolution of a population in nature. 



mi 




Left: Two speckled moths on a 
tree trunk. Which one is most 
likely to be eaten by a bird? 
Below and right: Three of the 
many breeds of dog that have 
been developed from the wolf 
over many thousands of years. 
This shows how the character- 
istics of a species can be 
changed by selecting which in- 
dividuals breed together. 
Top right: Tibetan spaniel. 
Bottom left: Scottish terrier. 
Bottom right: Saluki. 





108 




Above: Part of a "family tree" drawn by the German biologist 
Ernst Haeckel in 1866 to show how various animal groups could 
be related by evolution. 



Below: Animals often have similar features, which suggests they 
may have evolved from the same ancestor. The front limbs of 
these vertebrates are all made of the same bones (with five digits 
at the end) arranged in different ways. Each limb is adapted for a 
different way of life. But sometimes animals may have similar 
structures because they live in the same environment, not because 
they are related. For example, dolphins and fish look alike 
because they are both adapted for swimming fast in the sea. But 
they are not related. Dolphins are mammals. 




Tracing Family Trees 

Biologists sort living things and fossils into 
groups (classify them) based on certain features 
they share in common. The similarities between 
some groups suggest they may have evolved 
from the same ancestor. Some modern systems 
of classification suggest relationships between 
living and fossil plants and animals, which shows 
how they might have evolved. 

From Chaos to Order 

Until the middle of the 18th century, naturalists 
classified plants and animals in different ways. 
There was no standard way of describing or 
naming each kind of organism. So when natural- 
ists talked about their discoveries it was often 
difficult to know precisely which plant or animal 
they were referring to. The situation was chaotic 
and unscientific. 

An Englishman named John Ray was the first 
person to arrange plants and animals in a more 
scientific way. He realized that a system of 
classification had to be based on the structure of 
organisms, not the kind of food they ate or the 
climate they lived in. Carolus Linnaeus carried 
forward Ray's basic ideas. In 1753 he established 
the system of naming and classifying living 
things that is used everywhere today. 

The science of classification is called tax- 
onomy. Organisms are first split into kingdoms 
(such as the animal and plant kingdoms), which 
are then divided into smaller groups called phyla 
(singular phylum). The members of each phy- 
lum have certain features in common which 
separate them from members of other phyla. 
Each phylum is broken down into classes, classes 
are divided into orders, orders into families, 
families into genera (singular genus) and genera 
into species. 

A species is a group of plants or animals 
whose members have most features in common. 
They usually look and behave alike and can 
breed among themselves. (It is not always 
possible to find out about breeding behavior, so 
biologists sometimes have to base their classi- 
fications on just physical features.) Each species 
has two names. The first one is the name of the 
genus to which the species belongs and the 
second is a special name used only for that 
species. For example, the rabbit, Lepus cunicu- 
lus, and the hare Lepus timidus, are two species 
in the genus Lepus. 

109 



HOW FOSSILS ARK FORMED 




Below: This fossil of a 
seed fern Neuropteris 
is made of a thin film 
of carbon. 



Above: The footprint of a dino- 
saur called Cheirotherium, which 
walked over a patch of mud about 
150 million years ago. The mud 
hardened and was later covered 
by sediment, which preserved the 
footprint. 



ammonite 
died and 
was buried 
on the 
seabed. 





The diagrams above show 
how a fossil mold or cast 
may form. 



Above: The sticky resin 
from a conifer tree has 
hardened into amber to pre- 
serve this ancient insect. 



Below: These stone "tree trunks" are in Petrified Forest National 
Park in Eastern Arizona. {Petrified means "turned to stone.") 
They were formed when minerals dissolved in water seeped inside 
the wood and replaced the internal structure of the tree. 




Fossils — the Key to 
the Past 



The collection and study of fossils (the preserved 
remains of plants or animals) has enabled 
biologists to piece together the history of life on 
earth. Fossils provide the most direct evidence 
for evolution, although there are many gaps in 
the story they reveal. This is mainly because 
only a very small fraction of the plants and 
animals from the past are likely to have been 
preserved as fossils, although many fossils have 
yet to be discovered. 

Where are Fossils Formed? 

Plants and animals have to be buried quickly to 
stand a good chance of becoming a fossil. The 
most likely place for quick burial is in the sea 
where mud and sand washed off the land collects 
in layers called sediments. This explains why 
many fossils are of sea creatures, such as 
shellfish, sea urchins and corals. Most parts of 
the earth's surface have been covered by sea at 
some time in the earth's history and rocks that 
were once at the bottom of the sea have been 
pushed up into mountain ranges. So fossils of 
sea creatures can be collected in most places on 
dry land. 

Fossils can also form on land in lakes, ponds, 
natural tar pits and frozen earth. Mammoths 
preserved in the frozen soil of the Arctic for 
45,000 years still had a covering of hair and skin, 
and food in their stomachs. 



1 When an 
animal, such as 
this dinosaur, 
dies, its body 
may be buried 
quickly under- 




How Fossils are Formed 

Most fossils are formed when the hard parts of a 
plant or animal are dissolved away and replaced 
by minerals from the sediment they are buried 
in. This eventually forms a stone copy of the 
original organism. In some fossils, the hard parts 
are replaced so slowly that the finest details of 
the original may be preserved. It can take tens of 
millions of years for the process of fossilization 
to be completed. 

Shells may be buried and dissolved away so 
that a hollow space or mold remains after the 
shell has disappeared. If the space is filled with 
mineral material, a cast of the original shell is 
formed. 

Other Kinds of Fossils 

Stone copies, molds or casts are not the only 
sorts of fossils. The buried remains of plants are 
sometimes converted to thin films of carbon, 
which are preserved sandwiched between the 
layers of a rock. The soft parts of an animal, 
such as its skin, may occasionally form fossils. 
Impressions also exist of whole organisms, such 
as jellyfish or starfish. Whole insects have been 
preserved when they were trapped in the resin 
oozing from trees. The resin later hardened to 
form amber. 

Sometimes the animals themselves are not 
preserved but their tracks are. These are called 
trace fossils and include the footprints made by 
our ancestors one million years ago in Africa. 




Dating Past Life 

Fossils are formed from stone so they are 
associated with rocks. And because some rocks 
and fossils contain radioactive forms of elements 
(such as uranium and potassium) they can be 
dated. The basic principle behind radioactive 
dating is that each radioactive element decays at 
a known rate. The decay rates of elements used 
to date most fossils vary from several hundred 
million years to several billion years. So a 
radioactive element is like a clock ticking away. 

Scientists must find out two things before a 
date can be worked out - the proportion of the 
element that would have been in the rock or 
fossil when it formed and the proportion 
remaining today. From this, scientists can 
calculate the age of rocks and fossils. 

C14 Dating 

With less ancient specimens, the actual remains 
of animals and plants can be dated. All living 
things contain a certain amount of radioactive 
carbon (carbon 14). This carbon is being formed 
all the time by high energy cosmic rays which 
penetrate the earth's atmosphere. When an 
organism dies, it cannot take any more carbon 
14 into its body tissues. The carbon 14 then 
begins to decay at a known rate. So by testing a 
specimen to find out how much carbon 14 it 
contains, scientists can calculate its age. How- 
ever, this technique can only be used if the 
specimen is less than about 50,000 years old. 

Below left: A scientist uncovering a fossil Tarbosaurus, a huge 
flesh-eating dinosaur that lived more than 65 million years ago. 
Below right: The age of plant and animal remains up to about 
50,000 years old can be calculated from the radioactive carbon 
they contain. Older fossils are less radioactive. 



Mammals dominate 
the world 



The Fossil Record 
and Catastrophes 

Many scientists believe that the direction of 
evolution has been changed by physical catas- 
trophes that have dramatically affected condi- 
tions on earth. Biologists and geologists have 
found evidence of several such catastrophes in 
the long history of our planet. 

Enormous meteorites, perhaps six miles (ten 
kilometers) across have struck the earth in 
prehistoric times. Geological survey satellites 
can photograph the distinct outlines of huge 
craters, which are not easily detectable at 
ground level. There is some evidence that the 
dinosaurs may have become extinct because of 
changes to the earth's climate caused by a giant 
meteorite striking the earth. The birds and 
mammals evolved in a spectacular way after the 
dinosaurs became extinct. 

The ammonites, a great dynasty of sea 
creatures, existed for 330 million years. But they 
became extinct at about the same time as the 
dinosaurs. 

Doctors David Raup and John Sepkoski of 
the University of Chicago have claimed that mass 
extinctions have taken place at regular intervals 
of 26 million years during "the history of the 
earth. Such regular occurrences would be likely 
to have an astronomical cause. Many scientists 
do not accept all the claims by the Chicago 
scientists, but they do believe that random 
events, sometimes very dramatic ones, have 
changed environments on earth so much that life 
on this planet has been remodeled from time to 
time. And scientists agree that environments 
change (even if this takes place slowly over 
millions of years) and species change as they 
adapt to new environments. 

Below: If an environment does not change, its animals and plants 
may not change. Many species of lobe-finned fishes existed about 
350 million years ago. Today a fish called the Coelacanth is the 
last surviving member of this group (as far as we know). It may 
have survived because it lives in an unchanging, deep sea 
environment to which it is well adapted. 

.<^'\ 



112 



Origin of 
/ earth 



THE SCALE OF LIFE 

The time scale of life on 
earth is often difficult to 
understand. In the diagram 
to the right, the whole his- 
tory of life has been con- 
densed into one year. Man 
appeared late in the evening 
of December 31st and one 
human lifetime lasts just 
one second. 



Tertiary.—, 






^^^^^^ 





Sea scorpu 





Below: Scientists have collected evidence to show that the 
continents slowly move about the earth's surface like huge rafts. 
This idea is called continental drift. Evidence shows that the 
continents were once joined together in a huge supercontinent 
called Pangaea. This continent began to break up some 200 
million years ago and its parts (today's continents) moved slowly 
away from each other. Fossils of the plant Glossopteris and land 
animals such as Mesosaurus and Lystrosaurus have been found on 
continents that are now widely separated. The position of the 
continents affects the climate and this has probably affected the 
mrse of evolution o^er a long period of time. 



Below: The map below shows the maximum extent of the ice in the 
Pleistocene Ice Ages, which took place in the northern hemisphere 
between 1.8 million and 10,000 years ago. This affected the 
climate worldwide and caused evolutionary changes. Many 
animals and plants became extinct. Some moved south to warmer 
climates and those that remained adapted to survive the new 
conditions. Many of the animals, such as the woolly mammoth 
and the woolly rhinoceros, evolved warm coats. They lived 
around the edge of the ice sheets. But many of these animals 
appear to have died out because they were hunted by man. 



Lystrosaurus 



4 




How: Dinosaurs ruled the earth for about 140 million years but 
ey had all died out by about 65 million years ago. The reason for 
eir extinction is one of the great puzzles of the past, although 
any theories have been suggested. One of the most likely 
planations is a sweeping change in climate, caused perhaps by 
ntinental drift and earth movements, which cooled the earth, 
ther theories involve meteorites or comets from space causing a 



change in climate, or natural disasters, such as floods. Some 
scientists have suggested the dinosaurs may have been the victims 
of disease or plant poisons but these ideas do not explain why a 
variety of animals unrelated to the dinosaurs died out at the same 
time. Another theory is that small mammals ate the dinosaur eggs 
and helped to bring about their downfall. Which explanation do 
you think is most likely? 
\ 




The flesh-eating mammal-like reptile 
Lycaenops attacking a plant-eating 
dicynodont. These dinosaurs lived in 
Permian times - about 250 million 
years ago. 




Above: Although the members of a family have many of the same 
features, each individual (except for identical twins) is slightly 
different. Without this variation, evolution could not take place. 

Below: These diagrams show one of the experiments that helped 
Mendel to work out his laws of heredity. In the first diagram, you 
can see what happens when a tall and a short plant are 
cross-fertilized. Each parent plant has two genes for height but it 
passes on only one of these genes to each of its offspring. 



j5* genes in 
Sty tall plant 



genes in 
short plant 



The gene for 
tallness is 
dominant 
('overrules') 
the gene for 
shortness. 




Below: When two of the offspring are cross-fertilized (see below) 
they produce - on the average - three tall offspring for every one 
short offspring. Two of the tall plants have one gene for shortness 
but this is "overruled" by the dominant gene for tallness. 



genes in 
tall offspring 



genes in 
tall offspring 



X LmM 
k A 

t 



Mendel and the 
Laws of Heredity 



In any species, be it beetles or buttercups, there 
are variations in the features of the individual 
animals or plants. The theory of evolution states 
that those individuals with features best suited to 
their environment and way of life are more 
likely to survive. They are likely to produce 
more offspring than other individuals. Darwin 
and Wallace (see page 107) realized that plants 
and animals must be able to pass on their 
favorable characteristics to their offspring and 
that in this way species changed (evolved) over 
many generations. But they knew nothing about 
how this process, which is called inheritance or 
heredity, works. 

In 1866, only seven years after Darwin had 
published the Origin of Species, an Austrian 
monk, Gregor Mendel, published a scientific 
paper explaining the laws of heredity. But 
Mendel's work was ignored until three scientists 
rediscovered his results at the beginning of the 
20th century. 

Mendel's Experiments 

Mendel's research was carried out with garden 
peas and other plants in his monastery garden in 
Brunn, Austria (now Brno in Czechoslovakia). 
Peas were a particularly good experimental 
plant because they had characteristics (such as 
short or tall stems and smooth or wrinkled 
seeds), which could be easily observed and 
counted in experiments. Mendel transferred 
pollen by hand from the male to the female parts 
of his experimental flowers to produce seeds and 
carefully recorded the results. For example, he 
used the pollen from tall-stemmed plants to 
fertilize short-stemmed plants. All the offspring 
grown from the seeds had tall stems. (This went 
against the popular belief of the time, which was 
that the characteristics of the parents would 
somehow be blended together in the offspring to 
produce plants of medium height.) 

But what had happened to the short-stemmed 
characteristic? Had it been lost? Mendel con- 
tinued his experiment and went on to breed the 
tall-stemmed plants he had produced with each 
other. And he found that one in four of the 



offspring had short stems. You can find out 
more about how this happened in the diagrams 
on page 114. 

