Biology

Year 12
Year 12

Biology
 BIOLOGY
Year 12

GOVERNMENT OF SÄMOA
MINISTRY OF EDUCATION, SPORTS AND CULTURE
 Acknowledgements
The Ministry of Education, Sports and Culture would like to thank the following people
for their vision, patience and hard work in putting together this valuable book:

Cara Scott Consultant

Anna Egan-Reid Additional illustrations
Masa Fa⁄sau Robert Louis Stevenson’s Secondary School
Tamasoali‹ Saivaise CMAD
Desmond Mene Lee-Hang ICSPI Secretariat (UNESCO Office for the Pacific)

The MESC would like to thank Desmond Mene Lee-Hang (International Council for the
Study of the Pacific Islands secretariat) for advice on Sämoan herbal medicine.

Some of the material in this book is taken from the following texts and is used with the permission
of New House Publishers Ltd, Auckland, New Zealand and the listed authors/illustrators:
Biology Pathfinder Year 12 Author: David Relph
Series Editor: George Hook
Illustrations: Tony Mander
Photograph acknowledgements:
page 4 R. Morris, Dept Conservation
page 8 Ministry of Forestry
pages 27, 35, 61 Neil Andrews, SEM Technician, Plant and
Microbial Sciences Dept, University of Canterbury
page 35 Dr Paul Broady, Plant and Microbial Sciences Dept,
University of Canterbury
page 36 Duncan Shaw-Brown, Photographic Services, University
of Canterbury
pages 9, 65, 79, 83, 93 Royal NZ Forest and Bird Society
page 37 Manfred Ingerfeld, TEM Technician, Plant and Microbial
Sciences Dept, University of Canterbury
pages 34, 36, 59, 86 D. Stringer, SEM Technician, Engineering
Dept, University of Auckland
page 86 Associate Professor Brian Butterfield, University of
Canterbury
Science Pathfinder Year 11 Series Editor and author: George Hook
Illustrations: Tony Mander
Photograph acknowledgements:
pages 4, 5, 6 Neil Andrews, Canterbury University
pages 4, 5, 6 Dr Ian Hallett, Hort Research
pages 7, 10, 11, 23 Dave Relph
The Living World, Level Six Science
Authors: David Relph, Murray Black, Jan Jamieson

Emergency Clinic: A learning context for the human body

Author: Monique Curran
Illustrations: Warren Mahy

© Ministry of Education, Sports and Culture, Sämoa, 2004

Designed, edited and typeset by Egan-Reid Ltd, Auckland, as part of the Sämoa
Secondary Education Curriculum and Resources Project for:
Government of Sämoa Ministry of Education, Sports and Culture, 2004.
Funded by the New Zealand Agency for International Development, Nga Hoe Tuputupu-mai-tawhiti.
Printed through Egan-Reid Ltd.
Managing Contractor: Auckland UniServices Limited.
ISBN 982-517-063-8
Table Of Contents
Unit 1 Variety Of Life 5
Living Things 5
Micro-Organisms 8
Harmful Micro-Organisms 30
Diseases 33
Examples of Pathogens 37
Methods of Controlling and Curing 43
Diseases Use of Plants As Medicines 47
Unit 2 Cell Biology 58
Cell Structure 58
Respiration 65
Diffusion and Osmosis 67
Enzymes 72
Unit 3 Genetics 76
Cell Division 76
Inheritance 85
Unit 4 Plants 107
Photosynthesis 107
Plant Structure 111
Root Structure 114
Plant Processes 116
Asexual Reproduction 119
Sexual Reproduction 120
Germination 124
Co-ordination 126
Unit 5 Animals 129
Nutrition 129
Circulation 135
Gas Exchange 139
Excretion 144
Movement 145
Endocrine System 148
 Nervous System 149
Reproduction 153
The Effects of Drugs and Exercise 160
Unit 6 Environment 164
Adaptation 164
Community Inter-relationships 170
Conservation 175
Glossary 180
Key Vocabulary 182
Topic Specific Vocabulary 184
 Unit

Variety Of Life

This unit is divided into sections that cover living things and micro-organisms.
1
Living Things
In this section you learn to:
❑ describe the life processes carried out by living things
❑ classify living things into kingdoms

❑ describe features of the main groups of plants and animals ❑

use dichotomous keys to identify organisms.

Biology and life

Biology is the scientific study of life. It is the study of all living things – from
fragile butterflies which battle to survive on high alpine peaks to 40 metre strands
of wave-tossed giant kelp on rocky coast lines; from majestic lions of the African
savanna to tiny micro-organisms that live on their skin.
Biology is the study of humans and of the 1.5 million different kinds or species of
living things that are known (and of the many millions of species yet to be
discovered).
Humans are interested in biology because we too are part of the living world. We
are curious animals who want to know how life functions, and how we can coexist
with and use the living world around us.
If biology is the study of life, then first we must be clear what life is. When
compared with matter that is non-living, objects that are alive are characterised by
a number of special features.
Living things are made up of small units called cells. Living things use energy to
carry out movement, growth and reproduction. Living things also respire, sense
their surroundings, obtain nutrition and excrete wastes.
Use the letters MRS C GREN to remember the features of living things.
Move, Respire, Sense, Cells, Grow, Reproduce, Excrete, Nutrition.

5
6

Kingdoms
Organisms which are unicellular or multicellular (but lack complex organs) are
called ‘simple’ organisms. Organisms in the Kingdoms Monera, Protista and Fungi
are simple organisms.

Kingdom Monera Kingdom Protista Kingdom Fungi

• 10 000+ species • 55 000+ species • 100 000+ species
• most common organisms • simplest organisms with nuclei • multicellular and immobile
• unicellular • unicellular and multicellular • nuclei present in cells
• no nuclei or chloroplasts • mitochondria and chloroplasts • external digestion of food
• bacteria, blue-green algae • protozoa, algae, slime moulds • moulds, toadstools, yeasts
bacteria Amoeba

blue-green algae Euglena

Kingdom Plantae Kingdom Animalia

• 300 000+ species • 1 000 000+ species
• complex, multicellular • complex, multicellular
• live on land or in fresh water • must consume food
• make food by photosynthesis

Figure 1.1 Kingdoms

Kingdom Plantae – plants

The plants in Kingdom Plantae can be divided into groups which have similar
features.

Small, flat or Phylum Bryophyta – Mosses, Liverworts

tufted green
plants, found • 16 000+ species
in damp places • no true leaves
• no conducting tissue
• spores in capsules
Plants with
stems and
fronds, often in Phylum Pterophyta – Ferns
damp places
• 12 000+ species
• true leaves
Tall plants with • conducting tissue
sharp leaves • spores in capsules
and cones, in
many habitats
Phylum Coniferophyta – Conifers
Tall plants with • 550+ species
broad leaves • true leaves
and flowers, in • conducting tissue
many habitats • seeds in cones

Phylum Anthophyta – Flowering Plants

• 250 000+ species Dicot
class
• true leaves
• conducting tissue
• seeds in fruits
Monocot class

Figure 1.2 Classification of plants

BIOLOGY YEAR 12
 7

Kingdom Animalia – animals

The animals in Kingdom Animalia can be divided into groups which have similar
features. These groups can then be divided into small groups of even more similar
animals.

Phylum Echinodermata
– Starfish
6000+ species
Patterns in fives, spiny skin • tube feet

All-round symmetry

Phylum Cnidaria
– Stingers
Stinging tentacles • 9000+ species
• sac-like body

Phylum Annelida
– Worms
• 9000+ species
Length-wise symmetry Long, cylindrical segmented body

Phylum Platyhelminthes
– Flatworms
Flat, unsegmented body 13 000+ species

Phylum Mollusca – Shellfish

47 000+ species
Soft, unsegmented body, muscular foot, often in a shell mostly marine
• mantle secretes shell

Phylum Arthropoda
850 000+ species
Hard exoskeleton, segmented body with many limbs most successful group
variety of habitats
restricted in size

Class Chilopoda Class Insecta Class Arachnida Class Crustacea

– Centipedes – Insects – Spiders – Crustaceans
3000+ species 750 000+ species 57 000+ species 25 000+ species
three body parts two body parts two specialised
six legs eight legs limbs per segment

Figure 1.3 Classification of invertebrates

UNIT 1
8

Class Osteichthyes – Bony Fish

Aquatic
animals with • 19 700+ species
fins and • gills
scales • unprotected eggs
• marine and freshwater

Class Amphibia – Amphibians

Terrestrial
animals with • 2500+ species
four limbs and • lungs in adults
naked skin • unprotected eggs
• aquatic/terrestrial life cycle

Class Reptilia – Reptiles

Terrestrial
animals with • 6000+ species
four limbs and • breathe by lungs
scaly skin leathery eggs
some are aquatic

Class Aves – Birds

Terrestrial
animals with • 8600+ species
wings and • breathe by lungs
feathers • egg with hard shell
• a few are aquatic

Class Mammalia – Mammals

Terrestrial
animals with • 4500+ species
four limbs and • breathe by lungs
fur or hair • young born live
• a few are aquatic

Figure 1.4 Classification of backbone animals which belong to the phylum Chordata

Micro-Organisms
In this section you should learn to:
❑ describe the structure of viruses, bacteria and fungi
❑ culture bacteria or fungi
❑ investigate the growth, respiration or reproduction of bacteria or fungi
❑ explain how bacteria and fungi carry out the life processes: feeding, growth
and asexual reproduction
❑ explain why viruses are always pathogenic
❑ discuss how bacteria and fungi are used for economic, environmental or
medicinal purposes.

Micro-organisms
There are three main groups of micro-organisms which are important to people.
These are bacteria, fungi and viruses. Micro-organisms are very small organisms
which you can usually only see with a microscope. The cell of a bacterium is
smaller than 0.01 millimetres which is smaller than the cells in your body.
Even though micro-organisms are difficult to see, their activity can be helpful or
harmful to people, plants and animals. Harmful micro-organisms spoil food,
damage crops and cause diseases. Helpful micro-organisms break down wastes and
dead material to recycle the materials. They digest food in the gut of animals
including humans and they can make food.

BIOLOGY YEAR 12
 9

Yeast
Studying biology means finding out about living things. Most of us know
something about the plants and animals that surround us and therefore we want to
investigate further how they live and work. Our observations usually start with
what we see with our own eyes – the animals we see near villages, or keep at home
or in the biology laboratory; the plants in our garden, in plantations or the school
grounds. In this unit however we will study living things that are everywhere
around us but which we can’t usually see because they are so small.
For centuries people have been growing wheat, and pictures drawn 4000 years ago
show the ancient Egyptians used yeast to make bread. The recipe for bread making
requires yeast. People made beer and wine for many centuries before they realised
that yeast was involved. It was not until 1676 that Anton van Leeuwenhoek, using
one of his first microscopes, found that yeast was a living cell and that different
types of yeast cells could also be used for brewing beer and making wine.
The famous French scientist Louis Pasteur discovered in 1859 that when you mix
yeast, a single celled micro-organism, with sugar in dough you make carbon
dioxide gas and alcohol. It is the two products of this reaction that give bread its
light spongy texture and distinctive flavour. Pasteur called this special chemical
reaction fermentation ( fa⁄mafu). Because of the very large number of loaves of
bread made each day throughout the world there has to be a way to produce enough
yeast for all the bakeries. Each yeast cell is so tiny that it takes up to 25 billion
healthy cells to make up 1 gram – imagine how many cells must be included in the
tonnes of yeast that is used at the Vailima Breweries each week!

Yeast production
From a tiny speck the size of a pin head, 25 tonnes of yeast is grown in just 3 days.
The photos below show the process:

Figure 1.5 The process of growing yeast: a A lab technician transferring yeast cells with
a sterilised nichrome wire from a pure culture imported from Australia; b A very small
amount of the pure culture is added to the sterilised molasses sugar solution in a glass
flask where it grows rapidly, doubling the number of yeast cells ever four hours; c The
flask of yeast is then poured into a large stainless steel vessel where it continues to
grow. At the same time large volumes of sterilised air are pumped into the vessel to stir
the brew and to provide the oxygen to help the yeast grow rapidly.

Three days after starting, each flask that was set up has now produced 25 tonnes of
yeast! The yeast cells are separated from the mixture they were growing in, washed
and then stored in refrigerated tanks before being delivered to the bakeries or dried
to be sold in packets or small jars at the supermarket.

UNIT 1
10

Knowing your yeast

Population numbers
Describe how yeast cells increase their numbers. How quickly can they
double their number?
Other organisms called bacteria can double their number in only 20 minutes.
Suppose you started with 10 bacteria cells: draw up a chart recording how
Figure 1.6 Yeast cells as many cells there will be after each 20 minutes up to 4 hours (240 minutes).
seen under a microscope Now draw a graph of these results (time across the bottom, numbers of
bacteria up the side). Label your graph.
Describe what is happening to the number of bacteria cells and explain what
might happen to yeast cells living in the same molasses.
Questions
Write down definitions of the words in bold type.
How could you demonstrate that dry yeast in a packet on a
supermarket shelf is alive?
From the process shown in the photos on page 9 list examples of how they
show physics, chemistry, biology and technology in action.

Revising microscope skills to look at yeast

Can you remember how to set up and use a light microscope? If you are not
sure go to page 64. In this practical session you will revise your skills by
studying yeast cells.
Gear
Microscope, slide, coverslip, yeast.
What to do
Read through the following checklist carefully. When you can answer yes to
each item move on to the next.
Slide preparation
Did you clean the microscope slide and coverslip you collected and carry
them by the edges to avoid fingerprints?
Have you placed one drop of the liquid containing the yeast cells onto the
centre of a microscope slide?
Did you place the coverslip at an angle to the slide but just touching the edge
of the liquid?
Did you use a needle to carefully lower the coverslip over the drop?
When all your answers are YES you are ready to set up the microscope.
Setting up the microscope
Have you checked which side of the mirror you are using? (Use the curved
side if there is no condenser under the stage.)
(cont.)

BIOLOGY YEAR 12
 11

Have you turned the mirror to make the light reflect into the
microscope?
Did you turn the condenser lens as far up as possible and fully open the
diaphragm?
Have you adjusted the mirror to give you the most even and the brightest
light while looking through the eyepiece?
Have you placed your slide on the stage of the microscope and clipped
it in place?
Are the yeast cells right in the centre of the microscope stage and lined up
with the objective lens?
When all your answers are YES you are ready to look at your
yeast cells.
Looking at yeast cells
Is the smallest objective lens (low power) on the nosepiece clicked into
place?
Did you watch carefully from the side as you turned the coarse focus control
(the larger knob) to bring the objective lens to stop just above the slide?
Did the yeast cells come into focus as you slowly moved the objective lens
and the stage apart by turning the coarse focus?
If they did not, try again. If they are still not in focus, ask for help now.
Have you adjusted the diaphragm and condenser lens to get the best view of
your cells?
You are now ready to increase the magnification.
Did you watch from the side as you turned the nosepiece to the next most
powerful objective lens (high power)?
Did you turn the fine focus control knob to move the stage and lens apart
while you looked through the eyepiece?
Have your yeast cells come into focus clearly again?
When all your answers are YES you are ready to draw your yeast cells.
Drawing yeast cells
Using the high power lens draw a large, clear diagram of one yeast cell. This
diagram should be at least half a page and should have a title as well as details
about the magnification of your microscope.
If you have time your teacher may give you other activities such as counting,
staining or measuring the yeast cells.

UNIT 1
12

The structure of bacteria

There are thousands of different types of bacteria. Some are single cells and others
live as groups of cells joined together. Each type has its own special shape and
structure. The common shapes are coccus (sphere), bacillus (cylinder) and
spirillum (spiral).

Figure 1.7 Bacterial

cell structure

Figure 1.8 Shapes of bacterial cells

Bacterial cells are made up of cytoplasm and genetic material in the form of a long
chromosome. The cytoplasm is surrounded by a strong cell wall. Bacteria have no
cell nucleus and have none of the cell organelles found in plant and animal cells.
Because there are no organelles, the chemical reactions needed for life occur in
the cytoplasm of the cells.
Figure 1.9 Body and
Structure of fungi
reproductive structures of Some fungi are small organisms made up of one cell, for example yeasts. Others
a fungus can be large organisms made up of many cells such as moulds, mushrooms and
toadstools. The body, or mycellium, of a large fungus is made up of fine threads
Viruses called hyphae.
genetic Often we can only see the reproductive part of the fungus because the rest is
material growing through the material it is feeding on.
protein

case
Structure of viruses
Viruses are very simple organisms. They don’t have organelles found in plants and
animal cells and they even lack the cytoplasm found in the cells of bacteria and
fungi. They only have a covering made from protein and some genetic material.
The lack of cytoplasm means that the virus is unable to carry out the normal life
Figure 1.10 A virus processes that other living things can. Some scientists say that viruses are non-
living, but viruses do carry out one of the life processes and that is reproduction.
Virus Replication When a virus reproduces it must use the parts of a living cell to help it
produce copies of itself. This causes problems for people because as the
virus
1. attachment 2. insertionvirus reproduces it causes harm to the living cell. Often the cell dies as a
to cell of genes result of the virus reproduction. The process of reproduction used by viruses
genes
must always use a living cell as a host cell. This means that viruses always
host cell cause disease in the living organism whose cells they use for reproduction.
burst cell Some viruses only last three hours outside of a host cell before being unable
3. replication to reproduce again.
of virus The first step in virus reproduction is when the virus attaches itself to a host
4. release of cell. It then either enters the cell or puts its genetic material into the cell.
new virus new viruses The genetic material of the virus joins with the genetic material of the host
Figure 1.11 Virus cell. The virus genetic material takes over the functioning of the host cell,
stops the cell’s normal activities and causes the organelles of the host cell to produce
reproduction
many copies of the virus. The copies of the virus then leave the cell to repeat the
process in many other cells.
BIOLOGY YEAR 12
 13

Growing bacteria and fungi

If bacteria grow in good conditions, for example on agar plates, they reproduce to
form groups called colonies. After two or three days, the colonies are big enough
to be seen through a microscope. A single colony can have more than a billion
bacteria in it.
Look closely at the microscopic view of the bacterial colony and you will see the
individual cocci bacteria.
Fungi can grow on a food source, such as, fruit or bread. Fungi and bacteria can be
grown on agar plates. An agar plate is a dish with a lid which contains a layer of Figure 1.12 Colony of
agar jelly. Agar plates are used to grow bacteria and fungi because they contain the micro-organisms
conditions in which bacteria grow and reproduce quickly. Good conditions for
growth include nutrients, water and warmth. Some bacteria and fungi are aerobic
which means they also need oxygen for respiration. Some are anaerobic and do
not need oxygen for respiration.

Testing for micro-organisms

Agar plates can test where bacteria can be found. The plates have material such as
paper or hair placed on the surface of the agar and then removed. This inoculates
the plate, which means it transfers bacteria or fungi on to it. The plates are
incubated in a warm place and any bacteria or fungi from the material that
transferred on to the agar will grow into a large colony. A control plate is also
used. The control is a plate that has had nothing added to it. It is used to check if
the plates already had bacteria in them. If bacteria grow on the control it means that
the original agar contained bacteria. We therefore cannot reliably say that the Figure 1.13 Bacterial colony
bacteria grew from what was being tested.

Activity 1 Growing bacteria and fungi

Aim: To grow fungi and colonies of bacteria. Materials:

What to do Water
Nutrient agar, gelatin
Dissolve agar or gelatin and a very small amount of nutrients in water, then boil
or animal bones
to kill any bacteria. Cover and allow to cool slightly.
Dishes – petri dishes or
If agar or gelatin is not available, boil up some fresh animal bones in water jars with lids
for 2 to 3 hours to collect the gelatin. Sticky tape
Pour a 0.5 cm thick layer of agar or
gelatin into several dishes. Cover and 1. inoculation
allow the layer to cool and become solid. of plate
agar
3 Leave the cover on one dish and label it
cotton bud
‘control’. Tape it shut and turn it upside
down. petri dish
4 Use the rest of the plates to test if 2. incubation of
micro-organisms seal
bacteria and fungi are growing on
different surfaces or in different
materials. Do NOT spit in the dish or put
anything that may be carrying disease
causing bacteria on to it. Be careful not to remove the lid completely as you
place the materials on the dish. Instead partly open one side of the dish. If you
remove the lid bacteria and fungi in the air could land on the plate and spoil
your experiment.

UNIT 1
14

Example of possible tests include:

❑ Place sticky tape on a surface such as a desk, table, or door handle then
place it on the surface of the agar. Remove the tape after a minute. You can
also use a cotton bud to rub across a surface and then across the agar or
gelatin. Tape the dish shut and turn it upside down.
❑ Pour three to five drops of water, milk, or other liquid onto the agar
surface. Swirl the dish to spread the sample across the surface and then
pour off any extra liquid. Tape the dish shut and turn it upside down.
❑ Mix a small amount of soil with a small amount of boiled water. Then
pour a small amount of the water into the dish. Swirl it to get the water
over all the agar or gelatin surface and then pour off any extra water.
Tape the dish shut and turn it upside down.
❑ Place an object such as a leaf, soap, fingertip, or a key onto the agar or
gelatin. Do not damage the surface of the agar or gelatin. Remove it, then
tape the dish shut and turn it upside down.
❑ Leave a dish open to the air for 20 minutes. Tape the dish shut and turn it
upside down.
Leave the dishes in a warm place for 2 to 6 days. Check each day. Do NOT
remove the lids in case some disease causing bacteria are growing on the agar
or gelatin. Any small, round, shiny spots growing on the agar are colonies of
bacteria. Fungi will look furry. Record your results using drawings.

When finished burn the plastic dishes and jars unopened. Leave the glass jars
unopened and get rid of them through the rubbish system.

Life processes of bacteria and fungi

Feeding
Bacteria and fungi both feed by extracellular digestion. ‘Extracellular’ means that
the digestion of food occurs outside the cell. There are three steps in extracellular
digestion:
Fungi and bacteria live on their food source so the cell can secrete enzymes onto
the food.
The enzymes digest the food outside the cell.
The cell absorbs the digested food chemicals and uses them for growth and
respiration.

Fungi extracellular digestion

Enzymes released Food is broken down Nutrients are absorbed

hyphae enzyme food digested nutrients

released particles food absorbed

Figure 1.14 Fungi extracellular digestion

BIOLOGY YEAR 12
 15

Different types of bacteria and fungi have different ways of life. Some are
saprophytes. Saprophytes feed on dead plant and animal materials. Other bacteria
and fungi are parasites. Parasites cause diseases by feeding on plants and animals
while they are still living. Diseases bacteria cause include food poisoning, tetanus
and syphilis. Ringworm, thrush and tinea are diseases caused by fungi. Organisms
that cause disease are called pathogens.

Growth and reproduction

Bacteria
When bacteria grow, the cells increase in size. Nutrients are used to add Binary Fission
more cytoplasm and to increase the cell wall. When the cell is large enough, 1. duplication of
it will reproduce asexually by dividing into two cells. This process is called chromosomes

binary fission.
chromosome 2. pinching
During binary fission the genetic material is copied and each copy moves to
3. separation of cells
the opposite ends of the cell. The cell wall then grows across the cell splitting
the cytoplasm in half. Now reproduction is finished and two cells, with of cells
parent cell
exactly the same genetic material, have been produced.
Bacteria can reproduce very often, once every 20 minutes in good conditions. daughter cells

This means that the number of bacteria can increase very, very quickly. This fast Figure 1.15 Bacteria
rate of reproduction usually stops when the bacteria run out of space, food, or they reproduction by binary
are surrounded by their own toxic waste. The rate of reproduction is slower when fission
the temperature is too hot or too cold.

Fungi
The mycelium of a fungus is made up of many cells in long threads called hyphae
(see Figure 1.9, page 12). The hyphae grow longer when cells divide. This way the
fungi can grow into new food sources.
Fungi reproduce asexually by producing spores. When a fungus is ready to
reproduce, special structures called sporangia grow and produce millions of small,
light spores. The spores are released and float in the air. If the spores land on a
food source they germinate and grow new hyphae into the food source. The
resulting fungi is genetically identical to the parent.

Respiration
Oxygen is the gas in the air that we all breathe in to keep us alive. If we stop breathing
or oxygen is not able to get around our bodies we can die within minutes! We and most
other living things need oxygen to use as a raw material for respiration
– the chemical process that goes on all the time in our bodies to change food into
energy. The chemical equation for aerobic respiration (using oxygen) is as follows:

Aerobic Respiration
food (sugar) + oxygen carbon dioxide + water + energy
CH O + + energy
6 12 6 6O2 6CO2 6H2O +

UNIT 1
16

However, some micro-organisms do not need oxygen at all and can live in water,
mud or even inside our intestines – all places where no air can get. These micro-
organisms are often bacteria and fungi and because they live without air they are
called anaerobic. The reason that they are able to stay alive in conditions which
would kill us very quickly is that they use a different chemical reaction to produce
their energy. The chemical equation for anaerobic respiration is:

Anaerobic respiration (micro-organisms)

food (sugar) alcohol + carbon dioxide + energy
CH O + + energy
6 12 6 2C2H5OH 2CO2

Figure 1.16 Drinks made If you have studied the two equations carefully you will have already realised that a
by fermentation very important product of anaerobic respiration is alcohol. Although anaerobic
respiration is less efficient and does not produce so much energy, it is a process that
humans have found to be very useful.

Source Drink Fermented drinks

of sugar produced The alcohol that anaerobic respiration produces can be used in many kinds of
apples cider drinks. It is possible to control the flavour and other characteristics of the alcoholic
barley whisky drink that is produced by choosing a particular kind of sugar from a certain type of
ginger ginger beer plant, or by choosing a particular type of micro-organism (see Figure 1.17).
grain vodka
grapes wine The name fermentation ( fa⁄mafu) is given to all these changes which involve
hops beer
molasses rum
anaerobic respiration. Fermentation is obviously very important in the brewing
potato aquavit industry which produces wine, beer and spirits but it is also an important stage in
rice sake the production of tea leaves, silage and bread.

Figure 1.17 Example When the product is going to be a drink for sale it is important that the correct
of fermented drinks micro-organism starts the fermentation process and that no foreign bacteria or fungi
get into the brew. For example wine will quickly change into vinegar if certain
bacteria, called Bacillus aceti, get into the container where the grapes are
fermenting. These bacteria change the alcohol into sour-tasting acetic acid. You
may have recognised the smell of rotting fruit as ‘alcoholic’ but many different
types of bacteria in such an uncontrolled environment means that much of the
alcohol is changed to a variety of other unpleasant chemicals. However the
quotation below shows that alcohol is found in the decaying fruit that some birds
(like the New Zealand tui) like to feed on.

Just like the drunken humans, a tui in the same state draws
attention to itself – especially when it hangs upside down from
branches, chortling loudly! This type of uncoordinated behaviour
has been put down to the fermented nectar that the birds had
eaten. During hot summers it is common for sugary nectar in
flowers such as pohutukawa to produce enough alcohol to affect
nectar-eating birds such as tui, kaka and bellbirds.

BIOLOGY YEAR 12
 17

Investigation into the growth, respiration or

reproduction of bacteria or fungi
Investigations can involve research, practical work or design of your own
investigations.

Design type investigation

Activity 2 What conditions do bacteria prefer? Hints

Your group is to design and carry out an experiment to do one of the following: You must plan your
experiment carefully. Work
Temperature conditions out and record what gear
you need, what things you
Study the effect of different temperature conditions on the growth of
must do and how to record
bacteria. This will involve putting petri dishes containing bacterial colonies your results.
in a wide range of temperature conditions (e.g. from in the freezer to over For the nutrients
70°C if possible). experiment the petri dishes
with different nutrients will
Nutrient preferences need to be prepared first.
Study the effect of different nutrients on the growth of bacteria. A wide
range of nutrients (foods) can be tested by boiling a standard amount of a Take Care
food with agar and letting it cool and set in a petri dish.
There is a danger that
Nutrients you could choose include liquid from small samples of vegetables, you could culture harmful
fruits, meat, Marmite, etc. Don’t forget to try agar without nutrients. pathogens unless you
follow the correct routines
and always keep
conditions sterile.
Subculturing
Whichever experiment you do you will need to know how to subculture
bacteria. Subculturing is when you inoculate your prepared petri dishes with
bacteria from your original colonies. It is done as shown in the diagrams.

Sterilise the wire loop by passing it through a flame.

When the loop is cool, touch a bacterial colony with it.
Raise the lid of each petri dish just enough to gently sweep the loop across
the surface of the agar. Streak it several times, first one way then at right
angles.
Colonies should now be spread over the agar and the petri dishes are ready to
be used in your experiment.

a) c)

b) d)

UNIT 1
18

Materials:
Activity 3 Experiments on anaerobic respiration
2 boiling tubes Your group is to design experiments to answer one or more of the following questions.
Stoppers Using only the equipment listed you have to:
Length of plastic tubing ❑ Design the experiment (sketch the way you set up the apparatus and list
Olive oil what you will do).
Strong glucose solution ❑ Carry the experiment out and note your results.
Limewater Carbon dioxide
Samples of at least three
How can we show that yeast feeding on glucose sugar is carrying out
brands of yeast
anaerobic respiration?
Made-up solution of dilute
sulphuric acid (50 ml) CLUE: A sure sign that respiration is going on is the release of carbon
and potassium dioxide. If it is being released even though no oxygen is present then it is
dichromate (2 g)
likely to be anaerobic respiration.
Balance
Alcohol
Warming cupboard
or incubator How can we show that alcohol is produced by fermenting yeast?
Watch CLUE: A dilute solution of sulphuric acid and potassium dichromate is an
indicator of alcohol. It will turn from orange to green when heated if alcohol
has been formed. (Careful – because both acid and alcohol must be heated
very gently and carefully.) Don’t forget about controls!
Quality control in yeast
How can we test the rate of fermentation in different brands of yeast?
CLUE: Your teacher may be able to supply several brands of yeast. Some
brands may work more quickly than others.

Practical work

Materials:
Activity 4 Growing yeast cells
250 ml conical flask Here is how to grow yeast cells.
Molasses Mix 50 ml of molasses with water molasses
Water 50 ml of water in a 250
Cotton wool ml conical flask.
1
Dry yeast Add a few grains of dry
Incubator active yeast and plug the
flask with cotton wool.
Label the flask with your
name and the date then
place the flask in an yeast
incubator at 30°C.
2
Observe the flask each day for 3
5 days and record what you
incubator
see.

BIOLOGY YEAR 12
 19

Research

Bully beef and dehyd spud

Ask your grandparents and you may find that this was once a meal that was
quite common. In order to stop the food from going bad it had to be
preserved. In the case of the ‘bully beef ’ this meant soaking the beef (meat
from cattle) in salt water (brine), cooking it then putting this corned beef into
an airtight tin. For the ‘dehyd spud’ it meant drying the potato out
(dehydrating it) and turning it into flakes which were later mixed with water
again before eating.

Basic Facts
Without heat or moisture bacteria will not grow.
It is possible to sterilise food (killing any bacteria) then seal the food from
contact with any more bacteria. This is what is done with all tinned meat
and pet food in tins.
Certain chemicals can be added to foods to stop bacteria in them from growing.

Fruit juice
Fruit juices like these contain no
preservatives. Before the juice was
packaged it was sterilised by heating
to 75°C. When full, the package was
sealed so that no bacteria could get
in. While unopened the juice can
remain on a shelf for years. Once
opened, bacteria in the air can get in and grow on the juice, so you must keep a
container of juice that has been opened in a refrigerator until it is used up.

Preserving methods and their problems

Until very recently most food has been preserved from bacterial attack in one of
the following ways, each of which has some problems:

Chemical preservatives
Certain chemicals, such as sulphur dioxide (SO 2), can be added to food to kill any
bacteria in them, thus making the food last longer. However, in recent years research
has suggested that preservatives, and other chemicals added to foods to give them
colour and flavour, are bad for the body and may have serious effects on children’s
behaviour. That is why many people do not want food with preservatives and demand
labels on packaged food to show which have preservatives and which do not.

Heating
If living material is heated to above 50°C the chemicals inside the cells begin to
break down. As living material begins to boil, steam inside the cells bursts them
open and so the form and texture of the food substances change. The result of
being cooked is a change to a soft, mushy texture which lacks a lot of the goodness
of fresh food.

UNIT 1
20

Freezing
During normal freezing tiny crystals of ice break open the cells, changing the
texture of the food. For example, when a crisp fruit or vegetable is frozen then
thawed it becomes soft and mushy.

High-tech preserving by freeze-drying

The problems with the commonly used preserving methods mean that many people
are trying to find ways to preserve food without adding anything, but at the same
time to keep the original structure and chemical composition of the food.
One process used widely to achieve this standard of preservation for both food and
non-food materials is freeze-drying. Many freeze-dried foods are dry and hard and
inside specially sealed packets – Maggi soups, noodles, instant coffee, herb
powders and vegetables are a few common examples. They last for a very long
time without bacteria getting a chance to grow on them and decompose them. Yet
they have not been cooked, they are not frozen and they contain no preservatives.
They have been preserved because almost 98 per cent of the water inside the food
material has been very quickly removed without doing any damage to the chemical
structure of the food.
This is done by placing the food in a freezer at a temperature of -30°C and at the
same time creating a vacuum around the food – the equivalent to being 100
kilometres out in space! Any water is sucked out of the food and immediately
condenses on refrigerated coils to form ice. The frozen water can’t get back into the
food, which is removed from the drier before the ice can melt.
The flavour, colour and form of the freeze dried food is the same but because it
contains no water, bacteria cannot live in or on it. If it is sealed in foil or plastic no
air can get in and the food will now last for a very long time.

Food preservation technology

The technology of food preservation involves finding ways to stop bacteria from
growing in the food so that the food will last for a long time and still remain edible.
Some methods of preserving are very old, and have been used successfully for
centuries, while others are because of recent discoveries and inventions. They all
rely on one or more of the Basic Facts listed on the previous page.

Researching preserving
Food preserving is a major part of all of our lives. The following are some topics
for research. Your group should choose one or more:
Preservation methods
For each of the photographs on page 21 find out how the food has been
preserved – write a statement using information from the Basic Facts box.
Use the fruit juice example as a model.
Fresh and preserved food
People in Sämoa often use both fresh and preserved foods. Find out how these
foods are kept safe for people to eat. What preservation methods are used?
How is fresh food looked after? How do the methods used reduce the chance
of bacteria and fungi growth?
Milk preserving
Milk can be bought from the supermarket in several different forms each of
which has been processed to help it to keep longer. Your task is to find out
about each of the milks – powdered, long-life, condensed, pasteurised.

BIOLOGY YEAR 12
 21

Research how it has been processed, then compare the advantages and
disadvantages of each type of milk including facts and opinions about taste,
shelf-life, the technology required, costs and the popularity.
Shipboard food
At the time of Captain Cook and earlier, sailors who were at sea for months
had major problems with food and related health problems like scurvy. Find
out about their food, how it was preserved and why there were health
problems.

Traditional Maori Bottled food Tinned food

storage vessel

Frozen food Dried food Freeze-dried food

Figure 1.18 Methods of preservation

Helpful bacteria and fungi

Decomposition and recycling
The role that bacteria play in breaking down organic matter is huge. Sometimes
this role is helpful to humans and sometimes it is not. The following examples
show how useful bacteria can be, and also what can happen if things go wrong.

Cleaning up our wastes

Anyone care for a ride around the oxidation ponds at a sewage works? Well as you
can see in the photograph people actually do it! Of course it is not usually done for
pleasure – it is part of the scientists’ work in trying to stop the wrong sort of micro-
organisms from growing in the water.
The scientists are actually trying to get more oxygen into the water. A shortage of
oxygen means that anaerobic bacteria will thrive. They tend to produce unpleasant
Figure 1.19 Oxidation pond
smelling chemicals as they respire. Too many anaerobic bacteria means that winds being stirred up by a boat in
will blow smelly gases towards people living nearby. order to increase the
oxygen in the water
If plenty of oxygen is present then aerobic bacteria will thrive. The right sort of
bacteria will feed on the dirty waste from houses and factories and change it into
clean treated water. Bacteria that live in the oxidation ponds and sludge lagoons
shown in the diagram on the next page do just that – and more.

UNIT 1
22

Raw Sewage

Screens and Grit

Crusher
Grit
The solid particles from inorganic
(non-living) matter can be used as
landfill.

Sludge and Scum Boiler

Digestors Sludge Gas

Sedimentation Gas
Tanks In the digestors the sludge and scum is
heated to 37°C. Anaerobic bacteria
break down the waste to produce
carbon dioxide and methane gas. The
gas is used as fuel
Liquid to provide heat and electricity.

Sludge
Oxidation Ponds Sludge Lagoon

Dried sludge
After over a year in the sludge
Outlet ponds the sludge is free from
(treated water) harmful bacteria and is able to
be used as a soil conditioner.
The minerals it contains make
it useful as a garden fertiliser.

Figure 1.20 Flow diagram of sewage treatment plant

The milky way

When a dairy company emptied fresh milk into the Waipa River in New Zealand
they did not mean to kill all the fish. Yet that is exactly what happened, and the
reason for the deaths in the river is BOD – biological oxygen demand.
Most living things need oxygen to stay alive. Animals that live in water (fish)
absorb oxygen that is dissolved in water through their skin or through special parts
of their body called gills. The oxygen in the Waipa River that the aquatic animals
use is quickly replaced and the water remains fresh. The large volume of milk (10
000 litres) became the food for a huge population of micro-organisms, particularly
bacteria. As these bacteria fed and grew, they produced more and more bacteria.
More and more oxygen was used by the bacteria until there was no oxygen at all
Figure 1.21 Plastic Media. left in the water. This is why the fish died.
The secondary
sedimentation tanks are The biological oxygen demand is the amount of oxygen being used up by the living
filled with these little things in an area of water. The greater the BOD the more risk there is of some
objects. They provide a sensitive plants or animals dying, just as the fish did in the Waipa.
very large surface area on
which bacteria can grow

BIOLOGY YEAR 12
 23

Recycling nutrients
As plants grow they take the substances that they need for their development
(nutrients) from the soil through their roots. The soil would quickly run out of
essential nutrients if the nutrients were not replaced. The nitrogen cycle is an
example of how the main nutrient, nitrogen, is being replaced all the time. It relies
on the action of decomposer micro-organisms and is explained in detail on page
25.

Compost
While soil micro-organisms break down most dead organic matter in nature, humans
like to help the process along with farming and gardening. The dark organic material in
soil, produced by the rotting of vegetable or animal matter is called humus. We can
speed up the process of rotting dead plant matter into rich humus by setting up
conditions in which the decomposing micro-organisms operate best. A well organised
compost bin can produce rich humus in six weeks or even less.

What are the best conditions for decomposers? Most important is the need for
respiration to be aerobic because this is many times more efficient than anaerobic.
So there must be plenty of air around the decomposing matter. That is why people
who make compost ‘air’ it or dig up the matter they buried to decompose. Of
course there must also be plenty of the soil-living decomposers around – including
earthworms as well as micro-organisms. They all grow faster if it is not too cold
and they need moist but not soggy conditions.

Activity 5 Testing the conditions

What are the best conditions for decomposers?
Your group is to design an experiment to test one of the conditions that you think
are important for leaves to be broken down. If you have time your teacher may ask
you to do the experiment.
The following hints will help you:
At least four of the main conditions needed are mentioned in the above
paragraph on compost. Others are shown in Activity 6 – The perfect compost
bin. Choose one, or you may also like to test other conditions that you feel
might be important.
Remember the importance of controls for comparisons.
You will need to put the leaves in some type of container and control the
conditions that they are in.

UNIT 1
24

Activity 6 The perfect compost bin

Nobody knows all the answers for perfect composting, but the diagram shows what
a very successful compost maker might do.
Explain how each of the points listed below may help to make good compost
quickly.

f
i
h

e
c b

g
d

a Bin made of timber with gaps between.

b Total area of bin no more than one square metre.

c Compost directly on the soil.
d Compost material well chopped up first.
e Layers of stems between layers of leafy matter.
Handfuls of old compost and lime added. g
Watered as heap built up.
h Large stake through the middle – pulled out when complete to let air in. i Lid
put over the top.
j After several weeks the heap is turned and rebuilt.
After a few days the compost in the bin shown had become too hot to put your
hand into the middle. There was a little smell at first but it did not last long.
After two months it had all broken down. Even the seeds of weeds that had
been thrown on were dead.
a Explain why it got hot. b
Why did it smell at first?
c Explain how the seeds had been destroyed.

BIOLOGY YEAR 12
 25

Nitrogen collectors
Some of the most important bacteria live in soil. There are large numbers of them.
There are probably as many as 10 000 000 in just one handful of soil. Without soil
bacteria most plants would not grow successfully. The vital role of bacteria in
breaking down dead plants and animals is shown in Figure 1.22 below.
The nitrogen that decomposing bacteria release from dead matter is essential for
plants to grow. Bacteria feed on dead plants and animals and break down the
complex proteins into simple nitrate ions that plants can absorb through their roots.
Different bacteria are involved in different stages of the breakdown of organic
matter. This is what is going on when compost is being made. The faster the decay
the hotter the compost!
Certain plants called legumes (peas, beans, lupins, clover) are particularly useful
because their roots have nodules that contain bacteria called nitrogen fixers. These
bacteria are able to absorb nitrogen directly from the air and make it available to
plants. This makes such plants especially valuable.
Scientists are now trying to improve the ability of plants to obtain nitrogen by
finding ways of adding nitrogen-fixing bacteria such as Rhizobium to the roots of
plants. It is now possible to inoculate some seeds with Rhizobium bacteria.
Scientists are also trying to manipulate the genes of some bacteria to make them
more efficient nitrogen fixers.

Plants need nitrogen

to make proteins Animals get their
protein by eating
Nitrogen in the air plants
(The air is about 70% N)
N2

Dead plant and animal

matter and wastes
– Decomposing bacteria
NO3
Th e root s o f legumes
con tain no du le s wit h

break down protein into

b acteria that ‘fi x ’ n itrog en out of the air

nitrate ions that can be

absorbed by the roots
of plants

Figure 1.22 The nitrogen cycle

UNIT 1
26

Cellulose digesting bacteria

Cattle are an example of herbivores (animals that feed on plants) that have
cellulose-digesting bacteria in their digestive systems. Cellulose is the tough cell
wall of plant cells. Without these bacteria, the cattle cannot digest the cellulose.