Mendel did many experiments with different 
combinations of characteristics in his pea plants. 
In every case he got the same results. He worked 
out several basic rules of heredity (which are 
called Mendel's Laws). They have since been 
found to apply to other plants and also to 
animals. 

Mendel's Laws 

1. The characteristics of an organism are passed 
on from one generation to another by definite 
particles, which Mendel called factors. Today we 
call them genes. 

2. The genes normally exist in pairs, which are 
alternative versions of the same genetic instruc- 
tion. One of each pair of genes comes from the 
male parent and the other comes from the 
female parent. 

3. The genes of a pair may be dominant or 
recessive to each other. Dominant genes always 
have an effect on the individual, even if only one 
gene is present. But two recessive genes have to 
be present before they have an effect. So some 
genes can be present in plants and animals 
without having an effect on their characteristics. 

Where are the Genes? 

A few years after Mendel had carried out his 
researches, biologists concluded that the genes 
are in the nucleus of every cell, carried on 
structures called chromosomes. The name 
means "color body." Chromosomes were given 
this name because they take up colored stains 
easily when biologists prepare cells for study 
under the microscope. 

The chromosomes of all animals and plants 
exist in pairs. Each chromosome of a pair 
contains alternative versions of the same genes 
carried by its partner. A human cell has 23 pairs 
of chromosomes, a chicken cell 18 pairs, a 
mouse cell 10 pairs and a fruit fly cell 4 pairs. 
Biologists have done much of their research into 
genetics on a fruit fly called Drosophila. This is a 
convenient animal to use because it breeds 
rapidly (it has a lifespan of about 10 days) and it 
has a range of distinctive characteristics that can 
be used in breeding experiments. 

You can find out more about genes and how 
they work on the next four pages. 



1 




When a cell is about to divide, the 
chromosomes in its nucleus become 
visible as thread-like structures. 
They become shorter and thicker, 
probably by coiling up like a spring. 

CHROMOSOMES AND GENES 



II 11 B 

i U u n n n n 



M All At XXJIBffA « 



A* «A 



Above: The 46 chromosomes of a man, arranged in their 23 pairs. 
The X and Y sex chromosomes are named after their shape. 
Below: Part of a giant chromosome from the salivary gland of the 
fruit fly, Drpsophila. Many of the bands are the site of one or 
more genes. 




Life's Data Bank 



The body of anyone reading this book is made of 
about 100,000,000,000,000 cells. Each cell con- 
tains the same set of plans for making a human 
being and keeping its body working. The plans 
are in the form of coded instructions (genes) on 
the chromosomes in the nucleus of every cell. 
The instructions were present in the fertilized 
egg cell that all humans develop from. They 
were copied and passed on to each new cell as 
the human being grew and developed. You can 
find out how the instructions are copied on pages 
118-119 and on these two pages you can see what 
happens to the chromosomes that carry the 
instructions when a cell divides. 

Switching Off the Genes 

Although every cell in an organism contains all 
the instructions for making and controlling the 



characteristics of that organism, it uses only 
those instructions it needs to carry out its 
particular job in the body. The rest of the 
genetic instructions are somehow "switched 
off." How this happens is one of the greatest 
puzzles of biology but it may be connected with 
the position of the cell in the body. 

Mitosis - Making Identical Cells 

When a plant or animal is growing and develop- 
ing from a fertilized egg cell, all its cells divide to 
produce the cells that go to make up its tissues 
and organs. In a fully-grown organism only some 
of the cells continue to divide. This process of 
cell division is called mitosis. Each chromosome 
copies itself, then the nucleus divides into two 
and finally the whole cell splits into two identical 
cells. 



CREATING IDENTICAL CHROMOSOMES 



The diagrams below show the main stages in the process of cell 
division called mitosis. This produces new body cells in plants 



and animals and each division forms two new cells, which are 
identical to the original cell. 



J 




1. The cell before division begins. The 
chromosomes become visible in the nuc- 
leus. Only two pairs of chromosomes are 
shown for simplicity. 



2. It is now possible to see that the 
chromosomes have copied themselves. 
The copies are called chromatids. A 
structure called a spindle forms. 



3. The membrane around the nucleus 
breaks down and the chromosomes 
move toward the center of the spindle. 



f. ^ 



4. The chromosomes line up at the 
center of the spindle and attach to the 
spindle fibers. 




4 



fr 




5. The two chromatids in each double 
chromosome separate and move to oppo- 
site ends of the spindle. The cell begins 
to divide. 



6. Two new nuclear membranes form 
around each group of chromosomes and 
the cell divides into two. 



116 



Meiosis - Making Different Cells 

When reproductive cells (sperm, pollen and egg 
cells) are produced, a special type of cell division 
takes place. This is called meiosis. Meiosis 
halves the number of chromosomes so that when 
two reproductive cells join to form a new plant 
or animal, it will have the same number of 
chromosomes as its parent. This is how each 
species keeps the same number of chromosomes 
from one generation to another. 

But meiosis does far more than halve the 
number of chromosomes. The chromosomes 
also cross over each other and swop genes 
before the cell divides. This process reshuffles 
the genetic instructions so that each reproduc- 
tive cell has its own unique combination of 
instructions. (So, for example, no two sperm 
cells will have exactly the same combination of 
genes.) Two of these unique cells join to form a 
new individual in sexual reproduction (see pages 
56-59), which mixes up the genetic instructions 
even further. This explains why no two people 
(except for identical twins) are exactly alike. 

The variations caused by this system of cell 
division are very important in the evolution of 
living things. Darwin's idea of the "survival of 
the fittest" (see page 107) would be meaningless 
if there was not a range of genetically different 
organisms for nature to "select" from. The 
environment can only weed out the less well 
adapted individuals if there is plenty of variation 
in a species. 



Below: The human reproductive cells formed in meiosis have 
either an X or a Y sex chromosome. If two cells with X 
chromosomes join together at fertilization, a female will develop. 
A fertilized cell with one X and one Y sex chromosome will 
develop into a male. The X and Y chromosomes carry different 
instructions. For example, the gene for normal color vision is 
carried only on the X chromosome. If males have a defective gene 
for color vision on their one X chromosome, they will be color 
blind. But females have to inherit the defective gene on both their 
X chromosomes to be color blind. This is because the gene is 
recessive and is "overruled" if they have a normal gene (which is 
dominant) on one of their X chromosomes. 




ou have normal color 
ision, you will be able to 
a teapot in this 
picture. 






1 



SHUFFLING THE 
INSTRUCTIONS 

These diagrams show 
the process of cell 
division called 
meiosis. This takes 
place when sex cells 
(such as sperm and 
egg cells) are made. 
Only four 
chromosomes are 
shown for simplicity. 

1. The chromosomes 
appear as long 
threads. 



2. They pair up to 
form bivalents and 
shorten and thicken. 



3. It is now possible 
to see that each 
chromosome has 
copied itself. The 
copies are called 
chromatids. Each 
bivalent has four 
chromatids. 



4. The chromatids in 
each bivalent swap 
sections in a process 
called crossing over. 



5. The pairs of 
chromatids in each 
bivalent split apart 
and move to opposite 
ends of the cell. A 
spindle forms (as in 
mitosis) but this is not 
shown in the 
diagrams. The cell 
divides once. 

6. The cell divides 
again. Each one of 
the four new cells has 
half the number of 
chromosomes that 
were in the original 
cell. It also carries a 
unique set of genes on 
its chromosomes. 



117 



Making Proteins 
to Control Life 



Since the origin of life about 3.5 billion years 
ago, each generation of living things has had to 
copy its genetic instructions and pass them on to 
the next generation. On these two pages you can 
find out more about the instructions themselves, 
how they work and how they are copied. 

Genes - the Coded Instructions 

A gene is a section of a remarkable molecule 
called deoxyribonucleic acid or dna for short. 
dna is found in the chromosomes in the nucleus 
of cells. It controls the characteristics of living 
things by means of a chemical code of instruc- 
tions, dna is found in all living things, which 
suggests that all life on earth may have had a 
common origin. 

The structure of dna was discovered in the 
early 1950s by two scientists, Francis Crick and 
James Watson, who were working at the 
University of Cambridge, England. They re- 
ceived the Nobel Prize for their achievement, 
which was one of the most important contribu- 
tions to biology since the work of Darwin and 
Mendel. 

Crick and Watson showed that the structure 
of the dna molecule looks rather like a twisted 
ladder. The shape is called a double helix. The 
rungs of the ladder are coded instructions and 
the sides are made of sugar and phosphate 
molecules. The coded instructions are written 
with four chemical building blocks - adenine 
(A), thymine (T), guanine (G) and cytosine (C). 
These are called bases and they make up a four 
letter alphabet. They can only pair up in a 
certain way. A can only pair with T and G can 
only pair with C. A pair of bases is called a 
nucleotide. 

The order of the nucleotides along the dna 
strand spells out the instructions for the different 
characteristics of organisms. One gene may 
consist of up to a thousand pairs of bases. A 
bacterium called E.coli has about 4,000 base 
pairs on its single chromosome. No one knows 
how many base pairs are needed to spell out the 
coded instructions for a human being. But it may 
be more than ten million. 



HOW DNA IS COPIED 

The two strands of a DNA molecule are normally linked together. 
But when a cell is about to divide into two (see pages 116-117), the 
strands unwind so the molecule can make a copy of itself. All the 
DNA molecules in the nucleus of a cell are copied so the two new 
cells contain the same DNA as the original cell. 




When a DNA molecule makes a copy of itself, it first splits down 
the middle of the ladder. Some of the four building blocks that 
make up the rungs of the ladder are present in the nucleus. They 
are called adenine (A), thymine (T), guanine (G), and cytosine 
(C). A always links to T and G always links to C. The spare 
building blocks match up with their partners on the separated 
strands. This produces an exact copy of the original molecule. 

Spare bases 
(adenine, thymine 
guanine and cytosine) 




In this way, two molecules of DNA are built up, each identical to 
the original one. 



118 



HOW DNA MAKES A PROTEIN 

To make a protein, a DNA molecule first makes a copy of a small 
section of itself, which is like an order for making a particular 
protein. The copy is in the form of a molecule called ribonucleic 
acid or RNA for short. RNA is similar to DNA but has only one 
strand, a molecule called uracil in place of thymine and a sugar 

How Does the DNA Code Work? 

The coded instructions on the dna molecules 
control the production of proteins. And proteins 
control the characteristics of organisms. 

Proteins are the most common chemicals in 
living things. Each cell in your body contains at 
least 10,000 different kinds of protein. The most 
important proteins are the enzymes that control 
the rate of chemical reactions in cells, without 
being used up themselves. They are vital to life. 

Proteins are made of twenty different units 
called amino acids. The order of the amino acids 
determines the type of protein. But how does 
the four letter alphabet of the dna code spell out 
the messages for twenty different amino acids? 
The four letters are actually read in groups of 
three. (For example, the order of bases TAG- 
CATACT would be read as the three words 
TAG, CAT and ACT.) There are 64 possible 
ways of arranging four letters in groups of three. 
(Try working this out for yourself.) Only 20 
messages are needed for the amino acids, plus a 
message that means "stop, this is the end of the 
message for one protein. ,, So some of the 64 
possible messages are not used while others 
appear to have the same meaning. 

How Does DNA Make Proteins? 

dna remains in the safety of the nucleus. But 



called ribose in place of deoxyribose. It is called messenger RNA 
(mRNA) because it passes out of the nucleus and carries the 
message for making a protein to a ribosome. mRNA threads 
through a ribosome and its message is read by another form of 
RNA called transfer RNA (tRNA). tRNA molecules carry amino 
acids to the ribosome, where they link up to form a protein. 

proteins are made on structures called ribo- 
somes, which are in the cytoplasm of the cell 
(see page 10). A copy is made of a section of a 
dna molecule and this is sent out of the nucleus 
to a ribosome. There it controls the production 
of a particular protein. You can see how this 
complex process works in the diagram at the top 
of the page. 

Changing the DNA Code 

Very rarely, the dna code is changed in some 
way. This changes the proteins that are made 
and so alters the characteristics of organisms. 
Such changes play a part in the evolution of 
living things. 

Changes to the dna code are called mutations, 
after the latin word mutare, which means to 
change. There are two main sorts of mutation. 
One is a mistake in the code itself, such as one 
base pair being replaced by a different one. This 
takes place when dna reproduces itself. The 
other involves changes in the positions of large 
pieces of dna, which take place during cell 
division, especially in meiosis (see page 117). 
Many mutations are harmful causing the death 
of the organism. Other mutations have only 
slight effects or no noticeable effect at all. Some 
cause obvious changes in the organism. 



119 




The Origin of Life 



One of the greatest mysteries in biology is how 
life first arose on the earth about 3.5 billion 
years ago. What is the chemical link between the 
build-up of organic molecules (which have been 
made by scientists in experiments) and the first 
systems of molecules that reproduced them- 
selves? We may never really understand this gap 
between the living and the nonliving. One thing 
that seems certain to most biologists is that all 
life on earth had a common origin. The 
chemistry of life is very complex, yet it is the 
same in all existing lifeforms. And all life on 
earth uses the same language (the dna code) to 
transmit its characteristics from generation to 
generation. 

When scientists analyzed living matter they 
discovered an intriguing fact. Life is formed 
from the most common elements in the uni- 
verse. The human body, for example, is made of 
mainly hydrogen (the most common element), 
oxygen, nitrogen, carbon and phosphorus. 
(Actually we are about three-fourths water, 
which is why we have so much hydrogen and 
oxygen in our bodies.) The elements of life were 
therefore abundant before the origin of life. So 
how could they have joined together to form the 
molecules that make up living things? 



Scientists at the Ames Research Center in California have used 
this apparatus to recreate the sort of conditions in the earliest 
atmosphere on earth. In the experiment, a mixture of ammonia, 
methane, water vapor, nitrogen and hydrogen is heated by 
electric discharges. Amino acids - vital to all life on earth - are 
formed. 




1. 4,600-4,000 
million years 
fierce elec- 
trical storms 
raged on earth. 

thai radi- 
ation from the 
sun reached the 
earth's surface. 



Electrica 
storms 



MM 



2. About 4,000 
million years 
ago, water con- 
densed on the 
earth's cooling 
surface. Dis- 
solved gases 
from the primi- 
tive atmos- 
phere reacted 
to form organic 
molecules. 
During the next 
billion years 
the first living 
cells evolved. 




Org 
molecul 



Scientists have carried out many experiments 
which show how the molecules of life could have 
formed in the sort of atmosphere the earth 
would have had about four billion years ago. 
This is called a primordial atmosphere, which 
means "existing at the beginning." Professor 
Stanley Miller of the University of Chicago was 
the first to experiment with a primordial atmos- 
phere in 1953. He put together the "atmos- 
phere" in his laboratory apparatus and passed 
an electrical current through it. And some of the 
molecules of life formed in his apparatus. 

Many scientists have successfully repeated 
Professor Miller's experiments. Different com- 
binations of gases have been used to represent 
the earth's primordial atmosphere- and different 
forms of energy have been used to trigger the 
production of organic molecules. In the primor- 
dial earth atmosphere, the energy for the 
buildup of complex molecules could have come 
from lightning, radiation, volcanic eruptions or 
even meteorite impacts. Experiments show that 
the molecules of life do not form in the presence 
of oxygen. So they could not form in today's 
atmosphere. But scientists accept that the 
earth's first atmosphere was mostly hydrogen. 

The Chemistry of Early Life 

Most biologists believe that life almost certainly 
began in water, either in the sea or on the 

Right: Blue-green algae as they appear under a microscope. 
Relatives of these organisms probably survived on earth some 2.5 
billion years ago. 

Below: The diagram below shows how living cells could have 
evolved from simple to more complex types. 1 and 2 - A simple 
bacterial cell becomes incorporated in another cell in a form of 
symbiosis (see pages 88-89). In time it becomes a part of the larger 
cell called a mitochondrion (see page 10). 3 and 4 - In a similar 
way, a cell of an alga becomes incorporated in a second cell. It 
evolves into a structure called a chloroplast (see page 11). 5 - 
More complex cells eventually formed with both mitochondria 
and chloroplasts and these became the ancestors of plants and 
animals. 




cell 



shoreline. But what sort of molecules would 
have been needed for life to arise? 

The only molecules that can carry a vast 
amount of coded information and copy them- 
selves are the nucleic acids. These are the dna 
and rna molecules, which you can find out more 
about on pages 118-119. Nucleic acids would 
have had to form before the origin of life. 

Amino acids, the units that proteins are made 
of, would also have been essential. Proteins are 
the structural materials of life. The enzymes that 
control all the vital chemical reactions of life are 
also proteins. 

Nucleic acids and proteins each provide what 
the other needs in a living system. The nucleic 
acids can copy themselves but they would have 
had to produce the codes for proteins to be 
made. So these two chemicals somehow had to 
come together to produce life. When such 
systems began to copy (reproduce) themselves 
in a stable way, life would have begun. The first 
systems may have been unstable and life may 
have had to form several times before the right 
molecules came together in the right way. 

We may never know how molecules fitted 
together to produce the first life. But we know 
that amino acids link up to form proteins. And 
we can guess how proteins and nucleic acids may 
have come together to form a functioning, 
self-copying system. 




121 



Is There Life on 
Other Planets? 

Scientists have long wondered about the pos- 
sible existence of life on other plants in our solar 
system. Does the surface of Mars, the sea of 
Saturn's moon Titan or the dense water layer of 
Jupiter's atmosphere shelter life of any kind? 

Mars and Venus 

Before the space age, astronomers knew that 
Mars was cold with only a thin atmosphere 
because they could see right to its surface. But 
when the polar ice melted in summer, Mars 
seemed to darken as if vegetation was growing 
on its surface. Then American spacecraft sur- 
veyed Mars at close quarters and found that 
there was no vegetation. The Viking Landers 
the U.S. sent to the surface of Mars recorded 




some very unusual chemistry. But most scien- 
tists think there is no life on Mars. 

Before any spacecraft reached Venus, some 
astronomers suggested that Venus might have 
steamy jungles on its surface. But Soviet 
spacecraft which landed on Venus found that 
there was no water there. In fact the surface of 
Venus is several times hotter than boiling water. 
Even the most heat-resistant lifeforms would go 
up in smoke. 

Jupiter and Titan 

Jupiter is a gas giant with no solid surface. 
Observations have shown that it is a vast 
cauldron of organic chemistry. This may be 
similar to the pre-life chemistry of the earth. 

Another possible place for life is Saturn's 
moon Titan, which is one of the most fascinating 
places in the solar system. Titan's water is 
locked up as ice - the surface temperature is 
minus 356°F. The surface is completely hidden 

Left: American astronomers Garl Sagan and Frank Drake of 
Cornell University worked out this message. It is designed to tell 
any beings that may exist on other worlds the kind of creatures 
who sent it and where they are located in our galaxy. It is on a 
plaque carried by Pioneer 10, now on its way out of the solar 
system. 

Below left: This photograph of the earth's moon was taken in 
1968 by the Apollo 8 astronauts. There is no life on the moon 
because it has no water and no atmosphere. A planet without an 
atmosphere has a huge difference between night and day 
temperatures. 

Below right: The Apollo 8 astronauts also took this photograph of 
the earth from moon orbit. In the bottom of the picture are the 
lunar highlands. 




Below: The surface of Mars as 
seen in the photographs taken by 
the Viking Landers. 
One of the Landers is shown in the 
photograph to the left. 




Above: The dense, cloudy atmos- 
phere of Venus is mainly composed of 
carbon dioxide and nitrogen. It con- 
tains little water. Soviet spacecraft 
have shown that the suface is several 
times hotter than boiling water. 



Above: The United States' two Viking Landers were the only spacecraft launched 
especially to detect evidence of life on Mars. Each landed and tested the soil in 
special experiments. This revealed some very unusual chemistry but most 
scientists do not think this is caused by an unknown type of life. Future landings 
may provide definite answers. 



Below: A close-up of the swirling gas 
clouds on Jupiter. The surface clouds 
are about minus 184T (120°C). But 
the atmosphere get warmer and 
denser with depth. 




Below: The surface of Saturn's moon Titan is completely hidden by an orange 
atmosphere. This is 50 percent denser than the earth's atmosphere. Future 
spacecraft will attempt to find out if there is life on Titan. It would have to 
function without water, unlike life on earth. 




by an orange atmosphere, which is 50 percent 
denser than the earth's atmosphere. There is 
good evidence to believe that Titan may be 
covered by a sea of ethane and methane gases a 
mile deep. 

The radiation reaching Titan's atmosphere 
from Saturn and the Sun produces chemical 
reactions that form organic molecules in the 
atmosphere. These then fall through the atmos- 
phere and into the sea. This may have been 
going on for about four billion years. Such 
molecules probably formed in a sea of water on 
earth about four billion years ago. Could there 
be a form of life on Titan that can exist in a sea 
probably made of liquid ethane and methane? 
Future spacecraft to Titan will attempt to answer 
this question. 



Limits to Life 

Scientists interested in the remote possibility 
that life exists elsewhere in the solar system have 
to consider the range of conditions in which life 
can survive. Recent discoveries have shown that 
this range is greater than anyone imagined. 

One of the best examples of life in extreme 
conditions is of bacteria collected from super- 
heated water that pours from a vent in the 
seabed of the Pacific Ocean. The bacteria there 
live in a temperature of 680°F. Scientists are 
uncertain how living matter can hold together 
under such intense heat. Now that the known 
temperature range for life on earth has been 
increased, biologists can look again at some 
ideas about life in rather hot places, such as the 
water layer in Jupiter's atmosphere. 



123 



The Biotechnology Revolution 



Revolutionary changes to the world we live in 
(such as airplanes, computers and plastics) have 
been brought about by discoveries in the 
physical sciences. But the rapidly growing 
understanding of genetics and the biochemistry 
of cells could have an ever greater impact on our 
lives in the years ahead. The science of using this 
new knowledge for practical purposes is called 
biotechnology. Many people see it as a new 
industrial revolution. 

There is nothing new about some aspects of 
biotechnology. People have used microbes (such 
as bacteria and yeasts) in brewing, baking, and 
wine and cheese making for thousands of years. 
These processes take advantage of the fact that 
microbes naturally produce substances which 
are of value to people. 

Genetic Engineering 

But research in the sciences of genetics and 
molecular biology has sparked off a new interest 
in biotechnology. It is now possible for scientists 
to give bacteria genes (see pages 118-119) from 
other organisms, including humans. Genes are 
chemical codes of instructions for making par- 
ticular proteins. The foreign genes (plus the 
proteins that are produced as a result of their 
instructions) are reproduced billions of times as 
the bacteria grow and divide. So the bacteria can 
be used as "factories" for making proteins they 
would not normally produce. Some of the 
proteins, such as human growth hormone and 
interferon, are difficult to obtain in other ways 
and therefore very valuable. 

Bacteria are so abundant and have such a 
wide variety of genes that they can be used to 
process almost any substance. For example, 
some bacteria have genes which allow them to 
eat oil slicks and break down other toxic wastes. 
And special bacteria are now being produced by 
genetic engineering to solve problems of pollu- 
tion. 

Scientists can also use the techniques of 
genetic engineering to change the genes in 
domesticated animals and plants. This may help 
to make them grow faster or larger or be more 
resistant to diseases. Plants can also be given 
new genes to help them survive frost and 




Above: The biotechnology tree in this diagram shows the main 
uses of biotechnology in the modern world. 



Below: The white paste on this large drum is made of thousands of 
millions of bacterial cells. They are used to make enzymes in the 
production of penicillin antibiotics. 




124 




1. Gene on a human 2. Gene engineered into 

chomosome. nucleic acid of virus. 



I 




3. Virus injects nucleic 
acid into bacterium. 



5. The bacteria 
reproduce over and over 
again. The new gene 
causes large amounts of 
the human protein to be 
made. This is harvested. 



4. Gene becomes part of 
bacterial chromosome. 



Above: Microbes such as bacteria can now be made to carry the 
genes of other species, including humans. The genes carry 
instructions for making proteins, such as enzymes and antibodies. 
So bacteria can be used to produce large amounts of valuable 
proteins for use in industry and medicine. 

Below: This is a virus that infects bacteria (a bacteriophage). It is 
magnified 1.2 million times. Such bacteriophages are used to 
carry pieces of genetic information from one organism to another 
in the process of genetic engineering. 




drought. Medical scientists hope eventually to 
be able to cure inherited diseases, such as 
hemophilia, by giving patients new genes. 

Moving Genes Around 

Genetic engineering in biotechnology involves 
putting new genes into an organism, usually a 
bacterium, so it can make proteins it has never 
made before. There are usually four main stages 
to this process: 

1. Obtaining a piece of dna which contains the 
chemical code of instructions (the gene) for 
making a particular substance. (Enzymes are 
used to "snip out" a section of dna.) 

2. Putting the gene into a microscopic organism, 
usually a bacterium. 

3. Making the gene produce the foreign protein 
in its new home. 

4. Collecting the new protein. 

Plasmids - the Magic Circles 

Carrier molecules called vectors are used to 
introduce the gene into its new home. (The word 
vector comes from the latin for "carrier" or 
"bearer.") Certain types of viruses can act as 
vectors and so can little circles of dna called 
plasmids, which are produced by some bacteria. 
Plasmids often pass from one bacterium to 
another, even if they are different species. This 
is a natural process. 

The plasmid ring can be opened up using a 
special enzyme, called a restriction enzyme. A 
piece of dna from another species, such as a 
human being, can be "stitched into" the ring. 
When the plasmid enters a bacterium in the 
usual way, it carries the gene to its new home. 
There it causes the foreign protein to be made. 

The bacterium most often used as a home for 
new genes is called E. coli. It was chosen partly 
because it had been studied for many years and a 
great deal was known about its biochemistry. 
Once a plasmid is inside an E. coli cell, it makes 
copies of itself. If it contains a human gene, then 
that gene is copied as well. When the bacterium 
grows and divides, a few of the plasmids pass to 
each new cell. Before long, one bacterium will 
have produced millions of descendants exactly 
like itself, all containing the protein made as a 
result of the new gene. A population of cells 
produced by one ancestor is called a clone. All 
the cells in a clone have the same genetic 
make-up. 



125 



Living Factories 

The use of genetic engineering for industrial 
processes has several advantages. It allows 
microbes such as bacteria to change cheap raw 
materials into valuable products. They can 
produce substances that are difficult to make in 
other ways. The industrial processes involved 
use very little energy and work at low tempera- 
tures. This cuts down the production costs. 

Hormones and Genetic Engineering 

The hormone insulin controls the amount of 
sugar in the blood stream. It is needed to treat 
people suffering from diabetes who cannot make 
enough of the hormone. Insulin is extracted 
from the pancreas of pigs and cows but it can 
have some undesirable side effects. This is 
probably because it is not identical to human 
insulin and it is difficult to obtain as a pure 
product. 

Now the human gene for making insulin has 
been put into the bacterium E. coli and 
commercial quantities of human insulin are 




Above: The colonies of a bacterium called Bacillus subtilis in this 
photograph can be used as "factories" for making particular 
products. The red colonies are good producers and pink and gray 
are less suited. White colonies are non-producers. Techniques for 
identifying which bacteria are making the product are important 
in biotechnology. 



being produced. In September 1982, insulin 
from bacteria became the first genetically en- 
gineered material to be licensed for use in 
humans. 

Growth hormone is made in the pituitary, a 
small gland at the base of the brain,. It stimulates 
growth and is needed to treat some children who 
do not grow to a normal height. It is extracted 
from the brains of sheep. But only 0.005 grams 
of pure growth hormone can be obtained from 
half a million sheep's brains. Today just nine 
quarts of bacteria can produce the same amount 
of growth hormone. 

Interferon 

Interferon, a protein made by our cells, helps 
other cells to resist the effect of invading viruses. 
It was given its name because it appeared to 
interfere with the spread of viral infections. Until 
recently, interferon was very difficult to pro- 
duce. It was made in the laboratory by infecting 
human white blood cells with viruses. This 
stimulated them to produce interferon. But only 
small amounts are made by each cell and the 
interferon is difficult to separate from all the 
other materials. So interferon was a rare and 
expensive substance. 

But it is now possible to make interferon in 
large quantities by giving bacteria the gene for 
one type of human interferon. It may be very 
useful in medical treatment in the future, for 
example in the treatment of some viral diseases 
and perhaps some cancers. 