Biotechnology
Humans have found many ways of using micro-organisms to produce foodstuffs,
better crops, medical drugs and consumer products. This use of micro-organisms
for human ends is called biotechnology.
Yoghurt bacteria convert lactose sugar in milk into lactic acid. The lactic acid
solidifies the milk into yoghurt. Other bacteria are used to curdle milk for cheese
making. Pharmaceutical companies use genetically engineered bacteria to produce
chemicals for medical drugs. Special bacteria produce insulin which is used by
diabetics to control their blood sugar levels.
Yeasts are an important group of fungi that convert sugar into carbon dioxide and
alcohol by fermentation (a form of anaerobic respiration). These micro-organisms
are used to make bread rise and to ferment beer and wine (see page 9). Other fungi
produce chemicals called antibiotics that are used to fight bacterial infections.
Some viruses are used to control pest organisms, e.g. calicivirus (RCD) has been
introduced into New Zealand to control rabbit populations. This use of micro-
organisms to control pests is called biological control.

Revision
Match up terms with definitions.
micro-organism a micro-organisms made up of fine threads
bacteria b the control centre of a cell containing chromosomes
cell nucleus c a tough-walled resistant reproductive cell for
dispersal
cytoplasm d chemicals which break down large food molecules
cell membrane e the production of multiple copies of a virus
pathogen f the bulk of the cell where reactions of life occur
g an organism which feeds on dead organisms
digestive enzymes
h fine threads of a fungus which invade the host
binary fission i the part of the cell that encloses and controls
spore entry and exit of chemicals
j micro-organisms which do not have a cell nucleus
viruses
k ‘non-living objects’ which use cells to make new
replication copies
fungi m a disease-causing organism
saprophyte n the process of splitting into two organisms through
cell division
hyphae o a very small organism visible under the microscope

BIOLOGY YEAR 12
 27

Identify the following micro-organisms.

a) b) c)

Copy and label the three micro-organisms shown below. Choose from the
terms in the box.
Virus Bacterium Fungus i)
a) c) e) h)

d)
f) j)

g)
b)

cell wall • chromosome • genes • spores • cell membrane

cytoplasm • protein coat • hyphae • flagellum • spore case

Which of the three objects are considered to be alive? l

What activity do all three objects carry out?
m Why are these objects called micro-organisms?
Decide whether the following statements are true or false. Rewrite the false ones
to make them correct.
a You always need a microscope to see a micro-organism.
b Unicellular organisms consist of one cell only, but multicellular
organisms are made of many cells.
c Bacteria, fungi and viruses are all living organisms.
d Bacteria can be both helpful and harmful to humans.
e The genes of a bacteria are found on a single chromosome floating in the
cell cytoplasm.
f Organisms which live on dead bodies are called pathogens.
g Bacteria and fungi carry out digestion of food outside of their bodies. h
Spores are usually a form of sexual reproduction.
Viruses take over living cells and make the cells produce new viruses. j
Both bacteria and fungi play important roles as decomposers.

UNIT 1
28

Copy and complete the following paragraphs using the words in the box
below.
a Most bacteria are as they are unable to make their own food.
Bacteria digest their food by releasing digestive . Those which
live on and feed off larger organisms are called . Many bacteria
b cause disease and are .
Fungi are like plants, but are unable to make their own
. Fungi which feed on dead matter are , others are
c parasites. Fungi their food externally.
Viruses do not feed; they can only using living which
they invade. All viruses are as they damage hosts.

cells • consumers • digest • enzymes • food • immobile • parasites

pathogens • reproduce • saprophytes • pathogens

Describe events a) to c) in the diagram. d

Bacteria Reproduction
What is this form of reproduction
called? a)

e Is it sexual or asexual? f
chromosome b)
What is the advantage? g
What is the limitation? c)

parent cell
daughter cells

Describe events a) to d) in the diagram. e

virus Virus Replication
What is this form of reproduction a)
called? b)
genes
f Can viruses reproduce host cell
independently?
g How do viruses use their host cells? h burst cell

How do new forms of viruses arise? i c)

Why are viruses always pathogens? d)

new viruses

Describe events a) to c) in the diagram. d Fungal Reproduction

What is special about spores? a)
b)
e How are spores spread? spore spores
f What happens to the spores?
g Is reproduction sexual or asexual? case hyphae c)

BIOLOGY YEAR 12
 29

Write a short paragraph on each of the following topics: a

Fungi – Neither Plants nor Animals.
b Viruses – Living or Non-Living?
c Bacteria Lifestyles – Parasites, Pathogens or Saprophytes.
Describe the differences between the terms: a
unicellular and multicellular
b internal and external digestion c
inoculation and incubation.
Read the passage below, then answer the questions that follow.

Bird flu virus threat

Scientists are concerned that the bird flu virus, which first appeared in Hong
Kong in 1997, could turn into an epidemic which would rapidly spread across
the world. Hundreds of millions of people could be infected within months.

Flu viruses cause the illness influenza. Most flu virus strains produce
a relatively harmless infection, but some strains have devastating
effects on young and old people as well as those in poor health. In
1918 the Spanish influenza virus killed somewhere between 20 and
40 million people. In 1957 the Asian flu killed over a million people.
The bird flu virus is unusual because it appears to have crossed
the species barrier. Somehow the virus has been transferred from
its original bird hosts to human beings.
Initially about a quarter of the 17 people identified as having the virus
died. This indicated it was a very virulent strain. So far there has been
no evidence of person-to-person transmission of the virus, which would
be serious if it began to occur. All patients appear to have caught the
virus directly from birds or bird products. Hong Kong slaughtered over a
million chickens in an attempt to rid itself of the deadly virus.
Scientists have isolated the virus and are attempting to modify it
to produce a vaccine. The vaccine would contain a weakened
form of the virus, which would provide resistance to infection.

What is meant by the term ‘epidemic’?

Why are flu viruses usually able to spread so rapidly around the globe? c
What are the typical symptoms of the flu?
d Why is the ‘bird flu’ virus unusual?
e How could the virus have been transferred from birds to humans? f
What would the virus do once it had entered a human cell?
g Why is the ‘bird flu’ virus considered to be a virulent strain? h
What was the ‘good news’ about the ‘bird flu’ virus?
i How does a vaccine help give people immunity to a virus?

UNIT 1
30

Harmful Micro-Organisms
In this section you should learn to:
❑ describe examples of harmful micro-organisms

❑ describe common diseases caused by viruses, bacteria and fungi ❑

investigate a pathogenic disease that occurs in Sämoa.

Micro-organisms cause harm by damaging crops, timber, food and fabrics and
causing diseases. Viruses cause diseases such as colds and flu. They also cause
serious illnesses such as polio, hepatitis B and AIDS. Food poisoning is another
common problem caused by bacteria.

Meet the enemy

One of the most common causes of food poisoning is the bacterium
Salmonella. The disease that it causes is called ‘salmonellosis’ which
usually gives rise to violent vomiting, diarrhoea, abdominal pain and flu-like
symptoms 12 to 36 hours after eating the contaminated food. The bacteria can
get onto food from dirty cutlery or dishes, unclean work areas, unwashed
hands or rats and flies. One of the problems with Salmonella bacteria is that
they may infect animals that we eat for food, including poultry and their eggs,
Figure 1.23 Colonies of
cattle, pigs and sheep. In some cases infected hens will lay eggs in which the
Salmonella bacteria (x6)
yolk and white inside the shell are contaminated with the bacteria.

Healthy food gives our body a balanced diet and builds up immunity to disease.
However even more important than the type of food we eat is to make sure that we
do not get poisoned by eating food that contains harmful bacteria.

But is it safe to eat?

Healthy food is safe to eat when it has been stored, handled and served carefully
and does not have harmful bacteria living in it. Food which has bacteria living in it
is said to be contaminated. It is very important not to eat contaminated food
because it can result in poisoning which can make you very ill. You can’t always
tell by looking at food whether it has bacteria in it so you have to treat all food
carefully. Fortunately there are many things we can do to help protect us from food
poisoning. Each precaution mentioned in the boxes on the next page is based on
one or more of the following scientific facts:
Keeping the bacteria that are all around us away from the food that we are
going to eat will stop them from causing food poisoning.
Bacteria can be passed from one thing to another by touch so it is important to
make sure that anything that touches food is very clean. Being hygienic means
making sure that your hands, all equipment such as knives and spoons and any
bench tops on which the food is placed have no harmful bacteria living on
them.
Eating food while it is fresh means bacteria do not have a chance to grow on it
and contaminate the food.
Bacteria will grow rapidly when the conditions are suitable. They can double
their numbers every 20 minutes thus contaminating food in a very short time.

BIOLOGY YEAR 12
 31

Stopping any bacteria that might get onto the food from
growing will prevent them from doing any harm.
Bacteria cannot grow in cold or dry places, although
they will stay alive. To actually kill bacteria and
sterilise the food you have to boil it or add special
chemicals called preservatives.

Activity 7 Hygiene awareness

Hygiene awareness survey
Each group should prepare a survey as follows:
a Within your group, each person should choose
one of the five sets of instructions on page 32.
b Prepare a questionnaire to find out how carefully
people treat food. Do this by changing each
instruction in the box into a question.
c Each member of the group should give the
questionnaire to at least three people (try parents,
neighbours, people you know who work with
food).
d Make a group summary of the answers you give to
all the questionnaires. Figure 1.24
e From your results identify the most common things people do when Temperatures at which it
is safe to keep food
working with food that you consider unhealthy.
f Prepare a group report to the class. Be as creative as possible in your
presentation.
Healthy food poster
Your teacher will give you one of the set of instructions for keeping food
healthy. Your task is to present it as a poster with additional information about
the scientific reason for each instruction and appropriate illustrations.
3 Bacteria and food poisoning
Read the following information about what happened with listeria poisoning
in New Zealand. Discuss the consequences for the people involved.

Manslaughter charge follows listeria poisoning

Two directors of a shellfish processing factory will be charged with manslaughter
following the death of newborn twins from the bacterial infection listeriosis.
The twins’ mother had eaten shellfish processed in the South Island factory
while she was pregnant. Police claimed that the infection, which caused the
twins to die within half an hour of their birth, could be traced to the factory.
Sophisticated testing of the shellfish from the factory showed the presence of
listeria bacteria which do not usually cause serious infection in adults but
which can cause death of the foetus or a miscarriage.
Health officials often warn pregnant women not to eat foods in which
listeria is common, such as soft cheeses and pâté, and to reheat
thoroughly cooked and chilled meats and ready-to-eat poultry.
The factory has been closed since the positive listeria tests were reported.

UNIT 1
32

Instructions for keeping food safe

Buying food
❑ Choose meat, fish and poultry from a fridge or freezer.
❑ Check the ‘use-by’ date and make sure that you will be able to finish the
food before then.
❑ Buy cold food last and get it home quickly. Carry cold and frozen food in a
carry icebox or wrapped in newspaper.
❑ Do not buy unpacked food that you have seen someone else touch. ❑
Make sure raw and cooked foods are packed in separate bags.
Storing food
❑ Put food away as soon as you arrive home.
❑ Store raw and cooked food separately.
❑ Place raw meats on the lowest shelf of the fridge so their juices will not
drip onto other food.
❑ Make sure the refrigerator is cold enough – it should be below 4°C.
❑ Put leftover food into the refrigerator as soon as possible.
❑ Keep the refrigerator as clean as possible.
Preparing food
❑ Wash your hands before you start.
❑ Keep a hand towel in the kitchen so you don’t wipe your hands on
teatowels.
❑ People who are sick should stay out of the kitchen.
❑ Use clean knives, clean bench tops, clean cutting boards and clean
utensils.
❑ Use different cutting boards for raw and cooked foods.
❑ Keep pets out of the kitchen.
Cooking food
❑ Thaw food completely before you cook it – in the fridge or microwave is
best.
❑ Follow cooking times in reliable recipes.
❑ Cook food thoroughly – do not serve pink (half-cooked) poultry meat.
❑ Stir and rotate food in microwaves for even cooking.
❑ Cover food in microwaves so steam helps to cook.
❑ Leave microwave-cooked food to ‘stand’ after taking it out so it finishes
cooking.
❑ Serve hot foods hot and cold food cold.
Parties and picnics
❑ Keep the number of cooks to a minimum.
❑ Keep food in the fridge until it is served – ask neighbours to let you use
their fridge or store drinks in the laundry tub with ice to give you more
room.
❑ When you reheat food make sure it is piping hot right through to the
middle.
❑ Do not reheat foods more than once.
❑ Take food to picnics in carry iceboxes.
❑ Use canned food because this needs no preparation.

BIOLOGY YEAR 12
 33

Activity 8 Water safe to drink

Often water must be treated before it is safe to drink. The diagram below shows
what happens in a typical water treatment station.

RAW WATER 2 3 4 TREATED

1 CHEMICAL WATER
from DOSING
spring or dam SETTLING FILTERING ADDITION to town or city
The alum sludge The water flows Fluoride (F+) for
ANALYSIS Aluminium ANALYSIS
suplhate (alum) settles allowing through layers of dental health
Coliform bacteria: is added to it to be removed sand to remove Coliform bacteria:
15 per 100 ml gather together from the water any floating Chlorine (Cl) 0 per 100 ml
the organic particles keeps the water
Total organisms: matter in the bacteria-free Total organisms:
50 per 100 ml water forming a Lime helps 2 per 100 ml
sludge
pH: 7 preserve the pH: 7.7
water pipes
Turbidity: 5 NTUs Turbidity: 0.3 NTUs

Water Care Services

Dissolved solids: Dissolved solids:
80ppm 90ppm
Aluminium: 0ppm Aluminium: 0.04ppm
Iron: 0.2ppm Iron: 0.05ppm
Chlorine: 0ppm Chlorine: 0.2ppm
Fluoride: 0ppm Fluorine: 1.0ppm

Figure 1.25 Treatment of drinking water at a water filter station.

Compare the analysis of the raw and treated water.

Describe the differences between raw and treated water.
Explain what has been done to cause the differences in the raw and treated
water.
Find out how fresh water is supplied if there is a cyclone or flood.
Carry out research on your local water supply. What happens to make sure
people have water that is safe to drink?

Diseases
People have always suffered from diseases, but it is only in the last 130 years that
we really know what makes us sick and why people die from some illnesses.
Almost all diseases of plants, animals and human beings are caused by micro-
organisms. The micro-organisms that cause disease are called pathogens. Until the
19th Century more people died inside hospitals from disease than were cured or
treated by the doctors! Only as recently as the 1860s did the nurses and doctors
working in hospitals realise that they were the ones who were spreading micro-
organisms from their infected patients to the healthy ones. They then realised that it
was important to keep hospitals as extra clean as possible, to sterilise surgical
instruments, to use disposable gloves and gowns, to change patients’ bandages
often, and so on.

UNIT 1
34

Koch’s postulates show scientific Now, in order to identify an illness, a sample of

method. He said that: blood or tissue from the sick person is
taking a blood collected and sent to a diagnostic laboratory.
If a particular micro-organism A sample from
that is always present in a sick animal
samples taken from a sick
animal . . .
red blood
cells with
D
sick bacteria

animal
red blood
cotton
cells with wool
bacteria test tube
D . . . and if that animal of liquid
bacteria
then becomes sick
this shows that the C
pathogen that caused
the disease has been
identified. B . . . is grown
in a culture,
injecting an
animal

and then injected into a

healthy animal . . .

Then the best treatment can

be decided and a prescription
written.
Microscope or other techniques are used to
find the micro-organism. It is matched up with
known pathogens and when recognised the
doctor is notified.

Figure 1.26 Koch’s postulates and modern diagnosis

Today most of us know that the germs which make us sick are the tiny living things
we have been calling micro-organisms. One of the first doctors to show that this
was true was Robert Koch. His method was to first find the micro-organism by
using a microscope to look at the blood of a sick animal, then to grow the micro-
organism and inject it back into another animal to see if it became sick too. This is
still the standard way to prove an organism causes a disease and is known as
Koch’s postulates.
When we get sick we usually assume that a doctor or specialist will be able to tell
us what is wrong and how to get better. If the doctor is still unsure after having
made a first hypothesis he or she may then need to follow Koch’s postulates to find
out for sure what the disease organism is. Figure 1.26 above shows this.

Activity 9 Scientific methods in diagnosing illness

We use the methods of science all the time in everyday life. We use them when
working out what is wrong when we feel ill. Read the following:

When Sione woke up his head was throbbing and his throat felt raw. He
coughed once and let out a groan as he rolled over. He was expecting
his mother’s usual warning about being late for school but this morning
her voice softened when she heard Sione’s croaky voice.
‘It’s the doctor for you this morning,’ she said a few minutes later as she
checked his temperature on the special clinical thermometer. Sione was
glad to sip the glass of lemon-honey drink his mother had brought in but
all he really wanted to do was to lie down again and sleep!

BIOLOGY YEAR 12
 35

The things that you can see when you get sick are called symptoms.

The doctor listened carefully as Sione told her how he felt. She told Sione she
had a fair idea what was wrong with him but she just needed to check it out.
The stethoscope was cold as she moved it to various places on his back. She
waited while Sione coughed then asked him to take one more deep breath.
‘It’s a bit rattly in there,’ she commented. If Sione hadn’t been so
fascinated with the little torch shining down his throat he would have
heard the doctor asking him to open a little wider.
‘That’s better,’ she said, adding to herself, ‘Just as I thought.’
Before Sione could ask what was wrong a thermometer was popped
into his mouth and the doctor was gently pressing around his neck to
feel for any swelling.

The doctor was really carrying out a scientific experiment with Sione. After
listening to his symptoms she made up a hypothesis about what might be causing
his illness. She then checked each of the things about her idea, from what she knew
from her study at medical school, to see if they matched her hypothesis.

Listing symptoms
Make a list of all the symptoms Sione had and add at least two more that are not
mentioned.

Forming a hypothesis
List each of the things the doctor checked on Sione and suggest what you think
she was looking for.

The doctor sat down and began writing on a little pad.

‘This medicine will get you well again,’ she explained, handing Sione the
prescription for the chemist. ‘You have bronchitis. There are a lot of bacteria
living on the cells at the bottom of your throat and these have spread to the part
of the lung called the bronchus, causing the bad cough. The poisons made by all
those bacteria have spread around your body giving you the headache and the
fever. Your body is trying to fight off the bacteria – that is why your glands are
swollen – but if you take a 5 ml teaspoonful of this medicine three times a day
until it is finished it should kill all the bacteria. If he is not better by then make
sure you bring him back,’ she added to Sione’s mother as they left.

When the doctor had studied all the evidence she came to a conclusion about the
cause of Sione’s illness and was then able to give him the best treatment. She had
obtained some data, formed a hypothesis, tested the hypothesis and came to a
conclusion about what was the matter so she could decide how to treat it.

UNIT 1
36

Activity 10 Asking the right questions

Science involves obtaining accurate data, forming hypotheses and obtaining more
data to confirm or reject the hypotheses. Medical diagnosis is an example of
scientific method at work. Two important skills of the scientist are:
knowing the right question to ask and
recognising the useful answers. These skills are also important to the doctor.
In the activity below you will take turns at being the doctor and the patient and
from the interview must try to find the right treatment. Good luck!

A pain in the chest

How good are you at obtaining and interpreting data? This game is designed to
test your diagnostic skills. The patient’s first statement is: ‘Please Doctor, can
you do something about this severe pain in my chest?’ The doctor must
diagnose the cause of the pain using as few questions as possible.
RULES
a The object of the game is to see who within the group can correctly
diagnose the cause of the pain.
b Group members take it in turn to be the doctor, while the others are
patients.
c Each patient chooses one of the six chest problems in the chart of
symptoms opposite.
d The doctor questions each patient in turn about their symptoms (one group
member recording the number of questions needed to get the right answer).

e The patient must answer each question truthfully using information from the
chart. A little playacting is okay but extra symptoms cannot be added.

Other clues
The skilled doctor will have other information available to help with the
diagnosis. Each of the following may be very useful: the patient’s past medical
record, the time of year, the type of health problems common in the district,
the age of the patient.
For each of these clues discuss in your group why such information may be
useful.

Confirming the diagnosis

Make a list of the technical tools that a doctor has that may be useful in
confirming the diagnosis.

BIOLOGY YEAR 12
 37

Cause of Chest Location When pain occurs Type of pain

problems
Cracked rib At a specific spot When breathing deeply, Very sharp at one precise
on one side of chest. coughing or moving chest. spot – especially if chest is
Began after being hit by pushed. Bruise at site of pain.
a hockey ball.
Torn intercostal At a specific spot on When breathing deeply or Quite sharp. No bruising.
(between ribs) one side of chest. coughing. Began after
muscle trying to bowl a cricket
ball extra fast.
Shingles In a narrow band All the time. Not Acute pain and itching.
(virus infection) along lower ribs at affected by exercise.
one side. Row of More painful when
small red blisters. touched.
Pneumonia Throughout one When breathing deeply or Stabbing pain. Chills, high
(bacterial side of chest. coughing. fever and coughing.
infection of
one lobe of lung)
Angina (heart Middle of chest and Appears suddenly when Deep heavy pain with
not receiving up towards left exercising, and gets better nausea and feeling of
sufficient blood) shoulder and after the exercise stops. pressure on chest.
down arm.
Heartburn (acid Middle of chest Appears after meals and Burning sensation.
liquid from and up towards when lying down. Coffee
stomach rising throat. and alcohol make it worse.
into oesophagus)

Examples Of Pathogens
Our bodies are open to attack from many different pathogenic micro-organisms. They
each have their own way of entering the body. They each attack it in different ways and
cause different symptoms. There are far too many for us to examine them all, but we
can get a good idea of what they are like and how they function and spread by looking
more closely at a couple of examples – the common cold and meningitis.

The common cold – a familiar enemy

This is the one infection that we all suffer from and know well. Each person can Figure 1.27 Virus
expect to suffer two to three colds per year. When this is added up for the whole
population the common cold can be blamed for many hours of lost work and much
medical expense. Even though scientists have developed new treatments for many
diseases, nobody has found a way to cure the common cold.
Acute coryza is the medical term for ‘Cold in the head; an acute catarrhal inflam-
mation of the nasal mucous membrane’. It is caused by any one of a group of 120
different types of virus. The thing the viruses have in common is that they all infect
the cells that form the lining of the nose and throat in the area called the upper
respiratory tract. The very sensitive cells in this part of our body react to the
infection by swelling and by increasing the amount of mucus that they produce.

UNIT 1
38

The common cold viral infection generally works like this:

irritated throat coughing

blocked nose nose blowing

swelling and and sneezing

viral infection
mucus change in voice
blocked sinus headache
infection by
blocked ear bacteria
tube earache

Figure 1.28 Viral infection

Cold symptoms can disappear within 2 or 3 days but unfortunately the irritated
membranes of the nose and throat usually allow the entry of various bacteria which
cause further symptoms and can lead to complications.
The fact that so many different viruses could be involved is the main reason why it
has not been possible to develop a vaccine to prevent the common cold. So we have
to put up with a few days of discomfort until our own immune system has managed
to cope with the infection. This usually results in immunity to that virus for a few
months.

Activity 11 Testing the remedies

Consumer report
During the winter there are hundreds of advertisements for remedies for
colds and flu. How effective are they? You are to do a consumer report on
the claims of the various remedies.
a Bring to school as many different empty packets for remedies for cold and
flu symptoms that you can. If you can’t find any at home you could make
a note of what is on the chemist’s shelves.
b Draw up a chart, similar to the one below, with headings across the page. c
For each remedy, tick each column for the symptoms it claims to help. d In
the last column put comments from anyone who has used the remedy
about how effective they found it.
Designing a trial
You will not be able to test all the cold remedies, but you can design a
scientific way of testing some of them. Take one group, say sore throat
remedies, or blocked nose remedies. Write down an outline of the way that a
scientific test for their effectiveness could be done. Make sure that you
mention the following: design of the trial, numbers involved, controls,
measuring results.

Remedy Sore throat Tickle or cough Block Headache Fever Cost Effectiveness
throat

BIOLOGY YEAR 12
 39

Meningitis – a killer at large bone of skull

This is a serious disease. It attacks mostly small children – and perhaps 5 to 10 outer meninges

percent of these will die. fluid (cushion)

inner meninges
What is meningitis? brain
Meningitis is the name given to an inflammation of the ‘meninges’ or membranes nerve cord
that surround the brain and spinal cord. The meninges become infected by one of
several types of bacteria or virus that reach them through the blood or lymph. The Figure 1.29 The meninges
inflammation (swelling and other effects) happens when our immune system tries
to deal with the invaders and their poisonous wastes. The fluid around the
membranes becomes cloudy and contains many white blood cells as well as the
pathogen.
What causes meningitis?
Several kinds of micro-organisms can cause the symptoms of meningitis.
Amoebic Meningitis – This is very serious but fortunately very rare. It is caused
by a tiny one-celled animal which lives in the water of hot springs. It enters the
body through the mouth and nose openings. That is why people are often warned
not to put their head under water when they swim in hot springs.
Viral Meningitis – This is more common and several types of virus may cause
symptoms of meningitis. Viral meningitis tends to be not quite as severe as other
forms and those infected usually survive.
Bacterial Meningitis – This is, at present, the most important type of meningitis.
The most common culprit is a bacterium called Haemophilus influenzae Type b
(often referred to as Hib). Recent epidemics have involved another bacterium
called Neisseria meningitidis.
Pathogenic bacteria like these live as single cells and reproduce very quickly as each
one divides into two. This means that a very large population of cells can grow in a
very short time. As the cells grow they use the cells around them as food and at the
same time make waste chemicals (toxins) that are poisonous to living cells.

What are the symptoms of meningitis?

Meningitis is serious and if the symptoms shown here appear, you should get
medical help fast.

WHAT TO LOOK FOR IN BABIES

Vomiting, High-pitched Fretful Pale or blotchy skin Difficult Rash Fever

refusing food cry to wake

WHAT TO LOOK FOR IN ADULTS AND OLDER CHILDREN

Vomiting Headache Dislike Drowsiness/ Rash Fever

of lights Stiff neck coma

Figure 1.30 Symptoms of meningitis

UNIT 1
40

The life history of a meningitis epidemic

The doctor quickly became concerned as he began his examination of the

small child that had been brought into the clinic by his very worried mother.
The child obviously had a fever and although limp was holding his head as if
his neck was stiff. ‘He seemed quite all right earlier this morning’ the mother
said. ‘Then he began to vomit and he has been crying a lot and is so hot.’ The
doctor noticed some small purplish spots on the child’s skin and immediately
called his nurse. ‘Please prepare an injection of cefotaxime then ring for an
ambulance? I suspect this child has meningitis. He must be sent to the hospital
urgently.’

This happened frequently in Auckland, New Zealand during the winter of 1986,
and has also happened in the early 1990s. The child was showing symptoms of
severe meningitis. His chances of survival were not good without rapid treatment.

How it spreads
The meningococcal bacterium is present in a small number of people who are not
affected by it but who are carriers. It is spread in the tiny droplets coughed or
sneezed or even breathed into the air by carriers. Other people breathe it in and it
enters the blood stream through the moist surfaces of the nose and throat.
Nobody knows exactly why an epidemic starts and some people suffer more from it
than others but we know the following:
There seem to be some carriers at all times even when there is no epidemic
present – perhaps as high as 5 percent of people. So the source of infection is
always around.
It is more likely to spread among people in poor living conditions. If there is
overcrowding in a house, there are many smokers and if the general health of
the people is poor.
It spreads most when the climatic conditions are right. (In Auckland this
seems to be winter and spring. However, it is not like that in other
countries).
Some factor starts it off – it tends to develop when other infectious diseases of
the respiratory system (flu, etc.) are common and many people are coughing
and sneezing and have weakened membranes of the nose and throat.

Treatment of meningitis
Usually the infection is so sudden and severe that the body’s immune system has
difficulty in dealing with it, and death is quite possible unless special hospital
treatment is begun quickly. The patient should be kept in quiet, dark conditions.
Patients are usually given a drip to supply fluids and antibacterial and
anticonvulsant drugs. They are watched carefully for convulsions, low blood
pressure and other problems. The disease is likely to be critical and speed of
treatment is most important. If there are no complications the patient may be
recovering within a week. Follow-up with hearing tests is important.

BIOLOGY YEAR 12
 41

Activity 12 Analysing an epidemic

1 Diagnosing meningitis
From the paragraph in the grey box on page 40, list the symptoms and signs
that made the doctor suspect meningitis (there are at least five).
2 Analysing the table

Table 1.1 Cases of meningitis (Group A) in Auckland 1985/6

(All figures are rate per 100 000)
Ethnic Group All Ages Under 5 Under 15 District
Yrs Old Yrs Old North Central South
European 2.3 13.8 9.0 4.1 18.1 7.8
Maori 28.1 141.4 66.8 16.4 81.6 83.2
Pacific Islander 34.9 233.5 105.9 16.8 101.7 179.9
Overall 8.3 68.8 30.4 6.1 41.9 45.3

From the table of meningitis cases identify the people and district which were
most at risk.
List reasons why this group may be most at risk.
Explain why the figures are given as rate per 100 000 and not total
numbers.
Analysing the graph
Study the graph below and describe the rate of meningitis in New Zealand
apart from Auckland, for the 13 years shown.
Incidence of meningitis
200
175 Auckland – Group A
epidemic
150 New Zealand – All
cases reported
125
of cases

100

75
Numb
er

50

25

1980 81 82 83 84 85 86 87 88 89 90 91 92 93

Year
4 Publicity

In your group prepare publicity material (a poster, outline of a TV ad, a

notice to drop in letterboxes) warning people about the possibility of
meningitis in the coming winter, and explaining what to do to avoid it.

Return of the killer disease

In this age of extraordinary medical developments and high-technology research is
it possible to completely eradicate a disease from our Earth so that nobody will
ever get it again?
With the success of the World Health Organisation (WHO) in eliminating smallpox,
and its progress with the control of poliomyelitis and other diseases it seemed a very
realistic aim. But it may not be that easy, as the problems with TB (tuberculosis) show.

UNIT 1
42

TB
Tuberculosis (TB) is a disease in humans caused by the bacterium
Mycobacterium tuberculosis. It attacks the membranes lining many of the organs
of the body. Tuberculosis of the lungs is the most common form, destroying lung
tissue and leaving ‘cavities’ that show up on x-rays as light patches. It is spread
as droplets coughed up or spat out. It is particularly common in overcrowded
areas. Treatment of TB is usually successful with the antibiotic streptomycin,
although resistant strains are quite common. Until recently a vaccine known as
BCG was made available to all children early in their third-form year. Because of
this TB is now so rare that the vaccination programme has been stopped. BCG
(Bacillus Calmette-Guerin), the most widely used vaccine in the world, contains
Figure 1.31 Chest x-ray live bacteria from cattle. These bacteria have been weakened in the laboratory
until they are no longer able to cause disease. Once in the body BCG causes the
production of antibodies to fight TB.

The battle to eradicate tuberculosis

Look carefully at the graph of the number of cases of tuberculosis for New York
City in the period 1920–1991. This is typical of campaigns to eliminate TB. It
appeared to be on target until about 1980, but now the worldwide picture has
changed and is quite a frightening one. One-third of the world’s population is
infected with the TB-causing bacteria. Not all of these people become sick with the
disease, but TB does kill over 3 million people each year. Most important, this
number is increasing.
Compare the figure for TB in New Zealand. TB rates here have levelled off also,
and since 1989 they have actually been showing a slight rise. Some cases, but not
TB cases in New Zealand (numbers per 1000)

16000

14000 all, have arrived from immigrants from poor parts of Asia.
TB cases in New York over last 70 years

12000 18

10000 15
Why has the battle against TB suddenly become less effective? The vaccination
8000 12

6000 9
programme introduced in the 1950s was responsible for reducing the numbers of
4000 6 deaths to a very low level. However when a disease kills very few people, some
2000 3
people no longer bother about vaccinations because they think they are safe. This
1920 1940 1960 1980
means that the number of unprotected people in the population increases and so the
YEARS
disease can begin to spread again.
Figure 1.32 TB cases in
New Zealand compared to Some people are now infected with a drug-resistant strain of TB. The strain of the
TB cases in New York disease is increasing because there is nothing to kill it or control its spread. A
disease often becomes resistant when only one drug is used to treat it or the
treatment is not finished by the patient. If this happens some of the bacteria will
still be alive in the person’s body even though he or she may feel well again. The
bacteria that survive are the ones that have resisted the treatment and they then get
passed on to other people. As more resistant bacteria appear in the population an
epidemic can begin. This is what appears to be happening with TB.
Three things are very important in preventing the development of resistant strains
of diseases:
As many people as possible taking part in vaccination programmes.
Training doctors to use the drugs in the best ways.
Making sure that if a doctor gives a patient medication the patient uses it in the
correct way and does not stop taking it until it is finished.

BIOLOGY YEAR 12
 43

Activity 13 Disease research

Carry out research on the occurrence, effect and control of a pathogenic disease
that occurs in Sämoa.

Methods Of Controlling And Curing Diseases

In this section you learn to:
❑ investigate the effectiveness of antiseptics, disinfectants or antibiotics
❑ discuss methods of controlling and curing diseases, e.g. antibiotics,
vaccination, herbal
❑ explain the development of antibiotic resistance in pathogens and how it
can be prevented
❑ discuss how the human body defends itself against pathogens ❑
describe the effect of HIV on the immune system.

As people have increased their knowledge of how diseases spread they have been
able to develop effective methods to control them. The following seven points
show how some diseases are spread:
Droplets in the air from a cough or sneeze, e.g. colds and flu.
Dust and particles in the air or on material, e.g. smallpox.
Touching the infected area on another person, e.g. impetigo (school sores),
athlete’s foot.
Animals (big and small) carrying the disease, e.g. ringworm (cats), malaria
(mosquitoes), rabies (dogs).
Cuts and scratches from dirty objects, e.g. hepatitis (especially from used
syringes), tetanus (often from rusty nails).
Eating food containing bacteria or fungi, e.g. salmonella (food poisoning).
Untreated sewage, e.g. typhoid (from human faeces).

Activity 14 Medical history

Discuss how the procedures described in A, B, C and D in the box below have
improved medical practice. Record your ideas.

A. 17th Century
Hospitals were breeding grounds for the micro-organisms that cause disease
(pathogens). New patients were often put into the dirty beds from which dead
people had just been taken and rats and mice ran around everywhere.

B. 1854
Florence Nightingale was sent to Turkey in the middle of the Crimean
War. The conditions were terrible for both the soldiers and the doctors
but Florence and her nurses cleaned toilets and scrubbed floors,
sewed mattresses and washed the men and their clothes, setting an
example of how cleanliness could help save lives.

UNIT 1
44

C. 1865
Joseph Lister prepared a report called ‘The Antiseptic Principle in the
Practice of Surgery’, which explained the use of a chemical called
carbolic acid as a disinfectant. This was sprayed on the patient’s
wound during the operation, reducing the surgical death rate from 50
percent to 10 percent. Hospitals became safer places to be in.

D. 1929
Alexander Fleming was growing bacteria on plates of jelly. One night he accidentally
left a dish uncovered. When he found it later there was a mould growing on the plate
and his bacterial colonies had been killed. He took action at once to find the killer and
discovered that the mould, called Penicillium, made a chemical called an antibiotic.
Antibiotics made in laboratories are called penicillin.

Our body’s defence

With all the disease causing micro-organisms around, it is important for our bodies
to have a range of defences against them.

The first line of defence

In a military exercise guards are always placed at sites where they are in a position to
attack any enemy who might get in. Our body’s defences are like guards who stop an
enemy getting into a fort. In our body’s fight against disease the same sort of military
strategy is used. The skin is a barrier (or wall) and all the entry points (ways in) are
well guarded against micro-organisms. These main entry points for disease are the
openings that lead to moist places where there are living cells, for example, the eyes
and nose. Fluids such as tears, saliva and mucus protect the openings.

Eyes Tears not only keep the surface Nose The cells inside the nose make
of the eyeball from drying out mucus which is sticky and traps any
but also wash away invaders and pathogens. Lysozyme that is made
contain the deadly chemical called with the mucus will kill these trapped
lysozyme. micro-organisms.

Wind pipe and lung passages Tiny

3 Mouth Saliva made by glands inside hairs called cilia grow out of the cells that
the mouth also contains lysozyme line the tubes going into the lungs. The
which is poison to bacteria. cilia beat together to push the mucus
above them out of the wind pipe and into
the throat to be swallowed.

Stomach The acid in your stomach not

only helps to digest what you have eaten
6 Intestines Lysozyme is produced
but also kills most of the micro-
in the small intestine while further
organisms in your food. along in the large intestine an army of
friendly bacteria live – they benefit
from the free food that they get but at
the same time, because they are there
Urine Most bacteria are unable to first, they prevent other harmful
live and grow in urine because of the disease-causing bacteria from getting
presence of lysozyme. established in this part of your gut.

Skin This waterproof covering usually

stops any pathogens from getting to the
inside of our body. Special types of
chemicals called fatty acids make the
surface of the skin an unpleasant place for
many micro-organisms and those that do
try to grow on our skin get crowded out by
large numbers of friendly bacteria.

Figure 1.33 The first line of defence

BIOLOGY YEAR 12
 45

The second line of defence – our internal bodyguard

Any invading organisms that get through our body’s first line of defence and reach
the living cells inside the body are faced with our second line of defence. This is in
our blood system, which reaches all the cells in the body.
The marrow inside the long bones of our arms and legs makes the blood cells. The
white blood cells, called leucocytes, have the special job of stopping any micro-
organisms that do get in from harming our body. There are many different types of
these disease-fighting white cells and together they can deal with most invaders.

White blood cells

All the body’s white blood cells (leucocytes) begin their life in the same way. They
first form in the bone marrow then develop in one of many ways to form the
various disease-fighting cells of the blood and the lymph which make up the
amazingly complex internal defence systems of the body. Figure 1.34 is a very
simplified summary of the main types of leucocyte.
Foreign objects such as pathogens that get into our body have chemicals called
antigens on their surface. These are quickly identified and trigger off an attack on
the invaders.

3
B-lyphocyte phagocyte

1
2

antibodies
Figure 1.34 Disease-fighting cells

Immune deficiency
Although our immune system does an amazing job against its enemies there are
times when the immune system does not work properly. One situation where this
happens is leukemia (the disease which produces too many white blood cells).
Another is a virus called HIV, which attacks the body’s T-cells and eventually
stops them from working. Without these special T-cells to ‘switch on’ and ‘control’
the production of antibodies the body soon begins to lose the battle against disease-
causing micro-organisms that get into it.

UNIT 1
46

Activity 14 Our internal defence system

In your notebook draw up a chart with three columns like the one below and
complete the empty spaces using the information from this unit:

Type of defence Where in our body How it protects our

the work is done body
Lysozyme
Mucus
B-cells
Cilia
Acid
T-cells
Friendly bacteria
Fatty acids
Phagocytes

For each number on Figure 1.33 on page 44 and using Figure 1.35 below
name the type of defence that is operating.

Disease-fighting cells

Granulocytes These fast-

moving cells attack any foreign or
harmful matter that enters the body.

Phagocytes
Attacking and engulfing cells.
Macrophages
These cells swallow any dead or foreign
matter. They will clean up the wound.
Lymphocytes
Chemical-producing cells.

B-lymphocyte cells These T-lymphocyte cells

produce chemicals called antibodies These cells develop in the thymus gland.
which recognise the specific antigens of They send out instructions controlling the
a harmful organism and bind onto them attack as well as killing body cells that are
causing them to die. infected by antigens.

Figure 1.35 The body’s defences at work

BIOLOGY YEAR 12
 47

Use Of Plants As Medicines

Most of the time people are well, which means that they are in balance with the
natural, social and supernatural elements that make up their world. Stresses and
disturbances in the balance between a person and their environment causes them to
feel unwell. When this happens, people search for the cause of the stress or
disturbance. They either seek help from medical doctors and expensive modern
medicines or most likely (especially when the hospital is far away), most seek the
help of the local healer or taulasea.
The taulasea can use a range of treatments including internal or external medicine,
massage or fofo, manipulation or therapeutic counselling. These treatments can be used
singly (lë soa-gia) or in combination with each other (soa-gia le fofo). Each
taulasea has memorised numerous formulae for the making and use of medicines
from local materials. The materials are mostly from plants but other materials are also
used. Other materials include: salt water, freshwater, raw fish (fuga species), breast
milk, leaf ash, smoke, burning or crushed charcoal, warm air and spittle (which is
mixed with leaves when the taulasea chews them to soften them up).

Different types of plants, including trees, shrubs, creepers, grasses, ferns and
lichens are used. The parts of a plant that can be used to make medicines include
roots, leaves, trunk, rhizomes, shoots, sap, young leaves, mature leaves, immature
fruit, mature fruit, seeds and flowers. Often the plant parts are used to make an
‘infusion’. This is a liquid produced by soaking the plant parts in hot water. The
chemicals in the plant are released into the water.
The following are examples of plants used as medicines:

A⁄tasi or Polynesian cress (Rorippa sarmentosa)

a member of the mustard family
This plant is one of the most commonly used to treat infants. The
whole plant or just the leaves are crushed and used to make an
infusion given to infants to treat aliments and inflammation. Juice from
crushed leaves or heated leaves can be applied to boils and infected
wounds. This juice can be dripped into the eyes to treat eye injury.

Lega (ano) or turmeric (Curcuma longa L.)

a member of the ginger family
A mixture of lega powder and coconut oil is used to treat stomatitis (gutu
papala), blisters on the lips (⁄tiloto), skin sores (papala, pofi) and
inflammation (mümü or mageso). An infusion made from scrapings of the
rhizome can be used to treat stomachache (manava tigä), ulcers (puta
papala), diarrhoea (manava tatä) and urinary tract problems (tulitä).

flva or kava (Piper methysticum)

a member of the pepper family
An infusion of pounded root is used to treat stomachache, backache
(tua tigä) and pain in other areas of the body as well as venereal
disease (ma‹ afi) and urinary tract problems.

UNIT 1
48

flva⁄vaaitu tu (Macropiper puberulum)

a member of the pepper family
An infusion of the leaves is often used to treat ghost sickness (ma‹ aitu)
and is also used in massage of illnesses such as swellings (fula) and
inflammation that are believed to be caused by ghosts (säüa ailments).

flva⁄vaaitu sosolo (Piper graeffei)

also from the pepper family
An infusion made from scraped bark (valusaga o le pafi la⁄u) is used as a
potion for mouth infections (gutu papala) and coughs (tale). The juice
from crushed leaves is also used to treat ghost sickness, inflammation
and infected wounds thought to have supernatural causes.

Fiu or ginger (Zingiber officinale)

a member of the ginger family
An infusion of crushed or scraped rhizome is taken as a potion for
treating stomachache, stomatitis and respiratory difficulties (ma‹ sela).

Fu⁄fu⁄ (Kleinhovia hospita)

a member of the cacao family
Sap scraped from the inner bark is used to stop the bleeding from
cuts (lavea) and wounds (manu⁄). The sap (apulupulu) can also be
used to treat eye injuries and irritations (mata pa‹a).

Lau magamaga (Phymatosorus scolopendria)

a member of the common-fern family
This creeping fern is one of the most widely used medicinal plants. An
infusion of scraped rhizomes or crushed leaves is taken as a potion (vai
a le taulasea) for treating inflammation, childhood ailments, stomachache
and urinary tract problems. An infusion of crushed leaves is taken as a
potion or is applied to the skin to treat infected, hard to cure wounds.

Lau papata (Macaranga harveyana)

a member of the spurge family
A potion made from an infusion of scraped bark is used as a purgative
for treating internal ailments such as digestive tract disorders (fe¤fe¤),
intestinal worms (⁄nufe), and urinary tract problems.

BIOLOGY YEAR 12
 49

Matalafi (Psychotria insularum)

a member of the coffee family
This is one of the most frequently used medicinal plants and is believed to be the
one most effective in treating supernaturally caused ailments. It is used as a
potion, made from an infusion of crushed leaves or scraped bark, to treat
inflammation, infected wounds, swellings and various body aches (tino gagase).

Moso›i (Cananga odorata)

a member of the soursop family
An infusion of scraped bark is used to treat constipation (manava
mamau), stomachache, mouth infection, coughs, postpartum sickness
(failele gau) and an internal pain called to⁄la. A boiled infusion of the
leaves and flowers are used in a steam bath to improve wellbeing.

Vao vai (Peperomia pellucida)

a member of the pepper family
The crushed plant is applied to boils (ma‹ sua).

Further information can be found in the following books:

❑ Macpherson, C. and L. (1990) Sämoan Medical Beliefs and Practice
Auckland University Press: Auckland.
❑ Whistler, W. A. (1996) Sämoan Herbal Medicine
Isle Botanica: Honolulu.
Or simply ask your local Taulasea.

UNIT 1
50

Antiseptics, disinfectants and antibiotics

These three types of chemicals help us control the growth and reproduction of
micro-organisms. Antiseptics are chemicals that are used to kill micro-organisms
on human tissue and disinfectants are used to kill micro-organisms on surfaces
and fabrics. Antibiotics are chemicals that fungi produce to stop the growth of
bacteria. People have learnt to produce antibiotics and use them to make medicines.

Vaccination
Our bodies have a number of ways of defending us against infection by pathogens
but some pathogens are very nasty and can get past the defences. Vaccinations have
been developed to help our immune system fight diseases.
The chart below is a way of showing how our immune system operates to fight an
infection over a period of time. You can see that there is a time delay of up to 10
days between the first infection and the destruction of the disease-causing micro-
organisms by the leucocytes.
FIRST INFECTION
Micro-organisms ( ) get into body and . . .
increase in numbers causing . . .
disease symptoms to appear.

DAY 0 DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 DAY 7 DAY 8 DAY 9 DAY 10 DAY 11 DAY 12
A few B-cells stick to the antigen on the micro-organism . . .
which makes them produce plasma cells . . .
which make antibodies ( ) . . .
which tell the T-cells to destroy the micro-organisms RECOVERY

Figure 1.36 First infection

Once the micro-organism gets into your body the race is on. If the micro-organism
can increase in numbers faster than the cells and chemicals of the immune system
then symptoms of the disease appear in your body. It takes some time for our
immune system to overcome the micro-organism, so there is a period of time when
we are sick, but we recover when the immune system wins! This does mean
though, that there may be a risk of disease harming the body and even causing
death with the first infection. However, the next time the micro-organism gets into
your body the immune system is ready and waiting, as the second chart shows.

SECOND INFECTION
Micro-organisms ( ) get into body but . . .
cannot increase in numbers . . .
so no disease symptoms appear.

DAY 0 DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 DAY 7 DAY 8 DAY 9 DAY 10 DAY 11 DAY 12
Memory cells ( ) from the last infection . . .
quickly produce plasma cells . . .
which make antibodies ( ) . . .
which tell the T-cells to destroy the micro-organism PERFECT HEALTH

Figure 1.37 Second infection

Because the immune system works more quickly after the first infection,
sometimes pathogens will get into your body yet you will never know that you had
the disease. Before you were born you received antibodies from your mother
through the placenta, and as a small baby you received more antibodies through
your mother’s milk. After a few months the immune system is on its own.

BIOLOGY YEAR 12
 51

Vaccinations
One way to give your immune system a boost is to add antibodies with an
injection. Your body does no work to make these injected antibodies so this is
called passive immunity. Unfortunately the antibodies do not last very long and
your body is soon at risk of getting sick again. What you need is a way to get your
body to make antibodies before a pathogen gets into your body, so it is prepared to
fight the disease.
The other type of vaccination is an injection that tricks your body into thinking that
you have a disease so antibodies and memory cells will be made. These memory
cells can then swing into action as soon as any of the real pathogens get in. This
Figure 1.38 Small child
reduces the possibility of any harm coming to your body from the disease. It is having his two month
called active artificial immunity. vaccination

Where to next?
Medicine has developed ways to stop the huge epidemics of the past. But what of
the future? Here are a few facts to think about.
Limits on success
There are still many diseases for which there are no vaccines – typhoid,
dengue, hepatitis A and AIDS are some. AIDS is proving to be particularly
difficult.
It is very difficult to develop vaccines against some of the more complex
disease organisms such as worms and protozoa like the malaria pathogen.
Some of these organisms can cover themselves in a layer that the human
body’s immune system doesn’t recognise but they often change their
antigens during different stages in their life. Some can also grow and
reproduce in animals other than humans.
Disease elimination
As vaccines are cheap, easy to produce and safe and effective to use it has
now become possible to completely eliminate certain types of disease. So the
World Health Organisation (WHO) has completely eliminated the disease
smallpox from the world. No case of this very serious disease has been
reported anywhere since 1981. Another goal of WHO is the elimination of the
disease poliomyelitis. This will not only save lives but will also save a lot of
money at present being spent on vaccination.
Are we winning in the fight against disease?
More than 70% of the world’s children in developing countries receive some
immunisation before they are one year old. However the death rate is still very
high – the World Health Organisation says that more than 8000 children die
every day because they are not immunised against diseases for which there are
vaccines.

UNIT 1
52

Table 1.2 Immunisation programme

Injection When given Disease immunisation is acting against

BCG New born Tuberculosis
HB 1 New born Hepatitis
HB 2 4 to 6 weeks Hepatitis
DPT 1 6 weeks Diphtheria, Polio and tetanus
Polio 1 1 to 6 weeks Polio
DPT 2 10 weeks Diphtheria, Polio and tetanus
Polio 2 10 weeks Polio
HB 3 14 weeks Hepatitis
DPT 3 14 weeks Diphtheria, Polio and tetanus
Polio 3 14 weeks Polio
Measles and rubella 1 year Measles and rubella
DPT When begin school Diphtheria, Polio and tetanus

Activity 15 Understanding immunity

Make a list of the diseases included in Table 1.2, Immunisation programme.
Find out which of these you have been vaccinated against.
Explain the difference between active and passive immunity and between
natural and artificial immunity. Be sure to mention the effectiveness of the
protection as well as the different methods used.
Reducing disease in the future
If your group were responsible for spending a limited amount of money on a
worldwide vaccination development programme how would you spend it?
Prepare a case to present to the class in no more than five minutes. Your plan
must list priorities because you will not have enough money to do everything
you would like. First read the information under the heading ‘Where to next?’
Then be sure to consider the different needs of developed and developing
countries, the need for research as well as making sure every child is
vaccinated.

Activity 16 Diseases
Describe ways that diseases spread.
Discuss ways that people in Sämoa use to control and cure diseases.

BIOLOGY YEAR 12
 53

Antibiotic resistance
❑ Unfortunately, some bacteria develop resistance to a particular antibiotic.
Bacteria belonging to one species are not all the same. They can change
their genes by mutation. Some bacteria acquire resistance to a particular
antibiotic and are not killed by it. They multiply, passing their resistant
genes on to their offspring.
❑ As the antibiotic kills off bacteria, the bacteria population gradually changes to
a resistant strain. Scientists have to develop new antibiotics to fight these
resistant strains.
We can help to prevent the development of antibiotic resistant bacteria if we
carefully follow the instructions for any antibiotics we are taking. For
example, it is important to take all the antibiotics and not just some of them
and not to give up using them when we feel better.

Activity 17 Antiseptics and disinfectants

Set up the following investigation to test the effectiveness of different types of
disinfectant or antiseptic.
Firstly obtain identical sterile petri dishes with nutrient agar.
Next make up a standard solution of each antiseptic (e.g. 5 ml per 100 ml of
water).
Cut identical small disks of filter paper and label
them. Dip each in a different antiseptic. Dip bacterial antiseptic
one disk in water as a control. growth disks

Obtain bacteria from the same source by wiping a B

cotton swab over an existing colony. Lightly wipe
the swab over the agar in a petri dish. Drop the
C
antiseptic disks onto the agar.
Seal the dish. Place in a warm place for three
days. no bacteria control disk

Clear areas in the agar indicate bacteria are

absent. Observe the size of the clear area around each disk and decide
which antiseptic is the most effective.
The investigation could be changed to investigate the effect of concentration on
the effectiveness of the disinfectant or antiseptic. Design and carry out an
investigation to test the effect of concentration on the effectiveness of a
disinfectant or antiseptic.

UNIT 1
54

Revision
Match up terms with definitions.
fermentation a the growth of harmful micro-organisms in or on
pathogen your body
b a chemical which recognises and helps destroy
infection a pathogen
c a marker chemical on a pathogen
toxin d the ability to prevent an infection occurring
phagocyte e a white blood cell which produces antibodies
f a disease-causing micro-organism
antigen g the conversion of sugar into alcohol and carbon
lymphocyte dioxide by yeast
h when bacteria are no longer affected by an
antibody antibiotic
i the chemical produced by a pathogen which
antiseptic may poison cells
immunity j the chemical produced by fungi which is used
to kill bacteria
vaccination k a white blood cell which engulfs pathogens
l the chemical applied to a wound to prevent
antibiotic infection
antibiotic resistance m injection with dead or weakened microbes to
give immunity

Copy and complete the following table by listing harmful and helpful effects of
micro-organisms.
Micro-organism Harmful Effect Helpful Effect

viruses ❑ ❑
❑ ❑
bacteria ❑ ❑
❑ ❑
fungi ❑ ❑
❑ ❑

Identify the micro-organism involved.

BIOLOGY YEAR 12
 55

Decide whether the following statements are true or false. Rewrite the false ones
to make them correct.
a Decomposers are micro-organisms which are able to release nutrients
from dead matter.
b Herbivores need the help of fungi which live in their gut to break down
the tough cell walls of plants.
c Biotechnology can use micro-organisms to help humans.
d Antibiotics are used to fight both bacterial and viral infections.
e Viruses are all pathogens, but they can be useful when they are used for the
biological control of pests.
f All diseases are caused by pathogens.
g A pathogen can cause harm by destroying living tissue or by poisoning
cells with the toxins it produces.
h A pathogen produces antigens which are absorbed by lymphocytes which
then produce antibodies to attack that pathogen.
i Immunity occurs through antibodies.
Explain the difference between: a
an antigen and an antibody b
disinfectant and antiseptic c
immunity and vaccination.
Copy and complete the following paragraphs using the words in the box
below.
a White blood are involved in fighting . Phagocytes
any pathogens they encounter. Lymphocytes produce which
attack and help destroy particular types of pathogens. The antibodies
b recognise on the surface of the pathogen.
After your first infection by a particular , you gain natural
to further attacks due to the presence of in your blood. You can
gain immunity to a particular pathogen by being with
dead or weakened strains of the pathogen. This increases the level of the
c appropriate antibody in the .
Antibiotics are produced by and are taken internally by humans
to destroy . Some bacteria have developed to particular
antibiotics. A few of the bacteria are genetically different and are not
killed by the antibiotic. They increase in number and eventually produce
a resistant strain.

antibody • antigens • artificial • bacteria • blood • cells • engulf • fungi disinfectant clear
immunity • pathogens • resistance • vaccinated • pathogen • antibodies disk areas

In an investigation into the effectiveness of three disinfectants (A, B and C),

students inoculated a sterile agar plate with bacteria from an established
colony by wiping the surfaces with a cotton bud.
They dipped a small labelled disk into the first disinfectant and placed it on bacterial growth
the agar. They repeated this step for the other two disinfectants. The plate was
sealed and incubated for three days. Figure 1.39 shows the results. Figure 1.39 Agar plate with
a What is a disinfectant used for? bacteria
b What are the students actually testing?

UNIT 1
56

What does the word ‘sterile’ mean? Why was it important the plate was
sterile to begin with?
Why did they use bacteria from an established colony?
What is the difference between inoculation and incubation?
Why is it important that the filter paper disks were the same size? g
What do the filter paper disks do when dipped in disinfectant?
What do the pale areas in the photo indicate? What do the clear areas
around some of the disks indicate?
Which disinfectant appears to be most effective at killing bacteria? How do
you know this?
The teacher commented that their test was
not a completely fair test. Suggest why
it was not a fair test and how the
students could change their method to
make it fairer. (Hint – read label.)
The teacher also said that they should have included a control disk to
check that filter paper does not inhibit the growth of bacteria. What
should they do to the control disk to check this?
Suggest a limitation of this particular test of the effectiveness of
disinfectants in killing bacteria in general.
Read the passage below, then answer the questions.

HIV and AIDS

The disease AIDS (acquired immune deficiency syndrome) is caused by a
viral pathogen. The virus is called HIV (human immunodeficiency virus).
The virus first appeared in Africa in the 1980s and it is believed to
have originated in a monkey species.
The virus is transmitted from person to person in body fluids (e.g. blood and
semen). It can be transferred through sexual activity, blood transfusions and
by sharing needles. It is not caught by touching or coughing.
Once the virus enters the body, it invades lymphocytes which fight disease.
The virus remains dormant in the lymphocytes for up to ten years.
When it becomes active the virus takes over the lymphocyte cells and
makes them produce many more copies of the virus, which escape to
invade other lymphocytes.
The body’s immune system now ceases to function and the person is vulnerable to
many opportunistic infections. These include diseases such as thrush, diarrhoea,
tuberculosis, pneumonia and some cancers. When these symptoms occur, the
person then has AIDS. Often there are times of recovery followed by relapse.
Eventually the person’s health deteriorates and an infection proves fatal.

Researchers are developing drugs which may prevent the onset of

AIDS. They are also investigating vaccines, but as the HIV virus
mutates rapidly this is a difficult task.

What do the acronyms HIV and AIDS stand for? b

What type of pathogen causes AIDS?
c This pathogen has crossed the ‘species barrier’. What does this mean?
d Suggest three ways in which the spread of the disease could be reduced.

BIOLOGY YEAR 12
 57

What does it mean when a person is tested and found to be HIV

positive?
Why is there usually a long delay between infection with HIV and the
development of AIDS?
What are ‘opportunistic infections’? (If you do not know the word
‘opportunistic’ look it up.)
Why is it difficult to develop an effective vaccine?
To culture yoghurt, milk was heated until it nearly boiled. Yoghurt-making
bacteria were added when the milk had cooled to 20°C. The liquid was placed
in a water bath set to 35°C. The temperature and pH of the mixture was
monitored over three hours. The results are plotted on the double axis graph
below.

Temperature and pH of Yoghurt Culture

40 7
35 6.5

30 6
Temperature of culture °( C)

25 5.5

culture
20 5

15 Key: 4.5

10 temperature 4
pH of

pH
5 3.5
0 3

0 20 40 60 80 100 120 140 160 180

Time cultured (minutes)

What ingredients do you need to make yoghurt? b

Why was the milk heated till it nearly boiled?
c What was the milk inoculated with?
d Why was the culture put in a water bath?
e Describe the trend shown by the temperature graph line. f
Was the water bath thermostat accurately calibrated?
g Why was the water bath thermostat set to 35°C?
h Why do you think there were temperature fluctuations in the culture?
The student used a pH meter to find the pH of the culture. What does pH
indicate?
After 100 minutes, what was the temperature and pH of the culture? k
Describe the trend shown by the pH graph line.
Describe in words what happens to the acidity of the culture during the
experiment.
What would have caused this change in pH?
After 120 minutes the culture was no longer runny; why was this?

UNIT 1
 Unit

2 Cell Biology
This unit is divided into sections that cover cell structure, respiration, osmosis and
diffusion, and enzymes.

Cell Structure
In this section you learn to:
❑ use a light microscope to view prepared slides or wet mounts, e.g. onion
cells, human skin cells
❑ draw cells and tissues as seen under the microscope

❑ explain the relationship between cells, tissues and organs ❑

describe the differences between plant and animal cells
❑ explain the structure and function of cell components and organelles, e.g.
cell membrane, cell wall, nucleus, cytoplasm, vacuole, chloroplast,
ribosome, endoplasmic reticulum, mitochondria, Golgi bodies.
All organisms are made up of cells. Cells are very small, so small that you can only
see them using a microscope. All cells carry out the life processes that separate
living things from non-living things, e.g. nutrition and gas exchange. Cells are
called the ‘basic unit of life’ because some very small living things such as
bacteria, single cell organisms and some algae, are made up of one cell that can live
independently from other cells.
Figure 2.1 Single Although some cells can live independently, most cells live as part of a
cell organism multicellular organism. A human is a multicellular organism. Your body is made
up of many cells working together to keep you alive. Plants are also made up of
many cells working together.

How big are cells?

❑ You need to be familiar with these units:
1m = 1000 mm (millimetre)
1 mm = 1000 µm (micrometre)
1 µm = 1000 nm (nanometre)
❑ An amoeba is one of the largest unicellular organisms. At about 200
micrometres (µm) diameter it is just at the limit of human vision.

58
 59

❑ Most plant and animal cells are between 10 and 100 µm in diameter, which
means that you need a microscope to see them.
❑ Apart from the nucleus and chloroplasts, most of the fine structure of
cells is too small to be seen with a light microscope. An electron
microscope, which can show structures from 100 µm down to
0.1 nm in size, is capable of showing these smaller organelles. ❑
Some relevant sizes are:
– the largest cells are bird eggs, e.g. chicken egg at 60–70 mm
– the longest cells are nerve cells up to 600 mm
– most cells are in the range 10–100 µm
– most bacteria are in the range 1–7 µm
– mitochondria are about 1.5 µm long
– large molecules are 4–10 nm
– small molecules are 0.4–0.8 nm
❑ Bacteria have a cell wall but no nucleus.

Cell organelles
The cells from all organisms contain a range of different parts inside them. These
parts are called organelles. Organelles are so small that we need an electron
microscope to see them.

Generalised Plant Cell Generalised Animal Cell

cytoplasm nucleus
mitochondrion nucleus cell
endoplasmic cytoplasm membrane nuclear
reticulum lysosome envelope
vacuole

chloroplast
cell wall mitochondria ribosomes

vacuole cytoskeleton endoplasmic

cell membrane fibre golgi body reticulum

Figure 2.2 Plant cell Figure 2.3 Animal cell

All cells are surrounded by a cell or plasma membrane. The cell membrane is like protein
pore
both a wall and a gate that separates the cell from where it lives and controls what
materials enter and leave the cell. The different parts of the cell membrane are lipid
designed to transport materials in and out of the cell. lipid

The cell membrane is made up of two layers of lipid (fat) molecules. A small
Cell Membrane
number of protein molecules can also be found in between the lipid molecules. The
protein molecules form pores that control the movement of large molecules across Figure 2.4 Cell membrane
the cell membrane.
Plant cells have a cell wall outside the cell membrane. The cell wall is made up of
cellulose and it provides that cell with support. The strong cell wall gives plant
cells a fixed shape.

UNIT 2
60

The insides of plant and animal cells contain a jelly-like material called the cytoplasm.
The cytoplasm is also made up of fibres that form a cytoskeleton throughout the
cytoplasm. The cytoskeleton supports the cell, giving it shape and allowing some cells
to move. The following cell organelles are found in the cytoplasm.
Organelle Description Function

Nucleus Area of the cell Contains the genetic

surrounded by a double information that controls the
layer of membrane functioning of the cell
containing small pores
Golgi bodies A number of flat disc- Package chemicals that are
shaped layers of then used outside the cell
membrane
Mitochondria Sausage-shaped, with Carries out respiration
folds of membrane on
the inside
Ribosome Small, round Make proteins

Endoplasmic A system of membranes Provide a work surface for

reticulum and connecting tubes. chemical reactions and
Sometimes covered in passageways for moving
ribosomes materials
Chloroplast Oval shaped containing Carry out photosynthesis
layers of membranes
and also chlorophyll
Vacuole Membrane sacs. Large Store water, food or
in plant cells and small wastes
in animal cells

Chloroplast outer membrane

Mitochondrion Endoplasmic Reticulum
with Ribosomes inner
ribosomes membrane

granum

stroma
(fluid)

Figure 2.5 Mitrochondria, Endoplasmic reticulum and chloroplast

Plant and animal cells

There are three main differences between plant cells and animal cells. Plant cells
have:
❑ a cell wall that gives them a strong rigid shape
❑ chloroplasts that carry out photosynthesis
❑ large vacuoles that can take up most of the cell. A high level of water in the
vacuole provides pressure on the cell wall which gives the plant support.

BIOLOGY YEAR 12
 61

Cell, tissues and organs

Cells in multicellular plants and animals are specialised so that they can carry out
particular functions. Examples of specialised cells in animals are skin, nerve, bone
and blood cells. Examples of the functions of plant cells include to provide support,
to absorb water, to conduct liquids, to allow gases in and out, to make food,
forming protective surfaces and reproduction. Specialised cells have special
features that allow them to carry out their function.
The bodies of multicellular plants and animals have cells and groups of cells that
work together to carry out a particular function. A group of the same type of cell is
called a tissue. For example, muscle tissue in animals is made up of mostly muscle
cells that work together to allow the animal to move. Xylem is an example of a
plant tissue. The cells in xylem work together to move (transport) water from the
roots to all parts of the plant.
An organ is a collection of different types of cells which work together to carry out
a particular function. For example a leaf is an organ. It is made up of layers of
different sorts of cells that work together to carry out photosynthesis. The heart is
an organ. The heart contains muscle cells, nerve cells and connective tissue that
work together to pump blood around the body.

Activity 1 Cell structure

Matching terms with definitions.
cells a the organelle which is the site of protein synthesis
organelles b the organelle which is the site of photosynthesis
cell membrane c various structures within the cytoplasm
cytoplasm d the basic building blocks of living things
cytoskeleton e a whip-like extension of the cell membrane
f the semi-fluid substance filling the cell interior
Golgi body
g flat disc-shaped sacs in the cytoplasm
mitochondrion
h a sac containing digestive enzymes
endoplasmic reticulum i the structure which maintains the shape of a cell
ribosome j a sac containing water or storage products
lysosome k the double layer of lipids enclosing the cytoplasm
vacuole l the cellulose layer that surrounds plant cells
nucleus m the structure in a cell containing genetic
cell wall information
n a system of membranes and connecting tubes
chloroplast
o the organelle which is the site of cellular
flagellum
respiration

UNIT 2
62

Matching cell types to roles.

Animal Cells D microvilli

B
A

C dendrites

cell body axon

Match the animal cell types in the picture above with these roles:
nerve cells – long, thin cells with connections to other cells
absorption cells – cells with numerous finger-like projections to
increase the surface area available for absorption
muscle cells – long, thin cells with fibres that contract to change the length
of the cells
fat storage cells – cells with vacuoles filled with fat
blood cells – disc-shaped cells able to pass through tubes.
Match the plant cell types below with these roles:

Plant Cells
F G H

water transport vessels – long tubes with thickened cell walls, walls
perforated with pores
root hair cells – have long extensions for absorbing water h
epidermal cells – flat cells forming a layer, pores present
palisade cells – vertical cells stacked in parallel, they have many
chloroplasts for carrying out photosynthesis.
True or false?
Decide whether these statements are true or false. Correct the false ones. a
Most cells are less that one tenth of a millimetre in length.
b Cell membranes are made up of two layers of protein molecules.
c The folds in cell organelles provide a work surface on which complex
chemical reactions take place.
d Lysosomes contain the genetic information which controls cells.
e The cell wall of plants is made of layers of cellulose fibres placed in
different directions.
f The rows of tiny beating hairs on the surface of some unicellular
organisms are called flagella.
g The DNA in bacterial cells is not found in a separate nucleus. h
All cells have the same basic structure.

BIOLOGY YEAR 12
 63

Identifying the internal structure of cells.

This magnified view of a cell was taken by a transmission electron
microscope. Compare it with other cell diagrams.

From the list below label the parts above:

cell wall • cell membrane • cytoplasm • vacuole • mitochondria

chloroplasts • nucleus • nuclear envelope

Is this a plant or an animal cell? Give two reasons.

Describe the differences between plant and animal cells.
Explain the relationship between cells, tissues and organs.

Microscopes
We use different types of microscopes to investigate cells. For example:
❑ Light microscopes direct light through a thin, semi-transparent sample of
cells and we observe them after magnification by two lenses. These
instruments are able to resolve (clearly show in detail) objects bigger than
200 nm in size.
❑ Electron microscopes are expensive instruments which use a beam of
electrons to create an image. As electrons have much shorter wavelengths
than light waves, they can be used to reveal much smaller objects. The
photo of the cell above was taken through an electron microscope.
❑ Transmission electron microscope (TEM), electrons pass through an
extremely thin section of cells to produce an image which resolves objects
bigger than 0.2 nm. The image is a flat two-dimensional slice.
❑ Scanning electron microscope (SEM), electrons are bounced off a
sample to reveal the three-dimensional surface structure of cells or
organelles. An SEM will only resolve cellular objects bigger than 10 nm
in size.

UNIT 2
64

Using a light microscope

If you are to use a light microscope you need to follow a sequence of steps.

Make sure the low-power objective lens is in line with the barrel.
Look through the eyepiece lens and adjust the curved mirror so that light
enters the microscope.
Place the slide on the stage with the sample centred on the viewing area.

Looking from the side, wind the coarse focus

knob clockwise until the objective lens is Light Microscope
just above the slide. barrel
eyepiece
Do not wind down when you are looking lens nose-piece
through the lens! low-power
objective high-power
Look through the eyepiece lens and slowly
1 objective
turn the coarse focus knob anticlockwise coarse 8 slide
until the cells come into focus. focus 3 7 clip

54 6
stage
Adjust the condenser under the stage to give 9 2 condenser
the best lighting. mirror
fine
Gently move the slide about with one hand,
adjusting the focus with the other. focus base

When you have the best view of cells rotate in the high-power
objective lens.
Bring the image into sharp focus using the fine focus knob.
When you have finished, rotate the low power lens into line and remove the
slide.

Drawing cells
To record your observations of cells under the microscope, follow these
guidelines.
❑ Use unlined paper, a sharp pencil and a clean rubber.

❑ Select what to you need to draw and only draw the required detail. ❑
Figure 2.6 Human Sketch an outline of a group of cells. Make your drawing large.
epidermal cells (x400)
❑ Use sharp lines and no shading.

❑ Make sure the lines join up so that structures are complete. ❑

Add labels and a suitable title.
❑ On your drawing write the magnification. The label on Figures 2.6 and
2.7 give examples of how to do it.
Drawing cells
The photos opposite are typical of the views of cells you will see using a light
Figure 2.7 Leaf microscope. Draw a group of cells from each photo using the guidelines
epidermal cells (x100) above.

BIOLOGY YEAR 12
 65

Activity 2 Investigating cells and tissues

Aim: To use a microscope to investigate cells and tissues.
Make wet mounts, leaf tears and stained sections of various plant tissues so that
you can use a light microscope to investigate the structure of the cells and
tissues present.
Label drawings of the cells and tissues.
View prepared slides and make drawings of the cells and tissues.
Mount animal skin cells and view with a light microscope.

Respiration
In this section you learn to:
❑ write an equation to describe the process of respiration
❑ explain the importance of respiration and its relationship with
photosynthesis
❑ compare aerobic and anaerobic respiration
❑ investigate fermentation in yeast
❑ discuss how anaerobic respiration results in muscle fatigue.

All cells need energy to carry out their activities. Plants get energy
Releasing Energy in Cells
from the sun which they trap by the process of photosynthesis. Then yeast cells ANAEROBIC most cells
they use this energy in a series of chemical reactions called ethanol lactic acid
RESPIRATION
respiration. When animals eat plants or other animals they gain CO2 (no oxygen)
food molecules that can be used in respiration to release the energy. GLYCOLYSIS

Respiration is carried out by a series of different enzymes that are glucose

cytoplasm 2 ATP
attached to membranes. Cells only need small amounts of energy at a
time so respiration removes the energy from glucose and stores it as pyruvic acid
chemical energy in a molecule called adenosine triphosphate or
ATP. The ATP molecule can diffuse throughout the cell supplying cell AEROBIC
small amounts of energy. An active cell needs the energy from
millions of ATP molecules each second.
RESPIRATION
During respiration of a glucose molecule, the chemical energy is KREBS

released by two separate processes called glycolysis and

respiration. CYCLE
CO2
Glycolysis occurs in the cytoplasm of the cell. It is a series of
mitochondrion 2 ATP
enzyme controlled reactions which break down glucose molecules
membrane 32 ATP
into two pyruvic acid molecules. Two ATP molecules are formed in
this process.
O2
H2O
If oxygen is present in the cell, then aerobic respiration occurs next, Respiratory Chain
but if oxygen is absent then anaerobic respiration occurs.
Figure 2.8 Releasing
energy in cells

UNIT 2
66

Aerobic respiration
At the beginning of aerobic respiration, the two pyruvic acid molecules produced
by glycolysis diffuse into the mitochondria. In the mitochondria they go through
another series of enzyme controlled chemical reactions called the Krebs cycle.
ATP and carbon dioxide are produced during the Krebs cycle. Another series of
chemical reactions, called the respiratory chain, follow on from the Krebs cycle.
Oxygen is used during the respiratory chain reactions and water and 32 ATP
molecules are produced.
The following reaction is a summary of what happens to each glucose molecule.

Glucose + oxygen ➔ carbon dioxide + water + energy in 36 ATP

molecules
C6H12O6 + 6O2 ➔ 6CO2 + 6H2O + energy in 36 ATP molecules

When fats or protein molecules are used as the source of energy, they are first
broken down into molecules which can be fed into the Krebs cycle.

Anaerobic respiration
When there is no oxygen present only glycolysis can occur. In most plant and
animal cells, the pyruvic acid changes into lactic acid. This is called anaerobic
respiration. Lactic acid is a poison which builds up if anaerobic respiration is used.
In animals a build up of lactic acid causes muscle fatigue which, if it continues,
will cause the muscles to stop working. If oxygen becomes available again the
lactic acid is then changed back into pyruvic acid and the pyruvic acid goes through
aerobic respiration.
In yeast cells the pyruvic acid undergoes anaerobic respiration or fermentation into
carbon dioxide and alcohol. You will remember this process is used in wine and
bread making.

Activity 3 Respiration
Write an equation to describe respiration.
Explain the importance of respiration.
Explain the relationship between photosynthesis and respiration.
Explain how anaerobic respiration results in muscle fatigue.
Compare aerobic respiration with anaerobic respiration.

Materials:
Activity 4 Fermentation
Yeast Aim: To investigate fermentation by yeast.
Flasks
Make up a solution of 2 grams of glucose, 50 mls of water and 0.1 grams of
Balloons yeast in a conical flask.
Glucose
Make up a control solution of 2 grams of glucose and 50 mls of water in a
Water conical flask.
Place balloons over the top of each of the flasks.
Leave for 24 hours in a warm place. Record the increase in size of the
balloons.

BIOLOGY YEAR 12
 67

Activity 5 Temperature and fermentation

Aim: To investigate the effect of temperature on fermentation by yeast.
Use the reaction investigated in the previous activity as a starting point for your
plan. In your plan identify the following and describe how they will be used
to investigate the effect of temperature on fermentation by yeast:
❑ independent variable
❑ dependent variable ❑
controlled variables ❑
repeats.
Carry out your plan and collect the results.
Write out a report on your investigation.

Activity 6 Respiration data

You can find the rate of respiration in cells by measuring the uptake of oxygen or
the release of carbon dioxide gas. Gas Volumeter
syringe
In an experiment, a few yeast granules were sprinkled into a glucose solution and water drop
left for a period of time. A sample of the solution was placed in a volumeter which
measures changes in gas volume. The yeast cells respire anaerobically in the water, yeast in
so any change in gas volume is due only to the production of carbon dioxide. glucose solution

Why was glucose added?

Which direction will the water drop move, left or right? water
What is the syringe for? bath

Why is the volumeter in a water bath?

A similar volumeter without yeast was set up in the water bath. Why?
Figure 2.9 Gas volumeter

Diffusion And Osmosis

In this section you learn to:
❑ investigate the processes of diffusion or osmosis
❑ describe the processes of diffusion and osmosis
❑ explain the importance of diffusion and osmosis in cell transport.

An important part of the functioning of cells is the movement of materials,

including molecules and ions, in and out of a cell and also across the cell. Different
processes transport different materials. Some of these processes require the cell to
use energy and others do not.
Processes, such as diffusion and osmosis, do not require energy to transport materials
so are called passive transport. Active transport uses some of the cells energy to
carry materials from areas of low concentration into areas of high concentration.

UNIT 2
68

Diffusion of Molecules Diffusion

molecules
cell Molecules and ions in a solution move all the time. The particles bump into each other
diffusion
and as they do, they spread throughout a liquid without stirring the liquid. The
high concentration
movement of individual particles is random, but the overall movement of particles
occurs down the concentration gradient (from an area of high concentration of the
concentration
low
liquid to an area of low concentration). This is called diffusion. Cells are so small that
diffusion can carry a molecule across the cell in a fraction of a second.
Figure 2.10 Diffusion
of molecules How quickly diffusion occurs depends on a number of factors.
Molecule size: Small molecules move faster than larger molecules.
Temperature: Particles move faster at higher temperatures.
Concentration: Diffusion is faster down a steeper concentration gradient.
Molecules that enter or leave a cell must cross the cell membrane. The cell
membrane is selectively permeable, which means that some materials can pass
through it easily and others cannot diffuse across it. Water can pass in and out of a
cell easily, but sucrose sugar cannot.

Osmosis
Osmosis is the diffusion of water molecules across a selectively permeable
membrane from the side with the lowest concentration of dissolved substances,
called solutes, to the side with the highest concentration of dissolved substances.

Osmosis – Movement of Water Across a Membrane

lower water equal water

concentration concentration
water solute (cannot

equal movement
diffuses diffuse through when water con-
inwards membrane) centrations equal

Figure 2.11 Osmosis

Cells tend to have a higher concentration of dissolved materials than
Osmosis and Cell Shape
their surroundings. Therefore the process of osmosis takes water into
red blood the cell, creating pressure which helps to support the cell and keep it
cells firm. If cells are placed in pure water, the water will quickly move
into the cell. Plant cells will fill until cell contents are pushed up
cells in cells in a strong against the cell wall so much that no more water can enter. If animal
pure water salt solution cells, for example human red blood cells, are placed in water they
will fill until the cell membrane cannot hold the pressure and the
cells burst cell will burst.
cells shrivel If cells are placed in a solution with a high concentration of solutes,
Figure 2.12 Osmosis and then the water will move out of the cell by osmosis. In plant cells, the
cell shape removal of water causes the cytoplasm to move away from the cell wall. This is
called plasmolysis.
Single celled animals that live in fresh water use an organelle called a contractile
vacuole to collect and remove the water that enters the cell by osmosis. The
contractile vacuole stops the cell becoming so full of water that it bursts.

BIOLOGY YEAR 12
 69

Activity 7 Transport
Matching terms with definitions.
diffusion a lets molecules in solution pass through
osmosis b the movement of water across a membrane
solutes c molecules and ions dissolved in water
permeable d the movement from high to low concentration
active transport e the movement of molecules against a gradient

True or false?
Decide whether the following statements are true or false. Rewrite the false
ones to make them correct.
a Particles always diffuse from higher to lower concentration areas.
b Active transport requires energy to move particles across a membrane
down a concentration gradient.
c Some proteins carry certain molecules across cell membranes.
Investigating the effect of temperature on diffusion rate.
An experiment was set up to test the hypothesis that if you increase the
temperature it increases the diffusion rate. The time for a purple dye to
diffuse set distances in water at different temperatures was recorded.
Water Temp. 2 cm 4 cm 6 cm 8 cm 10 cm
10°C 60 s 114 s 210 s 300 s 450 s
20°C 30 s 66 s 108 s 282 s 222 s
30°C 12 s 30 s 55 s 80 s 125 s

Plot the three sets of data on the same graph. Use a key.
Do these results support the above hypothesis? Explain your answer.
Investigating the importance of surface area for cells.
Raw materials enter a cell by diffusion through the cell membrane. The
number of molecules which diffuse into a cell depends on its surface area.
To function efficiently a cell needs a large surface area relative to its
volume.
Imagine a cell is a cube with sides of 1 cm length; Hypothetical Cells
this ratio can be calculated using the following
1.5cm B
method: 1 cm A 1 cm 1.5cm 2 cm C
Surface Area = 6 x area of a single side 1 cm 1.5cm 2 cm
2 cm
6x1x1
6 cm2 3 cm E 2.5 cm D
Volume = width x depth x height
2.5 cm
1x1x1 3 cm
2.5 cm
1 cm3 3 cm

❑ Surface Area to Volume Ratio (SA:V) = 6:1 Figure 2.13 Hypothetical

cells

UNIT 2
70

Complete the calculations in the table for each cell.

Side Length Surface Area Volume SA:V Ratio
A 1 cm 6 x 1 x 1 = 6 cm2 1 x 1 x 1 = 1 cm3 6:1
B
C
D
E

Plot both surface area and volume versus side length on a dual vertical axis
graph. Use a key.
As the cell sides increase in length, which increases faster – surface area or
volume?
Describe what happens to the surface area to volume ratio as the cell
length increases.
Which cell would be most efficiently supplied with raw materials by
diffusion?
Cell shape may also be a factor in the SA:V ratio.
3.375 cm
Calculate the SA:V ratio for the cell shown opposite.
Compare this cell with cell B above which has the same volume. Which cell
1 cm
1 cm will be better supplied by diffusion? Is shape important?
Interpreting experimental data.
Figure 2.14 Cell
The following experiment was set up to measure the effect of increasing
sugar solution concentration on the rate of water uptake in potato cells by
osmosis.
Five small potato cubes were weighed and put into vials which contained
sucrose solutions as specified in the table.
After 24 hours the cubes were re-weighed and then the new weights were
recorded.

(final weight – original weight) x 100

% Weight Change =
original weight

Calculate the percentage weight change for each potato cube using this
formula:
Cube Sucrose Weight Weight after % Weight
Solution at start (g) 24 hours (g) Change
A 0.0 molar 1.2 1.5 +25%
Figure 2.15 Potato cube
in solution B 0.1 molar 1.4 1.6
C 0.3 molar 1.5 1.5
D 0.5 molar 1.4 1.1
E 0.7 molar 1.6 0.9

BIOLOGY YEAR 12
 71

Plot a graph of percentage weight change (vertical axis) versus solute

(sugar) concentration (horizontal axis).
Explain what this graph shows about the effect of increasing solute
concentration on water movement in and out of the potato cells.
Estimate the original solute concentration inside the cells.
Predicting experimental results.
The diagram shows three cells in different sucrose solutions.

Cells in Different Sucrose Solutions

cell A cell B cell C
5% sugar 5% sugar 5% sugar
solution solution solution

0% sugar solution 5% sugar solution 10% sugar solution

For each cell indicate the overall direction water would move through the
membrane (in/ out/ no net movement).
For each cell indicate the overall direction in which sucrose molecules
would move (in/ out/ no movement).
Which of the following cell drawings would best show the appearance of
each cell after five minutes?

Cells after Five Minutes in Solutions

1 2 3

Activity 8 Diffusion Materials:

Aim: To investigate diffusion of ammonia. Ammonia solution

Timer
What to do
Place a container of ammonia solution at the front of the room. Time how long it
takes for people in each row of desks to smell the ammonia.

Activity 9 Osmosis cup Materials:

Aim: To investigate osmosis in cells. Small cups cut out of a

potato – 2 cm x 2 cm
x 2 cm potato
What to do
Strong salt or sugar solution
Set up three beakers with water to a depth of 0.5–1.0 cm. Water
Place a potato cup into each beaker. Beakers
cup
3 Half fill one potato cup with water, one with Cover for beakers,
strong salt or sugar solution and leave one e.g. clingwrap, tin foil
empty. potato

Cover each beaker and leave for 24 hours.

Observe the level of the solutions in the potato cups.
Use what you have learned about osmosis to explain your results.

UNIT 2
72

Materials:
Activity 10 Plasmolysis
Plant material such as Aim: To investigate plasmolysis in a plant cell.
beet root cells, rhubarb
or red cabbage cells Prepare one slide of tissue mounted in water and another of the tissue
Strong salt or sugar solution mounted in strong salt or sugar solution.
Microscope Use a microscope to compare the tissue on the two slides.
Microscope slides
and coverslips Draw diagrams of the cells in water and strong solution.
Explain your results in terms of osmosis.

Enzymes
In this section you learn to:
❑ describe the structure and function of enzymes
❑ investigate the effect of temperature on enzymes
❑ discuss the effect of temperature on the structure and function of enzymes.

‘Induced fit’ model Enzymes are called biological catalysts because they control the speed
of all chemical reactions within our bodies. Each active cell can have
A B thousands of different chemical reactions occurring every second.
Nearly all of these reactions have to have an enzyme to help them
Substrates occur. Each different chemical reaction that occurs in cells needs a
different enzyme. Therefore there are thousands of different enzymes.
Active site Some enzymes are common. For example, every living cell has a set of
enzymes that control respiration – the reactions that release energy
Enzyme from food molecules. Specialised cells often have special enzymes
that do a special task. For example, the plant cells in a yellow flower
petal have the enzymes to make the yellow pigment (colour).
Enzymes that work inside a cell are called intracellular enzymes.
Extracellular enzymes are outside the cell where they do special
The binding of tasks such as digestion.
the subtrates
and enzyme
causes them to How enzymes work
change shape Most reactions have an energy barrier which must be overcome
slightly to fit
before the reaction can occur. Enzymes lower the amount of energy
needed for the reaction to occur by changing the molecules involved
in the reaction.
AB An enzyme is a special protein made up of one or more amino acid
Combined
substance chains folded into a special shape with a pocket called an active site.
The reactants involved in the reaction catalysed by the enzyme can fit
into the active site. These reactants are called the substrate of the
Enzyme enzyme. Each of the molecules involved in chemical reactions in the
cell has a specific shape, therefore each enzyme will only work with
The chemical nature and activity one reaction because only the substrate molecules involved in that
of the enzyme is unchanged and reaction will fit into the active site. When the substrate is joined onto
can be used again. the active site of the enzyme, the reaction occurs quickly.
Figure 2.16 ‘Induced fit’
model There are currently two models of enzyme activity. They are called the lock and
key model and the induced fit model. The induced fit model is becoming more
popular.