Vaccines 

Vaccines contain dead or weakened forms of a 
virus, which is produced in animals or cells in the 
laboratory. Some of the virus proteins stimulate 
us to produce antibodies. The antibodies pre- 
pare our bodies to fight a real viral infection 
later on. 

Vaccines can now be produced by genetic 
engineering. Scientists take the virus genes that 
code for the specific proteins that stimulate the 
production of antibodies. The genes are inserted 
into bacteria. The bacteria then make the 
proteins in large quantities and these alone are 
used as a vaccine. 

This technique allows manufacturers of vac- 
cines to avoid handling dangerous microbes. It 
also reduces the risk that vaccines contain live 
viruses. It may provide protection against dis- 



126 



eases such as influenza and rabies, that cannot 
be fought by normal vaccines. 

Agriculture and Genetic Engineering 

Agricultural plants have been given new genes 
in attempts to make them disease- and frost- 
resistant. And agricultural scientists are working 
to produce crops, especially cereals, that do not 
need fertilizers. 

Most plants get the nitrogen they need for 
growth from the soil. So to grow better crops, 
nitrogen has to be provided in the form of 
fertilizers. But fertilizers are expensive, es- 
pecially for third world countries. Yet there is 
plenty of nitrogen available in the atmosphere, 
which is 80 percent nitrogen. And certain plants, 
such as peas and beans, are able to use this 
nitrogen in a process called nitrogen-fixing. 
Bacteria in the roots of these plants extract 
nitrogen gas from the air and turn it into a form 
the plant can use. 

Biologists would like to use the techniques of 
genetic engineering to make it possible for 
bacteria to live in the roots of crop plants and fix 
nitrogen for them. They are even working on 
techniques to give the nitrogen-fixing genes from 
bacteria to the crop plants so that they could use 
nitrogen from the air. 

Microbe Farms 

Food can be grown very rapidly in the factory 
with the help of microorganisms. This food is 
called single cell protein (scp) . 

Biotechnologists have been using bacteria, 
yeasts and algae to produce food on a very small 
scale for some years. The microbes feed on some 
unwanted and abundant substances and multiply 
rapidly. The microbes themselves are made of 
proteins, carbohydrates, vitamins and minerals 
so they serve as a source of food. Most of the 
food produced like this is fed to domestic 
animals but some has been produced for humans 
to eat. 

There are two great advantages to using 
special microbes to produce food. One is that 
they can eat substances which are abundant but 
useless for feeding domestic animals. The other 
is that they can produce food at a faster rate than 
any other lifeform because they reproduce so 
rapidly. They do not take up valuable land and 
could provide a valuable source of food for the 
world's growing population in the future. 




Above: Root nodules on a bean plant, which contain bacteria that 
can fix nitrogen from the air. Genetic engineers may one day be 
able to give plants nitrogen-fixing genes. 

Below: One of the earliest forms of biotechnology - using yeast to 
make beer in a brewery. The frothy scum is caused by the action 
of the yeast on the malt. 




Below: The bacteria in this blue-green culture are concentrating 
copper salts. Such organisms are used to recover copper from 
mining ores and wastes which contain very little copper. It would 
be too expensive to recover the copper by normal methods. 
Bacteria can also be used to extract silver and rare metals from 
seawater. One day this may become a major industrial operation. 




Glossary 

Algae The simplest of plants. They have a plant 
body but no root, stem or leaves. Algae may be 
single-celled or many-celled plants and range in 
size from the microscopic to seaweeds. 

Amino acids The molecules that link up to make 
proteins. See protein molecules. 

Ammonite Member of a very large group of 
prehistoric sea creatures. They were related to 
the cephalopods (the octopus and nautilus). The 
ammonites became extinct some 65 million years 
ago. 

Amylase An enzyme which breaks up starch. 
The names of enzymes often end in "ase." 

Androecium All the stamens in a flower. 

Angiosperm A flowering plant, such as a daisy or 
buttercup. There are two groups of angiosperms 
- monocotyledons and dicotyledons. The word 
angiosperm means vessel seed - the seeds are 
protected inside an ovary as they grow. Angio- 
sperms and gymnosperms are together known as 
the seed plants. 

Annual rings Rings seen on the cut surface of 
logs and stems. They indicate the age of the tree. 
Stems grow from the center outward. Every 
year, the new xylem produced by secondary 
thickening produces one annual ring. Toward 
the center of each ring the cells are large and are 
made in spring when growth is most active. At 
the outside of the ring, the cells are smaller and 
are made later in the year. These cells form a 
darker band, so that each year's growth can 
easily be counted. 

Antibiotic A substance produced by one living 
organism which is poisonous to another. The 
most famous antibiotic is penicillin which has 
been used for more than 40 years to kill 
disease-causing bacteria. Penicillin is produced 
by several species of the mold penicilliurn. 
Antibiotics are widespread in the world of 
microbes, but only about 50 different antibiotics 
have been found suitable for medical use. 



Antibodies Protein molecules produced by the 
body to defend itself against invading microbes. 
Antibodies are also produced against toxins and 
surgical grafts from another person. This ca- 
pacity of the body to reject foreign tissues is the 
main problem in transplant surgery. 

Arachnids Arthropods that have eight legs in 
contrast to the insects which have six legs. 
Spiders and mites are the most common arach- 
nids. 

Arthropods Animals with outside skeletons and 
limbs that have many joints. Insects form by far 
the largest group of arthropods. Crabs, prawns 
and spiders are also examples of common 
arthropods. 

Auxin A chemical hormone that affects the rate 
or direction of plant growth. 

Bacillus A rod-shaped bacterium. A bacillus is 
responsible for tuberculosis. 

Bacteriophage Viruses which infect bacteria. 
Bacteriophages are now used in genetic en- 
gineering to insert selected DNA in bacteria. 

Biosphere The surface of the earth and the lower 
atmosphere where all living things are to be 
found. The biosphere includes all seas and 
oceans. 

Biotechnology The use of biological knowledge 
for practical purposes. 

Bulb A short underground stem wrapped in 
swollen leaf bases, for example, onion, daffodil. 
New plants can grow from its buds by vegetative 
reproduction. 

Calyx A ring of sepals on the outside of a flower. 

Cambium A meristem inside a plant stem or 
root. Cambium cells divide and grow to make 
the stem or root thicker, producing secondary 
thickening. There are two sorts of cambium. 
Vascular cambium makes new xylem and 
phloem. Cork cambium makes cork and second- 
ary cortex, giving the stem a thick waterproof 
coat to replace the epidermis. 



128 



Cambrian The period in earth history which 
lasted from 570 to 500 million years ago. A 
widespread abundance of sea life is recorded by 
the fossils of the Cambrian age. All the major 
groups of animals were present at this time 
except the vertebrates. 

Camouflage A disguise that hides a plant or 
animal from animals that eat it. Camouflage 
generally involves a pattern or color that makes 
the plant or animal difficult to see against its 
surroundings. For example, white feathers are 
camouflage for the ptarmigan, a bird that lives in 
snowy lands. 

Carbon The "backbone" element of life. Each 
carbon atom has the capacity to join with four 
atoms. It can thus form chemical structures 
essential to all life. 

Carbohydrates Organic molecules made of car- 
bon, hydrogen and oxygen. Sugars and starch 
are the best known carbohydrates. 

Carnivore An animal that feeds mainly on other 
animals. Carnivores, such as lions, are often 
called predators and the animals that they feed 
on are called their prey. 

Carpel A structure in a flower where seeds are 
made. A flower may have one or more carpels. 
A carpel generally has a sticky tip (stigma) 
connected to a swollen base (ovary) by a stalk 
(style). The carpels are together known as the 
gynoecium. 

Cartilage A tough whitish substance, flexible 
and strong, made of connective tissues. Gristle 
in meat is cartilage. 

Cellulose Chains of carbohydrate molecules. 
Cellulose forms the walls of plant cells. It is a 
fibrous material and therefore not easily 
digested. Animals that live on plants, like cows 
and sheep, have specially evolved digestive 
systems to obtain maximum nourishment from 
cellulose. 

Chlorophyll The green chemical pigment in 
plants. Chlorophyll traps energy from sunlight 
during photosynthesis and uses it to split water 
molecules into hydrogen and oxygen. 



Chloroplast A microscopic sac in green plant 
cells where photosynthesis takes place. Inside a 
chloroplast are layers or disks called grana 
surrounded by a liquid called stroma. In the 
grana, chlorophyll captures energy from sunlight 
and splits water molecules into hydrogen and 
oxygen. In the stroma, hydrogen and carbon 
dioxide are combined to make carbohydrates. 

Chromosome Rod-shaped structures visible in 
the nuclei of cells when they are about to divide 
lengthwise. It has been known for a long time 
that the chromosomes carry the chemical code 
of instructions that controls life. (See DNA, 
genetic and nucleic acids). 

Coelenterates The group of animals containing 
sea-anemones, jellyfish and corals. All live in 
water and most in the sea. Of the many-celled 
animals the coelenterates are the simplest in 
structure. They are the simplest form of life to 
have nerve cells. The coelenterates have been a 
very successful lifeform. Their ancestors (similar 
to today's animals) can be found in the fossil 
record of more than 500 million years ago. 

Collagen A fibrous protein. It is one of the main 
materials which bind cells and animal tissues 
together. Leather is the "fixed"' collagen of the 
skin. 

Cone A reproductive structure of a typical 
gymnosperm. The woody scales of a cone are 
basically modified leaves. Each scale can pro- 
duce reproductive cells. Cones are either male 
or female. Male cones produce pollen. They are 
small and do not live long. Female cones are 
larger and take up to three years to produce 
seeds. In animals, cones are light sensitive cells 
in the eye. 

Corm A swollen underground stem such as in a 
crocus. It contains stored food, and new plants 
can grow from its buds by vegetative reproduc- 
tion. 

Corolla A ring of petals in a flower, above the 
calyx. The word corolla means crown, and the 
petals are often the showiest part of a flower. 

Cortex The area of packing cells between the 
vascular bundles and the epidermis in a plant 



129 



stem or root. In animals, the cortex is the outer 
layer of the brain or kidney. 

Cotyledon A leaf in a seed. A cotyledon 
becomes the first leaf of the embryo plant, and 
may be quite different from all the other leaves. 
Cotyledons store food for the embryo plant. 
Only angiosperms and gymnosperms have 
cotyledons. 

Crustaceans A large group of the arthropods. 
Most crustaceans live in water. Shrimps, crabs 
and water-fleas are common examples. 

Cuticle The waterproof outer skin of a plant leaf 
or stem, on top of the epidermis. The cuticle is 
transparent and is not made of cells. 

Cytoplasm Everything enclosed by the cell 
membrane except the nucleus. Cytoplasm was a 
convenient description of the contents of cells at 
a time when it was not possible to know what 
cells actually contained. But cytoplasm is far 
more than fluid within the cell. It contains 
numbers of working molecules {enzymes), 
coded plans and instructions (carried by RNA), 
assembly units for proteins (ribosomes), energy 
generators (mitochondria) and other compo- 
nents of considerable complexity. 

Deciduous A plant that regularly sheds all its 
leaves. Deciduous plants usually lose their 
leaves at the end of the growing season, before 
the winter. Many angiosperms such as oak, 
beech and ash trees are deciduous. Larch is one 
of the few gymnosperms that is deciduous. 

Decomposer An animal or fungus that feeds on 
the dead remains or waste material of other 
living things. Decomposers break down their 
food into simple raw materials that can be 
reused by plants. 

DNA (short for deoxyribonucleic acid) This 
chemical carries the genetic code for all organ- 
isms, except some viruses. The code determines 
the form, development and behavior pattern of 
an organism. DNA is part of the chromosomes 
which exist within the nuclei of cells. 

Diatom A single-celled green alga with a silica 
case made of two halves that fit together, one 



inside the other, like a box. Diatoms are the 
main organisms of plankton. 

Dicotyledon A flowering plant with two 
cotyledons in its seed. Dicotyledons have broad 
leaves with veins in a net-like pattern. Their 
stems can grow thicker as well as longer, and the 
vascular bundles are arranged in a ring. The 
flowers have petals and other parts in fours or 
fives. Dicotyledons include all broad-leaved 
trees and most shrubs and herbaceous plants. 

Dinosaur A member of the major group of 
reptiles in earth history. Their extinction some 
65 million years ago is a biological mystery. 

Drupe A fruit with one hard stone surrounded 
by soft flesh and skin. The seed is inside the 
stone. Cherries, plums and peaches are exam- 
ples of drupes. A blackberry is several small 
drupes joined together. 

E.coli A type of bacteria widely used in 
research. 

Echinoderms A group of animals that includes 
starfish, which is distinct from other animal 
groups. Echinoderms are different from other 
lifeforms in their five-fold symmetry. Evidence 
from living animals and fossils indicates that 
their closest relatives were the distant ancestors 
of the vertebrates. 

Electron micoscope A microscope which enables 
us to see specimens by beams of electrons 
instead of light. The magnification obtained is 
far greater than is possible with the best optical 
microscopes. 

Embryo The youngest stage of a new individual, 
which develops from fertilized egg cells. The 
embryo is undeveloped. 

Endosperm A food supply inside a seed. Grain 
seeds and oil seeds, such as linseed, have a large 
endosperm. Some seeds have no endosperm and 
store food in cotyledons instead. Endosperm 
contains chemical substances that control the 
growth of the developing seed. 

Enzymes These are proteins made by the 
"machinery" of the cell. Enzymes greatly in- 



130 



crease the rates of chemical reactions within the 
cell. The chemistry of life would not be possible 
without enzymes. 

Epidermis A single layer of cells just below the 
surface of plant stems or leaves. With the cuticle, 
it provides a tough skin. In animals, the 
epidermis is the outer layer of skin. 

Epiphyte A plant that grows on the surface of 
another plant, but is not a parasite. For example, 
mosses growing on tree trunks are epiphytes. 
The word epiphyte means "on top of a plant." 

Ethane An odorless gas at normal temperatures. 
Ethane (C 2 H 6 ) is an organic molecule and a 
hydrocarbon because it is composed of both 
hydrogen and carbon. 

Evergreen A plant that keeps its leaves all the 
year round. Most gymnosperm trees such as pine 
and spruce are evergreen. 