BIOLOGY YEAR 12
 73

Enzyme Action: Lock-and-Key Model

Reaction rate
substrate molecule product molecules
sucrose glucose fructose
water
active site Activated Enzyme sucrase
Temperature

rising temperature speeds up

Enzyme sucrase complex reaction but eventually
1 Substrate molecule 2 Substrate binds to enzyme 3 Enzyme releases products unfolds the enzymes

enters active site and reaction occurs and repeats process Figure 2.18 Factors
affecting reaction rate
Figure 2.17 Enzyme action

Temperature affects the amino acid chains in enzymes. Each enzyme has a
temperature at which it works best or at the optimum rate. At temperatures below
the optimum, the reaction occurs slowly. At temperatures above the optimum, the
temperature causes changes in the shape of the enzyme. This means that the active
site is no longer the correct shape to catalyse the reaction and the rate of the
reaction will slow down. At high temperatures the enzyme shape changes so much
that it is said to be denatured, that is, it is not able to catalyse the reaction.

Activity 11 Enzyme reactions Materials:

Aim: To investigate the action of an enzyme. Starch solution

Make up a 4% starch solution by dissolving starch in boiling water. Allow the Iodine
solution to cool. Saliva

Take a small sample of the starch solution and

test it for glucose by adding two to three
drops of Benedict’s solution and heating it.
A blue colour indicates no glucose is starch saliva

present. saliva starch Benedict’s

Dribble some of your saliva into a small mixture solution

beaker and dilute it with an equal volume iodine

of water. Test a small sample of this saliva

to make sure no glucose is present.
Mix the remaining saliva with an equal
volume of the starch solution. Keep the
mixture at body temperature (37oC).
starch test
Take samples of this mixture every two
glucose test
minutes and test for both starch and for
glucose.
Write a report on this investigation.

UNIT 2
74

Activity 12 Temperature and enzyme activity

Aim: To plan, carry out and report on the effect of temperature on
enzyme activity.

Use the reaction you investigated in the previous activity as a starting point for
your plan. In your plan identify the following and describe how you will use
them to investigate the effect of temperature on the rate of an enzyme
controlled reaction:
❑ independent variable
❑ dependent variable
❑ controlled variables
❑ repeats.
Carry out your plan and collect the results.
Write out a report on your investigation.

Activity 13 Enzymes
Matching terms with definitions.
enzyme a the amount of energy needed to start a reaction
catalyst b a biological catalyst
intracellular c the process of releasing energy from food using oxygen
extracellular d the chemical that an enzyme acts upon
energy barrier e splitting glucose into two pyruvic acids
active site f occurs within the cell
substrate molecule g carries small amounts of energy about cell
ATP h occurs in the absence of oxygen
glycolysis i results in alcohol and carbon dioxide gas
aerobic respiration j reduces the energy barrier of a reaction
anaerobic respiration k occurs outside the cell
fermentation l the part of enzyme which substrate fits into

True or false?
Decide whether the following statements are true or false. Rewrite the false
ones to make them correct.
a Each enzyme can catalyse a wide range of reactions. b
Without enzymes most cell reactions would not occur.
c Enzyme-controlled reactions slow down at temperatures above 45°C. d
Mitochondria contain enzymes that control the process of respiration. e In
exercise, a muscle can build up lactic acid due to insufficient oxygen. f The
alcohol produced in wine-making comes from aerobic respiration.

BIOLOGY YEAR 12
 75

Interpreting a chemical reaction.

In the photo, apple slice A was left in the air for 24 hours; slice B was boiled
then left in the air for 24 hours; and slice C is freshly cut.
a Describe slices A, B and C.
b A student suggested that what happened to slice A was due to the action of
an enzyme in the fruit. Do you agree? Why? Figure 2.19 Apple slices
c Does the appearance of slices B and C support the hypothesis that
enzymes are involved in slice A?
Interpreting an experiment.
You can study the activity of an enzyme by using peroxidase. The peroxidase
enzyme is present in most cells and it reacts with hydrogen peroxidase and
rapidly breaks it down to release oxygen gas. If you place living cells in a
weak hydrogen peroxide solution, bubbles of oxygen gas (froth) indicate the
activity of peroxidase.
Three test tubes, each with a weak hydrogen peroxide solution, were set up as
shown and left for two minutes.
What do tubes B and C indicate about peroxidase?
Explain the difference between B and C
results. Peroxidase Experiment
What does A show?
A further tube was set up using crushed froth
raw potato. The result was similar to
C. What does this indicate about A B C
peroxidase? cooked ground-up raw
liver liver liver
Suppose you are asked to design an
experiment to test the effect of increasing temperature on peroxidase from
an animal liver.
What temperature range (lowest to highest temperatures) would it be
appropriate to test?
How would you set up the experiment so you could measure the effect of
increasing temperature.
The data shows the results of an experiment into the effect of temperature on
enzyme action.

Temp. Froth Height

20°C 12 mm
25°C 26 mm
30°C 54 mm
35°C 73 mm
40°C 82 mm
45°C 2 mm

Plot the data on a graph.

What does the graph show up to 40°C? Why does this occur? i
What does the graph show above 40°C? Why does this occur?

UNIT 2
 Unit

3 Genetics
Genetics is the study of inheritance, that is, the way in which characteristics, or
distinguishing features or qualities pass from one generation to the next. This unit
is divided into sections that cover cell division and inheritance.

Cell Division
In this section you learn to:
❑ explain the relationship between chromosomes, DNA, genes and alleles ❑
describe the behaviour of chromosomes in mitosis and meiosis
❑ explain the importance of meiosis in reducing the chromosome number ❑
discuss the role of meiosis and fertilisation in mixing genetic material.

Zygotes and chromosomes

❑ Life begins as a single-celled zygote formed when a sperm fertilises an egg.
The zygotes of humans, chimps and horses all look the same yet they develop
into different organisms. Why?
❑ The zygote nucleus contains many chromosomes, and each chromosome is
made of several thousand genes.
Figure 3.1 Zygote
genes

chromosome

Figure 3.2 Chromosomes

❑ All the genes in an organism’s zygote are called the organism’s genome. The
genome specifies (decides in detail) what species the organism will be and its
particular characteristics.
❑ Chromosomes are very long, thin thread-like structures which can coil up
Figure 3.3 Coiled up tightly into short, fat shapes. Chromosomes in this state are visible under
chromosome with a the microscope as cells divide.
duplicate ❑ All members of a species have the same number of chromosomes at the
zygote stage. The number of chromosomes is always an even number, e.g.
human zygotes normally have 46, chimp zygotes 48 and horse zygotes 64.

76
 77

❑ The chromosomes in a zygote have different sizes and shapes, but they can be Human Chromosomes
arranged into matching pairs. Human zygotes have 23 matching pairs. These
matching pairs are called homologous chromosomes. One chromosome of
each pair will have come from an egg and the other from a sperm. Human – arranged in 23 matching
egg and sperm have 23 each.
❑ Usually you inherit two genes for each characteristic – one gene from each or homologous pairs, each
parent. If one of those genes is at a site on a particular chromosome, then the
with a duplicate attached.
other gene will be found at the same site on the other homologous
chromosome.
Figure 3.4 Human
Chromosomes and genes chromosomes

❑ Chromosomes are complex structures made of molecules of

deoxyribonucleic acid or DNA for short. How does DNA carry genetic
information? gene gene
from from
❑ Each chromosome is made up of two long DNA molecules. Each DNA egg sperm
molecule has millions of chemicals called bases attached at regular
intervals along its length. There are only four types of bases, which are
called C, G, A and T for short.
❑ The two DNA molecules join together to form a ladder-like structure with
millions of rungs. Each rung of the ladder is formed by a pair of bases – a
base on one strand is attracted to a base on the other. But C bases can only fit
with G bases, and A bases can only fit with T bases.
❑ The scientists Watson and Crick discovered that the ladder structure is
twisted into a helix (a spiral shape). As there are two DNA molecules homologous
pair
involved they called this structure the double helix.
Figure 3.5 Homologous
one DNA molecule Double Helix Structure of DNA pair

‘rung’

other DNA molecule pair of bases (C with G, and A with T)

Figure 3.6 DNA

❑ Along each DNA molecule is a sequence of over a million bases, e.g.
ATTCCGATGGACTCGGAATCTCTT. . . Watson and Crick proposed
that a gene was actually a length of DNA several thousand bases long.
❑ Next, they proposed that the information carried by a gene is encoded in the
sequence of bases along a section of one of the DNA molecules. Just as Morse
code uses so many dots and dashes to represent a letter of the alphabet (three
dots represents ‘s’ and a dash and three dots represents ‘b’) so the genetic
code uses an ‘alphabet’ of just four bases which are arranged in triplets
(groups of three), e.g. ATT-CCG-ATG-GAC-TCG-GAA-TCT-CTT-. . .

Chromosones are made of DNA

A gene is a length of DNA DNA double helix

gene A gene B gene C

Figure 3.7 DNA double helix

UNIT 3
78

❑ The unique sequence of bases that make up a particular gene decides what the
structure of a unique protein will be. That protein then becomes part of
deciding the appearance of a particular characteristic. Each of the 80 000 plus
genes in your genome determines a different protein, which in turn determines
the appearance of a particular characteristic (e.g. your hair or eye colour).

A gene codes for a protein which determines a trait, e.g. blue eyes.

Mitosis
❑ A new organism grows from a single-celled zygote to an adult organism by
mitosis. Mitosis is when a cell divides to make all new cells except sex cells.
One cell divides into two, they each divide to give four, each of which divides
to give eight and so on. Eventually, the adult organism consists of billions of
body cells, each with an identical set of chromosomes
(e.g. human body cells all have 46 sets of chromosomes).

Mitosis in a Cell with Four Chromosomes

body cell
at start of 2. original
process 4 chromosomes
are duplicated
spindle

3. chromosomes
4 line up on the
spindle

4 5. cell divides
into two

4. spindle pulls
chromosomes
apart

Figure 3.8 Mitosis

❑ Early in mitosis, when chromosomes shorten, each chromosome appears with
an identical copy or duplicate attached. As mitosis proceeds duplicated
chromosomes are separated, resulting in each new cell having an identical set.
❑ Mitosis takes place where new body cells are being formed.

Passing on chromosomes
Genes pass from one generation to another on the chromosomes inside the gametes
(egg and sperm). Gametes are formed by the process of meiosis, which occurs in a
woman’s ovaries and a man’s testicles. Gametes have half the number of
chromosomes that body cells have and each gamete has a different collection of
chromosomes.

How does meiosis achieve this?

Meiosis consists of two cell divisions which result in four gametes. During meiosis the
original cell divides twice but the chromosomes are duplicated only once, so gametes
end up with half the normal number of chromosomes. The chromosomes are duplicated
early on. Duplication of chromosomes involves DNA self-replication.

BIOLOGY YEAR 12
 79

DNA Self-Replication
original 1. two DNA
code strands unzip
strand new code
strand
a new strand is built
onto each old strand

original anti-code
strand
new anti-code strand

Figure 3.9 DNA self-replication

❑ In the first division (first stage) homologous chromosomes separate. First they
are brought together and lengths of chromosomes are swapped. The
chromosomes then pull apart so that the two new cells get one chromosome
from each homologous pair. As members of pairs randomly separate each new
cell has a different collection of chromosomes.
❑ In the second division (second stage) the duplicated chromosomes separate
so there are gametes with only half the number of chromosomes as body
cells. Because each gamete gets only one chromosome from each
homologous pair, a gamete will have only one gene for each characteristic.
But a zygote will have two at fertilisation.

Meiosis in a Body Cell with Four Chromosomes

first cell second cell 5. cells divide
division division
1. each 2. homologous
chromosome chromosomes
duplicated join together

original body 3. homologous

cell with four chromosomes 4. duplicate
chromosomes
separated in
chromosomes
first division line up and
begin separating
gametes with only two
chromosomes

Figure 3.10 Meiosis in a body cell with four chromosomes

Remember: mitosis is a cell division which produces all new cells except sex cells
and meiosis is cell division which produces sex cells.
The following table compares the processes of mitosis and meiosis.
Mitosis Meiosis

Number of cells produced 2 4

Number of chromosomes Daughter cells have the same Daughter cells have the half the
number of chromosomes as number of chromosomes as the
the first cell first cell
Number of division One Two
Occurs in Some body cells of adult animals Only occurs in the reproductive
(e.g. skin) but not others (e.g. nerves) organs, ovary and testis
Purpose Growth, repair and replacement To produce gametes
of cells

UNIT 3
80

Meiosis produces gametes with only half the normal number of chromosomes.
Gametes must have half the number of chromosomes so that when fertilisation
occurs, and the genetic material from an egg and a sperm come together in the
zygote, the zygote will have the correct number of chromosomes.

Meiosis

Each parent has a unique combination of

genes.

2 chromosomes 2 chromosomes
A homologous pair of
chromosomes contains genetic
material from two parents.

During the first part of meiosis

the homologous chromosomes
pair, break apart and rejoin, often
resulting in sections of the
genetic code swapping over.

The second part of meiosis

results in gametes which each
have only one of the pair of
chromosomes – which has a
unique pattern of genes.

Fertilisation results in the

restoring of the original number
of chromosomes and those
chromosomes contain a unique
combination of genetic material
from both parents and
grandparents.

Figure 3.11 Human life cycle

BIOLOGY YEAR 12
 81

Activity 1
Match up definitions with terms.

zygote the shape which two DNA molecules form together

special sex cells with half the normal number of
nucleus
chromosomes
chromosomes the total collection of genes possessed by an organism d
the molecules which chromosomes are made out of e
gene
genes are expressed through these molecules
genome a group of similar organisms able to interbreed
successfully
characteristic
the long, thread-like structures which carry the genes h
species the ability of DNA to make duplicate copies
cell division which produces four gametes each
DNA
with half the normal number of chromosomes
homologous a pair of chromosomes, one of which came from
chromosomes each parent
the first cell of an organism after a sperm fertilises an
bases egg
double helix cell division which gives two cells with identical
chromosomes
genetic code the feature of an organism which is determined by
genes
proteins
these form the units of the genetic code
mitosis the structure within a cell which contains the
chromosomes
self-replication
the code which is used to specify information
gametes carried by genes
an inherited object which determines the
meiosis appearance of a characteristic

For each of these points explain the difference between the terms. a
gene and genome
b identical and homologous chromosomes c
body cells and gametes
d mitosis and meiosis.
Copy and complete the table then answer the questions below.
Number of Chromosomes in . . .
Species Egg Sperm Zygote Body Cell

humans 23 23 46 46
chimps 24 24 48
horses 32 64
dogs 78 78
cats 19

UNIT 3
82

What process makes sure that gametes have half the number of
chromosomes compared to body cells?
What process makes sure that a zygote has twice as many chromosomes as
gametes?
What process makes sure that body cells have the same number of
chromosomes as the zygote?
Decide whether the following statements are true or false. Rewrite the false ones
to make them correct.
a In sexual reproduction a zygote is the first stage of a new organism. b
Your genome is the complete collection of genes that were in your
zygote.
c All species have the same number of chromosomes.
d All members of a species have the same number of chromosomes in each of
their body cells.
e Normally you have two genes for each characteristic, one inherited from
each parent.
f Chromosomes are made of DNA and a gene is a length of DNA.
g The genetic code uses an ‘alphabet’ of four bases which are arranged into
three-letter ‘words’ called triplets.
Genes are expressed (that is, produce an effect) through proteins which
determine the appearance of a characteristic.
Chromosomes are duplicated by the process of DNA self-replication.
Mitosis produces four gametes with half the normal number of
chromosomes.
The diagram opposite shows the chromosomes in a body cell early on in mitosis
cell division. Note that each chromosome has a duplicate attached.
a What type of organism is this body cell likely to come from? How do you
know?
b Why have the chromosomes been duplicated?
c How many duplicated chromosomes are there in total? d
What produced the duplicated chromosomes?
e After cell division, how many chromosomes will each new cell have?
chromosome with duplicate

Figure 3.12 Chromosome

with duplicate

The chromosomes in Figure 3.13 were cut out and arranged into matching pairs
as shown in this diagram.
a How many pairs are there?
b What features are used to match up the chromosomes? c
What are these pairs of chromosomes called?
d Where did each member of a pair originally come from? e
Which pair is strange? Why?
Figure 3.13 Matching
chromosomes

BIOLOGY YEAR 12
 83

Label structures a) to e), then answer the questions below. f A B c)

a)
What type of cell division is shown?
C
How do you know?
What has happened to the chromosomes by stage B? b)
e)
What is happening to the chromosomes at stages C and D? E D

What two statements can you make about the chromosomes in the two
d)
cells shown at stage E? (number and nature)

Figure 3.14 Chromosomes

Label structures a) to e), then answer the questions below. f

d) D
What type of cell division is shown?
b) B C E
g How do you know? A
a) c) E
Where would this process be taking place in male and female
animals?
What has happened to the chromosomes by stage A?
D
What is happening to homologous chromosomes in stage B? k e)
What type of chromosome pairs have separated by stage C? l
What type of chromosome pairs are separating at stage D? Figure 3.15 Cell division
What two statements can you make about the chromosomes in the four cells
shown at stage E compared to the chromosomes in the original cell?
(number and nature)
If this process was occurring in a male what would the four cells
produced be called?
Read the passage below, then answer the questions.

The human genome project

The Human Genome Project aimed to identify all of the 30 000 genes
that humans possess and to determine the sequence of the three
billion base pairs that make up human DNA.
A genome is all the DNA in an organism at the zygote stage. This DNA contains
coded information for all the genes, but much of the DNA is redundant (having
more than it needs) and does not code for anything. So sequencing all of the
DNA takes much longer than finding the location of the genes.
The DNA is found in the 23 pairs of chromosomes that all human
body cells have. Teams of geneticists sequence the DNA of different
chromosomes or sections of chromosomes.
DNA is made up of four bases (C, G, A and T) that are repeated
millions of times in the genome. The order of Cs, Gs, As and Ts is
important. It decides if an organism is human or another species.
Because each person’s genome is unique (except for identical twins) and
samples from different people will be used, the reference genome will not
be an exact match for any one person’s genome. Geneticists estimate
that we differ in about 0.1% of our three billion base pairs.
Genes are lengths of DNA several thousand bases long and they
code for all the proteins in the body. These proteins determine the
structure, appearance and functioning of our bodies.

UNIT 3
84

Scientists isolate a protein and, from the way it is composed they identify
the sequence of bases of the gene. The task of the scientist is called
‘sequencing’. The scientists identify which chromosome carries that
sequence and where along that chromosome the sequence is. Because
each chromosome is millions of bases long, this is a difficult task.
The first stage of the Human Genome Project, which was to
determine the sequence of the 3 billion base pairs that make up
human DNA, was completed in June 2000.

What are the two aims of the project?

If we have about 30 000 genes and 23 distinct chromosomes, on average how
many genes does a chromosome carry?
If there are 3 000 000 000 base pairs in the genome – on average how
many base pairs long will a chromosome be?
What units are used in the genetic code?
Why will the reference genome not be any one particular person’s?
What percentage of the reference genome will be common for everyone?
How do geneticists map where the gene for a particular protein is
located?
When was the sequencing of the base pairs completed?
Study the diagrams below showing the processes of meiosis and mitosis, then
answer the questions underneath.

A B
23 46 46 46

23
46 23 46 46 46

46
23

Why are these diagrams likely to be of human cells?

Give two reasons why diagram A shows meiosis, and two reasons why
diagram B shows mitosis.
What are the functions of mitosis and meiosis?

BIOLOGY YEAR 12
 85

Inheritance
In this section you will learn to:
❑ investigate examples of continuous variation and discrete variation ❑
compare continuous variation and discrete variation
❑ solve monohybrid inheritance patterns involving complete dominance and
sex determination, e.g. punnett squares, family trees, resource material
❑ explain the role of the X and Y chromosomes in determining the sex of the
individual
❑ discuss examples of inheritance patterns in terms of: characteristics, traits,
genes, alleles, dominant alleles, recessive alleles, genotype, phenotype,
homozygous, heterozygous.

Variation
The range of variation among living things is so enormous that at first you might A bell-shaped curve
Graph measuring length in sea horses
think there is no pattern to it. One role of science is to measure things and try and
find patterns that help us to understand the world around us. Measuring variation
and recognising patterns has led to some important scientific discoveries.

Samples
When you measure variation patterns your first job is to make sure that your Skewed curve
sample is large enough. The size of your sample to be measured must be large so Graph measuring running speed of rabbits

that if you add more numbers to it there is very little difference to the pattern that
has appeared. Once this meant that plotting data was a huge task. Now the use of
computers makes the handling of large numbers much easier.

Bell-shaped or ‘normal’ curves Either/or graph

Graph measuring tongue-rolling ability.
Scientists found that when data on variations is plotted it so often forms a curve the
shape of a bell that this pattern became known as a ‘normal’ curve. This shows that
the greater the variation from the average the less often it occurs (Figure 3.16).

can cannot
Sometimes the curve of variation may be skewed which shows that most individuals’
variations are nearer to one end of the range of variations. See Figure 3.16. Figure 3.16 Bell curves

Either/or variations
You probably know from earlier studies that not all variations follow a wide range.
Some features are quite clear-cut. They are either one or the other of two
possibilities. In humans some of the best known examples of either/or variations
are tongue-rolling ability and earlobe shape (fixed or free).
It was the recognising of either/or patterns like these that led to the first breakthrough
in understanding how inheritance works. It has also led to our being able to predict
inheritance patterns. For example, you can predict that in any class of 30 students three
people are left-handed. Does this fit in your class? You may find your sample size is
too small. However, in the whole population the ratio has been found to be 1 in 10. So
how many left-handers would you expect in a school of 800 students?

UNIT 3
86

Activity 1 Interpreting variation

From the information on this page and your own knowledge try the following:
Divide the following human variations into either/or and gradual variations: eye
colour, skin colour, cleft chin, freckles, length of index finger, sex.
Think of reasons why a population of rabbits shows a skewed curve, when
their speed of running was measured.
Draw frequency graphs that you would expect for the following (put range of
variation on the horizontal axis and numbers on the vertical axis):
a body length in ulava‹ or freshwater shrimps
b flower colour in poppies (orange through to yellow) c
coconut tree height in a plantation grown naturally
d coconut tree height in a population grown from genetically selected ones for
tallness.

Activity 2 Patterns of variation

This activity is to measure variation in a large sample.
When you study patterns of variation you need plenty of data to make sure that any
patterns that you find are not too influenced by chance. With computers as a tool to
cope with large volumes of data, teams of people can investigate very large
samples quite easily.
Choose the investigation topic
Discuss with your teacher the example of variation the class wishes to
measure. You need a type of continuous variation for which you can obtain
large numbers of samples quite easily (e.g. leaf size in one species of shrub
in the school grounds or the height or weight of students in the school).
Work out the measurement details
Decide exactly what you are going to measure. The whole class must use the
same units and must use the same size groups so everybody’s results can be
compared.
3 Set up research teams
Divide the class into six research teams.
Gather the data
Each team must have four separate sets of data – numbered 1 to 4. A
Data collectors – should measure the samples.
B Data recorders – should fill in a separate record table for each collector
and add up the totals.
C Data processors – should calculate means for individual collections
and for the team.
Draw graphs
Draw graphs of the data from each person in your team.
Analyse the data
❑ Compare the results of one collector in your team with the other collectors
in your team and with the collectors in other teams. How does the overall
mean for one collector compare with the team and class mean?

BIOLOGY YEAR 12
 87

❑ Use the graphs that show the measurements for increasing numbers of
collectors. What happens to the results when the number of collectors
increases?
❑ When the graph stops changing greatly, even after more collectors are
added, you have reached the minimum size for an accurate sample. What
number of sample collectors is needed?
Present the results
Make a display of your results for the class or Science Department
noticeboard. Make sure students from other classes who look at the display
will understand exactly what you did and what you found out.

Regular ratios
When scientists analysed clear-cut variations they began to understand how
inheritance works. They saw that inheritance follows definite rules. Often when
they counted large samples they saw quite clear ratios. For example if green and
blue budgies are mated, about three out of four of the offspring will be green with
only about one in four blue. We can also predict that the ratio of tongue rollers to
non-tongue rollers in a class will be 3:1. Do pairs of either/or ratios always follow
a regular pattern?

Activity 3 Either/or ratios

Class ratios
In your class check if:
a The ratios of tongue rollers to non-tongue rollers will be approximately
3:1.
b The first of the following is more common than the second:
free ear lobes / fixed ear lobes
straight thumb / hitchhiker’s thumb
straight hairline / widow’s peak.

Activity 4 Our ancestors exploit variation

How would a dog have been useful to prehistoric hunters?
How would the planting of crops have affected the lifestyle of people?
How would the early farmers have been able to improve the quality of their
sheep and cattle?
Name a plant that was brought from America and is now an important crop in
Sämoa.
Choose a modern domesticated (tame) animal. Use three columns and list: a the
original characteristics that caused it to be domesticated
b the characteristics that would have been culled out
c the characteristics that would have been selected for.
Wild strawberries are tiny, rather tasteless fruit with lots of seeds. Draw
diagrams of wild and farmed strawberries and label them to show the
difference selection has made. Underneath the diagram write down any
difficulties the cultivated strawberry may have.
Modern wheat has been selected for many years. List features that would make
it difficult to survive in the wild.

UNIT 3
88

The following are data on hair colour that a student collected from other students.
Complete the table by calculating the percentages, then plot those percentages
on a pie graph. (Remember: 10% = 36°)
Hair Colour Number % of Class

brown hair 13
black hair 7
blonde hair 3
auburn hair 2

What type of variation is shown by this trait?

Read the passage below, then answer the questions.

The cloning of Jill the calf

❑ On 16 April 1998 the New Zealand scientist Dr. David Wells from
the Agresearch centre at Ruakura announced the first successful
cloning of a calf in the Southern Hemisphere. Born in March 1998,
Jill the calf is the offspring of a single ‘parent’.
❑ The team used methods pioneered by Scottish scientists who
cloned the first mammal in 1997.
❑ Jill’s ‘parent’ was not an adult cow but a 34-day old embryo. A body cell
was removed from this embryo and the nucleus extracted. The nucleus
contained all the chromosomes of the ‘parent’. An unfertilised egg was
taken from an adult cow and the nucleus of the egg removed and
discarded. This egg no longer contained any chromosomes.
❑ The nucleus from the body cell of the embryo was then inserted into the
‘empty’ egg. This egg now had all of the ‘parent’ embryo’s chromosomes.

❑ The egg was subjected to an electrical current which started cell

division. After multiple divisions, the egg developed into a new
organism made of millions of cells. Each cell had a set of
chromosomes identical to those the ‘parent’ embryo possessed.
❑ Growth and development continued as normal. Cells specialised
and developed into tissues. Eventually Jill the calf was born.
❑ If scientists can apply the technique to many body cells from a single
embryo, then they could rapidly clone herds of identical cows.

What does the term ‘cloning’ mean?

Why is cloning a method of asexual reproduction? c Is
cloning a natural or artificial method?
d What was in the nucleus extracted from a body cell of the embryo? e
Why was the nucleus of the unfertilised egg discarded?
What process made sure that all Jill’s cells contained an identical set of
chromosomes?
How could a scientist produce a cloned herd?
What might the potential benefits be of a cloned herd of animals? i
Why do many people object to the idea of cloning humans?

BIOLOGY YEAR 12
 89

Below are the left foot lengths of 40 students. Copy and complete the table by
adding up the tally for each length interval. Put the data on a bar graph, then
answer the questions below.
Length (cm) Tally Number

12.0–14.9 ✓
15.0–17.9 ✓✓✓
18.0–20.9 ✓✓✓✓✓✓✓
21.0–23.9 ✓✓✓✓✓✓✓✓✓✓✓
24.0–26.9 ✓✓✓✓✓✓✓✓✓
27.0–29.9 ✓✓✓✓✓
30.0–32.9 ✓✓✓✓
33.0–35.9 ✓

Is this an example of either-or, multiple or continuous variation? b

What sort of shape does your graph have?
c What is the mode (most frequent measurement) of the data?
Do you think differences in foot length are because of acquired or
inherited variation? (Give a reason for your answer.)
Plotting variation.
These are the heights of 18-year-old students.
Height Range Number

148–151 cm 1
152–155 cm 4
156–159 cm 4
160–163 cm 8
164–167 cm 11
168–171 cm 18
172–175 cm 12
176–179 cm 7
180–183 cm 2
184+ cm 1

Draw a bar graph of the data. Describe the distribution of heights. b

What type of curve is the graph like?
c Is height a continuous or discrete variable?
Since the start of the 20th Century, the average height of adults has steadily
increased. Do you think this is due to inheritance or upbringing? Give your
reasons.

UNIT 3
90

Interpreting variation.
About 75% of humans are right-handed, another 15% are predominantly right-
handed and 10% are predominantly left-handed. Right-handed parents usually
have right-handed children. For left-handed parents, half of the children tend
to be right-handed and the other half left-handed.
Is handedness continuous or discrete variation?
What evidence suggests that handedness is inherited?
The current view is that it is because of a single gene. The dominant gene
R+ strongly tends to cause right-handedness, but the recessive form of the
gene R– causes no bias in handedness.
Why would a person with just one R+ gene be right-handed? d
What genotype do left-handed people have?
e Why can offspring of left-handed parents be either left- or right-handed? f
Why are large numbers studied?

The study of genetics

At least 8000 years ago humans were already improving crops by selecting good
examples from existing crops. However, the plants selected were often the result of
variation in environmental conditions and their features were not inherited. In the
18th Century many plant breeders developed a method called hybridisation. If
they artificially crossed varieties of self-pollinating plants and then selected the
offspring for a number of generations they could produce stable forms that had
Figure 3.17 Sweetpea improved features from both parents.
The breeders noticed that they produced a generation by cross-fertilisation that was
fairly uniform but later generations were variable. They could not explain why.

Gregor Mendel (1822–1884)

The real breakthrough in our understanding of inheritance first came when a monk
named Gregor Mendel tested his ideas about the natural laws of inheritance in
experiments which he carried out in a very careful, patient and scientific way.
Mendel was a teaching monk who worked in the monastery garden. He chose
garden peas for his experiments. This was a good choice because garden peas are
normally self-pollinated plants and Mendel could artificially cross two varieties. He
could then follow the inheritance of their characteristics in future generations
without worrying that stray pollen from other plants might complicate results.
P
tall X short Mendel also was lucky he chose the garden pea because at that time existing
varieties showed seven pairs of contrasting characteristics (such as tall or dwarf
plant height and smooth or wrinkled seeds) which were inherited in a way that was
F1 X all tall
straightforward and easy to observe. But it wasn’t because Mendel was lucky that
he discovered the key to inheritance. You can see his careful, logical and scientific
approach in the following list of ideas that he used in planning his experiments.
F2 variable

Figure 3.18 Inheritance

BIOLOGY YEAR 12
 91

Mendel’s ideas
❑ Find distinctive either/or traits like tall and short in peas. ❑
Look at one characteristic at a time to start with.
❑ Use plants to work out the rules because pollination can be controlled.

❑ Use large numbers of identical matings to minimise chance effects. ❑

Analyse the results mathematically and look for ratios.
❑ Use the ratios to predict the outcome of further crosses to check the theory.

Mendel’s F1 cross Mendel’s F2 cross

showing cross between parent plants – tall showing second filial generation cross
and dwarf with F1 plants all tall. with 3⁄4 tall and 1⁄4 dwarf – Mendel’s
actual numbers are shown.

P1 X F1
F1 X

F2 787 277
all tall

Figure 3.19 Mendel’s F1 cross

Mendel’s F1 cross
One of Mendel’s experiments was a study of height in peas. This is called a
monohybrid cross because there is only one set of contrasting traits (i.e. height –
tall or short). His first parent or P1 plants were pure-breeding tall and short peas.
He took pollen from large numbers of the tall peas and used it to cross-pollinate the
dwarf ones. The dwarf ones had had their stamens removed so could not self
pollinate.
When he grew the seeds, he found that the plants were all tall. These offspring
were the first filial or F1 generation (filial refers to son or daughter). He concluded
that tall was dominant over dwarf and gave the tall traits the symbol capital letter
T and the dwarf small t. In about 1910 scientists began referring to traits – either
dominant or recessive – as genes, and contrasting genes controlling the same trait
set were termed alleles.

Mendel’s F2 cross
Mendel allowed the peas in the F1 generation to self-pollinate and collected their
seed. When this second filial or F2 generation matured, he found that three-
quarters of them were tall and one-quarter were short, a ratio of 3:1. There were
slightly more than 1000 plants in this sample. Imagine Mendel’s patience in
growing and analysing this many plants! This result showed that the dwarf allele
was not lost. It also showed there were no ‘in between’ types. He concluded that
each pea had two factors or alleles for height, one inherited from each parent.
These two alleles formed a gene pair. The gametes, the reproductive or sex cells,
each carried one of these alleles.
The genotype (structure of the alleles) of the F1 tall plants were different from the
alleles of the P1 (parent) tall plants and pure-breeding dwarf plants were said to be
homozygous (homos, same) because each has two identical height alleles,
and tt. The F1 plants resulting from the first cross got one tall allele, T, from the
pollen of the tall plant and one dwarf allele, t, from the ovule of the dwarf plant.
Their genotype Tt was heterozygous (heteros, different).

UNIT 3
92

Mendel carried out similar breeding experiments in which he used the other six
contrasting gene pairs in peas and in each case he got a similar pattern of results.
He later extended his work to find out how more than one set of traits were
inherited at one time. All this research allowed him to formulate some rules which
we now call Mendel’s Laws. These allowed the outcome of crosses to be predicted
when inheritance of a trait is uncomplicated.
Mendel published his results in a little-known journal in 1865 and at the time their
importance was not recognised. It was not until the early twentieth century, after
Mendel’s death, that other people rediscovered his work. Inheritance is seldom as
simple as in Mendel’s examples, and genes are often affected by other genes and
by other factors. However his work gave plant and animal breeders important
information to work from. It was a great scientific discovery.

Table 3.1 Results from Mendel’s breeding experiments

Parent traits F2 (second generation) nos. Ratios

tall x short stems 787 long : 277 short 2.84:1

yellow x green seeds 6022 yellow : 2001 green 3:01:1
round x wrinkled seeds 5474 round : 1850 wrinkled 2.96:1
green x yellow pods 428 green : 152 yellow 2.82:1
axial x terminal flowers 651 axial : 207 terminal 3.14:1
inflated x constricted pods 882 inflated : 299 constricted 2.95:1
red x white flowers 705 red : 224 white 3.15:1

Activity 5 Interpreting Mendelism

The rules about inheritance are not difficult, but you need to understand all the
technical terms. Write down definitions of each of the terms in bold type.
(Use the glossary in this book or a dictionary if you are stuck.)
Mendel made his breakthrough discoveries because he used good scientific
methods. Explain how:
a he was patient
b he used scientific methods
c he analysed his results carefully by using his mathematical skills d
he reduced the possibility of chance results
e he had some luck.
How can you check to see if he invented his results?
Write a sentence to explain why it was important that the environmental
conditions did not vary much in the monastery gardens where Mendel grew
his plants.
From the table of Mendel’s results work out the average ratio for the seven
experiments. None of these ratios is exactly 3:1. Explain why these results
are good evidence that a prediction of 3:1 is pretty accurate.
In your group, design and carry out an experiment of tossing a coin to get
heads or tails, to test that the effects of chance reduce as the sample size
increases.

BIOLOGY YEAR 12
 93

Mendel’s experiments showed that traits may be in pairs, that one trait is more
powerful than the other, and that traits are inherited by chance from each parent.
We can show that the laws of chance operate in the pea traits that Mendel
measured without having to do all the work that he did.

Table 3.2 Dominant and recessive alleles

Dominant trait and allele Recessive trait and allele
Round seed, R Wrinkled seed, r
Inflated pods, I Constricted pods, I
Yellow seeds, Y Green seeds, y
Coloured seed coat, C White seed coat, c
Axial flowers, A Terminal flowers, a
Green pods, G Yellow pods, g
Tall plants, T Dwarf plants, t

Note that the symbol for each trait is a letter – the same letter for each trait but
shown as a capital if the trait is dominant and a small letter if it is recessive.

Activity 6 Card game: Inheritance in peas

Play these games in pairs. Play them on the grid of 25 squares that you create. The
five squares across, and five squares down. Cards with pictures represent the pea
traits.
Each group of two players chooses one of the contrasting pea traits that Mendel
studied. These are shown in the table above.

Game One
Testing for dominance
Each pair of players chooses a pair of contrasting traits.
One player makes 20 cards for the dominant allele while the other makes 30 for
the recessive allele. Keep 10 of the recessive cards aside for the second board
game, the test cross.
Each card is to be no bigger than the grid spaces that are
created.
3 On each card choose a bright symbol for the dominant allele and a
dull one for the recessive allele. Write the allele symbol in a large
letter on each card, with dominant symbols in capitals and
recessive symbols in small letters.
Your cards now represent Mendel’s parent (P1) generation and
each card is a sex cell or gamete.
5 Each of you shuffles your cards and deal one card onto each square. Figure 3.20 Games cards

Place any dominant cards on top.

Copy the tally sheet on the following page and enter the appearance or
phenotype of these F1 offspring.
Now take half of the offspring each and shuffle them. You are now acting as if
you are the self-pollinating P2 (second generation) parents.

UNIT 3
94

Tally Sheet Shuffle and deal your cards, or sex cells, as before. Add up your F2
phenotypes.
Dwarf Tall
Repeat this procedure five times so that your results represent 100 crosses.
F1 Alternate the alleles you start off with.
F2 Add up the totals for the phenotypes of the F1 and F2 generations and
F2 express them both as percentages and as the nearest simple ratio.

F2 SUMMARY: Discuss the outcome of the game as a class and find out if each
group got similar results. Write down what this suggests to you about
F2 Mendel’s interpretation of his results.
F2
Game Two
Total for 100
Testing for hidden alleles
Ration

Figure 3.21 This is an Phenotypes were all Mendel could see. He could tell that individual F2 plants with
example of the score sheet the dominant trait had at least one dominant allele. But he could not tell if there
that you will need to record were two dominant alleles or if one was a hidden recessive allele. However if his
your results. Copy it, but theory about alleles was correct there was a way of checking.
do not write on it.
He could do a test cross or a back cross. This is what Game Two does.
The player representing dominant must decide to be either homozygous or
heterozygous. Choose 20 cards to represent sex cells from this individual
(20 dominants for homozygous or 10 of each for heterozygous).
The other partner represents a homozygous recessive and needs 20 recessive
cards. You may need the extra 10 cards.
Each shuffle your cards and deal one onto each square of the grid. Tally the
phenotypes.
Repeat the game, this time using the other dominant phenotype (the one not
chosen in No. 1). Cross it with the homozygous recessive as you did last time
and tally your results on a tally sheet.
SUMMARY: Discuss the outcome of the second game in class. Did all pairs
get the same results?
Questions
What does the appearance of even one recessive offspring tell you about the
genotype of the dominant parent for this trait?
Can a homozygous dominant parent ever have offspring that are recessive for
this trait?
Why do we need to study large numbers in genetic studies?
If you plant seeds labelled F1 would you expect seeds collected from them to
breed true? Explain your answer.
Why do you always use a homozygous recessive for a test cross?

BIOLOGY YEAR 12
 95

Genetics rules
A pair of genes contributes traits.
Genes for the same characteristic are called alleles.
Dominant alleles hide recessive ones.
Phenotype describes the way a characteristic appears.
Genotype lists the alleles present, three possible ways two alleles can combine
in cells.
Sex cells or gametes have one allele for each characteristic.
In a test cross, dominant phenotypes cross with recessive. Recessive
offspring show that the dominant has a masked recessive allele.
In heterozygous individuals one allele is dominant and one recessive.
NOTE: These are pretty much the rules that Mendel worked out to
explain what happens. He did not know about genes and chromosomes so
could not explain how it happened.

Genetics problems
Phenotype and genotype
❑ Gametes have one gene for each characteristic. At fertilisation, when a
sperm fuses with an egg to give a zygote, the new organism has two genes for
each trait – one inherited from each parent.
❑ The appearance of a characteristic is called the organism’s phenotype, e.g.
if the trait is tongue rolling, there are two phenotypes – rolling and non-
rolling. (The word ‘phenotype’ is made from type of phenomenon.)
Figure 3.22a Example of
❑ The genes an organism possesses for a trait are called its genotype. (The
person with one or two
word ‘genotype’ is made from type of gene.) Organisms usually have two roller genes
genes in their genotype for each trait (see opposite).
❑ For some genes there are alternative forms which are called alleles. For
tongue rolling, there is one allele which codes for the ability to roll one’s
tongue and another allele which codes for non-rolling.
❑ If the two genes in the genotype are the same allele, then the resulting
phenotype is obvious, e.g. a person with two roller alleles can roll and a
person with two non-rollers alleles can’t. When the two genes are the same,
the organism has a homozygous genotype and is said to be pure-breeding. Figure 3.22b Example of
person with two non-roller
❑ If the two genes are different, then the organism has a heterozygous genotype.
genes
Usually only one of the alleles will be expressed in the phenotype. If a person
has both a roller and a non-roller gene, it turns out that the individual can roll
their tongue.

Dominant and recessive genes

❑ The allele which is always expressed is called the dominant gene, and the
one whose presence may be hidden is called the recessive gene.
❑ The dominant form of a gene is written as a capital letter and the recessive as
the same letter in lower case. So, if the dominant tongue roller gene is
written R, then the recessive non-roller gene would be written r.

UNIT 3
96

❑ If a person has two roller genes (RR) then the individual has a homozygous
dominant genotype. If the person has two non-roller genes (rr) then the
individual has a homozygous recessive genotype.
❑ For a recessive gene to be expressed the organism must possess two of them
(e.g. genotype rr), but a dominant gene will be expressed whether you have
one or two of them (e.g. genotypes RR and Rr).
A single dominant gene will do as will two recessives!

Separation of Genes R 50% of Chance in genetics

R sperm ❑ In the ovaries and testicles many body cells undergo meiosis and
with R produce huge numbers of gametes.
Rr R
meiosis r ❑ When an organism produces gametes, the two genes it has for each
r 50% of trait are separated in such a way that each gamete gets only one gene.
heterozygous sperm If the organism is homozygous (e.g. a female who is RR) then 100% of
body cell r with r the gametes will have the same gene (all eggs will be R).
Figure 3.23 Separation of genes ❑ But if the organism is heterozygous (e.g. a male who is Rr) then 50%
of the gametes will land up with one allele (e.g. sperm with R) and
Success at Fertilisation 50% will have the other allele (sperm with r).
R 50% chance
that a sperm
❑ In our example, at fertilisation there will be a 50% chance that the
R with R makes it successful sperm has the dominant allele R and a 50% chance that it
r 50% chance has the recessive allele r.
that a sperm
egg with r makes it
Figure 3.24 Success at fertilisation

Activity 7 Punnet squares: predicting phenotypes

With a punnet square you can identify the possible genotypes of offspring. You
can then work out what the expected phenotypes will be and how likely they are to
occur.
Note that each of the boxes in the punnet
square is equally likely to occur, so there is a Punnet Square:
maternal phenotype: roller
25% chance that each zygote will happen. maternal genotype: Rr
Also, note that genotypes Rr and rR are the paternal phenotype: roller
paternal genotype: Rr
same. rR is written as Rr.
eggs
Problem: If two parents are both hetero- R r
zygous for the tongue rolling gene, predict R RR Rr
the chances they will have of getting the
different kinds of offspring (children).
sperm zygotes
Steps:
r rR rr
Write down the phenotype and genotype
of each parent: both father and
mother are rollers with an Rr
genotype. genotype chances: RR
25%, Rr 50% and rr 25%
Identify the type of gametes that each phenotype chances: roller
75% and non-roller 25%
parent will produce: both parents will
produce gametes with R and gametes
with r.

BIOLOGY YEAR 12
 97

To the left of the square write the genotypes of sperm: R and r. Above the
square write down the genotypes of eggs: R and r.
In each box record the genotype of the zygote formed if the sperm on the left
meets the egg from above: e.g. r sperm and R egg gives rR.
Identify the distinct genotypes and what the chances will be of getting each: RR
= 25%, Rr (and rR) = 25% + 25% = 50%, rr = 25% chance.
Finally decide what the expected ratio of the two phenotypes will be: ❑
rollers (RR and Rr genotypes) = 25% + 50% = 75% chance
❑ non-rollers (rr genotype only) = 25% chance

Activity 8 Pedigree charts: identifying genotypes

A pedigree chart identifies the genotypes of parents and their offspring (children).
A circle represents a female and a square represents a male. A mating is a
horizontal line that joins male and female. Offspring are placed on branches under
parents. Phenotypes are written outside and genotypes inside circles and squares.
Problem: The chart gives the natural hair shape of family members. There are two
basic phenotypes, curly (which includes wavy) and straight hair. The gene for curly
hair is dominant over the gene for straight hair.

Steps:
Decide on the symbols for the alleles: if the dominant gene for curly hair is
written C, then the gene for straight hair will be c.
You need two recessive genes for
Pedigree Chart:
the related phenotype: locate all gene – hair shape
straight-haired individuals and alleles – curly allele C
and straight allele c
write in their cc genotypes.
Offspring which have straight hair
must have inherited two c genes:
check their parents have at least mother mating cC father
one c in their genotype, and if they cC
do not, add a c. curly straight
Parents in which the recessive gene is offspring
expressed will pass on a c gene to cC cc cC cc
each of their offspring: make sure
each of these offspring has at least (Note: cC is the same as Cc.)
one c gene in their genotype.
You can now complete the genotypes of some individuals so that they will have
their phenotype stated: e.g. if an individual has a c gene and curly hair then
they must have genotype cC.
If for some individuals with the dominant trait you still do not know
whether they are CC or Cc: just write in C?

UNIT 3
98

Brown
Guinea Pigs

Activity 9 Problem solving

Table 3.3 Pea traits

Dominant trait and allele Recessive trait and allele

Round seed, R Wrinkled seed, r
Inflated pods, I Constricted pods, I
Yellow seeds, Y Green seeds, y
Green seed coat, C White seed coat, c
Axial flowers, A Terminal flowers, a
Green pods, G Yellow pods, g
Tall plants, T Dwarf plants, t

Describe each of the following genotypes as either homozygous dominant,

homozygous recessive or heterozygous.
Aa, RR, ii, Yy
What would the phenotypes of the following pea plants be?
cc, Gg, gg, RR
 List the gametes that each of the following genotypes could produce.
Aa, TT, Rr, ii
Use punnet squares where necessary to work out the phenotype ratios
produced by the following crosses.
Aa x Aa, Rr x RR, II x Ii
In guinea pigs black coat colour B is dominant to Aa X Aa, Rr X RR, II x Ii
brown coat colour b. What genotypes would the
offspring be if you crossed a homozygous black
male and a homozygous brown female? Black
Use a punnet square to show the result of a

cross between two guinea pigs with genotypes like the offspring in the
previous cross.
In a test cross of a black male guinea pig with a brown female, a brown baby is
born. What does this tell you about the genotype of the black male? Draw a
diagram which shows the cross.
If two heterozygous black guinea pigs mate and produce 20 offspring, how
many would you expect to be brown?
9 In budgies, green colour G is dominant over blue g.
Make up three genetics problems about breeding
budgies and use them to test a member of your group.
Green Blue
Budgies

BIOLOGY YEAR 12
 99

There are standard ways to setting out genetics problems which make them easier
to follow. Mendel’s experiment with tall and dwarf peas can be set out as follows:

Mendel’s tall x dwarf pea cross

T is the dominant allele (tall) and t
is the recessive allele (dwarf)
First Cross
P1 T T (tall) x t t (dwarf)
gametes T x t
F1 T t (tall) The F1 plants all have a
tall phenotype.
Second Cross
P2 Tt x Tt
gametes T,t x T,t

F2
t gamete

Tt genotype
T
tall tall phenotype
Tt tt
t tall dwarf

A probability grid (or punnet square) can be drawn to show the result of this
cross.
The ratio of the F2 phenotypes is 3 tall:1 dwarf.

Test cross
You can set out a test cross for an F2 dominant phenotype like this:
If the dominant is heterozygous If the dominant is homozygous

Tt x tt TT x tt
tall dwarf
tall dwarf
gametesT,t x t
gametes T x t

T t
T TT Tt Tt
tall tall tall
t Tt tt
tall dwarf

The ratio of the phenotypes is All the offspring are tall and
1 tall : 1 dwarf are heterozygous

UNIT 3
100

Activity 10 Revision
Match up definitions with terms.
gamete a the appearance of a characteristic
gene b the first cell of a new organism in sexual reproduction
characteristic c when the two genes an organism possesses are
different
fertilisation d alternative forms of a gene
zygote e the fusion of a sperm with an egg resulting in a
homozygous zygote
f when the organism has two dominant genes in its
recessive
genotype
homozygous g cells involved in sexual reproduction (egg and
dominant sperm)
genotype h the process of cell division which produces gametes
allele i a gene which will always be expressed
homozygous j an inherited object which affects the appearance of
a characteristic
heterozygous k a technique used to identify genotypes in a family
dominant gene l a technique used to predict the phenotypes of
recessive gene offspring
m an individual living thing
phenotype
n the two genes an organism possesses are identical
organism o when the organism has two recessive genes in its
meiosis genotype
p a gene which is only expressed if the organism has two
punnet square
q a feature whose appearance is determined by genes
pedigree chart r the two genes an organism possesses for a characteristic

Explain the differences between the terms below. a

characteristic and gene
b phenotype and genotype
c homozygous and heterozygous genotypes
d dominant and recessive genes.
The photo shows a father and son. The gene for straight hair (c) is recessive to
the gene which codes for curly or wavy hair (C).
a What are their phenotypes?
b What genotype will each have?
c Are the father and son homozygous or heterozygous?
d What can you say for sure about the mother’s genotype?
Figure 3.25 Father and
son e What can you say about the mother’s phenotype? (explain)
A daughter can roll her tongue but her mother cannot. The gene for tongue
rolling (R) is dominant over the gene which codes for non-rolling (r).
a What are their phenotypes?
b What genotypes would each have? c
Which person is homozygous?
d What can you say for sure about the father’s genotype and phenotype?

BIOLOGY YEAR 12
 101

Decide whether the following statements are true or false. Rewrite the false ones
to make them correct.
a Gametes have two genes per characteristic and organisms have one. b
Meiosis produces gametes and fertilisation produces a zygote.
c Phenotype describes the appearance of an organism for a characteristic,
whilst the term genotype describes the genes an organism has for that
characteristic.
d Organisms usually have one gene in their genotype for a characteristic. e
In a heterozygous genotype the two genes are the same.
f A dominant gene can mask the presence of a recessive gene.
g For a recessive gene to be expressed an organism requires two of them.
For a dominant gene to be expressed an organism needs to be
heterozygous or homozygous dominant.
Ovaries produce eggs and testicles produce sperm.
With a heterozygous individual, 50% of gametes will have a recessive gene.
In rabbits there is a gene which controls whether fur is brown or white. The allele
coding for brown fur (B) is dominant over the allele coding for white fur (b).
a Would a pure-bred rabbit be heterozygous or homozygous? b
What would the genotype of each of these rabbits be?
A pure breeding white female rabbit was crossed (mated) with a pure
breeding brown male and they produced five brown baby rabbits.
c What would the genotypes of each of these rabbits be?
When these brown baby rabbits reached maturity, a male and female were
mated and they produced the white and brown offspring shown in the
pedigree chart below.
d Complete the chart to show the genotypes of all rabbits (BB, Bb, bb or B?).

brown brown
female male

white female white male

In guinea pigs there is a gene which controls whether fur is black or brown. The Punnet Square:
allele coding for black fur (B) is dominant over the allele coding for brown maternal phenotype: brown
maternal genotype: bb
fur (b). paternal phenotype:
paternal genotype:

A breeder wanted black guinea pigs for her pet shop chain, but she was eggs

unsure whether her black male guinea pigs were all pure breeding for coat b b

colour. So she carried out test crosses to uncover any recessive brown
genes in her males. This meant she crossed each of the black male guinea
pigs with a brown female guinea pig and then checked the coat colour of sperm
zygotes
their offspring.
a Complete a punnet square to predict the expected offspring if a black
male was pure breeding for black coat colour.
genotype chances:
b Complete another punnet square to predict the expected offspring if a
phenotype chances:
black male had a recessive brown gene.

UNIT 3
102

The table below shows the actual results from her test crosses.
Male Offspring in Litter

Angus 5 black
Mac 3 black, 3 brown
Pesky 5 black
Rastus 3 black, 2 brown

Which males are likely to be homozygous dominant? Why? d

Which males are heterozygous? How do you know?
e Which males definitely have a recessive allele for brown hair?
f Which males should the breeder not use for her breeding programme?
In general why do breeders use test crosses, and what genotype does the test
cross organism need to be?
Read the passage below, then answer the questions.

Left- or right-handed?
❑ Approximately 75% of the human population are strongly right-
handed and approximately 90% are predominantly right-handed.
❑ Among the remaining 10%, there is a great deal of variability.
Some people are strongly left-handed and others are
ambidextrous (left-handed for some tasks and right-handed for
others).
❑ The preference of individual humans could be because of inherited
variation (i.e. genes) or because of an acquired variation (e.g.
training and social pressures in childhood) or a combination of both.
❑ Left-handedness does run in families and since far fewer people show left-
handedness then maybe left-handedness is because of a recessive gene.

❑ But if the reason was simply dominance and recessiveness, you would
expect that all children of two left-handed parents would be left-handed,
but it turns out that about 50% are right-handed and 50% left-handed.
❑ Identical twins have identical genotypes, so if genes decided their
left- or right-handedness then we would expect that if you knew
the handedness of one twin you should be able to correctly predict
the handedness of the other. But this does not turn out to be true.
❑ Many geneticists currently accept that our genes determine right-
handedness, but that left-handedness is more variable.
❑ The geneticist Marian Annett proposed that a single gene is
involved which has two alleles.
❑ The dominant allele R+ has a strong tendency to cause right-
handedness whether you inherit one or two.
❑ The recessive form of the gene R- does not cause left-handedness if you have
two of them, rather it does not produce a bias towards either form of
handedness. So people who have two recessive genes are free to develop
either left- or right-handedness or they may become ambidextrous.

BIOLOGY YEAR 12
 103

How is the human species unique? b

What does ‘ambidextrous’ mean?
c What evidence supports the idea that genes influence handedness?
What two pieces of evidence suggest that simple dominance and
recessiveness does not determine our handedness?
What two genotypes are right-handed people likely to have? f If
you have an R+ gene, what are you likely to be?
g If you have two R- genes, what are you likely to be?
With the gene coding for hair shape there are two alleles. Dominant gene C codes
for curly (including wavy) hair and c codes for straight hair.
There are two phenotypes (curly and straight) and three possible genotypes CC
(CC, Cc and cc).
In this activity you will investigate what offspring you can expect with each
combination of parents. It turns out that there are six distinct combinations of
parental genotypes possible. These are listed down the left side of the table. Cc
Complete the table by working out the chances of getting the different
genotypes and phenotypes amongst the offspring. A few are obvious, but
with others use a punnet square. cc
Parents Offspring Genotypes Offspring Phenotypes

CC x CC CC=% Cc = % cc = % curly = % straight = % Figure 3.26a–c Hair types

CC x cc CC=% Cc = % cc = % curly = % straight = %

CC x Cc CC=% Cc = % cc = % curly = % straight = %
Cc x Cc CC=% Cc = % cc = % curly = % straight = %
Cc x cc CC=% Cc = % cc = % curly = % straight = %
cc x cc CC=% Cc = % cc = % curly = % straight = %

Which combination involves two homozygous dominant parents? b

Which combination involves two homozygous recessive parents?
Which combinations of parents will produce only one type of phenotype
amongst their offspring?
Which combination of parents will give some offspring which are
different from both parents?
Explain why it is possible for two curly-haired parents to produce a
straight-haired child and why it is impossible for two straight-haired
parents to produce any curly-haired children.
Predicting phenotype ratios.
Complete punnett squares to predict the ratio of dimple- to non dimple-
chinned offspring for each of the following couples. Dimpled chin is caused
by a dominant allele D.
a Both parents are heterozygous.
b One parent has a non-dimpled chin, the other a heterozygous genotype. c
One parent has a non-dimpled chin, the other is homozygous for the
dominant allele.

UNIT 3
104

Two dimple-chinned parents have four children, two of whom have dimpled
chins and two of whom do not.
Show how the children with non-dimpled chins could have inherited the trait.
What must the parents’ genotypes be?
The parents decide to have another child. What are the chances that it will
have a non-dimpled chin?
Interpreting results.
When a pure-breeding black-haired guinea pig was mated with a pure-
breeding brown-haired one, all the offspring had black hair.
The difference is determined by a single gene.
a Which trait appears to be linked to a dominant allele? b
Would the offspring be homozygous or heterozygous?
One of the offspring was mated with a pure-breeding brown-haired pig. Half
of the next generation had brown hair.
c What does this confirm about the genotype of offspring from the first
mating?
Two offspring from the first mating were mated together.
d Predict the ratio of black- to brown-haired offspring in this cross (use a
punnett square).
Comprehension and interpretation.
Read the information below, then answer the questions.

Breeding pure strains

❑ For pet breeders it is important that animals breed true for a trait. In
the case of budgies, the colours blue and green are determined by
one gene which has two alleles. G, the dominant allele, codes for a
green coat, and g is the recessive allele coding for a blue coat.
❑ Tilimai wanted to breed blue budgies from several blue females, but both
of her males were green. To find out the genotypes of the males she did
back crosses. Each male was crossed with two blue females.
❑ For male A, the offspring from the two crosses were 4 and 5 chicks
respectively. All chicks were green. For male B, the offspring of one
cross were 4 green and 1 blue birds, and 2 green and 2 blue birds for the
second cross. One of the blue chicks was male and other two female.
❑ With the information she got from these back crosses Tilimai was
able to breed pure strains of blue budgies.

Why did Tilimai not have to back cross the blue females to identify their
genotypes? What was their genotype?
Why was the breeder initially unsure of the genotypes of the green
males? What genotypes could the green males have had?
After she saw the offspring of the back crosses, Tilimai was sure that the
genotype of male A was GG. Why?
She was also certain that male B was Gg. Why?
Which male bird would Tilimai use to ensure that the chicks were all
blue? What would its genotype be?

BIOLOGY YEAR 12
 105

Why did she breed each of the green males with two females?
What do you think would be the ratio of offspring from mating male bird B
and a blue female?
Corn cobs.
Figure 3.27 is a photo of dark and light seeds on an F2 maize cob. These
colours result from a pair of alleles for dark and light colour. Work out from
the photo
a what the two P1 plants were like
b what the cobs from the F1 plant would have been like.

X and Y chromosomes
Sex facts Figure 3.27 Corn cobs
The ratio of males to females is not exactly 50/50. Although the ratio of sperms
produced is 50/50 there are other factors. For example, Y sperms are slightly
more active and fertilise eggs more often. On the other hand male embryos
seem slightly more fragile so that more male embryos spontaneously abort and
male babies are more delicate at birth.
It is now possible to sort out X and Y sperms of cattle fairly accurately. At
present the process is too slow to be economically worth while.
Very rarely a mistake occurs in meiosis and the inheritance of maleness and
femaleness is not clear cut. Two examples are:
Klinefelter’s syndrome About one male in 1000 may inherit more than one
X chromosome (e.g. XXY or XXXY). These people may have undeveloped
testes and a slight tendency to develop female-like breasts.
Turner’s syndrome There is one X chromosome but no Y. The
reproductive organs, although female, are not fully developed. This happens
in one female in 3000.
It is just as well that humans produce large numbers of sperms. About 8% of
sperms and even more eggs have defective chromosomes.

What made me Male or Female?

The traits or features we inherit is determined by which parent we inherit a
particular gene from and whether that gene is dominant or recessive. However, for
one very important feature the method of inheritance is rather different. This is the
inheritance of our sex.
Maleness or femaleness is of course a very big part of our genetic make-up and
includes all sorts of things apart from sexual organs. Sex also affects the size and
shape of our body, the distribution of hair and fat on our body, voice and the
hormones we produce that can affect our emotions. All this is determined by the
way we inherit just one of our 23 pairs of chromosomes. The sex chromosomes
are called the X and Y chromosomes. Females have a pair of X chromosomes in
each cell and males have one X chromosome and a smaller Y chromosome. The
pattern of inheritance of X and Y chromosomes is shown in Figure 3.28.

UNIT 3
106

22 pairs 22 pairs
of normal of normal
chromosomes chromosomes
+XY +XX
XY XX

meiosis

Eggs
Y X X X each with
one X
XY XX

50% male 50% female

children children

Figure 3.28 How sex is determined

As the diagram shows, sex is determined by chance – whether an X or Y sperm is

first to reach and fertilise the egg. Half of the father’s sperms carry an X
chromosome and half a Y chromosome, so a population always has approximately
50 percent males and females. The Y chromosomes carry certain genes that cause
the body to develop male characteristics.

Activity 11 Number of boys and girls

Find out how many boys and girls there are in the families of your class. How close
is each family to the 50% females to 50% males ratio? How close is it to 50% of
each when all the families of class members are considered?
Why does the size of the sample make a difference?

BIOLOGY YEAR 12
 Unit

Plants

This unit is divided into sections that cover photosynthesis, plant structure, plant
4
processes and co-ordination.

Photosynthesis
In this section you learn to:
❑ investigate the process of photosynthesis
❑ write an equation to describe the process of photosynthesis
❑ investigate leaf pigments
❑ explain the importance of photosynthesis to plants and other living things.

Photosynthesis and Life

❑ Photosynthesis is the process by which green plants make food. Without
photosynthesis, no life would exist on Earth’s surface. All living things need
energy to live and because the source of energy is food molecules, the food-
making process of photosynthesis is vital to life.
❑ Organisms that make food molecules using raw materials and energy from the
environment are called producers. They include terrestrial (plants on land)
plants and aquatic algae. Other organisms must obtain food molecules ready-
made from producers. These organisms are either consumers (animals) or
decomposers (fungi and bacteria).
❑ Producers are able to manufacture all the other molecules required for life
(carbohydrates, lipids, proteins and nucleic acids) starting with
glucose and simple ions (e.g. nitrates) from the soil or the sea.

Summary of Photosynthesis
❑ Photosynthesis occurs in special centres of chemical activity called
chloroplasts which are inside leaf cells. Photosynthesis traps light energy
and changes carbon dioxide and water into glucose and oxygen.
❑ The conversion of raw materials into products can be summarised:

Carbon dioxide + water + light ➔ oxygen + glucose

6CO2 + 6H2O + light ➔ 6O2 + C6H12O6

107
108

Photosynthesis ❑ Photosynthesis is much more than the raw materials coming together. Glucose
light energy O2 molecules assemble step-by-step in the chloroplasts, and each step is
to controlled by a different enzyme – see Unit 9.
air
chloroplast ❑ A plant needs the molecule chlorophyll to trap light energy. Chlorophyll
glucose to makes leaves green as it absorbs the red and blue colours of the spectrum
that makes up sunlight.
CO2 rest of plant ❑ The sun provides a vast supply of energy, but less than 1% of the light which
from
air
reaches Earth is used in photosynthesis. Photosynthesis is a massive process
H2 O
making 200 billion tonnes of glucose per year, most of which is turned into
cellulose.
up
stem ❑ The raw materials for photosynthesis are carbon dioxide, which plants get
H2O from the atmosphere or sea water, and water, which terrestrial plants get
from the soil.
from soil
Activity 1 Investigation of photosynthesis
Figure 4.1 Photosynthesis
Checking controls.
As in all experiments, in your experiments with plants you need a control
before you can make a valid conclusion. A control is the part of an
experiment we use to compare the effect of changing conditions. Otherwise
you cannot be sure whether the factor is needed or not.
Problem: Will the experiment below confirm whether light is needed for
plants to make starch or not?
Check that the experimental setup has all known factors for the process, as
well as the one being tested: water ✓ warmth ✓ carbon dioxide ✓ plus
light ✓
Check the control has identical conditions except that the factor being tested
is absent: water ✓ warmth ✓ carbon dioxide ✓ no light ✓
Both plants were placed as shown for six hours. Leaves from each were
experimental set-up control set-up
tested for starch, but only the leaves from the plant in sunlight tested
positive for starch. This confirms that light is needed.
Figure 4.2 Experimental Research to find out how to test a leaf for starch.
and control set up
Design and carry out an investigation to prove that photosynthesis needs
carbon dioxide or chlorophyll or the effect of light (e.g. colour, length of
time in light, shading) on photosynthesis.

Activity 2 Leaf pigments

Aim: To extract and separate leaf pigments.

Extraction of leaf pigments (e.g. chlorophyll)

Chop some soft, green leaves into small pieces.
Place a pinch of sand in a mortar. Add a very small amount of ethanol or
acetone and the leaf pieces.
Crush and grind the leaf pieces with the pestle. This will break the cells open
and the leaf pigments will dissolve in the ethanol or acetone.
Filter the liquid to remove the leaf material and the sand. What colour is the
liquid? What is the main chemical in the ethanol or acetone?

BIOLOGY YEAR 12
 109

Separation of the leaf pigments

The leaf pigment extract needs to be as concentrated as possible for this
investigation. You may have to allow some of the ethanol or acetone to evaporate.
chromatography
Cut a strip of chromatography paper or filter paper so that it will fit into the
paper
length of a test tube.
About two cm from one end of the paper strip place a small dot of the extract.
Let it dry and then add another drop. Repeat this until you have a small
concentrated dot of extract.
Collect or prepare the solvent – 92% petroleum ether, 8% acetone.
dot of
Add one cm of solvent to the test tube and carefully fit the paper into the test chlorophyll
tube so that the solvent just covers the end of the paper, as shown opposite.
solvent
Leave until the solvent has almost reached the top of the paper. Remove the paper
from the test tube and allow to dry. Figure 4.3
Mark the bands of coloured pigment. Identify the pigments. Chromatography set up

Order on paper Colour Name

Closest to start Green-yellow Chlorophyll b

Green-blue Chlorophyll a
Dull yellow Xanthophyll
Furthest from start Yellow-orange Carotene

Repeat steps 1 to 6 to investigate the pigments in other coloured leaves.

UNIT 4
110

Activity 3
Time Sugar Interpreting a table.
Concentration The data was obtained when a scientist measured the sugar concentration in
of Day (% dry mass) grass in a paddock every 4 hours.
4 a.m. 0.45 a At what time of the day is the greatest concentration of sugar present? b
8 a.m. 0.60 Explain why the sugar concentration is higher in the afternoon rather
than in the morning.
12 p.m. 1.75
c The oxygen level was also higher within the grass leaves during the day
4 p.m. 2.00 than at night. Explain why.
8 p.m. 1.40 d When would the carbon dioxide concentration be highest within the
grass leaves?
12 a.m. 0.50
4 a.m. 0.47
C variegated

Analysing controls.
leaf
B There was an experiment to see if plants need chlorophyll, light and carbon
dioxide to make starch.
black A a A plant with green and white leaves was left in the dark overnight. b
strip clear, sealed The plant was set up as shown and left in sunlight for four hours. c
bag with
CO2 absorber Leaves A, B and C were removed and tested for starch.
Figure 4.4 Analysing
❑ Sketch leaf B and indicate which part would test positive for starch.
controls ❑ Which leaf was the experiment and which the control to test whether
CO2 (carbon dioxide) was needed?
❑ Which leaf was both the experiment and the control to test whether
light was needed?
❑ For the chlorophyll experiment, leaf C had two discs removed (Figure
4.5). The right disk had starch present but not the left. What do these
results indicate?

True or false?
Figure 4.5 Leaf C a Carnivores as well as herbivores depend on photosynthesis. b
Photosynthesis produces more oxygen than a plant requires. c
Photosynthesis increases as temperature rises above 40°C.
d Carbon dioxide is pumped into glasshouses to increase growth rates. e
The veins of leaves are for both strengthening and transportation.
f Most photosynthesis takes place in the spongy mesophyll cells of a leaf
(the tissue between the upper and lower surface).

BIOLOGY YEAR 12
 111

Plant Structure

Leaf structure
In this section you learn to:
❑ investigate the internal structure of leaves
❑ discuss the functions of leaf parts (what leaf parts do).

Food-making factories!
❑ Leaves are very well adapted to act as the light-gathering, photosynthetic The Leaf Food Factory
organs of plants. They are the food-making factories of land plants.
❑ Leaves have demands. The first is to expose as much of the leaf as possible to
light energy and the second is to conserve water and at the same time take in
the carbon dioxide the plant needs for photosynthesis.
Overall leaf features
❑ A leaf is basically a thin, flat, green organ. A flat leaf needs a large surface
area for collecting light energy. The leaves on a plant are often arranged in a
pattern to make sure that all get as much light as possible. Because they are
thin light can reach to all cells within the leaf.
❑ The petiole (stalk) holds the leaf blade up to the light. In some species, the
petiole can orientate (twist) the blade during the day to intercept (face and
catch) more sunlight. The network of veins which emerge from the petiole
provide strength for the blade.
Figure 4.6 Leaf food
❑ A waxy cuticle covers the leaf surface. The cuticle is transparent to light, but factory
limits water loss by evaporation. This is important because leaves would not
be able to photosynthesise if they lost too much water.
Internal structure of leaves
❑ The internal (inside) structure is also highly adapted for photosynthesis. The
photo (Figure 4.6) and diagram (Figure 4.7) show a section of a leaf as seen
under a microscope. There are four layers of cells. Look at the photo and
diagram as you read the description.

Internal Structure of a Leaf

upper waxy layer sunlight
epidermis

palisade
mesophyll
r
chloroplast
xylem a
te
vessel w
e
vein os

phloem luc
d
tube
d
g e
b
r e
o s
spongy s
b
a
le
mesophyll a
e
e
r
id n

r io e
g

lower u d y
o x
ap
bon
epidermis rv
o
te

a car

guard
cell stoma CO2
H2O O
2

Figure 4.7 Internal structure of a leaf

UNIT 4
112

❑ The upper and lower epidermis are single layers of cells that act as a
protective skin for the leaf. The epidermal cells also secrete (or prepare) the
cuticle wax that coats the leaf.
❑ The palisade mesophyll layer under the upper epidermis consists of closely
spaced vertical cells which receive most of the sunlight. They contain many
green chloroplasts – the sites (places) where photosynthesis takes place.

❑ The spongy mesophyll layer is between the palisade and lower epidermal
layers. The loosely packed, irregularly shaped cells create large air spaces that
allow air and water vapour to freely circulate throughout the leaf. These cells
have fewer chloroplasts than the palisade cells.
❑ The network of veins form part of the internal transport system of the plant.
Each vein or vascular bundle consists of long xylem vessels and shorter
phloem tubes. Water comes up from the roots through the xylem vessels
and diffuses out into the cells of the leaf. The glucose made in
photosynthesis is transported to other parts of the plant by the phloem
tubes.

Gas exchange and the stomata

❑ The stomata are microscopic pores in the epidermis that can open and
close. Generally, they are found in the lower epidermis of leaves, which
reduces (stops too much) evaporation of water from the leaves.
❑ During the day carbon dioxide gas diffuses (spreads) in, and water vapour
and oxygen gas diffuse out of the leaf. Differences in concentrations inside
Figure 4.8 SEM image of and outside the leaf cause these movements.
guard cells and stoma
❑ During the night, when there is only respiration in the leaf, oxygen gas
diffuses in and carbon dioxide gas diffuses out.
excess water Stoma Action ❑ Each opening or stoma is surrounded by a pair of sausage-shaped guard
loss guard cells cells. If guard cells absorb water they become turgid (swollen) and force
guard the stoma open.
❑ During the daytime stomata open and allow CO2 carbon dioxide in.
cells
stoma go Photosynthesis can be up to twenty times faster when the stomata are fully
limp
stoma closed open.
Figure 4.9 Stoma action ❑ The stomata play an important part in controlling water loss by evaporation. If
the leaf loses too much water the stomata close, but this slows down
photosynthesis.

BIOLOGY YEAR 12
 113

Activity 4
Matching terms with definitions.
photosynthesis a pair of cells surrounding a stoma
spectrum b the stalk of a leaf
chloroplasts c the waterproof layer outside of the epidermis
adaptation d the internal transport system of plants
chlorophyll e the microscopic pores on the surface of leaves
petiole f the process by which all plants make food
epidermis g the cells involved in transporting food (glucose)
around plant
cuticle h the different-coloured light which makes up sunlight
palisade mesophyll i a feature of an organism assisting it to survive
spongy mesophyll j the layer of closely packed vertical cells in leaf
vascular bundles k a cell swollen with water
xylem vessels l the molecule that traps energy from light
phloem tubes m the layer of loosely packed cells inside the leaf
stomata n the sites of photosynthesis in cells
guard cells o the cells involved in transporting water
turgid p the layer of cells forming the ‘skin’ of a leaf

Identifying leaf structures.

Match the labels with the lettered structures on the SEM (scanning
electron microscope) images of external and internal leaf structures.

Labels:

upper epidermis • lower epidermis • palisade mesophyll cell • spongy

mesophyll cell • air space • chloroplast • stoma • guard cells

UNIT 4
114

Root Structure
In this section you learn to:
❑ investigate types of roots
❑ describe different root types
❑ explain how roots adapt to carry out their functions
❑ investigate the structure of a root
❑ explain the functions of different regions of the root.

Roots of plants support the plant by holding it firmly in the soil. The roots also
absorb water and minerals from the soil. The roots of some plants, for example
yams, also help store nutrients.
Plant roots are also used for asexual reproduction. For example some plants have
underground stems called rhizomes which usually grow horizontally. New plants
grow from points along the underground stem.

Main Root Although all plants have roots with a similar structure they can have different types
of roots depending upon their way of life. Some plants have a tap root system. For
example mautofu has tap roots. A tap root system has one main root that can be
Lateral Roots
large and go a long way down into the soil. These roots are strong and give the
plant good support. Tap roots are also important to plants which live in very dry
Root Hairs climates, such as much of Australia, as the roots can grow a long way down toward
Root Tip water.
Figure 4.10 Root structure Grass plants have a fibrous root system which means they contain many small
roots. This type of root is made up of a large number of short roots that are about
the same size. A fibrous root system helps to stop the plant from being pulled out
when a herbivore eats the leaves.
The cells in a root are living cells. They receive nutrients that are produced in the
stem and they get oxygen from the surrounding soil. Pneumatophore roots are
special roots that grow up into the air from mangrove roots and have special
adaptations for living in mud that lacks oxygen. The pneumatophore roots are
designed to take oxygen from the air so that the root cells under the mud receive
enough oxygen to stay alive.
Adventitious root describes any root that grows in an unusual way. Roots that
grow from stems or leaves are called adventitious roots.

Seeds in a container Activity 5 Plant roots

Part 1
damp paper
Aim: Observe the structure of a growing root.
Collect a clear plastic or glass container.
bean seeds
Fill the container with enough newspaper or other paper so that seeds can be
clear container held in place between the paper and the side of the container.
Add water so that the paper is damp and has a small layer of water in the
Figure 4.11 Seeds in bottom of the container.
container
Place different seeds between the sides of the container and the paper in a way
that will allow you to observe and measure the growth of the roots produced
by each seed.

BIOLOGY YEAR 12
 115

Record observations and measurements over several days. Add water to the
paper as needed.

Part 2
Aim: To describe the root systems of different plants.
1 Find examples of plants with fibrous and tap root systems. Different areas of a root

Carefully remove a lump of soil containing as much of the root

system as possible. root hair

2 Wash the root system carefully to remove the soil. epidermis root hair

3 Observe and draw the root structure. Label the parts. cortex
}
}
region
phloem
Structure of roots xylem area of cell

The tip of each root has areas that carry out different functions (see differentiation
area of cell
Figure 4.12). elongation
The root cap is an area of cells that protect the important root root apical
meristem
meristem. (The meristem is a group of cells that are in areas of active
growth.) As the root grows longer, the root cap is pushed through the root cap
soil in front of the meristem. This reduces the chance of the meristem
getting damaged during growth. Figure 4.12 Different areas
of a root.
The root apical meristem is an area of cells that are able to divide.
This allows the root to grow longer. Each time a cell in the meristem divides, one of
the cells it produces becomes part of the root behind the meristem. The other cell
produced stays as a meristem cell that will grow and divide again to produce another
cell that will become part of the root behind the meristem.
Cell division in the meristem and cell elongation
Cell division Cell elongation nucleus

cytoplasm nucleus

nucleus cell wall cell

vacuole wall
1 cell 2 cells

Figure 4.13 Cell division in the meristem and cell elongation

After the meristem area is an area where the cells produced by the meristem
become longer. This process is called cell elongation. Cell elongation results in
growth that pushes the root meristem and cap further or deeper into the soil.
When cells have elongated, they then change into the different cells that the root
needs. This process is called cell differentiation. The type of specialised cell each
cell will become depends upon where it is in the root.
Above the area of cell differentiation is the root hair region. The cell membrane
of the epidermal cells in this area grow outwards to produce fine root hairs. These
increase the surface area of membrane through which the root can absorb water and
minerals from the soil. Plants need very large root surfaces so that they can absorb
enough water and minerals to support the stem and leaves. Grass plants can have
130 times more root surface area than they have stem and leaf surface area.

UNIT 4
116

Activity 6 Root structure

Aim: To investigate the inside structure of a root.

Root hair structure Use a hand lens or dissecting microscope to look at the outside
epidermis of the roots of a seed that has been grown on paper. Identify
cells root hair the areas of the root.
Look at prepared slides of root tissues or prepare your own slides
by cutting and mounting sections from roots. To do this:
cortex
❑ Hold the root in a material that is easy to cut,
soil
e.g. between two pieces of carrot.
cells

❑ Use a sharp blade, such as a scalpel, to cut very thin

particles

slices of root into a dish of water.

❑ Choose the thinnest slice and mount it on a microscope
slide, add a drop of water and cover with a coverslip. You
Figure 4.14 Root hair can add stains to show up the cells in the root.
structure

Plant Processes

Transpiration
In this section you learn to:
❑ describe the importance of transpiration
❑ investigate environmental factors that affect transpiration rates

❑ explain how environmental factors effect transpiration ❑

discuss adaptations of plants to reduce transpiration.

Transpiration (loss of water vapour from a plant) is important in the transport of

materials through the plant. This method of transport is called transpiration pull.
Transpiration pull: Over 90% of the water passing up a plant is lost through
water evaporates from
transpiration. The heat of the sun causes this on-going loss of water vapour from
stomata in leaves by leaves through the stomata.
transpiration

Water vapour leaves through stomata it has evaporated from moist leaf cells.
Evaporation increases the concentration of solutes (the substances which were
dissolved in the water vapour) inside the cells, and draws water out of leaf xylem
vessels into those cells by osmosis.
water moves up
vessels in stem by Water forms a continuous column inside the microscopic xylem vessels which run
pressure from below and from root to leaf. The loss of water from the leaf end of a vessel creates a tension
suction from above
or pull on the entire column of water. So the column of water rises. Water is pulled
water moves from cell to cell
upwards through a tiny tube because of the remarkably strong forces of attraction
across the root by osmosis between water molecules.
Plants use no energy to lift all these litres of water. All the energy comes from the
heat of the sun.

Activity 7 Analysing experimental data

Figure 4.15 Transpiration
The rate of transpiration is affected by environmental conditions. Figure 1.16 on
the opposite page shows a simple potometer, designed to measure the water loss of
a leafy twig. The potometer was placed in different conditions for 30 minutes. In
each case it was carefully weighed before and after.

BIOLOGY YEAR 12
 117

Under each condition the apparatus weighed less after 30 minutes. Explain why
the loss of water from the leaves causes the drop in weight, rather than
evaporation of water from the flask.
The table gives the weight of the potometer in each case:
Condition Start Finish Change
still air/ shade/ dry air 142 g 138 g g
still air/ sun/ dry air 137 g 129 g g
wind/ shade/ dry air 127 g 120 g g
wind/ sun/ dry air 119 g 105 g g
still air/ shade/ humid 103 g 101 g g

Calculate the weight change in each condition.

Draw a bar graph to display the changes in weight.
What condition caused the greatest water loss?
Describe how each environmental factor (wind, radiant energy and humidity)
affects the rate of transpiration, and explain why this might be so.
The effect of increasing the temperature on the rate of transpiration was
investigated too. All other conditions were kept constant. The results are shown
below:
Temperature 10°C 15°C 20°C 25°C 30°C

Water loss 2g 5g 8g 15 g 13 g

Plot the results on a line graph and describe the trend.

Suggest a reason why the rate of transpiration eventually fell, even though the
temperature increased.
When the investigations were complete, both sides of all leaves were
smeared with vaseline. In this case, the potometer’s weight did not change
over 30 minutes.
Does this confirm that weight loss was due to transpiration?

Effect of environment on transpiration

The rate of transpiration changes when the environment around a plant changes.
This is because factors such as temperature and humidity, change the rate at which
water evaporates from the surface of the leaf. Higher temperatures make the water
evaporate quicker. More wind and lower humidity increase the transpiration rate
because they increase the concentration gradient between the inside and outside of
the leaf. The larger the difference in the concentration of water between the inside
and the outside of the leaf, the quicker the rate of transpiration.
You can investigate the transpiration rate with a weight potometer. Potometers are
instruments which measure the rate at which a plant takes in water. This is an oil
indirect way of measuring the water loss by transpiration.
water

Figure 4.16 Potometer

UNIT 4
118

Weight potometer
You make a weight potometer by cutting a leafy branch and immediately placing it
in a flask of water. You place oil on top of the water to stop evaporation of the
water from the flask. You weigh the potometer very accurately, then place it in the
conditions being tested for at least 30 minutes and then weigh it again. The
potometer is easy to set up but must be weighed very accurately and it takes a long
time to get results.

Bubble potometer
This type of potometer can record very small water losses quickly and accurately
but is more difficult to set up.
Cut a small leafy branch, under water if possible and leave the cut end in the
rubber tubing water.
Put a short piece of rubber tubing and a 1 ml pipette in the water with the leafy
1 ml pipette
branch.
Push the end of the branch into the rubber tubing and then the end of the pipette
water into the tubing. Hold the end of the pipette under the water and use petroleum
air bubble
jelly to make the joins watertight.
bubble potometer
A bubble can be placed in the pipette by lifting the tip of the pipette out of the
Figure 4.17 Bubble water for a short time.
potometer Mark the position of the bubble on the pipette. The rate of transpiration can be
measured by recording how far the bubble has moved in a given time, e.g.
every five minutes for 20 minutes.

Activity 8 Transpiration
Aim: To investigate the effect of an environmental factor on transpiration
rate.
1 Set up a weight or bubble potometer and leave it to settle for 5 minutes.
2 Place the potometer in still, well lit conditions and take readings of the
position of the bubble every two minutes for ten minutes. This will give you
a set of results that you can use to compare other results against.
3 Change the conditions around the potometer and wait five minutes for the
plant to adjust to the new conditions. You could test different temperatures,
amounts of light, humidity or wind. The table below shows possible
methods of changing the environmental factor.
Environmental factor Possible method
Temperature Place a heat source near the potometer. Change the temperature by moving
the heat source further away.
Light Place the potometer beside a bright light. Fluorescent light is best because it
gives off less heat. Change the conditions by moving the plant further away
from the light.
Humidity Use a clamp stand to hold the potometer. Place the potometer and the beaker
of water inside a large plastic bag. The humidity can be raised by placing a
beaker of hot water inside the plastic bag. The humidity can be lowered by
using a chemical to absorb the water inside the plastic bag.
Wind Use a fan or hair dryer to change the amount of air that moves around the
potometer.

BIOLOGY YEAR 12
 119

Adaptations to reduce transpiration Leaf hairs and stomata in pits

Plants need to open the stomata to take in carbon dioxide and as a
lower epidermis gucral cells
result lose water (see Figure 4.19). The water is needed by the
plant for support so it is important that the plant reduces water
loss as much as possible. The drier the environment the more
important it is for the plant to reduce water loss.
underside of stomata
leaf
Plants have a number of different ways, called adaptations, to help
them reduce transpiration. (Adaptation is any characteristic which Figure 4.18 Leaf hairs
helps the organism to adjust to the conditions under which it lives.) For example,
different types of plants have different numbers of stomata on the surfaces of their
leaves. Some only have stomata on the lower surface of their leaves. The rest of the
cells on the surface of the leaf are covered in a waxy, waterproof cuticle to stop
water loss.
We have already seen that a flat leaf needs a large surface area for
collecting light energy (overall leaf features). Pit

The size and shape of the leaf is also important. Smaller leaves,
needle leaves and rolled leaves are all adaptations to reduce water stomata
loss. Some leaves have hairs and some have their stomata in a pit lower epidermis

in the leaf.
Figure 4.19 Stomata in
Hairs and pits help to reduce water loss because they hold a layer of still air against pits
the leaf, therefore they keep the concentration of water inside and outside the leaf
similar. When the concentration of water in the air outside the leaf is low, the leaf
will lose more water.