Food chain A sequence of events when a 
herbivore eats a plant, and then a carnivore eats 
the herbivore. This is a 3-link food chain. In a 
4-link food chain a second carnivore eats the first 
carnivore. Food chains are nearly always part of 
a food web. 

Food web Interconnecting food chains. Links 
between food chains occur when animals feed on 
different foods. There are usually many connec- 
tions between food chains so that each link of a 
food chain is always part of a food web. 

Fossil A permanent record of a prehistoric 
organism. A fossil usually consists of mineral 
material which has replaced the original tissues 
of the organism. Often only fragments of 
fossilized parts of an animal or plant are found. 

Frond The leaf of a fern. 

Fruit The ripe ovary of a flower containing the 
seed. A fruit such as a lupine, that dries out and 
splits open to shoot the seeds out is called 
dehiscent. A fruit such as a poppy that releases 
the seeds some other way is called indehiscent. 

Fruiting body A plant structure that makes 
spores. 



Gametes The male and female sex cells. These 
may be sperm and ova in animals, or pollen and 
egg-cells in seed plants. 

Gene A unit which determines an inherited 
characteristic of an organism. The characteristic 
may or may not be expressed (show itself in a 
particular organism). Genes are made of DNA 
and are part of the chromosomes which exist in 
the nucleus of the cell. 

Genetic Concerned with genes and heredity. 

(See DNA, nucleic acids and chromosomes). 

Genetic engineering The manipulation (en- 
gineering) of the genes for practical purposes. 
Genes that instruct the machinery of the cell to 
make a wanted protein are put into another 
organism, such as a bacterium, to produce that 
product in quantity. 

Genus The classification which includes the most 
closely related species. A genus may contain one 
or many different species. We belong to the 
genus Homo and the species sapiens. 

Germination The process in which a seed starts 
to grow. There are two different sorts of 
germination in flowering plants. In plants with 
hypogeal germination, such as broad beans, the 
cotyledons stay under the soil. In plants with 
epigeal germination, such as sunflowers, the 
cotyledons grow out of the seed and above the 
ground. 

Glands An organ or collection of cells which 
produce one or more special chemicals. These 
are released through vessels to either the inside 
or to the outside of the organism. Glands are 
associated with such processes as the digestion 
of food and the release of sweat. Some glands in 
animals secrete hormones into the blood stream 
(see hormones). 

Grooming An activity of an animal to keep its 
skin or coat, or another individual's skin or coat, 
in good condition. Grooming removes dirt and 
pests. 

Gymnosperm One of the cone-bearing plants or 
their close relatives. Gymnosperms make seeds 
but do not have flowers. The main group of 



131 



gymnosperms are conifers, for example, larch, 
spruce and pine. The word gymnosperm means 
naked seed - the seeds develop from unpro- 
tected ovules. Gymnosperms and angiosperms 
are together known as the seed plants. 

Gynoecium All the carpels in a flower. 

Hemoglobin The molecule which carries oxygen 
in the red blood cells of vertebrate animals. 
Some invertebrate animals also have hemoglobin 
in their blood. 

Hemophilia A genetic disorder which prevents 
blood from clotting. Hemophilia affects only 
males. 

Herbivore An animal that feeds mainly on 
plants, for example, a grazing animal such as a 
cow or a sheep. 

Hormones Chemicals that organisms produce in 
minute amounts but which can have dramatic 
effects on their life processes. Hormones play an 
important part in the lives of both plants and 
animals. Animal hormones usually go straight 
into the blood stream. A common hormonal 
effect is that produced by adrenaline which 
increases heart rate and raises blood pressure, 
producing a state of alertness and readiness for 
vigorous physical activity. 

Inflorescence A group of flowers on one stalk. 

Interferon A natural substance produced by cells 
to counter infections by viruses. Interferon 
inhibits the reproduction of viruses within 
infected cells. 

Invertebrate All animals which do not possess a 
backbone, although we do not usually think of 
single-celled animals, like the amoeba, as in- 
vertebrates. 

Liverwort A simple green plant related to a 
moss. Liverworts are mostly small and flat, with 
shoots simpler than those of a moss. They live in 
moist, shady places. 

Lymph The same as blood plasma (colorless 
blood fluid without the red cells). Lymph drains 
from the tissues and enters the lymphatic system 
of vessels. These eventually lead to the vena 



cava, the main vein in all four-legged verte- 
brates, as well as humans. 

Mammal An animal with a backbone which 
feeds its young on milk from mammary glands. 
Almost all mammals have hair or fur. Whales 
and dolphins have lost their fur during their 
evolution in the sea. All mammals maintain a 
constant body temperature (warm-blooded). 
The only other group of animals to maintain 
constant body temperature are birds. Man is the 
most advanced mammal, though whales and 
dolphins with their large brains must also be 
considered very advanced mammals. 

Marsupials A form of mammal found mainly in 
Australasia which bears its young in a very 
immature state. Young kangaroos, for example, 
are only 4 cm (lVz inches) long at birth and must 
find their way into the mother's pouch where 
they fasten securely to a nipple. Not all 
marsupials have pouches. 

Meiosis Cell division associated with the produc- 
tion of sex cells (sperm and ova). This process 
reduces the number of chromosomes in the 
nucleus by half. Thus, when male and female 
reproductive cells unite the number of chromo- 
somes possessed by the species is restored. 

Meristem A plant growing point. The cells in a 
meristem can divide so that the plant grows 
bigger. The main meristems are at the tip of 
each root and shoot. A meristem inside a plant is 
called cambium. 

Methane A gas at normal temperatures, color- 
less, odorless and inflammable. Methane is an 
organic molecule and a hydrocarbon because it 
is composed of hydrogen and carbon (CH 4 ). 
Mixed with air, oxygen or water methane is 
highly explosive. 

Micropyle A microscopic hole in the ovule of a 
flowering plant where the pollen tube enters 
after pollination. The micropyle can sometimes 
be seen as a small hole in a seed coat. 

Migration A seasonal movement made by many 
birds, fish and mammals, often between breed- 
ing and feeding grounds. Animals migrate to 
make the best use of food and warmth. 



132 



Mitochondria Small rod-shaped bodies within 
cells. The mitochondria produce the energy 
needed by the cell to drive its life processes. 

Mitosis Normal cell division in which exact 
copies of the chromosomes are made, one set of 
chromosomes going to each new cell before the 
old one finally divides. 

Mollusks A large group of animals including 
snails, mussels, oysters and whelks. Mollusks 
have soft bodies and most have shells. The 
largest and most advanced of mollusks are the 
cephalopods: the octopuses and squid. 

Monocotyledon A flowering plant with only one 
cotyledon in its seed. They have long, narrow 
leaves with veins growing side by side. Their 
stems can grow longer but not thicker, and the 
vascular bundles are scattered. The flowers have 
petals and other parts in threes. Monocotyle- 
dons include all grasses, palms and lilies. 

Monotremes Egg-laying mammals which survive 
only in Australasia. They are the duckbilled 
platypus and the spiny anteater. The platypus 
spends its life in water, much like a duck. The 
anteater is like a hedgehog and feeds on insects. 
In prehistory there must have been many kinds 
of monotremes in between these two extreme 
examples. 

Mutation A change in the genes (DNA) which 
produces an inherited change in the organism. 
Most mutations are changes in single genes. 

Mycorrhiza Root-like threads of fungi that grow 
in close association with tree roots. Both the 
fungus and the tree seem to benefit from the 
relationship. 

Natural selection The survival of members of a 
species best suited to live and reproduce in a 
given environment. 

Nectar A sweet liquid produced by many 
flowering plants, generally from the base of the 
petals. Nectar is collected for food by insects and 
other animals that visit the flower. 

Nucleic acids The DNA and RNA molecules. 
The unique structure of these molecules enables 



them to carry coded information. This infor- 
mation specifies and controls the form and 
development of all organisms. DNA holds the 
information within the cell nucleus. RNA carries 
copies of this information into the cell, where it 
is acted upon. (See also DNA and chromo- 
somes) . 

Omnivore An animal that feeds on both plant 
and animal material. Human beings are omni- 
vores. 

Organic Refers to matter of which living things 
are made. As this is highly organized matter, 
scientists called it organic. At one time all 
organic substances came from living things. But 
in modern times many organic substances are 
made in the laboratory and factory. 

Organic molecules In biology this refers to 
molecules formed by living organisms. How- 
ever, a great range of organic molecules are now 
man-made for many different purposes. All 
organic molecules contain the element carbon. 

Ovary The part of the female reproductive 
system in flowering plants and animals that 
makes egg cells. A ripe ovary in a flowering 
plant is a fruit. 

Ovule An area containing an egg cell in seed 
plants. The ovule has one or more protective 
coats called integuments. In angiosperms an 
ovule is inside an ovary. 

Palisade layer The layer of cells in a typical plant 
leaf that contains most of the chloroplasts. The 
palisade layer is just below the upper epidermis 
and gets more sunlight than the rest of the leaf. 

Parasite A living thing that gets its food from 
another living thing without necessarily killing 
it. 

Pesticide A chemical that is used to kill pests. 
Most pesticides are used to kill insects and are 
called insecticides. The use of pesticides must be 
carefully controlled so that food webs are not 
destroyed. 

Phloem The food pipeline in plants. It is made 
up of rows of living cells called sieve tubes 



133 



joined end to end, together with their support 
cells. Phloem is usually part of a vascular 
bundle. 

Photosynthesis The process in which green 
plants use energy from sunlight to convert 
carbon dioxide and water to make their own 
food. Photosynthesis takes place in chloroplasts. 

Pith An area of spongy packing cells in the 
center of a plant stem. Sometimes the pith is 
hollow. 

Placenta The organ in the uterus of pregnant 
mammals to which the growing embryo is 
attached. The embryo receives food and oxygen 
through the blood system of the placenta while 
waste products travel in the blood in the 
opposite direction. All mammals that reproduce 
in this way are called placental mammals. 

Plankton Microscopic plants and animals that 
live in great numbers in water. Plankton is the 
main source of food for many animals. Plankton 
that is mainly plants is called phytoplankton, 
and plankton that is mainly animals is called 
zooplankton. 

Plasma (Blood plasma) The liquid part of blood. 
It contains all the important substances of blood 
but no blood cells. 

Plasmid A section of DNA. Bacteria exchange 
plasmids as part of their natural behavior. 
Scientists use this capacity of bacteria to insert 
new DNA into organisms in research and genetic 
engineering. 

Platelets Minute fragments in the blood which 
play an important part in the clotting and sealing 
of wounds. 

Pleistocene The period in earth history from IV2 
million years ago until 10 thousand years ago. 
During this time there were four ice ages and 
modern man (Homo sapiens) evolved. 

Plumule The miniature shoot in a seed, part of 
the embryo plant. 

Pollen Yellow dust produced by gymnosperms 
and angiosperms. Each particle of pollen - a 



pollen grain - contains one male sex cell. Pollen 
grains must travel to a female sex cell in the 
ovule and fertilize it for seeds to grow. The 
journey to the ovule is called pollination. 

Pollination The transfer of pollen from male 
cones or anthers of seed plants to an ovule. 
Pollen travels by air, water or animals, particu- 
larly insects. In gymnosperms, pollen lands 
directly on the naked ovule. In angiosperms the 
pollen lands on a special area called the stigma, 
above the ovary, and grows a tube down into the 
ovary. 

Preen An activity of a bird to trim and clean its 
feathers, usually with its beak. 

Protein molecules Living tissues are made of 
proteins. Proteins exist in an almost limitless 
number of different forms. The units of proteins 
are smaller molecules known as amino acids. 
There are some 20 different amino acid mole- 
cules in living proteins. The amino acids are 
formed into long chains which fold up into very 
complicated structures. The form of these 
structures is always exactly the same for any 
given protein. The structure of the human 
hemoglobin molecule, for example, is always the 
same, unless faulty. The structure of a protein 
molecule matches its task in the body. 

Prothallus A small, flat disk that grows from the 
spore of a fern. The prothallus produces male 
and female sex cells that can grow into the main 
fern plant. 

Protista A name given to all single-celled 
organisms whether animals, plants, fungi or 
bacteria. 

Protozoa A name given to all single-celled 
animals. 

Radicle The miniature root in a seed, part of the 
embryo plant. 

Respiration This takes place within living cells 
where food is "burned" 1 in the presence of 
oxygen to release energy. 

Rhizome A swollen underground plant stem, 
such as in an iris. It contains stored food and can 



134 



produce new plants from its buds by vegetative 
reproduction. 

Savanna A dry grassy plain with few or no trees, 
in tropical regions. 

Secondary thickening Cells produced from the 
cambium of many seed plants that make stems 
and roots grow thicker. Wood is mostly xylem 
cells produced by secondary thickening. 

Segmented worms Worms, such as the earth- 
worm, are made of a series of units (segments). 
Each segment is a similar structure both inside 
and outside. The structures of blood vessels and 
nerves, for example, are repeated in each 
segment. 

Sepal A leaf-like structure that protects the bud 
of a flower. The sepals are together known as 
the calyx. 

Sorus A small patch, generally brown, on the 
underside of a fern frond where spores are 
made. Each sorus contains several sporangia. 

Species A group of organisms which resemble 
each other and interbreed. One species can 
seldom breed with another species, but there are 
a few exceptions to this rule. The species of 
plants, animals and other organisms therefore 
remain distinct. 

Sponges The simplest of all many-celled animals. 
Sponges are composed of many cooperating 
cells but they have no system of nerves. They 
live attached to rocks or the seabed. Except for 
one family of sponges all live in the sea. Most 
sponges are supported by a skeleton. A bath 
sponge is the skeleton of a certain type of 
sponge. 

Sporangium (pi. sporangia) A structure that 
makes spores in fungi, algae, mosses and ferns. 
In mosses, the sporangium is a special case with 
a lid and is called a capsule. 

Spore A reproductive cell of a fungus, alga, 
moss or fern, capable of growing into a new 
plant. Some spores have tough protective coats 
that can survive periods of drought or cold. 
Some single-celled animals make spores to help 



them survive adverse conditions. 

Stamen A structure that makes pollen in a 
flowering plant. Each stamen has a stalk (fila- 
ment) and an anther, where the pollen is made. 
The stamens together are known as the 
androecium. 