Activity 9 Plant adaptations

Aim: To investigate the adaptations that a plant has to reduce transpiration.
Use graph paper to investigate the surface area of a leaf. More water is lost from
leaves with higher surface area.
Use a microscope to investigate the number of stomata on the upper and lower
surfaces of a leaf. You can remove the epidermis from the leaf by using clear
nail polish or acetone. Cover part of the leaf in clear nail polish and then tear
the area of nail polish away from the rest of the leaf tissue. Place the nail
polish piece, with leaf epidermis attached, onto a slide. You can also use this
to see if the stomata are in pits of the leaf.
Use a dissecting microscope to view the surfaces of leaves to investigate the use
of hairs to reduce transpiration.

Asexual Reproduction
In this section you learn to:
❑ describe a range of types of asexual reproduction
❑ explain the advantages and disadvantages of asexual reproduction.

Asexual reproduction is a quick method that plants use to reproduce themselves

when conditions are good. Asexual reproduction results in offspring that are
genetically identical to the parent plant. It allows a plant to quickly form offspring
to take advantage of the good conditions for growth.

UNIT 4
120

The disadvantage of asexual reproduction can be that the offspring are all
genetically identical to the parent plant. If conditions change, the offspring may not
be able to adapt to the new conditions and they won’t grow as well. It also means
that the offspring have to grow close to the parent and therefore they are likely to
be competing with it for resources. That is why most plants also carry out sexual
reproduction so that they can produce genetically different plants that are dispersed
away from the parent plant.
The table below describes the main natural methods of asexual reproduction in
plants. The first five examples use modified stems for asexual reproduction.

Method Examples Description of method

Runner Vanilla (vanila) New plant grows from areas called nodes in stems that grow
Strawberry along the ground
Rhizome Ginger (fiu) New plant grows from nodes in stems that grow under the
Bermuda grass ground
Corm Taro (talo) New plant grows from a bud on a short, thick, upright
Gladiolus underground stem
Tuber Sweet potato (umala) New plant grows from buds on the swollen tips of
Yam (ufi) underground stems
Bulb Onion (aniani), lily New bulb forms from a bud on a short underground stem
Suckers Banana (fa‹) New plants grow as suckers from the base of the stem
Vegetative Mexican hat plant New plant grows from tissue or an organ, for example, a leaf
reproduction African violet that drops or is separated from a plant
Cuttings Hibiscus (⁄ute) People take small branches from plants and grow them.

Activity 10 Asexual reproduction

Aim: To investigate examples of asexual reproduction.
Use the information on the table above to find and observe examples of plants
carrying out asexual reproduction. Draw a diagram to show how the new or
offspring plants form.
Take cuttings from different plants, grow the plants in your biology classroom.
When they have developed roots, use them to plant around your school or
village.

Sexual Reproduction
In this section you learn to:
❑ investigate the structure of wind and insect pollinated flowers
❑ discuss the structure and function of wind and insect pollinated flowers

❑ investigate the structure of seeds and fruits ❑

explain the development of a seed and fruits
❑ compare different methods of seed dispersal.

BIOLOGY YEAR 12
 121

Insect- and wind-pollinated flowers

feathery
stigma
Structure of flowers
Flowers contain the sex organs of plants. Most flowering plants are
ovary
hermaphrodites, that is they have both male and female organs in the
same flower. The male organs produce pollen and the female organs reduced
petal
produce eggs.
Most flowers have these structures:
❑ Sepals and petals: Sepals are a leaf-like cover which protects young large anther
flower buds, while petals attract pollinators.
Wind Pollination
❑ Stamens (male organs): These consist of long filaments (stalk) which
bear pollen-producing and fertile sacs called anthers. A flower usually has Figure 4.20 Wind
several stamens. pollination
❑ A pistil (female organ): This consists of an ovary that bears a pollen
landing-pad, called the stigma, on top of a long style. The ovary
contains ovules, each with an egg.

Adaptations for pollination

❑ Wind is a less sure way of transferring pollen so grasses produce large
amounts of light, smooth pollen. Their anthers dangle in the wind to release
pollen grains, which are caught by the feathery stigma.

Activity 11 Flower structure

Aim: To investigate the structure of wind- and insect-pollinated flowers.
Collect two or three flowers that are insect-pollinated.
Collect two or three flowers that are wind-pollinated. You may have to look
carefully to find them. Wind-pollinated flowers are green and are often very
small compared to insect-pollinated flowers.
Draw the structure of one insect and one wind-pollinated flower.
Write notes around the drawing which explain the difference between the two
flowers.
Figure 4.21 Flowers that
Use a hand lens or microscope to look at the detail of the part of both types of use different methods of
flower. Draw diagrams and write notes to compare their structures. pollination

Identifying Pollination Adaptations.

The photos illustrate flowers that use different
methods of pollination.
The birch tree catkins opposite are male flowers,
which release large amounts of light pollen.
Give three reasons why this plant is likely to be
wind-pollinated.
The curved flax flowers opposite have nectar at the
base. Tui are long-tongued birds of New Zealand
which feed on nectar.
Suggest two features of flax flowers that help
ensure tui transfer pollen between flowers.
Lupin flowers are bee-pollinated. When a bee lands on the keel petal, the
anthers spring out and brush the bee’s abdomen with pollen.

UNIT 4
122

List two adaptations lupin flowers use to attract bees.

Suggest a reason why lighter insects do not successfully pollinate lupin
flowers.

Seeds and fruits

Sexual reproduction of plants involves the development of seeds. Each seed
contains a small embryo plant and the food it will require until it can grow big
enough to carry out photosynthesis to make its own food.
Pollination is when the male and female gametes join to form an embryo inside the
ovules (the sex cells) of the ovary. Each fertilised ovule develops into a seed with a
tough outside seed coat called a testa. The rest of the ovule around the embryo
develops into food storage areas.
The ovary of the flower and sometimes the surrounding parts develop into fruit.
Some fruits are fleshy and others are dry. Ifi and talie are examples of dry fruits.
Tamato and esi are examples of fleshy fruits. The function of all fruits is to
protect the seed and to help disperse the seeds away from the parent plant.

Type of fruit How fruit is formed Description of fruit Examples

Simple Formed by one or 1 Fruit wall dry, splits when mature Bean
more ovaries from the 2 Fruit wall dry, does not split Ifi, sunflower
same flower when mature Banana
3 Fruit wall fleshy
Aggregate Formed by many ovaries Many mature ovaries joined to a large Strawberry
from the same flower stem end called the receptacle
Multiple Formed by many ovaries Many mature fruits grown together Pineapple
from different flowers

Structure of monocotyledon and dicotyledon seeds

testa endosperm testa

plumule

radicle
} embryo

plumule
cotyledon
embryo { radicle cotyledon

bean seed maize seed

Figure 4.22 Structure of monocotyledon and dicotyledon seeds

BIOLOGY YEAR 12
 123

Seed dispersal
Dispersal means to be separated and moved apart in different directions, to be
scattered. Seeds are dispersed in several ways. If the seeds of a plant land on the
ground next to the adult parent they grow up and compete with it for light, nutrients
and water. Plants produce fruits so that the seeds are able to be carried away from the
parent. This reduces the chance of competition between the parent and the offspring.

Dry ovary – explodes in heat Wing’s end parachutes use wind dispersal
wing made by the ovary
wall helps to carry the
fruit away from the
ovary wall parachute of hairs parent plant
helps to keep the
fruit in the air

seeds
fruit
remains of flower fruit with a seed in

Animal dispersal

hooks which catch onto remains of flower strawberry

an animal’s fur
ovary (apple core) strawberry seeds can

go through the
digestive system of an
seed protected by animal without being
harmed
a hard coat

Figure 4.23 Methods of seed dispersal

Activity 12 Seeds and fruit

Aim: To investigate the structure of different seeds and fruits.
Collect five or six different types of seeds.
Draw the shapes of the seeds. Record the sizes and special features of the
seeds.
Soak some bean seeds in water overnight. The next day, open the seeds by
removing the testa. Look at the seeds under a
dissecting microscope. a) sycamore seed
Split the seed apart to show the embryo. Look at it under
b) dandelion
a dissecting microscope. Draw the parts inside the seed
seed.
c) hookgrass seed d) mangrove
Identifying Dispersal Adaptations. seed
f) apple
The diagram on the right shows eight fruits or seeds
which have different methods of dispersal. Match
e) raspberry fruit
each fruit or seed up to a method below:
fruit
a dispersal by passing through an animal’s gut b
dispersal by external attachment
to an animal
c dispersal by floating in water d g) drying broom
dispersal by wind pods
h) sticky paspalum seeds
e dispersal by ejection from a pod.

UNIT 4
124

Germination
In this section you learn to:
❑ investigate conditions needed for germination
❑ explain the process of germination including the conditions needed
❑ investigate plant growth
❑ discuss the role of meristematic tissue in plant growth.

Germination is when the embryo plant grows inside a seed to become a seedling.
The structure of a seed is designed to protect the embryo plant from the time it is
formed until the time it germinates. The embryo inside the seed is in a dormant
state which means that the chemical reactions of life have slowed down, they have
slowed so much that the embryo doesn’t grow.
At the beginning of germination, water enters the seed through a small hole in the
testa. The seed swells as more and more water enters. The seed swells so much that
the testa splits. This allows oxygen from the surrounding air to enter the seed
easily. The chemical reactions of life, particularly aerobic respiration, begin
working very quickly. Starch is stored in the cotyledon which is the primary leaf of
the embryo. Enzymes break this starch into soluble molecules that are transported
to the now growing radicle and plumule. (The radicle is the root of the embryo
and the plumule is the first apical bud or rudimentary shoot.) These molecules are
used for growth and for respiration that supplies the energy needed for the growth.
This is why germinating seeds need oxygen.

plumule

radicle

Figure 4.24 Germination of a dicotyledon seed

The temperature that is best for germination is different for different plants. Some
plants in Sämoa need warmer conditions to start germinating than seeds of plants in
cooler parts of the world. The time of the year when germination begins is not as
important in Sämoa as it is in cooler places. This is because the climate in Sämoa
provides good plant growth conditions all year round.
Most seeds can germinate in the light or the dark but some seeds will only
germinate in the dark and others will only germinate in the light.

Activity 13 Germination
Explain the roles of the following in germination:
water oxygen enzymes
Explain why temperature is less important to seed germination in Sämoa than
in places like New Zealand.
Mangrove seeds start to germinate and grow a root before they fall from the tree.
Why is this necessary?

BIOLOGY YEAR 12
 125

Interpreting Experimental Results.

In an experiment on germination 120 fresh seeds were soaked in water for a
day, then half were killed by being immersed in boiling water. The dead and
living seeds were placed in separate, dark, closed petri dishes and left for 12
days.
Every second day 10 germinating seeds and 10 dead seeds were removed Dry Weight of Pea Seeds
and heated to evaporate all water. Then each group of 10 seeds was 0.8

(g)
weighed and the average weight of the seeds calculated. The results are 0.7

e
e
s
0.6
plotted on the graph. 0.5

of
dead seeds

gh
Describe what happened to the weight of the dead seeds.

ei
w
0.3
0.4

Describe what happened to the weight of the germinating seeds. c 0.2 live seeds

Mea dry
Explain the difference in the results. 0.1
0 1 2 3 4 5 6 7 8 9 10 11 12

Designing Experiments. Days since soaking

Some students were discussing the conditions bean seeds need to germinate. Figure 4.25 Graph of ‘Dry
The students all agreed that water was essential, but could not agree weight of pea seeds’
whether any of the following conditions were necessary or not:

• warm temperature • soil • darkness • oxygen

Describe how you would set up an experiment to test whether each of the
above four conditions was necessary for germination. The seeds have been
well soaked and kept moist. Include a control in your design.
Some seeds will not germinate if they have not gone through a time of
dormancy (inactivity), often over a cold period.
Explain how a dormancy period could be an advantage.
Carry out one of the investigations you designed for number 5 above.

Plant growth
Plants grow bigger because cells divide, cells get larger and Meristems in a shoot
cells change into special tissues. Plants are different from
animals because they can continue to grow taller and thicker Young leaves
throughout their lives. They can do this because they have Apical meristem
areas of tissue, called meristems, which contain cells that
keep dividing to form new cells. Plants have two different
types of meristems. Primary growth occurs from the apical Area at cell elongation

meristems which you find at the shoot and root tips. The Bud
cells in the apical meristem divide and some of the cells grow
longer which makes the plant taller.
Secondary growth is in areas around the stem called lateral Vascular Lateral meristem

meristems. The lateral meristems form circles of cambium tissue

cells around the stem. (The cambium is a strip of cells which gives rise to daughter Figure 4.26 Meristems in a
cells.) The cambium cells divide often. The new cells form xylem cells (wood cells) shoot
on the inside of the cambium and phloem on the outside. This process continues
over the life of the plant and causes the stem to get wider and wider.

UNIT 4
126

Secondary Growth The older xylem vessels towards the centre of the stem of trees develop thicker and
growth ring
stronger walls and become wood. The dead wood in the centre of the tree is strong
wood cambium
and is called heartwood. The living phloem, cambium and xylem just under the
bark (phloem
bark of the tree are called the sapwood. Every year a tree develops new sapwood.
and cork) At different times of the year the diameter of the xylem in sapwood is larger than
others. These differences appear as growth rings that can be seen when the trunk of
Figure 4.27 Secondary
growth
a tree is cut. We can tell how old a cut tree is by counting the number of growth
rings, because one growth ring equals a year.

Activity 14 Plant growth

1 Describe where the apical meristem is.
2 What is the apical meristem for and what does it do?
3 Explain the difference between primary and secondary growth.
4 Explain how the lateral meristem increases the width of a plant stem.
5 Explain the difference between heartwood and sapwood.
Figure 4.28 Electron 6 Interpreting Microscope Images:
microscope view of wood The microscope images show the arrangement and types of tissue in the
vascular bundles of a Dicot and a Monocot plant.

phloem
cambium
xylem

How does the arrangement of vascular bundles in monocots differ from

dicots?
What tissue is absent in the monocot vascular bundle?
What implications does this absence have for the size that monocot
plants reach?
Investigate plant growth through research, experiments or designing and carrying
out your own investigation. Investigations could relate to effect of
environmental factors on growth, e.g. temperature, different light intensities or
shading, mineral deficiencies, soil types, colour of light, wind, humidity.

Co-ordination
In this section you learn to:
❑ describe role of hormones in plants
❑ investigate plant responses to stimuli
❑ explain plant responses to light, gravity and touch.

BIOLOGY YEAR 12
 127

Plant responses
Plants can’t move around like animals, therefore it is important they sense and
respond to their environment. Plants can respond to their environment by moving
their individual parts such as petals and leaves but most of the time plants respond
by changing their growth.

Plant hormones
❑ Hormones control how plants respond to environmental stimuli. Hormones are
chemical messengers which are made in the part of the plant that detects the
stimulus, then transported to the parts where the responses occur. There are
many different plant hormones. Often a hormone will have different effects
when it reaches different parts of a plant.
❑ Hormones called auxins cause the tips of growing stems to grow towards Effect of Auxin
directional light. Light-sensitive chemicals in the cells of shoot tips cause a cell
division auxin
hormone to migrate to the darker side of the plant. It stimulates the growing zone
cell
cells on that side to elongate (increase in length) more rapidly than the ones on elong-
the lighter side. This bends the stem towards the light source. ation
zone
❑ Gibberellins set off the process of seed germination and makes cells expand in
growing shoots. Cytokinins promote cell division. Abscisic acid makes sure Figure 4.29 Effect of Auxin
seeds and deciduous plants stay dormant over winter. Ethylene makes sure
fruit ripens and leaves fall off deciduous trees in autumn.

Plant sensitivity and responses

❑ Although we tend to think of plants as being insensitive (having no feelings)
and immobile (cannot move), they respond to environmental cues and use
them to orientate themselves. Often these responses mean that roots grow
slowly or shoot tips in certain directions, but some leaves can open and close,
some flowers can track the sun, and tendrils can twirl in circles.
❑ When a plant grows towards or away from an environmental stimulus it is
called a tropic response. If the plant grows towards the stimulus it is
called a positive tropism, and if it grows away it is called a negative
Figure 4.30 Phototropism
tropism. Different parts of a plant may respond in different ways. growth towards light
❑ Phototropism is when a plant grows towards or away from light coming from
a certain direction. The shoots of the seedlings show a positive tropism
towards light coming from the right.
❑ Other tropic responses include: geotropism to gravity; hydrotropism to
water; chemotropism to chemicals; thermotropism to heat; and
thigmotropism to touch (which the bean plant opposite has shown).

Activity 15 Responses
Figure 4.31 Thigmotropism
Part one: Light – growth towards or away
from touch
Aim: To investigate the effect of light from one side on the growth of
bean seeds.
Germinate four groups of three to five bean seeds. Draw diagrams to
describe the shape and size of the plants.
Place the groups around a bright light source. Draw diagrams to describe the
shape and size of the plants over five or six days.
Write a conclusion for your results.
Write a discussion in which you explain the effect of light on plant growth.

UNIT 4
128

Part two: Gravity

Aim: To investigate the effect of gravity on the growth of bean seeds.

Draw a circle on a piece of cardboard or paper. Mark the points that are
quarter of the way around the circle.
Stick a bean seed on the quarter marks around the circle. Make sure that the
side of the seed with the embryo plant is facing out of the circle.
Use clamp stands to hold the cardboard upright.
Diagram: Testing the effect of gravity on bean growth.
Draw diagrams to describe the shape and size of each plant over five or six
days.
Write a conclusion for your results.
Write a discussion in which you explain the effect of gravity on growth of the
shoot and the root.

Part three: Investigating trophic responses

Interpreting Experimental Results.
Some oat seeds were germinated in a container. When the shoots were
about 1 cm above the soil, they were treated as follows:
A B C D
A tip untouched
B tip removed C
foil cap on tip
D lower shoot in foil.
After three days in a black box which only let in light from one end, the
seedlings had grown as shown opposite.
A B C D
Why was seedling A included in the experiment?
What do the results for B and A indicate about the region of the shoot
which is sensitive to the direction of light?
How does the result from treatment C support the hypothesis that the tip is
sensitive to the direction of light?
What do the results for D and A indicate about the involvement of the
lower shoot in sensing light direction?
Identifying Tropic Responses.
Decide which tropism is involved in the following and whether it is a
positive or negative response:
a Runner bean tendrils wind around an object they contact. b
Root tips grow towards soil with a high water content.
c Exposed root tips grow away from a light source. d
Root tips grow downwards in response to gravity.
Designing an Experiment.
Your task is to test the hypothesis that when ripe fruit gives off ethylene gas
the gas makes unripe fruit ripen faster. You need three unripe mangos, one
unripe banana, one very ripe banana and three plastic bags.
a Describe how you would test the hypothesis.
b What results would you expect if the hypothesis was true? c
What implications do the results have for fruit exporters?

BIOLOGY YEAR 12
 Unit

Animals

This unit is divided into sections that cover nutrition, circulation, gas exchange,
5
excretion, movement, endocrine system, nervous system, reproduction and the
effect of drugs and exercise.

Nutrition
In this section you learn to:
❑ explain the importance of the essential nutrients, e.g. carbohydrates, lipids,
protein, minerals (iron, calcium, iodine), vitamins (A, B, C, D), fibre, water
❑ investigate the effect of nutrient deficiencies, incorrect diet and eating
disorders on humans
❑ explain the structure and function of the human digestive system
❑ investigate the presence of nutrients in food, e.g. proteins, lipids, starch,
glucose
❑ explain how food tests are carried out.

Food molecules contain nutrients and are the source of energy for life. Yet unlike
plants animals cannot manufacture their own food. So all animals must eat food to
get these nutrients. Living things that eat food are called consumers.
The nutrients in food molecules provide the raw materials for growth and repair of
damaged tissue. Different nutrients are used in different ways and often come from
different sources:
Carbohydrates: Sugars are the main source of readily available energy for cells.
Complex carbohydrates, such as glycogen, are used for energy storage in
animals. As plant tissue is mostly carbohydrate, herbivores and omnivores
need plenty in their diet. Taro, breadfruit, bananas and other starchy foods are
rich in carbohydrates. Carnivores are more likely to use fat or protein in meat
for energy. One gram of carbohydrate supplies 18 kJ of energy.
Lipids: Fats and oils are energy-enriched compounds. However, the energy is
less readily available because lipids are stored in special fat cells. Lipids are
also used to construct cell structures such as membranes. Herbivores get lipids
from fruits and seeds, which are often rich in oils. Carnivores get lipids from
fatty tissue found in meat. Margarine and butter are common sources of lipids
for humans. One gram of lipid contains 40 kJ of energy.

129
130

Proteins: Proteins are made out of the amino acids which are essential because
they build new tissue and make the enzymes which control metabolism (the
chemical reactions carried out by cells). Carnivores get protein from meat,
while herbivores get it from plant tissue such as seeds. Humans eat eggs,
cheese and milk as other sources of protein. One gram of protein gives 17 kJ
of energy.
Minerals: We need small amounts of these ions (e.g. calcium and iron) which
are in grains, fruit, eggs, milk and meat. Iron is for the production of
haemoglobin to transport oxygen in the blood. Calcium is for strong, healthy
bones and teeth. Iodine makes the thyroid gland function properly.
Vitamins: Animals need these complex compounds to make certain
enzymes work. Most are only manufactured by plants.
Vitamin A is for good eyes and good night vision. It is in orange and dark
green vegetables.
Vitamin B1 works with an enzyme involved in respiration. It is in pork,
beans, peas, peanuts and whole grains.
Vitamin C is for healthy teeth and gums. It is in fruits and vegetables,
cabbage, tomatoes and green peppers.
Vitamin D helps our body to absorb and use calcium and phosphorous to
develop strong bones. It is in dairy products and egg yolk. Vitamin D is
formed in the skin when it is exposed to sunlight.
Fibre: Soluble fibre absorbs water during digestion and helps the food to move
through the intestines. Insoluble fibre is the main material egested (that
comes out of the body) in faeces. Cellulose from plant cell walls is the major
source of fibre for humans. Cereals, wholemeal bread, nuts, fresh fruit and
vegetables are high in fibre.
Water: Most of our body is made up of water. Water is important because it is
part of such chemical reactions as digestion and respiration. Water dissolves
other materials such as oxygen and glucose and acts as a transport medium
for many different materials. All foods have much water in them but water is
needed in such high amounts that most animals have to drink extra water.

Activity 1 Nutrients
Aim: To record information about nutrients.
Make a table that records the key points in the information about the
function and sources of nutrients.
Work in groups of two or three. Practice explaining the importance of the
different nutrients to each other.
Investigate and discuss the effect of nutrient deficiencies, incorrect diet and
eating disorders on humans.

Testing for nutrients

We can test for starch, glucose, protein and lipids. The following table shows a way
to test food and the result if the food has the nutrient:

BIOLOGY YEAR 12
 131

Testing for starch Testing for glucose

Method Method
Add a few drops of iodine to the food solution. Add a few drops of Benedict’s solution and heat in a
water bath.
Results Result
The iodine turns black if starch is present. Colour change. Green means a small amount of glucose.
Yellow means a higher concentration of glucose.
Red orange means lots of glucose.
Blue means no glucose.
Testing for protein Testing for lipids

Method Method 1
To the solution being tested add an equal To 1 ml of ethanol add liquid food or crushed up
volume of 15% sodium hydroxide. Then add solid food. Shake then add 1 ml of water.
a few drops of 1% copper sulfate solution.
Result Result 1
A purple colour shows protein is present. If the liquid is cloudy white, fat or oil is present.
Method 2

Place a small amount of the food on brown paper

or newsprint.
Squeeze.
Result 2
If lipid is present it will give the paper a shiny
clear appearance.

Note: You may need to grind up food samples in water before you test them.

Activity 2 Testing foods for nutrients Materials:

Aim: To test for starch, glucose, protein and lipid in a variety of food A range of different
types of foods
samples.
Test tubes
Starch test Starch solution
Glucose solutions of
Set up a control test tube by testing starch solutions with iodine. Use this different concentrations,
positive result to compare the food tested against. e.g. 0.001%, 0.1%,1.0%
concentrations
Use iodine to test a range of foods for starch.
Protein, e.g. egg white
Glucose test Lipid, e.g. butter

Set up a set of control test tubes by testing the different concentrations of Iodine solution
glucose solutions with Benedict’s solution and heat it in a water bath. Use Benedict’s solution
this positive result to compare the food tested against. 15% sodium
hydroxide solution
Use Benedict’s solution to test a range of foods for glucose.
1% copper sulfate solution

Protein Ethanol or paper

Set up a control test tube by testing egg white with sodium hydroxide and
copper sulfate. Use this positive result to compare the food tested against.
Use sodium hydroxide and copper sulfate to test a range of foods for protein.

UNIT 5
132

Lipids
Set up a control test tube by testing butter with ethanol and water or paper. Use
this positive result to compare the food tested against.
Use ethanol and water or paper to test a range of foods for lipids.
Draw diagrams to explain how to carry out a test for starch, glucose, protein and
lipid.

Human digestive system

The human digestive system is a series of organs linked together. The organs carry
out the following four processes:
Ingestion – getting food into the digestive system.
Digestion – breaking down larger food molecules into smaller ones.
Absorption – diffusion of small food molecules into the blood.
Egestion – removal of undigested waste food.
The human digestive system includes the following organs for digesting food:
Human Digestive Tract Mouth: Food is prepared for swallowing. The teeth cut and grind up the food.
The tongue moves the food around the mouth. The salivary glands secrete
salivary
glands water and enzymes. The saliva sometimes does part of the digestion and it
mouth
2 oesophagus
lubricates the passage of food (makes it easier to swallow).
3 stomach
Oesophagus: This short tube has circular muscles that contract in waves called
peristalsis. Swallowing is when the peristalsis pushes a moistened ball of
food from our mouth to our stomach.
Stomach: This is a muscular-walled bag where food is mixed with gastric juice,
liver 4 pancreas which is made of water, hydrochloric acid and pepsin (an enzyme that
5 gall 6 small
digests protein under acid conditions). The soupy mixture in the stomach,
bladder intestine
7 large called chyme, goes in small amounts through a round sphincter muscle into
rectum intestine the small intestine.
anus
Pancreas: This organ releases digestive juices, which break down all food
Figure 5.1 Human types, into the small intestine.
digestive system Gall Bladder: Bile juice is also released into the small intestine. It provides the
alkalines (solution in which hydroxide ions are present) which our different
digestive enzymes need, and breaks fats up into tiny droplets.
Villi Small intestine: This very long tube with a muscular wall helps mix food and
villi on digestive juices. It is lined with many tiny, finger-like projections called villi,
ridges in
intestine which are rich in blood vessels. The villi increase the surface area for
villi absorbing the small digested food molecules.
blood Large Intestine: Its main purpose is to reabsorb water from undigested food.
vessels This helps store water in the body and makes waste food solid. The faeces
Figure 5.2 Villi (waste matter, what the body cannot digest) are stored in the rectum, then
egested (pushed out of the body) through the anus.

Activity 3 Human digestive system

Aim: To develop understanding of the structure and function of the
human digestive system.
Work in groups of two or three.

BIOLOGY YEAR 12
 133

Write a story that describes the journey and all the changes that take place when
a piece of food travels from the mouth, through the digestive system and out
the anus.
Copy the diagram of the human digestive system and add notes around it to
explain how each organ functions.
Matching terms with definitions.
nutrition a the waves of contraction of circular muscles
consumers b a food-processing tube
ingestion c obtaining and processing food
digestion d the finger-like projections in the small intestine
absorption e digested food entering body cells
egestion f ions needed in minute amounts
metabolism g the chemical which cuts up food molecules
vitamins h a carbohydrate which is difficult to digest
minerals i complex chemicals needed by animals
gut j breaking down large food molecules
digestive enzyme k all chemical reactions in a cell
peristalsis l the elimination of undigested food
villi m getting the food into the gut
cellulose n living organisms which cannot make their own food

True or false?
Decide whether the following statements are true or false. Rewrite the false
ones to make them correct.
a The removal of waste food from the gut is called excretion.
b Food is a source of energy and of raw materials for new tissue. c
Lipids are a source of readily available energy in cells.
d Enzymes are a type of protein that control reactions by acting as
catalysts.
e Enzymes in the small intestine of mammals need alkaline conditions. f
The sphincter is a circular muscle that closes off the stomach.
Finding energy usage.
The table shows the amount of energy we use in different activities. a
Display this data on a bar graph.
Activity Energy Used

sleeping 4.2 kJ/min

sitting 5.5 kJ/min
standing 7.0 kJ/min
walking 15.0 kJ/min
exercise 30.0 kJ/min
light work 15.0 kJ/min
heavy work 40.0 kJ/min

UNIT 5
134

The second table shows the number of hours three people spent in one day in
various activities.
Activity Student Shop Worker Forestry Worker
sleeping 9 hr 9 hr 9 hr
sitting 10 hr 5 hr 4 hr
standing 2 hr 2 hr 2 hr
walking 2 hr 2 hr 1 hr
exercise 1 hr 0 hr 0 hr
light work 0 hr 6 hr 2 hr
heavy work 0 hr 0 hr 6 hr

Calculate the daily energy usage that each of these three people use.
List the hours you spend on each activity in a typical day. Work out how
much energy you use.
Why do females usually need less energy than males?
Interpreting Experiments.
The test tubes shown below were set up to test whether the enzyme amylase
converts starch to maltose (malt sugar, the natural sugar in flour and wheat).
Each test tube was heated for two minutes. (Benedict’s turns yellow or orange
when heated if there is maltose.)

Tube A Tube B Tube C

starch distilled starch
solution + water + solution +
Benedict’s Benedict’s amylase +
Benedict’s

Tube C gave a positive test, but A and B were negative.

Why were test tubes A and B included in the experiment?
What does the result for test tube C indicate about the action of amylase on
starch?
Test tubes containing starch and amylase were placed in the conditions
shown below. After 10 minutes each had Benedict’s added before being
heated for two minutes.

Tube D Tube E Tube F Tube G

in in weak weak

ice warm acid alkali

water solution solution

Tubes D and F tested negative, but E and G were positive.

What do the results for D and E indicate regarding the effect of
temperature on starch digestion?
What do the results for F and G indicate regarding the effect of pH
(hydrogen ion concentration) on the action of amylase?

BIOLOGY YEAR 12
 135

Circulation
In this section you learn to:
❑ state the importance of an internal transport system in animals ❑
explain the structure and function of blood and blood vessels ❑
describe the basic structure of the human circulatory system
❑ discuss the roles of the circulatory and lymphatic systems for transport.

The need for internal transport

Only in some very small animals (e.g. unicellular organisms) can diffusion by
itself transport materials around the organism. In large, multi-cellular animals,
diffusion is too slow and they require an internal transport system. Oxygen and
digested food molecules have to be carried to cells. Carbon dioxide and other 100%
wastes have to be removed to prevent cells being poisoned. In addition, hormones, 90%
antibodies and water have to be transported around the body. 80% plasma
70% ~60%
An internal transport system needs a way of transporting these materials. Animals
such as humans, have blood to transport these materials around the body. 60%
50% red
Blood 40% cells
~38%
Blood is tissue made up of different parts:
30%
❑ Plasma is the liquid part of the blood. It is made up of mostly water and it 20% white
contains proteins (e.g. enzymes, clotting factors) and a range of different 10% cells
dissolved substances (e.g. minerals, glucose, urea). ~2%

❑ Red blood cells. There are very many red blood cells in the blood. They have
a flat shape and are full of haemoglobin. Their function is to carry to oxygen.
Figure 5.3 Blood
❑ White blood cells are important for fighting infections by bacteria, fungi and composition
viruses.
❑ Platelets are small pieces of cells, packed with enzymes that help the blood
to clot whenever a blood vessel is cut.

Circulation system
The circulation system is made up of a series of tubes called blood vessels and a Internal Transport in Mammals
pump called the heart. vena cava head and arms

pulmonary
There are three different types of blood vessel: arteries, capillaries and veins. artery aorta pulmonary
Together these blood vessels form a continuous system of tubes that carry the vein
lung lung
blood to all parts of the body.
❑ Arteries carry blood away from the heart. They have thick elastic walls. As the
blood is forced along the arteries by the pumping action of the heart, the walls heart aorta
expand and then return to normal.
hepatic liver
❑ Capillaries are very small blood vessels that are only a few cells thick. portal
vein
Oxygen, nutrients and other materials diffuse through the walls of the vena intestines
capillaries and into the surrounding cells. Carbon dioxide and wastes diffuse cava
from cells into the capillaries. kidneys
legs capillary bed
❑ Veins carry blood back to the heart. They have thinner walls. Blood is helped
back to the heart by the squeezing action of the body muscles. Veins have one-
way cup-like valves that prevent blood flowing backwards. Figure 5.4 Circulation
system
The heart has two separate pumps that beat together. There is a separate circuit
going to the lungs to oxygenate the blood and back to the heart and a second circuit
from the heart, around the body and back to the heart.

UNIT 5
136

The right auricle receives deoxygenated blood from the body. It

Heart Structure and Function contracts, pushing blood through a valve into the right ventricle, which
pulmonary y
toth artery contracts to pump blood to the lungs.
d
o

e b
h

n s
e

o
t
l

u
g
g t n
s u
aorta l

The left auricle receives oxygenated blood from the lungs. It

e

vena cava o
m t
h

y
contracts, pushing blood through a valve into the left ventricle, which
r

e
o
d
pulmonary
b
vein
h contracts to pump blood out of the aorta and then around the body to
left auricle
t

m
o
r
the capillaries and back to the heart.
f
right At rest, the heart beats at about 70 beats/min. Nerve impulses trigger it
auricle
to beat much faster in response to exercise, excitement or fear. This
left ventricle
right ventricle supplies more blood so that the cells get more oxygen during exercise,
excitement or fear.
Figure 5.5 The human heart

Artery and Vein

connective tissue

muscular tissue

elastic tissue

inner skin

lumen
Artery Vein

Figure 5.6 Artery and vein

The lymphatic system
The lymph system is a system of tubes that begin beside the cells in
Lymph system the body. The tubes join together until they form one larger tube
that returns the fluid they carry to the blood. The body needs the
lymph system because pressure from the heart squeezes water in
Lymph enters the blood plasma out of the capillaries and surrounds all the cells in
main veins the body. This helps with the transport of material to the cells but it
Lymph node means that the body has to gather the fluid, called lymph, and return
it to the blood. This is the job of the lymph system. The lymphatic
system is also important for the transport of fatty acids from the
digestion of food. Fatty acids are absorbed by the small intestine
and enter the lymphatic system. The fatty acids travel with the lymph
and are added to the blood with the rest of the lymph.
Lymph Main lymph The tubes of the lymph system go through areas called lymph nodes.
reservoir duct The lymph nodes filter the lymph to remove harmful bacteria and
viruses from the lymph. The special white blood cells in the lymph
Figure 5.7 The lymph nodes carry out this function.
system Activity 4 Circulation

Aim: To record information on the human circulation system.

Explain why large animals need an internal transport system.
Describe the parts that make up the tissue called blood.
Make a table to describe the differences in the structure of arteries,
capillaries and veins.
Draw a diagram to describe the pathway of blood through the heart.

BIOLOGY YEAR 12
 137

The circulation system is made up of three parts: the heart (a pump), blood and
blood vessels. Explain how the three parts work together to provide cells with
oxygen and to remove wastes.
Describe the structure of the lymphatic system.
Explain how the lymphatic system works along side the circulation system and
the digestive system.
Drawing a triple-axis graph.
A triple-axis graph is a useful way to display the results of an experiment
which measures the effects of changing conditions on two different
processes in an organism. This helps us to make comparisons even if the
units for the two processes are quite different.
Problem: Draw a triple-axis graph to show what happens to heart rate and
blood pressure after the body ceases to exercise.
Time Heart Rate Blood Pressure
(min.) (beats/min.) (mm Hg)
1st 132 184
2nd 130 178
3rd 128 142
4th 104 120
5th 85 108
6th 72 104

Mark out an even scale for time along the horizontal axis. Label the axis and
add the units.
On the left vertical axis construct a suitable scale to cover the range of heart
rate values. Space the divisions equally. The scale does not need to start at
zero. Label the axis.
On the right vertical axis construct a suitable scale to cover the range of
blood pressure values. Label the axis.
Plot the two sets of data and draw a smooth curve through each set of points. e
Add a key and a title for the graph.
Matching terms with definitions.
heart a the part that produces many white blood cells
arteries b the chemical that carries oxygen in the blood
veins c the vessels taking blood away from the heart
capillaries d the muscular lower chambers of the heart
auricles e a liquid portion of the blood
ventricles f the network of tiny blood vessels
blood g the ducts that move fluid back into the blood
plasma h the muscular organ which pumps blood
erythrocytes i biconcave red blood cells
haemoglobin j the internal transport medium of vertebrates
leucocytes k cell fragments involved in clotting blood
platelets l the thin-walled, upper chambers of the heart
lymph system m white blood cells involved in defence
lymph nodes n blood vessels with valves that return blood

UNIT 5
138

True or false?
Decide if the statements are true or false. Correct the false ones. a
Veins need valves as they carry blood under higher pressure. b The
pulmonary vein is the only vein carrying oxygenated blood. c A
human heart beats about 100 000 times a day.
d Plasma transports carbon dioxide to body cells. e
Blood clots form when platelets are activated.
Investigating fitness.
A pulse is the rhythmical beat of an artery, which is caused by your heart
pumping. Pulse rate is a very good indicator of the work your body is doing
and of your level of fitness. That is why doctors often test the pulse of their
patient.
A pulse which is easy to find is in your wrist 2–3 cm back from the thumb
Figure 5.8 Taking a pulse
joint. Find your resting rate by placing two fingers on the pulse of the
opposite wrist, while sitting still. Feel your pulse beating. Count the beats for
30 seconds and multiply the number of beats by two. Get somebody with a
stopwatch or a watch with a seconds hand to tell you when 30 seconds are up.
Repeat this three times, then average the results to get your resting pulse rate.

Why take the pulse several times and average the results?
Repeat the steps above under the following conditions when you are:
lying down standing walking hopping.
Draw a bar graph to display your results and summarise the relationship
between pulse rate and activity level.
A good measure of your fitness is the time your heart takes to return to its
resting rate after hard exercise.
Run hard for 100 m, then while seated get someone else to record your
pulse rate for 30 seconds every minute for 10 minutes. Multiply the result
by two in each case.
Plot this data on a line graph and write a sentence which summarises what
the graph shows.
Find out about oxygen debt. Explain why your pulse takes some time to
return to normal after exercise.
What does the length of time your pulse needs to return to its resting rate
indicate about fitness?
Using the above method, how would you identify the fittest person in your
class?
Comprehending information.
Read the passage below, then answer the questions.

Circulatory disease
❑ Heart and circulatory problems cause about 45% of all deaths in many
developed countries each year. Circulatory problems develop in a
variety of ways. Atherosclerosis is when the arteries narrow
because of the build-up of fatty deposits (plaque) on the inner walls
of the arteries. This can lead to high blood pressure which is caused
when the heart has to work harder to push blood around the body.

(cont.)
BIOLOGY YEAR 12
 139

❑ If an artery is blocked by plaque or blood clots, the tissues it leads to start to

lack raw materials. A stroke is the result of what happens in blood vessels
which lead to areas of the brain. A heart attack is when there is a blockage
of one of the coronary arteries which supplies blood to the heart muscles.

❑ Damaged valves or an aneurism (bubbling out of a weakened artery)

can cause heart problems. Birth defects include a ‘hole in the heart’
– usually a gap between the ventricles, which allow oxygenated and
deoxygenated blood to mix. Surgery can usually fix this problem.
❑ Why are circulatory diseases the number one killer in most developed countries?
Sometimes it can be because of a weakness a person has inherited from
ancestors and that cannot be changed. However, statistical studies show that
some lifestyle factors are related to an increased risk. Those things which cause
circulatory disease but which we can change are diet (especially fatty food),
smoking, weight, lack of exercise, continual stress and diabetes. It is also more
common in males and older people generally.

Why would ateriosclerosis (hardening of the arteries) cause high blood

pressure?
Why would the mixing of blood between ventricles as a result of a ‘hole in
the heart’ be harmful?
For each lifestyle factor, say how it would increase the risk of heart
disease.
Although more men are at risk of circulatory disease, this is changing and the
disease is becoming more common in women. Suggest reasons why.

Gas Exchange
In this section you learn to:
❑ explain the difference between respiration, gas exchange and breathing ❑
describe the breathing process in humans
❑ explain the structure and function of the human respiratory system.

All animals carry out respiration to release energy from food. Respiration is a
series of chemical reactions that take place in all living cells. Respiration needs
oxygen gas to take in and releases carbon dioxide. Therefore to survive, all animals
must exchange these two gases with the environment. They must absorb O 2
(oxygen) from the air, soil or water and release CO 2 (carbon dioxide) in return.
This is called gas exchange. Movements of our chest, called breathing, are used
to get air into and out of the lungs so that gas exchange can occur.

Breathing
Breathing is in two phases: you take air in or inhale and you breathe out or exhale.
The lungs are enclosed in an airtight rib cage so that during inhalation, the lungs
can pull in the air by changes in the shape of the chest area. The muscles between
the ribs contract and pull the ribs upwards and outwards. At the same time the
diaphragm contracts and is pulled down and flattened. These two actions increase
the volume of the chest and this pulls air into the lungs.

UNIT 5
140

Breathing Action
trachea

chest cavity

ribs

inhalation diaphragm exhalation

Figure 5.9 Breathing action

During exhalation the rib muscles and the diaphragm relax. This causes the volume
inside the chest to become less and this forces the air out of the lungs.
Structure and function of the respiratory system
Humans are very active animals. This means that we need a respiratory
Human Gas Exchange System (breathing) system which can supply the large amounts of oxygen we need
for respiration.
trachea (windpipe)
Air enters the body through the nose or mouth and moves down into the
cartilage
rib lung
chest through a large tube called the trachea (or windpipe). The walls of
rib heart the trachea contain rings of cartilage that hold it open so that it doesn’t close
muscles and stop the air flowing in and out. The cells in the nose and trachea produce
bronchus mucous and have tiny hairs called cilia. These are used to clean the air. The
chest
mucous traps dirt, such as dust and pollen, that comes in with the air. The
cavity cilia beat back and forward to push the mucous and trapped dirt out of the
trachea.
The trachea divides into two smaller tubes called the bronchi. The bronchi
diaphragm
divide again and again into thinner and thinner tubes called bronchioles.
Each bronchiole ends in a small sac called an alveoli. The alveoli are
Alveolar Structure
surrounded by blood capillaries.
blood Air blood
The oxygen in the air that has travelled into the alveoli dissolves in a thin layer of
low in high in
oxygen oxygen
water on the inside membrane of the alveoli. It can then pass through the membrane,
bronchiole
through the wall of the capillary and then into a red blood cell. At the same time,
carbon dioxide from the blood travels from the blood plasma through the capillary
wall, through the alveoli wall and into the air inside the alveoli. This exchange of
carbon dioxide and oxygen is called gas exchange.
blood alveoli
Activity 5 Gas exchange
capillaries
deoxygenated
blood air
oxygenated
blood Aim: To record information on the human gas exchange system.
plasma red
blood
cells 1 Copy and complete the following table to compare breathing, gas exchange
alveolus
and respiration.
blood
Breathing Gas exchange Respiration
capillary

Figure 5.10a Human What it is

respiratory system and
Figure 5.10b Aveoli Where it occurs
Purpose
Describe, using diagrams and text, the process of breathing.

BIOLOGY YEAR 12
 141

Describe, using diagrams and text, the structure of the human respiratory
system.
Explain how the parts of the respiratory system work together to supply
oxygen to the body and remove carbon dioxide.
Matching terms with definitions.
respiration a the hard external skeleton of animals such as insects
gas exchange b fine tubes running from the skin to all organs
permeable c the chest action that causes air to leave the lungs
medium d very fine blood vessels which pass individual cells
organ e membrane which allows gases to pass through it
gills f the liquid part of the blood
exoskeleton g the chest action that causes air to enter the lungs
tracheal system h the gas exchange organs used in water
lungs i the breakdown of food in cells to release energy
alveoli j the substance inside or surrounding an organism
capillaries k the structure of an organism made of many cell types
haemoglobin l the muscular layer separating chest from abdomen
plasma m the internal gas exchange organs used on land
breathing n the microscopic air sacs found in the lungs
diaphragm o the bulk movement of air in and out of the body
inhalation p the exchange of oxygen and carbon dioxide gases
exhalation q the electrical signal sent along a nerve cell
nerve impulse r the molecule in red blood cells which attracts oxygen

True or false?
Decide whether the statements are true or false. Correct the false ones. a
Respiration is the process of breathing air in and out of the lungs.
b Gas exchange organs need to be kept moist and have a large surface area. c
External gills on tadpoles provide a large surface area for diffusion of
gases.
d The lungs of birds are less efficient than those of mammals.
e The internal gas exchange systems of land animals prevent drying out. f
The breathing rate of humans is determined by oxygen levels in the
blood.
g The insect tracheal system takes air right to their tissues.
h Pressure changes in the chest cavity cause air to rush in and out of lungs. i
The spherical shape of alveoli maximises their surface area.
Analysing surface area to volume (SA:V) ratios.
The oxygen demand of an organism is related to its volume. Its oxygen supply
is related to the area of its gas exchange surface. The
higher its surface area to volume ratio, the more efficient gas 1 mm
1 mm A
exchange is.
1 mm

C
D

UNIT 5
142

Imagine cube A is a unicellular organism that uses its surface for gas
exchange. Its surface area is 6 mm2 (six 1 mm2 sides) and its volume is
1 mm3.
What is its surface area to volume ratio?
Multicellular ‘organisms’ B, C and D are each made of eight
cells. Each cell has the same dimensions as the one above.
Calculate the surface areas of ‘organisms’ B, C and D. c
Find the volume of each organism.
d What is the ratio of surface area to volume for B, C and D?
Which of the three ‘organisms’ has the most efficient gas exchange
surface?
An earthworm is a relatively large animal that relies on its skin for gas
exchange. Does it have an efficient shape for gas exchange? Give a
reason.
A similar principle applies to heat loss – organisms with a ratio of high
surface area to volume lose heat more rapidly. Which ‘organism’ would
be able to conserve heat best?
Analysing gas usage.
The table shows the percentage gas composition of air inhaled and exhaled
by a student after exercise.
Gas Inhaled Air Exhaled Air

N2 79.0% 79.0%

O2 20.7% 14.6%
CO2 0.04% 6.2%
H2O varies saturated

Why is the percentage of nitrogen gas unchanged?

Why is the percentage of oxygen gas in exhaled air less than in inhaled air?
Why is there a greater percentage of carbon dioxide gas in exhaled air
than in inhaled air?
Where does the exhaled water vapour come from?
The breathing rate and breath volume of the student were measured. You can
find breath volume by blowing gently through a tube and displacing the water
inside a large upside-down container. The following are the student’s results
before and after exercise:
Activity Breaths/ Min. Average Breath Vol. (ml)
resting 16 180
after exercise 26 375

From this data calculate the total volume of air breathed during a resting
minute.
If air is 20.7% oxygen, how many millilitres of oxygen did the student
breathe in during a resting minute?
If during rest blood absorbs one sixth of the oxygen inhaled, how much
oxygen would blood have absorbed during a resting minute?

BIOLOGY YEAR 12
 143

Calculate the total volume of air breathed in during the minute after
exercise.
If air is 20.7% oxygen, how many litres of oxygen did the student breathe in
during the minute after exercise?
If one sixth of the oxygen inhaled during exercise is absorbed by the blood,
how much oxygen would the student absorb in the minute after
exercise?
How much extra oxygen did the student absorb in the minute after
exercise compared with the normal rate?
Why was this additional oxygen required after exercise? (See the topic on
anaerobic respiration on page 66.)
Analysing experimental results.
Water temperature affects the breathing rate of fish, because the amount of
oxygen dissolved in water varies with the temperature.
The table shows the average breathing rate of a goldfish at different
temperatures. (The breathing is measured by counting the number of times
the goldfish’s gill covers open.)
The fish was originally in a small bowl with water at 20°C. The temperature
was varied by adding ice or warm water.
Temp. (°C) Breaths/Min.

10 6
15 9
20 13
25 22
30 31

The number of breaths are the average figures over three consecutive
minutes. Why were averages used?
Which is the baseline data? c
Plot the data on a line graph.
What does the graph tell us about the effect of temperature on the Fish Gas Exchange
breathing rate of a fish? 6

What does the data suggest about whether oxygen gas is soluble in water as
temperature increases?
7
Interpreting biological diagrams. 1

The diagram opposite shows how a fish uses its gills to transfer oxygen from
the surrounding water to its blood.
Match up these descriptions of the events involved with numbers on the
3
diagrams. 5
a Water enters through the mouth of the fish.
b Water flows between the folds on the gill arches. 4 2

c Deoxygenated blood flows into the gills from the body.

d Blood in the capillaries moves in the opposite direction to the water flow. e Figure 5.11 Fish
Dissolved oxygen moves from the water, through the gill membranes, gas exchange
into the blood capillaries.

UNIT 5
144

Oxygen-rich blood flows out of the gills, off to the rest of the body. g
Water passes out under the gill cover.
Measure your breathing rate when resting.
Plan, carry out and report on an investigation into the effect of an activity on
breathing rate. The investigation could involve comparing people of different
ages, males and females, or people with different levels of fitness.
Dissect the respiratory system of a pig or chicken.

Excretion
In this section you learn to:
❑ explain the importance of excretory systems in animals
❑ describe excretory products and organs, e.g. carbon dioxide and lungs, urea
and kidney, sweat and skin
❑ explain the structure and function of the human excretory system.

Human Excretory System

Living cells carry out a large number of different chemical reactions. These
vein
chemical reactions are called metabolism. Some of the reactions produce waste
products that must be removed from the body, for example CO 2 and urea.
aorta
Excretion involves the removal of the wastes produced by metabolism in cells.
kidney
vena The major excretory organ of humans is the kidney, which filters unwanted
cava artery ureter substances out of the blood and at the same time keeps the substances which the
bladder
body still needs. Urea is the main waste the kidneys remove. Urea is a poisonous
waste product so it must be removed quickly. Water is used to dilute the urea so
muscle that it doesn’t poison the body. This means that the kidneys of humans also help the
body to keep the correct amount of water.
urethra
Humans have two kidneys that lie on the back wall of the abdomen. The kidneys
Figure 5.12 Human
are supplied with high pressure blood by the renal arteries. After it has been
excretory system
filtered, blood leaves the kidneys through the renal veins. Our kidneys filter about
180 l of blood a day.
Tubes in the kidneys called nephrons carry out the filtration of the blood. Each
human kidney has more than one million microscopic nephrons. When the kidneys
filter the blood they push all the small chemicals in the blood out of the blood and
into the nephrons inside the kidney. These small chemicals include urea, glucose,
minerals, vitamins and water. Because the body still needs some chemicals such as
glucose, some minerals and vitamins, the body reabsorbs them from the nephrons
and diffuses them back into the blood. Some water is always lost with the urea.
This loss must be replaced by drinking.

Kidney and Nephron Structure

kidney capillary tubule
knot
artery vein
artery
capsule
vein
loop

collecting
ureter duct
Figure 5.13 Kidney and nephron structure

BIOLOGY YEAR 12
 145

The urea and other wastes form a water solution called urine. Urine passes down the
ureter tubes to the bladder, where it is stored. The bladder is a muscular bag that
holds up to 400 ml of urine. When full, the expanded walls of the bladder stimulate
nerve receptors to send an impulse to the brain to initiate opening of the sphincter
muscle at the base of the bladder. This allows urine to flow out of the urethra, through
the penis in males, or an opening in front of the vagina in females.

Other excretory organs

The lungs and skin also act as excretory organs. Carbon dioxide is excreted from
the lungs during gas exchange. The skin is important in the excretion of salts. The
excretion of salts is part of the way in which the skin helps to keep the human body
cool at a temperature of 37oC. When the body sweats it loses water and salts and
the evaporation of the water away from the skin removes heat.

Activity 6 Excretion
Aim: To record information about the human excretion system.
Describe, using diagrams and text, the structure of the human excretory
system.
Explain how the parts of the excretory system work together to remove
wastes from the body.
Describe the roles of the lungs and skin in excretion.
Carry out a dissection of the excretory system of a pig or chicken.

Movement
In this section you learn to:
❑ describe the importance of movement for survival in animals ❑
explain how voluntary muscles cause movement
❑ explain the importance of the skeleton for movement in vertebrates.

Even the smallest of animals have some system to support their bodies, and almost
all animals need some way to move – to find or catch food, to locate mates, and to
escape enemies.
Vertebrate animals such as humans, have a skeleton on the inside of their bodies.
Types of Joints
This is called an endoskeleton. The endoskeleton is made up of bones. Bones are
living tissue made from bone cells, nerves and blood vessels. The bone cells are shoulder
surrounded by a matrix of tough collagen fibres and calcium phosphate crystals. It
is the matrix that gives bones their hard rigid properties.
Bones are held together by ligaments (bundles of white tissue that join two or
more bones or hold organs in place. Where two bones join is called a joint. Joints
can be fixed so that there is no movement or they can be a flexible joint. The
flexible joints in your arms let you move your arm at the shoulder, elbow, wrist, ball-and-socket
hand and fingers. Slippery cartilage is at the ends of bones and lets bones slide over
each other when they move. Figure 5.14 Shoulder joint

UNIT 5
146

Antagonistic Muscles Muscles and movement

biceps Animals, move by contraction of muscles. Muscles are made of cells that contain
contracts protein fibres that can move over each other to shorten (contract) or lengthen
(relax). The cells in muscles are in groups that form long fibres. Each muscle is
made up of several fibres. The ends of the muscle fibres form tough tendons. The
tendon tendons join onto bones on the other side of a joint. This means that when they
triceps contract, the bone on the other side of the joint moves.
contracts
joint Muscles work in pairs to move parts of an arm or leg. One muscle contracts to
move a bone while the other muscle relaxes and lengthens. The second muscle can
Figure 5.15 Muscle pairs then contract to pull the bone back again while the first muscle relaxes. The
diagram in Figure 5.15 shows one muscle, the biceps, pulling the forearm towards
the shoulder. Another muscle, the triceps, will pull the forearm in the opposite
direction.
Movement is caused by the muscles of the skeleton. These muscles are called
skeletal muscles. These muscles are under our conscious or voluntary control.
(A voluntary muscle is any muscle which our will controls. When you want to do
something, e.g. take a step forward, you are using voluntary muscles. Some parts
that voluntary muscles control are the arm, thigh, neck.) This is different from the
muscles in our heart, which are under involuntary control. Our body automatically
causes the involuntary muscles to contract and relax and we don’t have to think
about it to make it happen.

Activity 7 Movement
Aim: To record information about skeleto-muscular systems.
Investigate a range of different chicken and pig bones. Record information and
observations about the similarities and differences between bones.
Why is it important that humans and other animals move themselves?
Explain how the skeleton is important for movement in animals.
With diagrams and words explain how a pair of muscles causes movement of
an arm or a leg.
Matching terms with definitions.
hydrostatic a the chemical forming the insect exoskeleton
exoskeleton b support provided by surrounding medium
chitin c a tough, flexible substance made of collagen
endoskeleton d tending to float or rise in fluid
bone matrix e the part that attaches muscles to bones
cartilage f a type of muscle that beats regularly
ligaments g an internal skeleton made of bone
joints h a part that connects adjacent bones together
filaments i the microscopic contracting units in muscles
tendons j a curved surface which can create lift
antagonistic k the hard skeleton enclosing an organism
cardiac l the part where bones meet, and which often allows movement
buoyancy m gas-filled buoyancy organ
swim bladder n muscles which work in opposition
aerofoil o consists of collagen and calcium crystals

BIOLOGY YEAR 12
 147

True or false?
Structure of a Joint
Decide if the statements are true or false. Correct the false ones.
synovial membrane
a An earthworm moves by contracting layers of muscle against the fluid
cartilage
inside its body.
ligament
b A disadvantage of an exoskeleton is that it must be moulted before an
synovial
arthropod can grow any larger. fluid
c A tortoise has an exoskeleton only.
d Muscle fatigue occurs when insufficient oxygen reaches muscles.
e The muscle contractions that push food along the gut are consciously
controlled.
Figure 5.16 Structure of
f No matter how strong your biceps muscles become, they will not be able joint
straighten your arm.
g The shape and structure of a bird’s wings give a clear indication of its
main mode of flight.
Relating function to structure.
Study the joint shown opposite, then answer the questions.
a What are the functions of components A to D of the joint? b
What type of joint is it?
c Where do you find a hinge joint?
d What can hinge joints do and what can’t they do?
e Where in your body will you find a ball-and-socket joint?
f What can ball-and-socket joints do and what can’t they do?
g Where in your body is a joint that allows both rotation (turning on an
axis) and a nodding movement.
Relating muscles to movement.
Study the diagram which shows the four main groups of muscles in action
as an athlete accelerates in a race, then answer the questions below.

hamstring
muscles
calf
quadriceps
muscles muscles

Achilles
tendon
shin muscles

What happens to the leg when the quadriceps contract? b

What happens to the leg when the hamstrings contract?
c What happens to the foot when the shin muscles contract? d
What happens to the foot when the calf muscles contract? e Are
the muscles under voluntary or involuntary control?
f Name two pairs of antagonistic muscles in the diagram.
What happens if a pair of antagonistic muscles contract at the same
time?
Why do athletes find that contracting a pair of antagonistic muscles
together good exercise?
What would happen to a foot if the Achilles tendon snapped?

UNIT 5
148

Endocrine System
In this section you learn to:
❑ explain the role of hormones in animals
❑ name endocrine glands and their secretions
❑ explain what hormones do, e.g. adrenaline, insulin, oestrogen, thyroxin.

The co-ordination of internal processes (acting in combination), the sensing of

stimuli (external information) and the responses to it, are co-ordinated by the
nervous and endocrine system in animals.

Human Endocrine System In vertebrate animals, the endocrine system helps to maintain the body so that it
pituitary gland thyroid gland works normally. The endocrine system is many different glands that release
controls controls hormones into the blood. A hormone is a chemical messenger between cells. Each
other rate of
glands metabolism hormone has a different function and is produced by one cell but causes a change in
pancreas a cell or organ in a different part of the body. For example, the pituitary organ that
adrenal gland
controls sits underneath the brain controls the hormones that control the human reproductive
glands blood system. Hormones reach glands and organs to control growth, reproduction and the
control sugar
stress daily processes of living.
reactions
The following table shows information about four of the hormones that the human
endocrine system produces.
ovaries testicles control Hormone Where Acts on Function
sexual features
from
Figure 5.17 Human
endocrine system Adrenaline Adrenal A range of To prepare the body for ‘flight or
gland different cells fight’. Causes increased pulse
and respiratory rate. Limits blood
flow to the skin and digestive
system
Insulin Pancreas Liver cells Cause the liver to remove glucose
from the blood after a meal. This
helps to keep the amount of
glucose in the blood steady
Oestrogen Ovaries Uterus Stimulates growth of the lining of
cells the uterus
Thyroxin Thyroid A range of Controls the metabolic rate and
different cells growth rate

Activity 8 Endocrine
Aim: To record information on the endocrine system.
What is the role of hormones in animals?
Copy the diagram of the endocrine system and the hormones each secretes.
Discuss the function of different hormones.

BIOLOGY YEAR 12
 149

The Nervous System

In this section you learn to:
❑ describe the importance of human senses
❑ explain the central nervous system in humans
❑ explain the structure of nerve cells and what they do, e.g. sensory and motor
❑ discuss the significance of reflex actions
❑ investigate how an invertebrate responds to external stimuli, e.g. food,
temperature, light, touch, humidity or gravity.

Sense organs
Humans and other animals need to detect changes in their environment. Some
changes can be immediate as when a predator or prey arrives. Other changes can be
over time as when a weather pattern changes over a month. If an animal can sense
changes in the environment it can respond to the change. For example, an
insect that senses a predator may scuttle under a stone or Eye
burrow in the ground to avoid being eaten. Lid Superior rectus muscle

Choroid Sclera
Animals have many sense organs. Each organ is sensitive to
a different stimuli. For example, eyes are sensitive to light Ciliary body
Conjunctiva Retina Vitreous humour
and ears are sensitive to sound. Each sense organ contains Cornea

Pupil Optical axis Yellow spot (fovea)

receptors. A receptor is a nerve cell that can change a
Aqueous humour Lens Blind spot
particular type of stimulus into a nerve impulse. The nerve Iris Suspensory ligament
impulse travels to the brain where it is interpreted. The brain Optic nerve

may send a nerve impulse down a motor nerve to instruct the Lash
muscles to respond to the stimuli. For example, if light is too Lid
Inferior rectus muscle
bright the brain will instruct the iris in the eye to close.
The skin contains a range of receptors able to detect different stimuli. For example: Diagram 5.18 The eye

❑ Mechanical receptors detect touch, pressure or pain. Different numbers of

these receptors are in different areas of the body. For example, we have many
of them in our fingertips and lips.
❑ Thermal receptors in the skin detect external temperature changes.
❑ Chemical receptors are sensitive to chemicals in the environment, in the air
or dissolved in food. In most mammals, these receptors are concentrated on
the tongue and in the nose. Receptors in the human tongue are sensitive to
four tastes – sweet, sour, salty and bitter.

Receptors in Skin
Connective tissue Nerve fibre
Nerve ending

Connective
tissue

A B C D

Touch Sensitive Sensitive to pain Sensitive to Pressure sensitive

temperature change

Diagram 5.19 Receptors in the skin

UNIT 5
150

Nervous System Smell is a more complex sense. Receptors in the nose are able to detect a huge
number of different odours based on a lock-and-key model. The molecules of the
odour fit into specially shaped molecules on the surface of receptor cells, which
brain
then trigger a nerve impulse.
central
nervous The highly complex eyes of humans can detect dim light, movement, shape and
system
colour, as well as focus over a wide range of distances. Binocular vision, with
both eyes facing forward, allows humans to judge distances very well. Animals that
spinal are preyed on often have eyes on the sides of their heads, e.g. rabbits and mice, so
cord
they can see nearly all around.
In humans, hearing is important, particularly for speaking, but other animals (e.g.
peripheral
bats) depend more on hearing (e.g. for echolocation) and are sensitive to a different
nervous range of sound frequencies. Bats, which live in dark places and don’t have strong
system eyesight make high-frequency sounds and have strong hearing. By listening to the
echo of these sounds they can find food and avoid flying into obstacles. The human
ear is designed to convert different frequency sounds into distinct electrical
messages, which are sent to the brain for interpreting.

Figure 5.20 Nervous system Activity 9 Invertebrate responses

Aim: To investigate the responses of an invertebrate animal to an
external stimuli.

Plan, carry out and report on an investigation into the responses of an invertebrate
animal to an external stimuli, e.g. snail. The external stimuli can be one of: food,
temperature, light, touch, humidity or gravity. Begin your investigation with a
question. For example, ‘How does the snail respond when touched by different
objects?’ Remember to repeat the test using lots of different individual organisms.

The nervous system

Vertebrates have a central nervous system which consists of a large brain
connected to the spinal cord found inside the backbone. The nerves in the rest of
the body form the peripheral nervous system.
The central nervous system receives information from all over the body. The
central nervous system co-ordinates the body’s responses to the information it
receives. For example, if you see a ball somebody throws towards you, your central
nervous system will decide to either ignore it, catch it or get out of the way. The
central nervous system then communicates, through nerves and hormones, with
other parts of the body to carry out the chosen response.

Nerve Cells
Cell body
Sensory Neuron Nucleus

Brain cell
Axon

Dendrite

Axon

Motor Neuron

Cell body Muscle fibres

Figure 5.21 Nerve cells

BIOLOGY YEAR 12
 151

The structure of a nerve depends on its function in the nervous system. Motor
nerves are very long and thin. They begin in the spinal cord and end in the skeletal
muscles. Impulses in the motor nerves cause the muscles to contract. The nerve
cells in the brain are round and have lots of branches that connect them to other
brain cells.

Reflex action Automatic association

neuron
Response
When a stimulus (e.g. a thorn prick against a finger) triggers the receptor cells in a muscle
sensory organ (e.g. skin), information is sent along a sensory nerve as electro-
chemical impulses to the central nervous system. Here the information is processed motor spinal
and the finger may make an automatic response called a reflex action. Impulses neuron
cord
sensory
along motor nerves to muscles stimulate action (e.g. remove finger from the ouch!
neuron
thorn). The information will also be relayed to the brain and the brain will make a
Figure 5.22 Reflex action
conscious response (e.g. avoid thorns in future).
A reflex action gives a quicker response to a stimulus than the normal response that
goes from receptor to brain and back to the muscle. The reflex action is quicker
because the distance the nerve impulses travel are shorter – from the receptor to the
spinal cord and to the muscles. Coughing, swallowing, response of the iris of the
eye to changes in light and the withdrawal reflexes in the hand and foot are all
examples of reflex action.

Activity 10 The nervous system

Aim: To record information about the human nervous system.
Why is it important for humans and other animals to sense their
environment?
Carry out research to find out how one of the main sense organs works.
Describe the nervous system in humans.
Explain why the central nervous system is important for helping an animal to
survive.
Explain what the central nervous system does.
Draw diagrams to describe the structure of different types of nerves.
Explain how the different types of nerve cells work in humans.
What is a ‘reflex action’?
Why are reflex actions important to survival of the organism?
Find the term from the text:
a maintaining a steady internal state b
the gland which produces insulin c a
polymer made of glucose units
d balancing the internal water volume
e how body temperature varies with the environment f
how body temperature is kept constant
g the large, complex homeostatic organ with many different functions
glands and their associated hormones i a
chemical messenger between cells j an
organ which secretes hormones
k the hormone involved in maintaining blood sugar levels l
cells able to generate a nerve impulse

UNIT 5
152

a cluster of neurones
a bundle of neurones reaching an organ o
something detected by a receptor cell p a
cell able to detect a stimulus
q the coiled-up tube able to detect sounds r
structures which help you stay upright
True or false?
Decide whether the following statements are true or false. Correct the false
ones.
a Blood sugar levels are affected by insulin, which is secreted by the
adrenal gland.
b Marine fish release large amounts of dilute urine.
c The evaporation of sweat off the surface of your skin cools your body. d
Bird behaviour patterns tend to be learned rather than instinctive.
e The thyroid gland secretes a hormone that affects the rate of metabolism. f
The owl has binocular vision, so it is likely to be a predator.
g The eye position of the cow enables it to judge distances well.
h The role of the ear bones is to both amplify and transmit sound waves.
Relating function to structure. Structure of the Human Eye
The diagram shows the main g
structures of the human eye and
the way an image forms on the f a

retina. e
d
Match up the letters in the c b
diagram (right) with the terms
below:

❑ Cornea: curved, transparent protective surface

❑ Iris: ring of muscle which controls the size of the pupil
❑ Pupil: opening which allows light through
❑ Lens: transparent, flexible, disk-shaped structure
❑ Ciliary muscles: attached to the lens
❑ Retina: made of light-sensitive receptors
❑ Optic nerve: transmits visual information to the brain

What are the two functions of the cornea?

Why do iris muscles alter their tension in dim light?
If the surface of the lens does not have the correct curve, how would this
affect sight?
How would contracting the ciliary muscles affect the shape of the lens? e
There is a blind spot on the retina. Where might this be?
f The image on the retina is upside down. Explain why.
What must the brain first do to the visual image it receives from the
retina?
What happens to the eye when we focus on close then distant objects?

BIOLOGY YEAR 12
 153

Reproduction
In this section you learn to:
❑ explain the structure and function of the human male and female
reproductive systems
❑ describe gametogenesis, fertilisation and embryonic development
❑ explain how materials are exchanged between the mother and the embryo.

Animals use different methods of reproduction

❑ Some corals and fish produce and release thousands of eggs at the same time.
They release them into the water for the male to fertilise. When young have
hatched they have to survive by themselves.
❑ Birds produce fertilised eggs with a hard covering (shell) around them.
When the young hatch, the adult birds look after and feed the young in a
nest.
❑ Turtles produce eggs with a tough flexible outer shell. They lay their eggs
and then leave the young to hatch and look after themselves.
Each of the methods animals use has advantages and disadvantages for both the
parents and the offspring. Predators eat a large number of the offspring of animals
that produce large amounts of eggs so that only a small number of the young
survive to become adults. For example, sea birds called skuas eat young penguins
and turtles or eat the eggs of turtles. When this happens, the animal is in
‘population balance’. This means that the adults that die are replaced by about the
same number of individuals.
Humans usually produce one offspring at a time and then look after that offspring
for many years to make sure that it lives to reproductive age. Humans also improve
the success of reproduction by:
❑ transferring sperm from the male to the female

❑ growth and development of the offspring inside the mother

❑ feeding the offspring with milk.

The use of this reproductive strategy and the way we are able to change our
environment to suit us, means that we are not in ‘population balance’ and the
numbers of people on Earth is still increasing.

Human reproduction
Gametes
The first step in reproduction is the making of sex cells called gametes. Human
gametes are also called ovum and sperm. In animals male gametes are called sperm
and form in the testes. In females the gametes are called ova (or eggs) and form in the
ovaries. The female produces on ovum every month. The ovum develops inside the
ovary and then bursts out the side of the ovary into the oviduct. It travels down the
oviduct towards the uterus (also called womb). If there are no sperm in the female
reproductive system the ovum dies and is passed out the vagina.

The male produces millions of sperm in a tiny tube inside the testis. The sperm live
for a few days and if they are not released they are reabsorbed.

UNIT 5
154

Conception
A baby is conceived when the parents have sexual intercourse. When the male
becomes sexually aroused his penis becomes hard and erect and can be placed into
the female’s vagina which becomes moist and slippery. When the male ejaculates
(discharges seminal fluid) millions of sperm pass from his penis into the female’s
vagina. The sperm swim up through the uterus and into the oviduct. Fusion of the
egg and sperm (when the egg and sperm come together) takes place (fertilisation).
The fertilised egg (zygote) starts to divide and moves down the oviduct to the
uterus. By the time it reaches the uterus it is a ball of cells called an embryo. The
embryo embeds itself into the wall of the uterus.

Sperm travels
Fertilisation
up the oviduct
takes place in
to the ovum
the oviduct

The fertilised ovum

Each month an ovum divides to form an
is released. This is embryo
called ovulation

Implantation:
the embryo sinks
into the lining of
the uterus
Ovary containing
the eggs (ova)

Lining of
uterus

Conception

Figure 5.23 Conception

Menstruation
A female does not menstruate (misses her period) if she is pregnant. Normally the
inside wall of the uterus builds up each month with a thick lining ready to receive a
fertilised egg. However, if there is not fertilisation then the uterus sheds the lining.
Blood and dead cells flow down the vagina. This is called menstruation. Usually a
woman uses a tampon or pad to collect the blood.

BIOLOGY YEAR 12
 155

Female Reproductive System

Oviduct: Carries the ovum

to the uterus

Uterus: A muscular bag in

which the fertilised ovum Ovaries: Produce an
develops into a baby ovum each month

Cervix: A ring of
muscle that closes Vagina: A tube leading
the lower end of up to the uterus
the uterus

Figure 5.24 Female reproduction system

Male Reproductive System

Testis: Produces sperm

Sperm tubes: These carry

sperm from the testes to the
penis

Seminal vesicle
Penis: Sperm pass from here Prostate gland
into the female’s vagina This gland produces fluid
which mixes with the sperm to
form semen
Erectile tissue: Spaces in this tissue fill
with blood and make the penis hard and
Anus
erect

Scrotum: A bag that hangs Urethra: A tube for both urine

outside the abdomen and and sperm
contains the testes

Figure 5.25 Male reproduction system

UNIT 5
156

Activity 11
Copy or trace the diagrams and label the parts A to E.
Match the following descriptions to the correct part of the diagram.

Place where sperm Gland which secretes Carry sperm

are made. fluid to mix with sperm. to the penis.

A baby passes The lining of Place where the

through these this part is shed smear tests are
parts during birth. once a month. taken from.

Place where
Contains tissue fertilisation occurs. A bag which hangs
that may fill with outside abdomen so
blood causing it to sperm are stored at a
become erect. Ovulation occurs lower temperature.
in this place.

C A

B
D
C

a Trace the diagram and

label the parts 1 to
1
5.
Describe the steps a 2
woman would take
to confirm she was
pregnant. 3
How could she
discover whether
the baby was a boy 4
or girl?
5

BIOLOGY YEAR 12
 157

Ultrasound
Ultrasound checks if a baby is developing correctly. A small probe is placed over
the skin of the area that is being investigated and a beam of high-frequency sound
is fired in short pulses through the body. These sound waves are then reflected
back to the probe and converted into an electrical signal which the computer turns
into a picture. Ultrasound is commonly used to produce pictures of unborn babies.
It can also be used to detect abnormalities in parts of the body such as the organs in
the abdomen.

Figure 5.26 Ultrasound scans

Development of the baby

After fertilisation, the zygote divides and forms a Uterus Fallopian tube
small ball of cells. The ball of cells goes into the Embryo Ovary

soft uterus wall and grows to form an embryo.

The cells in the embryo continue to grow, divide
and specialize as the embryo develops. The cells
A: Implantation (10 days)
in different parts of the embryo specialise to
become different types of cells. For example, Embryo

some cells in the head area will become brain

B: 6 weeks
cells, others will become bone cells and others will
become part of hair follicles. The baby will
continue to develop and grow while inside the
E: Birth
uterus. The time a baby spends in the uterus is (9 months)
Placenta
called the gestation period. The gestation period
for most human babies is nine months
Umbilical
When the ball of cells first goes into the uterus
C: 4 months cord
wall some of the cells form the placenta. The
D: 7 months
placenta is an area where the blood of the mother
and the blood of the embryo come close together Amnion

so that the embryo can receive oxygen and food

from the mother and the mother can take wastes
such as carbon dioxide away. Figure 5.27 Development of
the baby

UNIT 5
158

Activity 12 Human reproduction and development

Aim: To record information on the human reproductive system.
Draw and label the parts of the human reproductive system.
Explain the functions of the labelled parts.
Describe the processes of ovum and sperm formation and fertilisation.
Draw diagrams to show how the baby develops in the uterus.
Explain how the placenta works to keep the baby alive when it is in the uterus.
Explain the role of the placenta.

Constructing life cycle diagrams

Life cycle diagrams are used to show the different stages and the crucial
events during the lifetime of members of a species.
Identify the stages involved: zygote, embryo, foetus, juveniles,
sexually mature male, sexually mature female, sperm, eggs.
Arrange the stages in order around a circle and connect up the stages
using arrows.
Indicate where crucial events occur: meiosis, gamete release,
fertilisation, development, hatching or birth, growth, puberty.
If the species undergoes a metamorphosis, indicate where the event occurs
and label the different forms involved.
Indicate the sections of the life cycle involved in sexual and asexual
reproduction.

BIOLOGY YEAR 12
 159

Activity 13
Matching terms with definitions.
asexual reproduction a when eggs are fertilised inside the female
sexual reproduction b the change of body form during life cycle
binary fission c when eggs are fertilised in the environment
fruiting body d the tube which transports eggs to the uterus
parthenogenesis e the spore-producing organ of a fungus
external fertilisation f the foetal organ which absorbs nutrients
internal fertilisation g the organ which produces milk
metamorphosis h reproduction involving two parents
copulation i the period of development in the uterus
ovulation j the period of gaining sexual maturity
oviduct k releasing of eggs from an ovary
ejaculation l the later stage of development of embryo
uterus m asexual reproduction by splitting in two
placenta n the organ inside which embryos develop
foetus o new offspring from unfertilised eggs
gestation p the release of millions of sperm from penis
mammary gland q the act of mating which transfers sperm
puberty r reproduction by a single parent organism

True or false?
Decide if these statements are true or false. Correct the false ones. a
Sexual reproduction is important as it results in varying offspring. b
Organisms produced by parthenogenesis are identical to siblings. c
Mussel eggs are externally fertilised, so mussels produce few eggs. d
External fertilisation needs water for gametes to meet.
e Gestation is the length of a menstrual cycle.
f The mother’s blood passes through the foetus.
g Puberty is initiated by male and female hormones.

UNIT 5
160

The Effect Of Drugs And Exercise

In this section you learn to:
❑ investigate effects of drugs on society

❑ describe the effects of alcohol, drugs, and smoking on the body ❑

investigate effect of exercise on the breathing or pulse rate
❑ describe the effects of exercise on the body.

Alcohol
Alcohol is a poisonous chemical. Large amounts taken quickly can kill a person.
Once alcohol is in our system, our liver has to work hard over several hours to
metabolise it (break it into simpler compounds) to remove the poisonous bit and
make it safe. While this is happening, the alcohol travels in the blood and causes
effects on the organs. The most noticeable effect of alcohol is the effect it has on
the person’s brain and nervous system. Alcohol depresses or slows down the
functioning of the brain. It reduces the person’s ability to think, control themselves,
remember things and make precise movements. It reduces emotions such as
tension, worry, boredom, and shyness, making mixing with other people easier.
Unfortunately it increases the person’s confidence by decreasing their judgement
and sense of responsibility. This can often lead to antisocial behaviour, violence,
abusiveness and dangerous driving.

The effects of alcohol

Immediate effects Long term effects

BRAIN BRAIN
Action is slowed down causing Brain cells are killed and cannot
changes in judgement, self- be replaced. Eventually causes
control and ability to think. loss of memory, judgement,
learning ability.

BLOODSTREAM
Causes red blood cells to clump BLOOD AND HEART
together, slowing circulation May inflame heart muscle
and reducing oxygen carrying and cause increased
ability. amounts of fats to form.

LIVER LIVER
Begins to break down the Cells inflamed and gradually
alcohol in the blood at a rate of destroyed – eventually leading
about 7gm (1 drink) per hour. to cirrhosis or liver destruction.
Bile secretion may be reduced
and hepatitis may develop.
STOMACH
Drinking too much, too fast
may cause vomiting. Alcohol STOMACH
absorbed directly into blood Lining may be irritated,
stream. resulting in ulcers.
Absorption of some
vitamins may be reduced.
KIDNEY AND BLADDER
Irritates the kidney, causing an
increased loss of fluids and
dehydration. PANCREAS
Cells are irritated, blocking flow
HANGOVER of digestive enzymes. This may
The pain and distress that may lead to upset digestion,
appear some hours after heavy damage to pancreas cells and
drinking. It is simply the side susceptibility to diabetes.
effects of alcohol on the body.
Because alcohol has a pain
relieving or anaesthetic effect a
hangover appears after the
alcohol has gone.

Figure 5.28 The effects of alcohol on the body

BIOLOGY YEAR 12
 161

Alcohol also effects the body. Some of the effects of alcohol are short term, but
other long term effects can occur as a result of frequent drinking.

Activity 14 Alcohol
Aim: To investigate the use of alcohol.
Develop a table recording information on the long-term and short-term
effects of alcohol on the body.
A number of different activities could be carried out to investigate the effect of
alcohol on the people in Sämoa. For example:
❑ Find out about the types and amounts of alcohol sold in Sämoa. What
laws are there about making and using alcohol?
❑ Have a discussion about ‘is alcohol a problem or not?’.
❑ Research and discuss the importance of alcohol in: i
health (e.g. the human body)
finances (e.g. household income/budget)
family unit (e.g. divorces, domestic violence, etc) iv
accidents (e.g. car accidents, etc).

Drugs
The term drugs refers to any chemical that people use, legal or illegal, that causes
an effect in their body. Even medicines that the doctor prescribes for a patient can
be harmful if not used correctly or if a person other than the patient uses them.

Activity 15 Drugs
Aim: Investigate the effect of drugs on the people in Sämoa.

A number of different activities could be carried out to investigate the effect of

drugs on the people in Sämoa. For example:
Have a class debate about the importance of staying drug free.
Survey peoples attitudes on the use of drugs such as pain relief (e.g.
panadol, paracetamol), viagra and marijuana.
Research the statistics on drug use in Sämoa.
Discuss, with a pharmacist, the common prescriptions and over the counter
drugs used in Sämoa. What problems do these
drugs cause? Cigarette smoke
2.8% toxic chemicals
Effects of smoking CO2 etc. 0.1%
The smoke from a cigarette has a number of effects oxygen 20% including nicotine,
dust and tar
on the body. One cigarette causes your blood vessels 3.2% CO
to become narrower. This increases your pulse rate nitrogen 13.6% CO2
as much as 15 beats per minute because the heart
has to work harder to push the blood around the water vapour 13.6% oxygen
body. The blood capillaries in the skin close down, (variable)
which causes the temperature in the fingers and toes 57% nitrogen
to become lower. The cells lining the lungs and air
passages have tiny hairs called cilia that remove the
dust and bacteria from the air. The chemicals in 8% wet particles
cigarettes stop the cilia from working for up to 15 Figure 5.29 Cigarette smoke
minutes. This means that dust and bacteria can get into the lungs.

UNIT 5
162

The carbon dioxide is a waste that burning produces. Its presence reduces the
amount of oxygen our blood can carry.
Carbon monoxide is a poisonous waste product from burning. It joins onto the
haemoglobin in red blood cells and stops them from carrying oxygen. This is the
main reason why smoking affects the performance of athletes.
Nicotine is a drug that affects the heart, blood pressure, blood vessels and brain.
Dust irritates the tubes in the lungs, causing mucous to form.
Tar is a sticky chemical that covers the lung surface and reduces gas exchange. It
and the other chemicals in cigarette smoke cause cancer.

Long term effects of smoking

Heart and circulation Nervous system

blood vessels become addictive and can be very
narrower difficult to give up
blood pressure increases smell and taste sense
heartbeat rate increases reduced
fats in the blood increase
blood clotting speeds up
white cells anaesthetised
by nicotine
heart disease risk Skin
increased blood vessels narrowed
reducing circulation of
blood
Lungs temperature lowered
cells lining bronchial drying out of skin
tubes anaesthetised and wrinkles develop as skin
eventually destroyed dries out
walls of alveoli damaged
mucus forms and can’t be
got rid of easily
risk of bronchitis, Digestive system
emphysema, TB appetite dulled
increased possibility teeth stained
of lung cancer intestine walls contract
more often
laxative effect
Pregnancy blood sugar levels
increased risk of increase
spontaneous abortion ulcer risk increased
babies tend to be born
underweight

Cancer Illness
risk of cancer increases in smokers have more days
these places: of illness than non-smokers
lungs white cells are less able
mouth and lip to handle infection
throat
bladder

Figure 5.30 Long-term effects of smoking on the body

Activity 16 Smoking
Aim: To investigate the effect of smoking on people in Sämoa.
Develop a table which records information on the long-term and short-term
effects of smoking on the body.
A number of different activities could be carried out to investigate the effect of
smoking on people in Sämoa. For example:
❑ Have a class debate about the problems associated with smoking.

BIOLOGY YEAR 12
 163

❑ Survey people’s opinions to find out which age groups in Sämoa are
smoking and how many cigarettes they smoke a day. Find out the types
of cigarettes teenagers use, the number they smoke per day and where
they get the cigarettes.
❑ Research the statistics on smoking-related problems in Sämoa.
❑ Discuss, with a health professional, the effect on society if a number of
people smoke heavily.

Effects of exercise
Regular exercise increases the fitness of our circulation and respiratory systems so
that the person can carry out the activity they require in everyday life easily and
without getting puffed. Exercise also improves the body’s strength, stamina,
suppleness and resistance to disease.
A change in the pulse rate with exercise is an indicator of fitness. Although the
heart rate varies from person to person, it averages about 72 beats per minute in an
adult at rest. It is lower in very fit people and higher in children and elderly people.
The pulse rate rises when we exercise. If we are more unfit the pulse rate will rise
higher and will take longer to return to normal.
The heart of a fit person beats more powerfully. This pushes more blood around
the body with each beat, so the heart doesn’t have to beat as often. More food and
oxygen can be supplied and the wastes removed more efficiently. As a result, the
other parts of the body, muscles, skin, digestive system, all work more efficiently.
Regular exercise greatly slows down the forming of fatty cholesterol deposits that
can block up the blood vessels and cause heart disease.
The muscles of a fit person are harder, stronger and can work for longer. Exercise
results in an increase in the number and size of the capillaries in the muscles. This
means that the muscle cells get better supplies of food and oxygen when they need
them.
The lungs of a fit person can absorb a greater amount of oxygen during each
breath. This is partly because more capillaries have developed in the lungs and
partly because the muscles that work the chest are more efficient.
The body needs more energy during exercise. Therefore more food is needed or fat
stored in the body can be used, so weight becomes less. Posture (the position of the
body and the limbs as a whole) also improves because the muscles are stronger and
hold the body more firmly. If the circulation is improved because of exercise we
pick up fewer infections and our body can fight them better. Exercise and fitness
that results, also makes people feel better.