Stoma (pi. stomata) A small hole in the 
epidermis of a plant leaf that can open and close 
to control the flow of air and water vapor in and 
out of a leaf. Each stoma is controlled by two 
sausage-shaped cells in the epidermis, called 
guard cells. 

Symbiosis The close association of two different 
kinds of organisms to their mutual benefit. Good 
examples are lichens which are formed of green 
algae and fungi. The algae use sunlight to make 
food while the fungi provide water and some 
protein. 

Synapse The gaps between nerve cells across 
which nerve impulses pass. An impulse is 
changed from an electrical signal into a chemical 
and back into an electrical signal for the purpose 
of crossing a synapse. Such a substance is called 
a chemical transmitter. 

Taxonomy The science of classifying living 
organisms. 

Termite An insect that looks like an ant (but is in 
fact related to cockroaches), and that lives in 
large colonies. Some termites live in huge towers 
that they build out of mud. Most live in the 
tropics. Some grow special fungus gardens in 
their nests and use the fungus to add to their diet 
of vegetable matter. 

Territory A patch of land defended by an animal 
against other members of the same species. 
Some animals hold territories all year round, 
others only at breeding time. 

Transpiration Evaporation of water from the 
leaves of plants. Transpiration causes water to 
travel from the roots, up the stem and Out 
through the leaves. Transpiration supplies all 
parts of the plant with water, which it uses to 
make food, and it helps the leaves and stems 
keep their shape. 



135 



Tropism A change in direction or rate of growth 
of a plant root or shoot in response to the 
environment. Tropisms are controlled by chemi- 
cals called auxins. 

Tuber A rounded swelling at the end of an 
underground shoot or root. For example, a 
potato is a tuber. A tuber contains stored food 
and new plants can grow from its buds by 

vegetative reproduction. 

Vaccination The introduction of dead or inactive 
bacteria or viruses into the blood stream. The 
presence of these are enough to cause the cells 
of our immune system to make antibodies. 
These antibodies will then protect us against 
future infections by the disease. 

Vacuole A small drop of fluid within an animal 
cell. In plants vacuoles are larger, occupying 
most of the volume of the cell. 

Vascular bundle A group of vessels, sieve tubes 
and supporting cells (xylem and phloem) that 
carry food and water around a plant. 

Vegetative reproduction A process in which 
some plants can produce new plants from a small 
part of themselves without the need for flowers 
or seeds. Rhizomes, tubers, bulbs and corms are 



organs of vegetative reproduction. 

Vertebrate An animal with a backbone. The 
backbone is sometimes called the vertebral 
column. 

Virus A simply constructed system which only 
becomes alive when it enters a living cell. It then 
uses the "machinery" of the cell to make more 
viruses. Although viruses are a common cause of 
disease, they do not all cause disease. Viruses 
are so small that they can only be seen and 
studied with an electron microscope. 

Vitamins Substances needed in minute amounts 
for the health of animals. Vitamins are different 
and unrelated substances. 

Xylem The water pipeline in plants. In flowering 
plants xylem is made of rows of dead cells called 
vessels joined end to end. Xylem is usually part 

of a vascular bundle. 

Yeasts Single-celled fungi of great practical 
value to man in the production of wine and beer 
and in baking. 

Zygote A fertilized egg before it begins to divide 
and develop into a new organism. The cell 
resulting from a male and female cell coming 
together. 



136 



Index 

Page numbers in italics refer 
to illustrations. 

A 

Actin 33 

Adaptation 10, 113, 117 
Adenine 118 
Adipose tissue 54 
ADP42 

African violets 80 
Aging 30, 61 

Algae 20, 20, 82, 82, 102, 727, 127, 128 
Alpine flowers 69 
Alveolus 44, 45, 68 
Amber 7 70, 1 1 1 

Amino acids 39, 47, 119, 7 79,121,128 

Ammonite 7 70, 112, 128 

Amniotic sac 59 

Amphibians 18, 37,57,92 

Ampulla 53 

Amylase 40, 128 

Androecium 69, 128 

Anemone 15, 75, 77 

Angel fish 703 

Angiosperm 23, 68, 128 

Angler fish 85 

Animals 14-19, 74-79, 727: cells 70, 72, 
11-13; classification 109; defense 86-87, 
86-87; desert 98, 98; diet 38-39, 38-39, 
84-85, 84-85; energy 42, 42-43; 
endangered 104-105, 104-105; 
evolution 106, 107, 113; forest 101, 707; 
grassland 100, 700; homes 90-91, 90- 
91; lifespan 61, 67; mating 90-91, 
90-91; migration 97, 97; movement 32- 
33, 32-33; nervous system 46-48, 46- 
48; partnership 88-89, 88-89; 
reproduction 56-57; senses 57, 52-53, 
52-53; skeleton 30-31, 30-37; skin 54- 
55, 54-55 

Annelids 15 

Annual plants 75 

Annual rings 79, 128 

Ant 8, 89, 92, 94 

Antelope 86,92, 100, 101 

Anthers 69, 70, 70, 77, 72, 72, 73 

Antibiotic 24, 27, 724, 128 

Antibodies 34, 37, 126, 128 

Antler91, 707 

Ant-lion 85 

Anus 40 

Aorta 36 

Ape 95, 95, 101 

Apomixis 70 

Appendix 38, 40 

Arachnids 16, 16, 128 

Archaeopteryx 7 72 

Arctic tern 97 

Armadillo 86 

Artery 34, 35, 35, 36, 54 

Arthropods 16, 128 

Arum lily 72 

Athlete's foot 24 

Atrium 36, 37 

Auxin 78, 128 

Axon 46 

B 

Baboon 95 

Baby: animal 92-93, 92-93, 96; human 58, 

59, 60, 60 
Bacillus 128 

Backboned animals see Vertebrates 
Backswimmer 43 

Bacteria 8, 9, 9, 26-27, 26-28, 34, 38, 727, 
123; use in industry and medicine 124, 
125, 725, 126, 726, 127 



Bacteriophage 28, 725, 128 

Balsam plant 76 

Barbs: feather 55; seed 77 

Barbules 55 

Bark 7 7,22,79 

Barrel cactus 98 

Base pairs 118, 119 

Bat 73, 85, 92,97 

Beagle, H.M.S. 107 

Bean 75, 78, 127, 727 

Bear96, 101, 103 

Bee 1 6, 23, 70, 72, 73, 73, 87, 89, 94 

Beech tree 63, 101 

Bee orchid 23 

Beer 25, 727 

Beetle 43, 84, 85 

Begonia 63, 80 

Biceps 33 

Biennial plants 75 

Bile 40 

Bindweed pollen 69 
Biosphere 8, 128 

Biotechnology 124-127, 724-727, 128 

Birch tree 24, 77 

Bird-eating spider 76 

Bird of paradise 90 

Birds 78, 19, 37, 32, 36, 57, 55, 57, 99: 
courtship 90, 91,97; endangered 104, 
705; migration 97, 97; nest 92-93, 
92-93; respiration 45 

Bird's nest orchid 67 

Bison 100 

Blackberry 75, 81,87 
Blackbird 77 
Bladder 41, 58, 58 
Bladder wrack 20 

Blood 12, 72, 30, 34-37, 34-37, 40, 41 , 47, 

42, 44, 45, 54 
Bones 30,30,37,34, 39,52 
Bonsai tree 79 

Brain 13, 19,44, 46, 47,48, 48,50, 53, 54,61 

Breathing see Respiration 

Breeding 95, 114, 115 

Bristlecone pine tree 61 

Bronchiole 45 

Bronchus 45, 45 

Bud 80, 80-87 

Buffalo 87, 100 

Buffon, George 106 

Bulb 67, 80, 80, 98, 128 

Burrow 92, 100 

Buttercup 69, 81 

Butterfly 76, 55, 57, 97, 97, 101 

c 

Cactus 98, 98 
Caddis-fly larva 102, 702 
Caecum 38 
Calyx 69, 128 
Camarasaurus 30 
Cambium 79, 79, 128 
Cambrian 7 72, 129 
Camel 98 

Camouflage 86, 96, 129 
Capillary 35, 47, 44,45, 54 
Capsule 76,83 
Carbohydrates 39, 66, 129 
Carbon 8, 10, 14, 129 
Carbon cycle 9, 9 
Carboniferous 7 72 
Cardiac muscle 32 
Caribou 97, 97 
Carnivore 38, 84, 100, 129 
Carpel 74, 75, 129 
Cartilage 30, 37,45,46, 129 
Caterpillar 57, 87, 89 
Catkin 23, 69, 71 

Cell 10-13, 70-73; aging 61; energy 42, 
42; evolution of 120-121, 727; viral 
infection 28, 28, 29, 126 see also DNA 

Cell division see Meiosis; Mitosis 



Cellulose 1 1, 77, 38,129 
Cenozoic. 7 72 
Centipedes 16 

Central nervous system 46, 47 
Centrosomes 70 
Cephalopods 17 
Cerebellum 48 
Cerebrum 48, 48 
Cervix 58, 59 
Cheetah 32, 100 
Chimpanzee 93 
Chitin 17,26,31 
Chlorophyll 7 7,20,66, 66, 129 
Chloroplast 11, 7 7, 66, 727, 129 
Choroid 50 
Chromatid 7 76, 7 77 
Chromoplasts 77 

Chromosome 70, 58, 1 15-1 17, 775-777, 

725, 129 
Cilia 72,45 

Circulation of the blood 35, 35, 36, 37 
Clam 703 

Classification 106, 109 
Clavicle 30 
Clone 125 
Clownfish 89 
Coal 8, 9, 9,21 
Cochlea 53 
Coconut seedling 78 
Coelacanth 7 72 
Coelenterates 15, 75, 129 
Collagen 30, 33, 54, 129 
Colon 40 

Color blindness 117 

Compound eyes 57 

Compound leaf 63 

Cone 22, 22, 68, 68, 129 

Conifers 22, 68, 77, 101, 772 

Continental drift 7 73 

Coral 15, 75, 703, 7 72 

Coral weed 20 

Corm 80, 129 

Corn 71, 75, 75 

Corn cockle 8 

Corolla 69, 129 

Corpus callosum 48 

Cortex 47, 48,129 

Cotyledon 75, 75,78,129 

Courtship 91 

Cow 38, 38, 88 

Cowper's gland 58 

Crab 16, 76,86,103 

Cranesbill plant 76 

Cranium 30 

Cretaceous 7 72 

Crick, Francis 118 

Cricket 90, 98 

Crocodile 18, 93, 7 72 

Crustaceans 16, 76, 129 

Cuckoo 93 

Cuckoo pint plant 80 

Curare 33 

Cushion star 77 

Cuticle 16, 37, 54,62,130 

Cuttlefish 17 

Cycads 7 72 

Cytoplasm 70, 1 1, 1 19, 130 
Cytosine 118 

D 

Daffodil 74, 80 
Dandelion 70, 76, 77 
Darwin, Charles 106, 707 
Darwin's frog 93 
Dating see Radioactive dating 
Decay bacteria 8, 9, 9, 27, 84 
Deciduous 96, 101, 130 
Decomposer 84, 130 
Deer 86,91, 97, 101, 707 
Dendrite 46 

Deoxyribonucleic acid see DNA 



137 



Dermis 54 
Desert 98, 98 
Devonian 7 72 
Diabetes 124 
Diaphragm 45 
Diatom 20, 82, 130 
Dicotyledon 75, 130 
Diet 38-39 

Digestion 13, 27, 38, 38, 39, 40, 40 
Dinosaur 18, 19, 30, 110, 7 7 7, 1 12, 7 73, 130 
Disease 27-29, 27-29, 1 25, 1 26, 1 27 
DNA (Deoxyribonucleic acid) 10, 118-120, 

118-119, 121, 125, 130 
Dog 78,47,55,91, 708 
Dogfish 43 
Dog's mercury 71 
Dolphin 52, 93, 703 
Dormouse 79 
Double helix 118 
Dragonfly nymph 37, 102 
Drone fly larva 43 
Drosophilia 115, 7 75 
Drugs 27, 29, 33 
Drupe 75, 75, 130 
Dryopteris 83 
Dung beetle 85 
Duodenum 40 

E 

Eagle 79 

Ear see Hearing 

Ear fungus 24 

Earth 8, 8, 106, 110, 112, 720, 121, 722 
Earthstar 25 
Earthworm 15, 75, 84 
Echinoderms 17, 77, 130 
E. coli 11 8, 125, 126, 130 
Eel 97, 702 

Egg 19, 39, 56, 57, 57, 58, 59, 92-93 

Egg cell 72, 57, 58, 59, 59, 68, 74, 82, 1 1 6 

Electron microscope 130 

Elements 8 

Elephant 100, 101 

Embryo 57,59, 59, 130 

Endangered species 104-105, 104-105 

Endocrine glands 49 

Endolymph 53 

Endoplasmic reticulum 70, 7 7 

Endosperm 74,75,78,130 

Energy 10, 70, 20, 38, 39, 42, 42, 45, 48, 64, 

65, 66, 121, 124 
Environment 107, 108, 112, 117 
Enzymes 70,25,39,40,61,67,119, 724, 

125, 130 
Epidermis 72,54, 62, 131 
Epididymis 58 
Epiglottis 40 
Epiphytes 88 
Epithelial cell 72 
Ethane 123, 131 
Evaporation 8, 64 
Evergreen 131 

Evolution 22, 23, 106-112, 106-112, 113, 

114, 774, 117, 119 
Excretory system 41,47 
Exoskeleton 16, 37, 54 
Eye 50-51, 50-57, 7 77 



Fallopian tubes 58, 58, 59, 59 

Family tree 109, 709 

Fanworm 85 

Farsightedness 57 

Feathers 55, 55, 90, 90 

Feedback system 49, 49 

Female reproductive system 58, 59 

Ferns, 21, 27, 83, 83, 707, 7 72 

Fertilization 57, 58, 59, 59, 74, 7 77 

Fibrin 35 

Fibula 30 



Filament: flower 71, 72; muscle 33 
Firefly 90, 90 

Fireweed see Willow-herb 

Fish 18, 78, 37,42, 43, 52, 57, 102-103, 

102-103, 104, 7 72 
Fish eagle 79 
Fisher spider 102, 702 
Flatworm 15 
Fleming, Alexander 24 
Flight 78, 19,37,32,45 
Flowering plants 22, 64, 68-75, 69-74, 78, 

80-81,80,89,99 
Fly 72, 1 15, 7 75 
Fly agaric 24 
Foam-nesting frog 92 

Food: animals 38-40, 38-40, 45, 61, 84-85, 
84-85, 94; chain 84, 85, 131 ; microbe 
produced 127; plants 64, 66, 66-67; web 
85, 131 

Forests 101, 707 

Fossil 106, 706, 107, 110-111, 110-111, 131 
Fox 96 

Frilled lizard 87 

Frog 18, 78, 32, 42, 52, 57, 57, 87, 90, 93, 101 

Frond 21, 27, 83, 83, 131 

Fruit 23, 23,75,76, 76,77, 131 

Fruitfly 115, 775 

Fruiting body 24, 25, 82, 96, 131 

Fungus 8, 24-25, 24-25, 88, 96 

Fur 55 



Gall bladder 13, 40 
Gametes 57, 131 
Ganglia 46 

Gene 115, 7 75,117,118,124-126, 725,131 
Genetics see DNA; Chromosomes; Nucleic 
acids 

Genetic engineering 124, 725, 126-127, 131 

Genus 109, 131 

Germination 78, 83, 131 

Gills 42, 43 

Giraffe 100, 107 

Glands 49, 131 

Glomerulus 47 

Glossopteris 1 1 3 

Glow worm 90 

Goat 86, 99 

Goblet cells 45 

Golgi body 70, 7 7 

Goose 45, 97, 105 

Gorse pod 76 

Grana 66 

Granular layer 54 

Granulocyte 34 

Grass71, 77,75 

Grasshopper 90 

Grasslands see Savannas 

Grass snake 86 

Grazing animals 23, 38, 38, 86, 100, 700 
Greenpeace conservation 705 
Grooming 95, 131 

Growth: human 49, 58-59, 60, 1 16, 1 17; 

plant 78-79, 78, 116 
Growth hormone 124, 126 
Guanine 118 
Guard cells 65, 65 
Gut 15, 38,38 
Gymnosperm 22, 68, 132 
Gynoecium 69, 132 

H 

Haeckel, Ernst 709 
Hair follicles 54, 54,55 
Harvest mouse 92 
Hawthorn berry 77 
Hay fever 71 
Hazel 69 

Hearing 30, 52-53, 52-53 

Heart 1 3, 73, 19, 33, 35, 35, 36-37, 36-37, 



Hedgehog 87, 96 
Hemicidaris 106 
Hemispheres, brain 48 
Hemoglobin 34, 43, 132 
Hemophilia 35, 125, 132 
Herbivore 38, 84, 101, 7 73, 132 
Heredity 114-115, 114-115 
Hermit crab 88 
Heron 103 
Herring 18 

Hibernation 18,42,99 
Hilum75 

Hippopotamus 100 
Holly 69, 70 

Honeybee 32, 38, 72, 72, 94 
Honeysuckle 72 
Hoof 99 

Hooke, Robert 10, 7 7 

Hormones 48, 49, 49, 58, 1 24, 1 26, 1 32 

Horn 55, 97 

Horse chestnut leaf 63 

Horsefly 57 

Human body 118, 120: blood 34-37, 34- 
37; cell 116-117, 777; diet 39,39; 
digestion 40, 40; excretory system 41, 
47; life span 60; nervous system 46-49, 
46-49; reproduction 58-59, 58-59; 
respiration 44-45 44-45; skeleton 30, 
30-37; skin 54-55, 54-55 see also DNA; 
Gene 

Hydra 46, 56 

Hydrogen 8, 9, 10, 66, 120, 121 
Hyphae 25, 67 
Hypothalamus 48, 49 

I 

Ibex 99 

Ice Ages 7 73 

Ileum 40 

Immune system 61 

Impala 32, 97 

Impulses 46, 47, 47,49, 50 

Indehiscent fruit 76 

Inflorescence 71, 132 

Inheritance see Chromosome; Heredity 

Insects 16, 37, 32, 37, 42, 43, 46, 51, 54, 89, 

90,93,94, 102, 7 70, 7 72 
Insulin 124 

Interferon 124, 126, 132 
Intestines 13, 73, 38, 38, 39, 40, 40 
Invertebrate 14, 17, 37,46, 46, 54, 103, 132 
Involuntary muscles 32, 33 
Iris 50, 81, 87 

J 

Jaw 38, 39 
Jellyfish 15, 30, 103 
Jenner, Edward 29 
Joints 37 

Jungle plants 63, 88, 88 
Juniper cone 68 
Jurassic 7 72 



Kangaroo 19, 79,57,92 

Keratin 54, 55 

Kidneys 41, 47 

Killer whale 52, 52,84, 103 

Knee cap 30 

Koala 38 

Krill 103 

Kudu 100 

L 

Lactic acid 33 

Lady's slipper orchid 704 

Lamarck, Jean Baptiste 107, 707 

Lamellae 66 

Lamprey 89 

Langur 95 



L38 



Larva 43, 102, 703 
Lateral line 52 

Leaf 13, 21,21, 22, 23, 62-63, 62-64, 65, 66, 

78, 80,87,82,83,86,96 
Leaf-cutter ant 8 
Learning 60, 93 
Lens 50, 50,51,57 
Lenticels 65 
Leopard 100 
Lettuce pollen 69 
Lichens 25, 25 
Life see Living matter 
Life expectancy 61 
Life in solar system 122-123 
Life span 60, 60 
Ligament 31 
Light rays 50, 57 
Limpet 84 

Linnaeus, Carolus 106, 109 
Lion 39,84,85, 100, 700 
Liver 13, 73,40,40,41 
Liverwort 21, 21, 83, 132 
Living matter 8, 10,20, 106-107, 116-121, 
7 76-727 

Living together 88-89, 88-89, 94-95, 94- 
95 

Lizard 18, 87, 98 
Lobe-finned fish 7 72 
Lobster 42 
Locust 42 
Loris 8 

Lotus plant 77 
Lucretius 106 
Lugworm 43 

Lung 73, 34, 37, 41 , 42, 44-45, 44-45 

Lungfish 18, 42 

Lycaenops 7 73 

Lymph 37, 37, 132 

Lymphocyte 34, 37 

Lysosomes 70 

Lystrosaurus 113 



M 

McCay, Dr. Clive61 
Mackerel 103 

Male reproductive system 58, 58 
Mallard duck 90 
Malpighian layer 54 

Mammal 19, 32, 34, 37, 47, 53, 55, 95, 98, 
132 

Mammoth 110, 113 
Markhor horn 55 
Marrow 30,34 
Mars 122 

Marsh marigold 102 
Marsupials 19, 132 
Mating signals 90-91, 90-97 
Mayfly nymph 43 
Meadow grass 77 

Meat-eating animals see Carnivores 
Meat-eating plants 67, 67 
Medicine 724, 125, 126 
Medulla 47, 48 
Medusa 56 

Meiosis 1 17, 777, 7 78, 1 19, 132 
Membrane 37, 39, 42, 44, 45, 66 
Memory 48 
Mendel, Gregor 114 
Mendel's Laws 115 
Menstrual cycle 58, 58, 59 
Meristem 78,79, 132 
Mesosaurus 7 73 
Mesozoic 7 72 

Messenger RNA see mRNA 

Metatarsals 30 

Methane 123, 132 

Microbes 124, 725, 127 

Micropyle 74, 74, 132 

Microscopic organisms 72, 14, 26, 42, 82 



Midrib 63 

Migration 97, 97, 132 
Midwife toad 93 
Miller, Stanley 121 
Millipede 16, 7 72 
Minerals 39 
Mink 103 
Mite 16 

Mitochondria 70,42, 727, 133 
Mitosis 117, 777, 133 
Molar tooth 39 
Molds 24 

Mollusks 17, 77, 102, 133 

Monarch butterfly 97, 97 

Monkey 86, 95, 95,101 

Monocotyledon 75, 133 

Monod, Jacque 10 

Monthly period see Menstrual cycle 

Monotremes 19, 133 

Moon 722 

Mosquito 16, 43 

Mosses 21, 27, 82, 82, 707 

Moths 16, 76, 73, 87, 87, 90, 108 

Motor nerve 46, 47, 47 

Mouse 92, 96 

Mouth 37, 39, 40, 43 

Movement 32-33, 32-33, 47, 47, 48 

mRNA 779 

Mucus 45, 49 

Muscle 32-33, 32-33, 36, 39, 40, 47, 47, 50, 

51,55, 59,61 
Mushroom 25, 96 
Musk ox 87 
Mussel 17 
Mutation 119, 133 
Mycelium 25 
Mycorrhiza 89, 133 
Myelin 46 
Myofibrils 33 
Myosin 33 
Myrtle 73 

N 

Natural selection 107, 108, 133 
Nautilus 703 
Nearsightedness 57 
Nectar 72, 73, 133 
Ne-ne goose 105 

Nerve cells 12, 72, 13, 15, 36, 46, 47, 47, 48 

Nerve impulses 47, 50, 50, 52, 53, 54 

Nervous system 46, 46, 48, 61 

Nest 92, 93, 94 

Neuropteris 1 10 

Newt 90, 102 

Nitrate 9 

Nitrite 9 

Nitrogen 8, 127 

Nitrogen cycle 9, 9 

Nitrogen fixing 127 

Noise decibels 53 

Nose 45,49 

Nucleic acids 26, 28, 28, 121, 133 
Nucleolus 70 
Nucleotide 118 

Nucleus 70, 7 7,74, 74, 78, 115, 1 16, 7 76, 

118, 778, 1 19 
Nut 77 

Nymph 37, 43 

o 

Oak tree 79, 101 
Obelia 56 
Ocean 9, 20 

Octopus 17, 77,46, 46,51 

Omnivore 84, 133 

One-celled animals see Protozoa 

Onion 23, 78 

Operculum 43 

Optic nerve 50 

Orchid 67,72,73, 73, 704 



Ordovician 7 72 

Organic molecules 10, 121, 123, 133 
Organs 13, 73 

Origin of life 120-121, 120-121 
Origin of Species, Trie (Darwin) 107 
Oryx 105 
Ostrich 87, 93 

Ovary 58, 59, 68, 69, 74, 74, 75, 75, 133 

Oviduct see Fallopian tubes 

Ovulation 59 

Ovule 68, 69,74, 74, 133 

Ovum see Egg cell 

Owl 57,85, 96, 100 

Oxpecker89 

Oxygen 10, 34, 35, 35, 36, 37, 42, 44, 44, 45, 

48,65, 66, 120, 121 
Oxygen cycle 9, 9 
Oxyhemoglobin 34 
Oyster 17 

P 

Palaeozoic 7 72 

Palisade layer 72,62,133 

Pancreas 13, 40 

Panda 704 

Pangaea 113 

Paramecium 72 

Parasite 15, 56, 67,89, 89, 133 

Parrot fish 703 

Partnerships 88-89, 88-89 

Pasteur, Louis 27, 27 

Patella 30 

Pavlov, Ivan 47 

Pea 70, 127 

Peacock 90 

Pea crab 76 

Pear 75 

Pecking order 95 
Pelican 37 
Pelvis 30, 37 
Penicillin 24, 124 
Penis 58, 58 
Pennycress 76 
Pepsin 40 
Perch 102 
Perennial plants 75 
Peristalsis 38, 40 
Permian 7 72 

Pesticide 104, 704, 105, 133 

Petal 69, 71,72, 74 

Petrified Forest National Park 7 70 

Phalanges 30 

Pheasant's feather 55 

Phloem 72, 73, 23, 62, 64, 64, 67, 79, 134 

Photosynthesis 9, 20, 21, 66, 66, 134 

Phylum 109 

Phytoplankton 103 

Pigment 20, 28, 50, 66 

Pika 99 

Pike 102 

Pine needle 73, 63 
Pine tree 22,61 
Piranha 702 

Pituitary gland 49, 49, 126 

Placenta 59, 134 

Planets 122-123, 122-123 

Plankton 20, 20, 103, 134 

Plant eaters see Herbivores 

Plants 9, 9, 20-23, 20-23, 121 : cells 10-13, 
7 7- 73; characteristics 114-115, 7 74; 
classification 109; desert 98, 98; diseases 
28, 29; endangered 104-105; evolution 
106-107, 706; food 66-67, 66-67; forest 
101, 707; fossil 1 10-1 1 1 7 70; leaf 62-63, 
62-63; life span 61 ; partnerships 88-89, 
88-89; pipelines 64, 64; pollination 68- 
73, 68-73; reproduction 80-83, 80-83; 
respiration 65, 65; seeds 74-78, 74- 78 

Planula 56 

Plasma 34, 134 



139 



Plasmid 125, 134 
Platelets 34,34,35, 134 
Platypus 19, 79 
Play 60 

Pleistocene 7 73, 134 
Pleural membranes 44 
Pleurococcus 20 
Plum 75 

Plumule 75, 75, 134 
Pod 75, 76, 76 
Poison 87, 87,104 
Polio 29, 29 

Pollen 72, 22, 23, 68-74, 68-73, 1 14, 1 17, 
134 

Pollination 70-73, 70-73, 134 
Pollinia 73 

Pollution 104-105, 104-105, 108, 724 
Polyp 56 

Pond life 43, 83, 102, 702 
Pond skater 102 
Poppy 74, 75 
Porcupine 54, 87 
Potato 23,28,67, 67,81,87 
Potter wasp 92 
Prairie animals 100 
Prairie dog 92, 100 

Prehistoric animals 16, 17, 18, 19, 106 
Prehistoric plants 20, 21, 22 
Prehistory 110-113, 110-113 
Primordial atmosphere 121 
Primrose 70 
Prostate gland 58,58 

Protein molecules 7 7, 39, 67, 1 18-1 19, 7 79, 
121, 134; use in industry and medicine 
124, 125, 725, 126-127 

Prothallus83, 83, 134 

Protista 14, 134 

Protoplasm 1 1 

Protozoa 14, 56, 134 

Puberty 58 

Pulmonary artery 36 

Pulmonary vein 36 

Pupa 57 

Pupil, eye 50 

R 

Rabbit 84, 86, 92,96 
Radial muscles 50 
Radiation 720, 121, 123 
Radioactive dating 1 1 1 
Radula38 
Rafflesia 73 