Activity 17 Effects of exercise

Aim: To investigate the effects of exercise on the body.
Develop a table recording information on the long-term and short-term
effects of exercise on the body.
Plan, carry out and report on an investigation into the effect of exercise on
breathing and pulse rate.
Carry out research to find out about the long-term effects of exercise on the
body.
Develop a series of survey questions to find out about people’s attitudes to
exercise.

UNIT 5
 Unit

6 Environment
This unit is divided into sections that cover adaptation, inter-relationships and
conservation.

Adaptation
In this section you learn the adaptations of organisms in relation to habitat and
environment and:
❑ investigate how an organism’s adaptations help it survive in a particular
habitat or environment, e.g. structural, behavioural, functional, (e.g. body
temperature, heart rate), life history
❑ explain how the activities of humans affect the relationship between an
organism and its environment.

Habitat and environment

Many living things don’t just live anywhere. If you want to find slaters you look in
damp, shady places because you won’t find them in exposed sites. If you want to
find mangroves you look in swamps. Organisms are found in particular places
called habitats. Each habitat is the home of several species of plants and animals.
The species in a particular habitat have adaptations that suit the environment in that
habitat. Therefore they won’t be found in other habitats where the environmental
conditions are very different. For example marine organisms can’t live in a
freshwater environment.
Figure 6.1 Predatory starfish
The environment of a species includes all the conditions or factors experienced in
its habitat. Different environmental factors are important for different organisms.
Light is an important environmental factor of a seedling which grows in a forest but
it is not so important for an earthworm which lives in the soil beneath the seedling.
In fact worms don’t have eyes because they don’t need them.
There are biotic and abiotic environmental factors.
Biotic factors are caused by the other species that are living in the habitat for
example, food supply, predation, parasites, grazing, competition and the actions of
humans.
Figure 6.2 Mussels Abiotic environmental factors are physical or climatic conditions for example, light,
salinity (saltiness of sea water), exposure due to tides, day-length, rainfall, humidity,
temperature, dissolved oxygen, carbon dioxide, pH levels, wave action and wind.

164
 165

Adaptations
To survive day-to-day each organism must carry out the life processes which
include movement, respiration, sensitivity, circulation of materials, growth,
excretion and nutrition. Each species of organisms has special inherited features
called adaptations which helps it to survive and reproduce in its habitat.
Type of
adaptation Description Examples
Structural Physical features ❑ Spiders have a silk gland and
or spinnerets that are used to make
morphological their webs
❑ Flies have bulging eyes which
allow all-round vision
❑ Breadfruit trees have leaves with
a large surface area to trap
sunlight
Physiological Processes that the ❑ Snakes ability to produce poison
or organism can carry ❑ Human gut cells make enzymes
functional out to digest food
❑ Ability of some plants to produce
nectar
Behavioural Ways in which ❑ Spider spinning a web –
and responses members of a each spider species spins its web
species act, either in a particular way
individually or as ❑ Fish swimming in a group for
a group protection against larger
predators
❑ Plants grow towards the light
Figure 6.3 Adaptations –
wings as structural
Biological drawings adaptations, gums’
leaves produce toxins,
Structural adaptations are often shown in biological drawings. spinning a web is a
behavioural adaptation

Biological drawings
One way to obtain information about adaptive
features is by careful observation and accurate
drawing.
You don’t need to be an artist to make effective
biological drawings; just follow these basic
steps.
The photo shows a flea.
Steps:
Use a sharp pencil to make clear line drawings on
unlined paper.
Measure and record dimensions.
Rule up a grid and mark measurements using a
suitable scale.

(cont.)

UNIT 6
166

Lightly draw an outline of the shape of the

organism.
Observe sections of the organism and fill in one square
at a time.
Make separate sketches of special features such as
mouth parts, sense organs, limbs, etc. Include notes
with arrows to explain details.
Tidy up your drawing, erase the grid, and label the parts neatly.

Activity 1 Adaptations
Matching terms with definitions.
organism a an aspect of surroundings which affects an organism
habitat b physical or climatic factors
species c structures which help a species survive in a habitat
environmental d an individual living thing, e.g. a plant or an animal
behavioural e the process which helps a species survive in a habitat
biotic factors f places where members of a species are found
abiotic factors g the actions of organisms which aid survival
adaptation h factors which are due to other species
structural i a group of organisms which are able to breed
physiological j a feature which enables a species to fit its habitat

True or false?
Decide whether the statements are true or false. Rewrite the false ones to
make them correct.
a The ecological niche of a species is the place where its members live. b
The environmental factors that are important depend on the habitat. c
Trampling of plants by animals is a biotic environmental factor.
g The release of pheromones is a physiological adaptation. h
The flexibility of human hands is a behavioural adaptation.
i Some plants change their growth form as they mature, which means they are
better adapted to new environmental conditions.
Classifying adaptations.
The white-spotted tussock moth arrived in Auckland, New Zealand in 1996
from another country. It is an invader that could severely damage foliage. The
species had not been well studied, so before they eradicated it, Ministry of
Figure 6.4 White spotted Forestry ecologists had to identify its habitat and adaptations. They discovered
tussock moth caterpillar that:
i The tussock moth has specialised life cycle stages.
The caterpillar eats plant material rapidly.
The adult female lays about 300 eggs.
There are up to three life cycles per year.
v Optimum breeding temperature is about 20°C.
The female adult releases pheromones.
vii The caterpillar gut digests leaves in alkaline conditions.

BIOLOGY YEAR 12
 167

Decide whether each of the above adaptations is structural,

physiological, behavioural or related to life cycle.
Suggest how each adaptation helps survival.
To eliminate the moths, firstly scientists used pheromone traps to
determine the moth’s distribution (to find in which area the moth was
plentiful). Then there was aerial spraying from planes and helicopters
with an organic chemical called Btk. Btk is made up of a bacterium that
lives naturally in the soil (Bacillus thuringiensis, variety kurstaki). The
insecticide releases a toxin under alkaline conditions.
Which adaptations had ecologists found most useful in deciding how to
attack the moth invasion?
Explaining adaptive features.
Giraffes live on the African savanna (grassland with scattered trees). This
habitat has a rainy season, but it is hot and dry for most of the year. The dry
grassland is dotted with acacia trees, which are tough and very thorny. There
are many other browsing animals, and also predators such as lions. Water can
only be obtained from widely spaced water holes. Suggest how each feature
listed below helps giraffes survive in this habitat:
a intestine with microbes for digesting cellulose in leaves b
tough tongue
c eyes on the side d
patterning on fur e
very long legs
hard hooves g
good sight h
tough skin i
long neck
j fast runner
k live in a herd.
Explaining adaptive features.
The sundew is a tiny plant found in swampy places. Environmental factors
include:
❑ poorly drained soil
❑ acidic soil short of nutrients
❑ a cold and damp climate
❑ small insects breeding in bogs.
Few plants can thrive in such an inhospitable habitat. The sundew does as it
has specialised adaptations. Explain how each of the following features could
assist sundews to survive in this habitat:
a the plants are very small and low growing Figure 6.5 Sundew plant
the plants naturally have a very slow growth rate
the leaves are covered by hairs with drops of sweet, sticky liquid d
the leaf hairs bend over any insect that lands on the leaf
e the sticky liquid contains digestive enzymes.
Drawing an animal.
Complete a biological drawing of this snail to show the external features.
Label the shell, the foot, the tentacles, and the eye at the tip of each
tentacle. Figure 6.6 Snail

UNIT 6
168

7 Drawing a Plant.
Complete a drawing of this plant to identify structural adaptations.
Remember:
be accurate
use a grid
draw to scale
be neat and clear
label the parts.
Figure 6.7 Drawing a plant
Investigating behavioural adaptations.
Behavioural adaptations are often more difficult to study than structural ones.
A group of students investigating why slaters always seem to be found under
objects designed a preference chamber, which was used to offer slaters a
range of conditions for an environmental factor.

cardboard surround to
ensure light is directed
vertically cool, even lighting
transparencies
printed in different
grey blocks
box with sand
and 25 slaters

In three experiments, they tested the preferences of slaters for light,

temperature and soil dampness. In each experiment 25 slaters were put into
the chamber and left for one hour to move to the preferred conditions.

Light full partial light heavy complete

light light shade shade shadow
No. of slaters 0 0 0 4 21

Temp (°C) 5 10 15 20 25 30

No. of slaters 0 1 7 14 3 0

Moisture very slightly quite very completely

in soil dry damp damp damp saturated
No. of slaters 0 3 15 7 0

Draw a series of three bar graphs to display the preference data. b

Summarise the habitat preference of slaters.
Make a drawing to show how the students could modify the chamber to
test for humidity preference.
The students also placed the slaters in a chamber with uniform
conditions throughout. What would have been the purpose of this?

Activity 2 Investigation of adaptations

Aim: To investigate the adaptations of a single species.
Use observations and written resources to find out about the structural,
physiological and behavioural adaptations of a living thing.

BIOLOGY YEAR 12
 169

Place a drawing or picture of the living thing in the centre of a page.

Around the drawing record information about as many of its adaptations as
possible.

Endangered species
Biological communities usually contain a wide variety of species. Unfortunately,
when humans modify natural communities one of the most common consequences
is the loss of species.
Sämoa has a very poor record when it comes the fate of indigenous (native)
species. Not only have we destroyed or put under threat of extinction our native
bird species, including our manumea, but also many native fish, insects and plant
species such as the asi manogi (sandalwood).
Native birds such as manumea, manutagi, segavao, fuia and iao are becoming
endangered. Three factors are causing the loss of these birds:
Humans have released competing species. For example, the exotic birds that
people brought to Sämoa to control the tick on cattle. These birds end up
competing against local native birds and have dominated the native birds’
natural habitats. This is an example of biological control gone wrong.
Humans have released predatory mammals such as cats, dogs and rats.
These mammals prey on the native species.
Humans have destroyed the natural habitat of the native species through
clearfelling for plantations or residential purposes.
The Department of Lands, Survey and Environment and South Pacific Regional
Environmental Programme (SPREP) have become famous for their efforts to save
the turtles, bats and other native species whose numbers fell drastically in the late
20th Century. One problem with endangered species is that often we know very
little about the lives of the endangered species and the numbers of individuals are
so small that the species conservation people cannot afford to make mistakes.

Maintaining biodiversity
Biodiversity is the range of species present in a community. Biologists who believe it
is important to retain as high a biodiversity as possible give the following reasons:
Genetic variation is important for the future. Loss of species now, will limit
the range of species in the future.
Species that we have not yet studied could be the source of future discoveries
of scientific and economic importance. For example, the bark of a pine found
only in one part of America has become an important part of some medicines
for heart disease.
All living species have a right to exist.
If we have varied ecosystems the world becomes a more attractive and
interesting place.

Activity 3 Biodiversity
As preparation for a short talk prepare notes on the arguments for and
against retaining indigenous biodiversity. Say who will benefit and why.
Give your talk to a small group.

UNIT 6
170

Community Inter-Relationships
In this section you learn to:
❑ investigate the inter-relationships that exist between organisms in a local
community
❑ explain how inter-relationships help maintain a community and its
organisms, e.g. predation, commensalism, mutualism, parasitism
❑ explain, with examples, the different roles of different trophic groups in
food chains and webs.
A biological community consists of all the plants and animals that live within a
natural boundary. The size of the community may range from as small as the living
things in a puddle to all the organisms that make up an entire forest. The inter-
relationships between the organisms in a community are sometimes co-operative,
but more often the relationships are competitive or exploitative.
These relationships can be intra-specific which means between members of the
same species for example, parents caring for their offspring. The relationship can
be an inter-specific relationship which means between members of different
species, for example, when two different types of tree are growing beside each
other. They compete for light and space.

Co-operative relationships
Co-operative relationships are when members of the same species work together
to ensure mutual survival. For example, hunting animals, like lions, that hunt
together in groups. Some animals share the rearing of young or have different roles
within the group. In the fo fish the male carries the eggs and young in its mouth.
Male wolves look after the pups when the mothers stop feeding them (six months
after birth).

Inter-specific competition
Inter-specific competition is when individuals from two different species both
use the same resource, e.g. food, a nesting site or a rock on the beach. Plant species
compete with each other for light, water, nutrients and space to grow. Fast growing
plants have an advantage when competing for light as they are quickly able to grow
over top of the other plants and get the most sunlight.

Exploitation
Exploitation occurs when one organism feeds upon another. Browsing animals
feed on the tissue of woody plants and grazers feed on the tissue of soft plants.
Predator species exploit prey species by feeding on them. Scavengers are
organisms that feed on dead material and material left over from a predators kill. A
cone shell or mata poto is a predator. It captures moving prey such as sea worms
Figure 6.8 Mata poto
and small fish by spearing them with its spear-shaped tongue.

Commensalism
Some species live in association with another species. They benefit by
obtaining food, shelter, or some other advantage. The other species is unaffected by
the relationship. For example, epiphytic ferns grow on high branches of trees to
gain more light but the tree is not affected. The messmate fish lives in the intestine
of the sea cucumber. It comes out to get food and will return to the sea cucumber if
in danger.

BIOLOGY YEAR 12
 171

Mutualism
In this relationship both of the species benefit. Micro-organisms in our intestines
benefit by receiving food and shelter. In return we benefit from the digestive action
they have on our food. Lichens are small organisms that are made up of two species
that are living together in a mutualistic relationship. The fungi and the algae that make
up lichen are no longer able to live independently. Another example is the algae that
live in a mutual relationship inside the mantle of the giant clam or faisua.

Clown fish or tufi shelter among the tentacles of sea anemones. The fish give off a Figure 6.9 Faisua or
mucous substance to protect themselves from the anemones stinging cells. The sea Giant clam
anemone gets scraps of food from the clown fish and the clown fish get protection
from the sea anemone.

Parasitism
In a parasitism relationship one species lives on or in a host organism obtaining food
and shelter. A well adapted parasite does not kill its host but may irritate the host or
harm it by taking some of the host’s food. Fleas are an example of a parasite.

Saprophytes
These are organisms that feed on wastes and dead material and decompose it.
Bacteria and fungi are examples of saprophytes. Maggots are also saprophytes.

Activity 4 Inter-relationships
Diagram 6.10 Clown fish
1 Produce a table that summarises the above information on relationships and and sea anemone
gives examples. For example:
Relationship Description Example

Matching terms with definitions.

community a feeding on the tissue of soft plants
exploitation b a relationship which two species benefit from
intra-specific c all plants and animals living in a defined area
inter-specific d interactions between members of same species
e feeding on the tissue of woody plants
browsing
f a relationship when one species lives on another to
grazing
obtain food
predation g when bacteria and fungi feed on dead matter
scavenger h a species which provides food or shelter
commensal i interactions between different species
host species j a relationship when species live with another without
harming each other
mutualism
k hunting another animal species for food
parasitism l species that feed on predator’s left-over food
saprophytism m the utilisation of another species for food

True or false?
Decide whether the following statements are true or false. Rewrite the false
ones correctly.

UNIT 6
172

a All the different species of plants and animals in a rock pool make up a
biological community.
Competition between harrier hawks for territory is classed as intra-specific. c
Commensalism always involves two species which cannot live apart.
d A well-adapted parasite does not usually kill its host.
Classifying relationships.
Identify these feeding relationships.
a Frogs feeding on small insects.
b Moulds growing on bread and absorbing nutrients from it. c
Bees feeding on nectar from flowers.
d Small reef fish living amongst the branches of coral. e
Ants feeding on a dead cricket.
f Weeds growing with lettuces in a neglected vegetable garden. g
Fleas living in the fur of a cat.
h The alga and fungus which make up a lichen.
Chitons grazing on green slime on rocks at high tide. j
Year Rabbits Hawks
Manumea feeding on seeds.
1984 2 – k Tiny wasps laying eggs on the pupae of German wasps.
1985 13 – Graphing and analysing hypothetical data.
1986 58 – In 1984 rabbits arrived in an isolated valley in New Zealand which had
1987 195 – plenty of food and was predator-free. A pair of hawks arrived in the area in
1988 358 2 1988. The table shows the numbers of rabbits and hawks over 15 years.
a Draw a line graph to show the rabbit population numbers over the full
1989 420 6
period.
1990 360 8 b Describe the rabbit population growth before the arrival of predators.
1991 232 12 What is this type of curve called?
1992 95 10 c On the same graph, but using a different scale on the right vertical axis,
plot the hawk numbers.
1993 138 6
d Describe the impact of the hawks on the rabbit population between 1989 and
1994 260 5 1992.
1995 87 7 e What is the shape of the rabbit graph after 1992?
1996 162 4 f Explain the relationship between rabbit and hawk population numbers
1997 98 7 after 1992.
1998 142 5 Analysing life-history strategies.
Complete the table below for mussels and swans.
Aspects of Reproduction Mussel Swan

number of young
size of young
rate of maturing
amount of parental care
formation of pair bonds
reproductive seasons

Do the species display pure short- or long-term strategies?

List the advantages and disadvantages of short-term and long-term
strategies.
BIOLOGY YEAR 12
 173

Interpreting competition.
The photo shows two species of barnacle living at the high tide level on
rocks. The large species is Elminius and the smaller Chamaesipho.
a What resources could the barnacles compete for? b
Describe the intra-specific competition shown. c
Describe the inter-specific competition shown.
d Would the intra- or inter-specific competition be strongest? Why?
Figure 6.11 Two species
e The smaller barnacle Chamaesipho is more common. What could this of barnacle
suggest about its lifestyle?
f The habitat of barnacles appears to be restricted to the surface of hard
rocks. Why might this be so?
Studying niche differences.
The three species of burrowing shellfish shown below seem to share similar
ecological niches. They are all filter-feeders that live in the fine sand of
sheltered, sandy beaches.

Shellfish Location and Distribution on a Sandy Beach

beach surface upper tugane upper beach

lower wedge
shell mid-
beach
cockle
tugane
wedge shell cockle

sand lower beach

Their distribution between the high and low tidal zones is plotted on the kite
diagram. The width of the kite is proportional to the numbers present at that
site.
Describe what each kite diagram shows about the distribution of the
species involved.
The cockles and wedge shells coexist in the same beach area. Suggest how
competition for space between the two species might be minimised.
The smooth-shell bivalve sand-burrowing molluscs also feed in the same way
(using their siphons to filter a stream of micro-organisms out of the
water). What habitat factor might explain their distribution?

Activity 5 Investigation of a local community

Aim: To investigate a local community and identify interrelationships
between organisms.
Draw a map of an area which shows the location of a range of plants and
animals.
Make a list of possible examples of inter-relationships between the
organisms found in the area.

UNIT 6
174

Food chains and webs

All of the species in a biological community are linked through feeding
relationships. These feeding relationships are shown in food chains and food webs.
Food chains show a single set of feeding relationships.
All food chains and webs begin with a producer. A producer is a green plant that
can carry out photosynthesis. The arrows in the food chain go from food to feeder.

producer herbivore
Primary Secondary
photosynthetic browses or carnivore carnivore eats
plant grazes plants eats herbivore primary carnivore

For example:
Seaweed ➔ cat’s eye whelk ➔ seagull
Plankton ➔ coral ➔parrot fish

Food Web of a Passionfruit Vine Food webs show a number of interconnected food chains.
cat

thrush
Activity 6 Food chains and webs
spider
mantis
Aim: Identifying feeding levels.
fantail Use these codes to identify the feeding levels of organisms:
ladybird lacewing

caterpillar leafhopper P = producer, H = herbivore, C1 = primary carnivore, C2 = secondary carnivore,

C3 = tertiary carnivore D = decomposer
Identify the feeding levels of the organisms listed in the food chains above.
snail aphid
Identify the feeding levels of the organisms listed in the food web above and the
passionfruit vine following food web.
leaf litter

slater earthworm

Figure 6.12 Food web of

a passionfruit vine

Figure 6.13 Food web diagram

Identify possible feeding levels for the following organisms:
lulu, ve⁄, lupe, miti tai, segasega maufi, pe⁄ vao, pili, üü, amu, faisua,
alamea, fe¤.
Draw up food chains and food webs for other local organisms.

BIOLOGY YEAR 12
 175

Conservation
In this section you learn to:
❑ investigate a local environmental issue
❑ discuss causes and effects, and suggest possible solutions for
environmental issues
❑ explain why it is important to recycle nutrients using the carbon and
nitrogen cycles
❑ compare both the long-term and short-term effects of using biological
controls on the environment, as opposed to the use of chemical controls
such as pesticides.

Recycling of chemicals
There are a number of chemicals necessary for growth and maintenance of all
organisms in a community. Carbon, oxygen, hydrogen, and nitrogen are chemicals
organisms need in large amounts. Many other elements, such as phosphorus and
sulfur are needed in small amounts. These chemicals are continually being cycled
from an environmental store, through the community, and then back to the store
again. An environmental store is a place in the ecosystem such as the atmosphere
or soil where the chemical can be found outside of the living things.

Carbon cycle
The most important element is carbon whose atoms form
the backbone of all complex molecules in organisms. The Carbon Cycling in a Terrestrial Ecosystem
carbon cycle shows the movement and storage of carbon in
carbon dioxide (CO2)
an ecosystem. io
n in the atmosphere
t
a

Carbon is the key raw material in photosynthesis. Plants get

r
i
r

e
sp
respiration
carbon from carbon dioxide in the atmosphere and use it to photosynthesis
Producers
produce carbohydrates. The plant then uses the
carbohydrates and minerals from the soil to make all the
chemicals that the plant needs to live. For example, Carnivores
cellulose, fats and proteins. Herbivores
death and wastes
The carbon passes through the trophic levels of the
combustion
community as plant and animal tissue is eaten. When
Decomposers
herbivores eat the plants, they gain the carbon the plant has
(fungi, bacteria)
used. The herbivore uses the carbon chemicals in the food to past fossilisation
make the chemicals needed for its body. When the
herbivore is eaten, the carbon passes onto the next coal, oil (fossil carbon reservoir)
organism. The carbon in wastes and dead material passes to Figure 6.14 Carbon cycle
the decomposers.
Carbon is released back to the environmental store in the atmosphere through
respiration by plants, animals and decomposers.
Some carbon has been locked up in natural gas, coal and oil reservoirs, which were
formed millions of years ago when dead organisms became buried in swamps or
under sediment on the sea floor.
Currently, the level of carbon dioxide in the atmospheric store is rising faster then
the plants of the Earth can use it. This is due to the huge increase in the amount of
fossil fuels being used by people, e.g. petrol. The increase in carbon dioxide in the
atmosphere is causing international concern as it is a ‘greenhouse gas’ and is
contributing to global warming.

UNIT 6
176

atmospheric
carbon dioxide
Nitrogen cycle
(CO2) Nitrogen is an essential element required by plants to make amino acids which are
A A A B A the chemicals that are joined together to make proteins. See also page 25.
hawk tussock
Adding fertilisers, containing nitrogen compounds, to the soil can increase the
rabbit
availability of nitrogen for plants.
C C

Activity 7 Nutrient cycles

C
soil Explain why nutrient cycles are important in the ecosystem.
bacteria
Copy the diagrams of the carbon and nitrogen cycles into your books.
Figure 6.15 Interpreting
cycle diagrams Interpreting cycle diagrams
a Identify the trophic levels of the four organisms shown below. b
Name the processes indicated by arrows A and B.
c Which trophic level carries out both processes A and B? d
Arrow C involves two processes. What are they?
e Which trophic levels are essential for ecosystems to function? Why?

Environmental issues
Introduced species
A threat to the stability of biological communities that humans cause is the
introduction of new species. This creates new relationships and may cause major
changes to communities.
Humans have introduced many exotic (non-native) plant and animal species. Some
were brought to Sämoa on purpose, but many arrived accidentally and unnoticed,
e.g. insects coming on ships. Many exotic species are useful to humans for
example, farmed animals.
Some species did little harm to other species, but others have caused major
problems, for example, the mile-a-minute plant. Some exotic species directly harm
organisms useful to humans for example, taro leaf blight and rhinoceros beetle.
Others damage native species through exploitation or competition for example, the
African snail and cats. Cats are a major predator of native organisms.
Introduced species are usually not such a problem in the country they come from
because in that country there are some species that compete with it and others that
exploit it. Therefore, in its own country it fits into the natural inter-relationship in
the community. Usually these inter-relationships don’t exist in the new country.
Introduced species often have to be controlled using biological control. Biological
controls have advantages and disadvantages which mean that sometimes people use
chemical controls instead.

BIOLOGY YEAR 12
 177

Activity 8 Introduced species and biological control

List examples of species that have been introduced into Sämoa.
Mark, on your list, which introduced species have become environmental
problems.
Explain why introduced species are usually not a major problem in the
country they come from.
Research an example of biological control used in Sämoa. Find out the
following:
❑ What are the advantages of using a biological control?
❑ What are the disadvantages of using a biological control?
❑ Compare the effects of the use of the biological control with the use of
chemical controls, such as pesticides.

Deforestation
A rainforest is a dense forest found in tropical and temperate areas with high
humidity and heavy rainfall throughout the year. Few issues have raised such
worldwide concern as the rapid and continuing removal of tropical rainforest,
which is one of the world’s major ecosystems. This became an issue in the 1920s,
and so far, in spite of worldwide alarm, we seem to be powerless to stop it.
Rainforest destruction means loss of habitat for plants and animals and disrupts the
lives of local people and people in neighbouring countries. The problem has
become so large that it is affecting local and global weather patterns.
Tropical rainforests cover less than 6% of the Earth’s surface, yet they are home to
more than half of the species on our planet. Rainforests are the oldest and most Figure 6.16 Tropical
rainforest
diverse, productive and complex ecosystems on Earth.
The complex layer structure of rainforest provides a host of micro-habitats, and
the heavy rainfall and high temperatures allow rapid growth all year long. The key
to their value is biodiversity. Some ecologists calculate over 30 million species of
plants and animals live in these forests. Many are still unknown. Newly discovered
species are proving to be a vast store of potentially valuable medical drugs, foods
and biological control agents. Apart from the scientific potential of the forest, we
need to consider the basic right of rainforest species, including the indigenous
human forest-dwellers, to survive in their habitat.
Why are the rainforests being destroyed at such an alarming rate?
Population pressure: Most of rainforests are in countries, such as Brazil,
Indonesia and the Congo. These countries have rapid population growth and
many poor people. People clear the forests to grow food. Unfortunately once
the forest is cleared, the soils rapidly lose their fertility and do not support
good crops for long.
Cattle ranchers: Large-scale ranchers move in and sow grass and graze cattle
on the cleared land. The cattle are used to supply an overseas beef market.
Forest clearance by commercial plantation owners is also a factor.
Timber milling: Large timber companies lease forest and mill it for the
valuable hardwood timber. The South-east Asian rainforests found in
Indonesia and Malaysia are the main world hardwood suppliers. In most
cases, timber companies have short-term leases and have no interest in
sustainable milling.

UNIT 6
178

Facts and figures

❑ Humans have already destroyed over 50% of the world’s rainforests.
❑ Less than 9 million square kilometres still remains (6% of the total land
area).
2 2
❑ Each year 150 000 km of rainforest is destroyed – 100 000 km is cleared
and 50 000 km2 logged – an area about the size of two football fields goes
every second!
❑ Less than 10% of the forests are being managed sustainably.
❑ It has been calculated that at the present rate of destruction about 135
species of rainforest plants and animals are becoming extinct each day!
❑ The economic value of one hectare of forest is $13 650 per year if
Figure 6.17 Deforestation
sustainably harvested, but only $262 if used as cattle pasture.

Climate change
Tropical rainforests are an important part of the global weather system. The water
evaporated from rainforests is the main source of moisture in tropical air.
Reduced forests means reduced rainfall. The rainfall distribution changes and this
leads to droughts in new areas, flooding in other areas and soil erosion. This has
happened around the southern edge of the Sahara.
The vast rainforests act as carbon sinks absorbing the carbon dioxide, one of the
‘greenhouse’ gases that are linked to global warming. Large-scale forest
destruction also affects how the Earth’s surface reflects the rays of the sun.
Scientists now suspect that this factor may be affecting wind patterns and ocean
currents, and may be linked to climate changes in other parts of the world.

Saving the remaining forests

A number of groups of people are very concerned about the destruction of the
rainforest and some have become activists that protest to governments of countries
where rainforest destruction is occurring.

Passionate quotes made about rainforests

‘Rainforests are the finest celebration of nature ever known on the planet.’
NORMAN MYERS
Those who destroy the rainforest are acting ‘with the savage unthinking
ferocity of drunken apes in an art gallery. Whereas pictures can be repainted,
tropical rainforests can’t be recreated’.
GERALD DURRELL
‘The destruction of two trees is the price of one hamburger.’
ANONYMOUS

BIOLOGY YEAR 12
 179

The problem of rainforest destruction is so widely recognised that the United Nations
has spent over $16 billion on a Tropical Forestry Action Plan to halt the destruction.
In spite of this, the UN has had little impact – in fact recent reports suggest increasing
rates of destruction. At the 1992 Earth Summit meeting, developing nations with
rainforests were unwilling to co-operate in what they saw as an effort by wealthy
countries to restrict resource development in poorer regions.

Indonesia, for example, argued that debt reduction by selling timber and clearing
land for increasing population is more important to them than long-term
environmental programmes. To make the problem worse, there is much corruption
and often the logging companies are associated with the political rulers. Often
sustainability agreements are not enforced. Tensions can be so high that in Brazil a
prominent conservationist was killed by ranchers.
The original forest-dwelling tribes have little voice. They have to adapt or die. In
Brazil, there were once over six million forest-dwellers. Now there are fewer than
200 000!

Activity 9 Local environmental issues

Aim: To investigate a local environmental issue.
Your teacher will instruct you to work as a class or individual on this topic.
Select a topic from the list below or select an environmental issue that is
relevant to your village or island:
❑ deforestation
❑ overuse of chemical pesticides and fertilisers
❑ reclaiming of mangrove areas
❑ dumping rubbish in riversides
❑ using Derris plant root or Clorox or dynamite to catch fish
❑ over-fishing
❑ catching undersized fish
❑ industrial pollution
❑ marine oil spills
❑ lack of proper sanitation threatens aquifers and the water table
❑ effects of introduced species on local wildlife.
Find out about the topic so that you can complete the following:
❑ Describe how or why the topic is an environmental issue.
❑ What is the cause of the issue?
❑ How are local people affected by the issue? ❑
What are people trying to do about the issue?
❑ Suggest possible solutions to the issue.
❑ Give your opinion as to which is the best solution. Give biological,
economic or social reasons to support your opinion.
Use a range of resources to find out about the issue:
❑ guest speakers
❑ field work investigations
❑ printed resources
❑ interviews with local people.

UNIT 6
180

Glossary
Word/phrase Meaning

adenosine an enzyme that links water intake and respiration in plants by transfer of
triphosphate (ATP) energy.
aerobic needing oxygen for respiration.

aerobic respiration a type of internal respiration in which glucose and oxygen get broken down

into carbon dioxide, water and ATP molecules.

allele different forms of a gene.

anaerobic not needing oxygen for respiration.

anaerobic a type of internal respiration found, for example in yeast, in which no oxygen

respiration is used and pyruvic acid is broken down into lactic acid.
antibiotic able to destroy pathogenic bacteria or a medicine to destroy pathogenic

bacteria. The first antibiotic development was penicillin that was extracted
from a mould.
antigens any substance which stimulates the production of antibodies, e.g. bacteria,

foreign red blood cells.

antiseptic a substance applied to living tissue (e.g. externally on a wound) to kill micro-

organisms on human tissue.

asexual type of reproduction that does not depend on sexual process.

back cross to get offspring by mating a first generation cross to one of the original

parental types.
bacterium a type of micro-organism.

(plural bacteria)
binary fission the way single cells (e.g. bacteria) reproduce, by splitting in two.

biological oxygen the amount of oxygen required for aerobic purification, the amount of

demand (BOD) oxygen being used by living things in an area of water.

cellulose forms the wall of cells in all plants.

chloroplast special centres of chemical activity inside a leaf cell.

coliform bacteria organisms that enter natural streams by deposit of animal and human waste.

concentration the amount of a substance in a given volume.

consumers living things which cannot make their own food.

control part of an experiment used to compare the changing of conditions. Most

experiments need a control to ensure the conclusion is justified.

cytoplasm the material basis of a cell apart from that of the nucleus.

cytoskeleton the fibres that form the cytoskeleton, support the cell, give it shape and

allow cells to move.

BIOLOGY YEAR 12
 181

Glossary
Word/phrase Meaning

decomposers living things that live on the breaking down of dead plant or animal matter.
diffusion general transport of matter when molecules and ions mix in liquids.

disinfectant a powerful chemical which kills micro-organisms.

dispersal to separate and move apart in different directions, become scattered.

dominant an allele which is always expressed when it is present.

enzyme protein used to speed up cell reactions.

express/expressivity the extent to which a gene shows an effect.

extracellular the digestion of material by enzymes secreted from a cell and acting outside

digestion a cell.
fermentation conversion of sugars into alcohol using yeast.

flagellum structure which helps bacteria to move.

(plural flagella)
foetus a young mammal within the uterus of the mother from the formation

development of the organs until birth.

fungus a type of micro-organism.

(plural fungi)
gametes sex cells.

gas exchange the phase in respiration in which a living organism takes in oxygen from its

surroundings and gives up or exchanges the oxygen for carbon dioxide.

gene a unit of the genetic code which controls a characteristic.

Golgi bodies flat, disc-shaped layers of membrane, scattered particles, that are packages

chemicals use outside the cell.

glycolysis enzyme-controlled reactions which break glucose molecules into pyruvic

acid molecules.
homologous pair pairs of similar genes or chromosomes.

homozygous a genotype when both alleles are the same.

lymph a colourless fluid that circulates the body of mammals.

T-lymphocyte cell a cell that develops in the thymus gland.

tissue a group of cells forming a continuous fabric.

xylem a plant tissue.

zygote fertilised egg cell.

GLOSSARY
182

Key Vocabulary
Vocabulary Collocations Derivations
adaptations structural adaptations to adapt

physiological adaptations
behavioural adaptations
anti- antibiotics

antibodies
antigens
a cell a host cell

the cell wall

the cell membrane
cell differentiation
unicellular cellular
multicellular
extracellular digestion
concentration the greatest concentration

the sugar concentration

the carbon dioxide concentration
control the biological control

chemical controls
decomposers decomposer micro-organisms decomposer

to be determined inherited features are determined by genes

sex is determined by chance

diagnosing diagnosing meningitis diagnosis

diagnosing illness
effectiveness the effectiveness of antiseptics and disinfectants

the effectiveness of antibiotics

fibre fibre in your diet

muscles fibres fibres

to form a hypothesis

immunity immunity to disease

passive immunity
active artificial immunity
immune deficiency immune
to be immunised against diseases to be immunised
immunisation
nutrients recycling nutrients

essential nutrients
nutrient deficiencies nutrient
nutrient preferences
preserving food preserving

food preservation technology preservation

preservation methods
preserved food preserved
recycling recycling of chemicals

relationship an intra-specific relationship

an inter-specific relationship
co-operative relationships
the relationship between an organism and . . .
feeding relationships
a parasitism relationship
a mutualistic relationship
interrelationships between organisms an interrelationship
community interrelationships

BIOLOGY YEAR 12
 183

Key Vocabulary
Vocabulary Collocations Derivations
resistance bacteria acquire resistance to an antibiotic

antibiotic resistance
a drug-resistant strain of TB resistant
a system a system of membranes and connecting tubes

the digestive system

the immune system
the respiratory system
the circulatory and lymphatic systems
the excretory system
the skeleto-muscular system
the endocrine system
the nervous system
the internal defence systems of the body
the global weather system
transpiration transpiration rates

transpiration pull
the effect of environment on transpiration
variation variation patterns

inherited variation
acquired variation
continuous variation
discrete variation
either/or variations
independent variable a variable
dependent variable
controlled variable variability

Useful structures
❐long filaments bearing pollen-producing sacs called anthers.
❐the symptoms and signs that made the doctor suspect meningitis.
❐ an inflammation of the ‘meninges’ or membranes that surround the brain and spinal cord. ❐ a
threat to the stability of biological communities that is caused by humans.
Naming
❐Organisms which are unicellular or multicellular but lack complex organs are referred to as ‘simpler’ organisms. Organisms in the
Kingdoms Monera, Protista and Fungi are simple organisms.
❐Organisms that make food molecules using raw materials and energy from the environment are called producers.

Defining
❐An organ is a collection of different types of cells working together to carry out a particular function.
❐The leaf is an organ which is made up of layers of different sorts of cells that work together to carry out photosynthesis.

Examples
❐Examples of specialised cells in animals are skin, nerve, bone and blood cells. Examples of the functions of plant cells include providing support,
absorbing water, conducting liquids, allowing gases in and out, making food, forming protective surfaces and reproduction.
Comparing and contrasting
❐ When compared with matter that is non-living, objects that are alive are characterised by a number of special features. ❐ Some
bacteria are single cells and others live as groups of cells joined together.
❐Some fungi are small organisms made up of one cell. Others can be large organisms made up of many cells. ❐
Animals, unlike plants, cannot manufacture their own food.
Making general statements about a class of things
❐ All organisms are made up of cells. ❐
All cells carry out the life processes.
Restricting the generalisation
❐Organisms usually have one gene in their genotype for a trait.
❐Almost all diseases of plants, animals and human beings are caused by micro-organisms.
❐Although some cells can live independently, most cells live as part of a multicellular organism.

KEY VOCABULARY
184

Describing physical structure

❐ Bacterial cells are made up of cytoplasm and genetic material in the form of a long chromosome. ❐ The
body, or mycellium, of a large fungus is made up of fine threads called hyphae.
❐The cell membrane is made up of two layers of lipid molecules. A small number of protein molecules can also be found in between the lipid
molecules.
❐ Plant cells have a cell wall outside the cell membrane. The cell wall is made up of cellulose and it provides that cell with support. ❐
Bacteria have no cell nucleus and no cell organelles.
❐The cytoplasm is surrounded by a strong cell wall.

Expressing changes in quantity

❐TB rates here have levelled off.
❐They have been showing a slight rise.
❐Reducing the numbers of deaths to a very low level.

Expressing movement of substances

❐ against a gradient ❐
across a membrane
❐down a concentration gradient
❐from higher to lower concentration areas

Expressing measurement
❐bigger than 10 nm in size

❐ the cell of a bacterium is smaller than 0.01 millimetres ❐ in

the range of 10 to 100 µm in diameter
❐ structures from 100 µm down to 0.1 nm in size ❐
up to 600 mm
❐to a depth of 0.5–1.0 cm

Topic specific vocabulary

Related to Chapter 1: Living things and micro-organisms leucocytes
the phylum the bone marrow
kingdoms leukaemia
pathogens, a pathogenic disease, pathogenic micro-organisms, HIV
pathogenic bacteria lysozyme
fermentation mucous
coccus phagocytes
bacillus vaccination
spirillum hepatitis A
the organelles poliomyelitis
the cytoplasm AIDS
aerobic respiration, anaerobic respiration
Related to Chapter 2: Cell structure, respiration, osmosis and
enzymes diffusion, and enzymes
saprophytes nucleus
binary fission vacuole
the mycelium of a fungus chloroplast
hyphae ribosome
spores endoplasmic reticulum
to subculture bacteria, subculturing mitochondria
nodules Golgi bodies
nitrogen fixers cytoskeleton
cellulose digesting bacteria endoplasmic reticulum
biotechnology membrane sacs
genetically engineered bacteria connective tissue
inoculation to resolve objects
incubation the Krebs cycle
contaminated food glycolysis pyruvic
opportunistic infections acid lactic acid
Koch’s postulates solutes plasmolysis
symptoms diffusion biological
inflammation catalysts amino acid
amoebic meningitis chains to be
toxins denatured
carriers
membranes of the nose and throat
an epidemic to catalyse a reaction
tuberculosis (TB) peroxidase
medication

BIOLOGY YEAR 12
 185

Topic specific vocabulary

Related to Chapter 3: Cell division and inheritance heartwood and sapwood
mitosis the vascular bundles
meiosis tropism
a zygote Related to Chapter 5: Nutrition, circulation, gas exchange,
the genetic code excretion, movement, endocrine system, nervous system,
gametes reproduction and the effect of drugs and exercise
the genome lipids, fatty acids
homologous chromosomes amino acids
deoxyribonucleic acid or DNA eating disorders
the double helix ingestion
the Human Genome Project absorption
monohybrid egestion
hybridisation oesophagus
Mendel’s F1 Cross, Mendel’s F2 Cross peristalsis
a punnet square pancreas
phenotype gall bladder
genotype small intestine
alleles large intestine
pure-breeding plasma
pure strains platelets
heterozygous arteries
homozygous capillaries
a dominant gene the right/right auricle
a recessive gene the lymph nodes
dominance pulse
recessiveness inhalation
a pedigree chart exhalation the
trait diaphragm the
X and Y chromosomes trachea the
bronchi
Related to Chapter 4: Photosynthesis, plant structure, plant bronchioles an
processes and co-ordination alveoli kidneys
leaf pigments nephrons urea
consumers
the cuticle
the epidermis, the epidermal cells the ureter the
the palisade mesophyll layer bladder vertebrate
the spongy mesophyll layer animals an
vascular bundle endoskeleton
the phloem tubes ligaments tendons
a stoma, stomata adrenaline insulin
guard cells oestrogen thyroxin
xylem cells
rhizomes
a tap root system
a fibrous root system stimuli
pneumatophore roots receptors
an adventitious root system reflex action
the root cap gametogenesis
the meristem embryonic development
meristematic tissue the uterus
a weight potometer the testis the
a bubble potometer placenta
asexual reproduction conception
seed dispersal fertilisation
hermaphrodites menstruation
sepals Related to Chapter 6: Adaptation, inter-relationships and
stamens conservation
the petiole biotic environmental factors
the pistil abiotic environmental factors
an ovule biodiversity
testa predation
germination commensalism
the cotyledon inter-specific competition
the radicle the exploitation
plumule ecological niches
the cambium cells exotic plant and animal species
the apical meristem deforestation
the lateral meristem carbon sinks

KEY VOCABULARY
 nzaid
© Ministry of Education, Sports and Culture, Sämoa, 2004