Rainforest 101, 707, 704 
Rattlesnake 100 
Raup, Dr. David 112 
Ray, John 106, 109 
Receptor cells 49, 49, 53, 53 
Recessive gene 115, 117 
Rectum 40, 40 
Recycling8, 9 

Red blood cells 12, 30, 34, 34, 35, 39 

Red deer 707 

Redwood tree 22, 22 

Reeds 102 

Reflex action 47, 47 

Refraction 50, 51 

Releasing factor (RF) 49 

Renal system 41, 47 

Reproduction 22-23, 49, 56, 58-59, 58-59, 

80,83-84,83-84,107,117 
Reptiles 18, 37,57,61,93,98 
Resin 7 70, 1 1 1 
Resin duct 73 

Respiration 9, 42, 42, 43, 44-45, 44-45, 65, 

134 
Retina 50, 50 

Rhinoceros 54,84,87,89, 104, 113 
Rhizoids21,27 
Rhizome 21, 81, 87, 135 
Ribonucleic acid see RNA 



Ribosome 70, 7 7, 1 19 
Ribs 30, 44, 45 

RNA (Ribonucleic acid) 7 79, 121 
Rocks 8, 9, 106, 110 
Rodent 100, 101 

Root 9, 21 , 23, 62, 64, 64, 65, 78, 78, 79, 80, 

83, 97, 98, 727 
Rose 23 
Roundworm 15 
Rumen 38 
Runner81,82 



s 

Saccule 53 
Salamander 87 
Saliva 40,47 
Saluki 708 
Sanicle 77 

Savanna 100, 700, 135 
Saxifrage 99 
Scab 35 

Scabious seeds 77 

Scapular 30 

Scavengers 100 

Scent 91, 95 

Sclera 50 

Scorpion 43, 93 

Scotch pine pollen 68 

Scottish terrier 708 

SCP (Single cell protein) 127 

Scrotum 58 

Sea anemone 15, 75, 77, 84, 88, 89 

Sea horse 93 

Seal 91, 95, 103 

Sea life 103 

Sea lily 7 72 

Sea otter 85 

Sea scorpion 7 72 

Sea slug 77 

Sea snail 84 

Sea turtle 97 

Sea urchin 17,87, 706 

Seaweed 20, 20, 66, 82 

Sea worm 103 

Sebaceous glands 54 

Secondary thickening 79, 135 

Sediment 110, 111 

Seeds 21 , 22, 23, 68, 68, 70, 74-78, 74-78, 

Segmented worms 15, 135 
Self pollination 70 
Sensory cells 49, 50, 53, 54 
Sensory nerves 47, 47, 48, 49 
Sepal 69, 74, 135 
Sepkoski, Dr. John 112 
Sewage waste 104, 105 
Sex cells 57, 58-59, 58-59, 82, 82, 83, 117, 
777 

Shark 30, 86, 103 
Sheep 84, 99 
Shell 17 

Sidewinder snake 98 
Sieve plate 72 
Sieve tube 64 
Silk 76 
Silurian 772 

Single cell protein see SCP 

Single cells 20, 26, 42, 82 seealso Protozoa 

Sinus 37 

Sitka spruce 22 

Skeleton 75,16,17, 78,30-31,30-37, 32 
Skin 54-55, 54-55 
Skull 30, 31, 38 
Smell 49 

Smooth muscle 33 
Snail 17, 77, 38, 43, 102 
Snake 18, 85,87,98, 101 
Snapdragon 73 
Soil 8, 9, 21 



Sorus83, 135 

Sound waves 52, 53 

Space exploration 122-123, 122-123 

Sparrow 36 

Spawn 57 

Species 109, 114, 117, 135 
Speckled moth 108, 708 
Speech 48 

Sperm 72, 56, 57, 57, 58, 58, 59, 1 17 

Sphagnum moss 27 

Sphincter muscle 32, 50 

Spider 16, 76,102, 702, 7 72 

Spinal cord 46, 46, 47, 47 

Spindle 7 76, 7 77 

Spiny anteater 19 

Spiracles 42, 43 

Spirogyra 82 

Sponges 14, 74, 135 

Spoonbill 97 

Sporangium 83, 135 

Spore 24, 25, 25, 82, 82, 83, 83, 97, 135 

Spruce 22 

Squid 17,46,51 

Squirrel 101 

Squirting cucumber 76, 76 
Stamen 69,74,135 
Stapelia flower 72 
Starfish 17, 77,46 

Stem 62, 63, 64, 64, 65, 65, 80, 81 , 98, 98, 
114 

Steppe animals 100 
Sternum 30 

Stigma 69, 70, 70, 71 , 77, 72, 74, 74 

Stinging nettle 87 

Stoma 73,65,65,67,135 

Stomach 73,32,38,40 

Strawberry 75, 81,87 

Striped muscle (striated) 33, 33 

Stroma 66 

Style 69, 74 

Sundew plant 67 

Sunflower 78 

Sunstar 77 

Survival of the fittest 107, 117 
Swallowtail butterfly egg 57 
Sweat glands 41, 54, 55 
Sweetlip fish 88 
Swimming crab 76 
Swordtail 702 

Symbiosis 24, 25, 88, 89, 121,135 
Synapse 47, 47, 135 
Synovial fluid 37 

T 

Tadpole 42, 57,102 
Tarsals 30 

Taste buds see Sensory cells 
Taxonomy 109, 135 
Teeth 38, 38-39 

Temperature, body 19, 32, 34, 54, 54, 98 

Tendon 33 

Tentacle 75 

Termite 16, 94, 94, 135 

Tern 93, 97 

Terrapin 90 

Territory 91, 95, 135 

Tertiary 7 72 

Testa 75 

Testicles 58, 58 

Throat 52 

Thymine 118 

Thyroid stimulating hormone (TSH) 49 
Thyroxine 49 
Tibetan spaniel 708 
Tibia 30 
Tick 16 

Tiger moth 87 
Timothy grass pollen 69 
Tissue 13, 73,29, 35, 38, 39,42 
Titan (moon) 122, 723 



140 



Toad 87, 90 

Toadstool 24, 25, 96 

Toe bones 30 

Tomato 75 

Tongue 49 

Tonsils 37 

Tortoise 18, 61 

Tortoiseshell butterfly 76 

Touch receptors 49 

Trachea 42, 45 

Tracheoles 42,43 

Transfer RNA seetRNA 

Transpiration 64, 135 

Transplant 34 

Tree catkins 23, 69,71, 77 

Trees 22, 22, 23, 64, 68, 68-69, 75, 79, 79, 

88,96, 101, 705, 7 70, 7 72 
Triassic 7 72 
Triceps 33 
Trilobite 706, 7 72 
tRNA 7 79 

Tropical rain forest 101, 707, 704 

Tropism 78, 136 

Trout 102 

Trypanosome 56 

Trypsin 40 

Tuberculosis 27 

Tubule 47 

Tulip 28, 75 

Tumbleweed 77 

Tuna 103 

Turtle 18,61,86,97 

u 

Ulna 30 

Umbilical cord 59 
Uracil 7 79 
Urea 47, 55 
Urethra 58, 58 
Urine41,47 

Ussher, Archbishop 106, 706 



Uterus 58, 58, 59 
Utricle 53 

V 

Vaccination 27, 29, 29, 126, 136 
Vacuole 11, 77, 136 
Vagina 58 

van Leeuwenhoek, Anton 27 
Vascular bundle 79, 136 
Vector 125 

Vegetative reproduction 80, 136 
Vein 34,35, 35,36; leaf 63 
Vena cava 36, 41 
Ventricle 36, 37 
Venus 122, 723 
Venus fly trap 104 

Vertebrate 14, 17, 18, 73, 30, 30, 37, 46, 709, 
136 

Vessel cells 64 
Vetch pod 76 
Villi 39 

Virus 28-29, 28-29, 37, 125, 725, 126 
Vitamins 39, 136 
Vole 96 

Voluntary muscles 32, 33, 33 
von Plenciz, Anton 27 
Vulture 84,85, 100 

w 

Wallace, Alfred Russel 107, 707 

Wasp 92, 92, 94 

Water 39, 40,47,42 

Water beetle 43, 102 

Water crowfoot 63 

Water cycle 8 

Water lily 102 

Water plants 20-21, 20, 65, 77, 102, 702, 
103 

Water scorpion 43 
Water snail 43, 102 
Watson, James 118 



Weasel 96, 96 
Weaver bird 92 

Whale 14, 20, 52, 52, 97, 103, 104, 105 
Whelk 77, 88 

White blood cell 72,34,34 
White rhinoceros 84, 105 
Wild goat 99 

Wildlife protection 104-105, W4-105 

Willow-herb 70 

Wind: pollination 70,71 

Wine 25, 27 

Windpipe 45 

Wing 18, 32 

Wobbegong 86 

Wolf 84,85, 101 

Womb see Uterus 

Woodlands 80, 101, 707 

Woodlouse 16 

Woodpecker 707 

Woolly mammoth 1 13 

Woolly rhinoceros 113 

Worms 15,30,46, 102 

Wrasse 88 



X 

Xanthoria parietina 25 

Xylem 72, 73, 23, 62, 64, 64, 66, 79, 79, 136 



Y 

Yeasts 25, 124, 127, 727, 136 
Yellow water lily pollen 69 
Yucca plant 73 

Z 

Zebra 57, 100 
Zooplankton 103 
Zebra angel fish 703 
Zygote 57, 136 



ACKNOWLEDGEMENTS 

4 right Gene Cox; 5 center University of Birmingham; 8 left 
NASA, top right N.H.P.A, center right Brian Hawkes, bottom 
right P.Morris; 11 top Ann Ronan Picture Library; 12 top 
N.H.P.A/M.Walker; 14 Biofotos; 15 bottom right N.H.P.A; 16top 
P.Morris; 17 top P.Morris, bottom right Biofotos; 18 center 
ZEFA, bottom left N.H.P.A, bottom right, Biofotos; 19 top 
N.H.P.A, center Nature Photographers, bottom left A.N.I.B, 
bottom right G.R.Roberts; 20 top Gene Cox, 21 bottom Biofotos; 
22 left P.Morris; 23 top right N. Callow/Nature Photographers; 24 
left Heather Angel, bottom right M.Chinery: 25 bottom left 
Heather Angel, bottom right M.Chinery; 26 bottom left British 
Museum (Natural History), bottom right Gene Cox; 27 left Mary 
Evans Picture Library, right ZEFA; 28 top and center Crown 
Copyright (1985), bottom Gene Cox; 29 top ZEFA, bottom left 
Glaxo Research, bottom right W.H.O; 30 left Dinosaur National 
Monument, Utah; 31 top left P.Morris, top right Heather Angel, 
center and bottom right Michael Rubens; 32 top N.H.P.A, center 
Heather Angel; 33 bottom Gene Cox; 34 top right Gene Cox; 38 
bottom left Gene Cox; 39 bottom right J.A.Carter; 41 bottom left 
Gene Cox; 43 center left Biofotos; 44 bottom left Gene Cox; 46 
center Gene Cox; 51 bottom left Biofotos; 52 top P.Morris, 
center N.H.P.A; 55 top Heather Angel, center Biofotos, bottom 
right P.Morris; 56 center Gene Cox; 57 top left Heather Angel; 58 
top British Museum (Natural History); 60 top ZEFA, bottom 
Anthea Seveking; 61 Robert Harding; 63 Gene Cox; 64 Gene 
Cox; 67 top Gene Cox, bottom left Burbridge/Nature Photo- 
graphers, bottom right Brian Hawkes; 68 bottom left Repro- 
duced by kind permission of the Director, Royal Botanic 
Gardens, Kew, bottom right British Museum (Natural History); 
69 center ZEFA, bottom British Museum (Natural History); 71 
top Heather Angel; 72 top N.H.P.A, bottom Biofotos; 73 top left 



N.H.P.A; 74 top A to Z Collection, center G.R.Roberts; 75 Gene 
Cox; 76 top and center M.Chinery, bottom right Heather Angel; 
77 bottom left N.H.P.A; 78 top Robert Harding, bottom left 
G.R.Roberts; 79 top A to Z Collection; 80 top Heather Angel; 81 
top M.Chinery; 82 top Gene Cox; 83 bottom left Heather Angel; 
84 center SATOUR, bottom Heather Angel; 85 top Biofotos, 
bottom right P.Morris; 86 top left Biofotos, top right N.H.P.A, 
bottom right M.Chinery; 87 bottom M.Chinery; 88 top Biofotos, 
center N.H.P.A, bottom Heather Angel; 89 center Biofotos, 
bottom M.Chinery; 90 top N.H.P.A, bottom Nature Photo- 
graphers; 91 top Brian Hawkes, bottom Kenya Tourist Office; 94 
bottom P.Morris; 95 top and bottom ZEFA; 96 top M.Chinery, 
bottom left N.H.P.A, bottom right A to Z Collection; 98 top 
N.H.P.A/K.Switak, center Natural Science Photos/Dick Brown; 99 
left ZEFA, right Brinsley Burbridge/Nature Photographers; 100 
left and right N.H.P.A, 101 bottom right N.H.P.A; 102 top 
N.H.P.A; 104 top left ZEFA, top right R.G.Argent/N.H.P.A, bottom 
right Shell; 105 top Greenpeace, center Edward Ashpole, 
bottom M.Chinery; 106 left Mansell Collection, top right 
Biofotos, bottom right Imitor; 107 left and center Imitor, right 
Royal College of Surgeons/G.Rainbird; 108 left M.Chinery, 
center, top left and bottom left Marc Henrie/Pedigree Chum; 109 
top Imitor; 110 top left Biofotos, top right Imitor, center right 
Institute of Geological Sciences, bottom left ZEFA; 111 Zofia 
Kielan-Jaworowska; 115 center Paediatric Research Unit, Guys 
Hospital; 120 top Ames Research Laboratory; 121 Imitor; 122 
NASA; 123 NASA; 124 bottom Beechams; 125 bottom 
R.Newsam/University of Kent; 126 University of Birmingham; 
127 top Heather Angel, center ZEFA, bottom R.Newsam/ 
University of Kent; 

Picture Research: Jackie Cookson 



141 



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Biology 

Encyclopedia 




ISBN □-5Efl-flElb?- c 1 



Medicine • Ecology • LifeCy< 



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