CAPS
Natural Sciences
Learner’s Book
8
M. Bester • A. Clacherty • S. Cohen • J. Cowan • S. Doubell • A. Joannides
G. Lombard • E. Nkosi • S. Paarman • K. Padayachee • R. Sadie
L. Schreuder • M. Slamang • E. Ungerer
Platinum Natural Science Grade 8
Learner’s Book
Maskew Miller Longman (Pty) Ltd
Forest Drive, Pinelands, Cape Town
website: www.mml.co.za
© Maskew Miller Longman (Pty) Ltd 2012
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in
any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written
permission of the copyright holder.
Every effort has been made to trace the copyright holders of material produced in this title. We would like to apologise
for any infringement of copyright so caused, and copyright holders are requested to contact the publishers in order to
rectify the matter.
First published in 2013
Print ISBN: 978-0-636-14091-2
ePDF ISBN: 978-0-636-15204-5
Edited by Sian Hemmings
Contents
Term 1
Term 2
Life and living
1
Matter and materials
71
Topic 1
1
2
6
Topic 4
71
Photosynthesis and respiration
Unit 1 Photosynthesis
Skills focus Variables and fair tests
Skills focus Carrying out practical
investigations
Unit 2 Respiration
Topic revision
Topic 2
Interactions and interdependence
within the environment
Unit 1 Introduction to ecology
Unit 2 Ecosystems
Unit 3 Feeding relationships
Unit 4 Food chains and food webs
Unit 5 Balance in an ecosystem
Unit 6 Adaptations
Unit 7 Conservation of the ecosystem
Project
Select and study an ecosystem
Topic revision
7
11
14
15
16
18
22
28
35
40
44
48
50
Topic 3
Micro-organisms
51
Unit 1 Types of micro-organisms
52
Skills focus Measure length and use a
scale
56
Practical task Investigate the factors that affect
the growth of yeast
58
Unit 2 Harmful micro-organisms
60
Unit 3 Useful micro-organisms
66
Topic revision
68
Term 1 Practice test
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69
Atoms
Unit 1 Atoms – the building blocks of
matter
Unit 2 Subatomic particles
Unit 3 Pure substances
Unit 4 Elements
Unit 5 Compounds
Unit 6 Mixtures of elements and
compounds
Topic revision
72
74
79
81
83
87
88
Topic 5
Particle model of matter
89
Unit 1 The concept of the particle
model of matter
90
Unit 2 Change of state
96
Unit 3 Density, mass and volume
98
Unit 4 Density and states of matter 100
Unit 5 The density of different
materials
102
Skills focus Raise questions about
issues
105
Unit 6 Expansion and contraction of
materials
106
Unit 7 Pressure
110
Practical task Use the particle model of matter
to explain changes in state,
density and pressure
112
Topic revision
114
Topic 6
Chemical reactions
Unit 1 Reactants and products
Skills focus Chemical reactions and
chemical equations
Topic revision
115
116
120
122
Term 2 Practice test
123
Practice examination: Terms 1 and 2
241
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Term 3
Term 4
Energy and change
125
Planet Earth and beyond
191
Topic 7
Static electricity
Unit 1 Friction and static electricity
Topic revision
125
126
134
191
192
194
Topic 8
135
136
Topic 11 The solar system
Unit 1 The Sun
Unit 2 Objects around the Sun
Practical task Interpret facts about the solar
system and write about
the planets
Unit 3 Earth’s position in the
solar system
Topic revision
Topic 12 Beyond the solar system
Unit 1 The Milky Way galaxy
Unit 2 Our nearest star
Unit 3 Light years, light hours and
light minutes
Unit 4 Beyond the Milky Way galaxy
Topic revision
209
210
213
Energy transfer in electrical systems
Unit 1 Circuits and current electricity
Unit 2 Components of an electrical
circuit
Skills focus Draw electric circuit
diagrams
Unit 3 Effects of an electric current
Practical task Make and use an
electromagnet
Topic revision
138
143
144
150
152
Topic 9
Series and parallel circuits
153
Unit 1 Series circuits
154
Skills focus Predict and write
a hypothesis
156
Unit 2 Parallel circuits
157
Unit 3 Output devices
159
Skills focus Build electric circuits and
draw circuit diagrams
160
Topic revision
162
Topic 10 Visible light
Unit 1 Radiation of light
Unit 2 The spectrum of visible light
Unit 3 Opaque and transparent
substances
Unit 4 Absorption of light
Unit 5 Reflection of light
Unit 6 Seeing light
Unit 7 Refraction of light
Topic revision
163
164
166
Term 3 Practice test
189
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168
171
173
177
182
188
202
204
208
216
220
224
Topic 13 Looking into space
225
Unit 1 Early viewing of space
226
Unit 2 Telescopes
231
Skills focus Draw a scientific diagram 237
Topic revision
238
Practice examinations: Terms 1 and 2
Terms 3 and 4
239
242
Glossary
Index
Acknowledgements
246
251
255
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Term 1: Life and living
Topic
1
Photosynthesis and respiration
Starting off
You learnt in Grade 7 that the biosphere is where life
exists. The biosphere includes all living organisms,
such as plants, animals and micro-organisms.
Living organisms need energy to sustain life. In
this unit you are going to learn where this energy
comes from and how it is made available to living
organisms.
Activity 1
Figure 1 The biosphere includes all living organisms.
Revise knowledge of living
things
Look at Figure 1.
1. Write the names of the living organisms that
you see in the picture.
2. Write the names of the non-living things that
you see in the picture.
3. How do you know if something is living or
non-living?
Topic 1: Photosynthesis and respiration
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Unit
1
Photosynthesis
Key words
• interdependent –
two or more things
that depend or rely
on each other
• radiant energy –
energy contained
in electromagnetic
radiation
• photosynthesis –
radiant energy is
converted into
potential energy
which is stored in
food, and oxygen
is released
• chemical
reactions –
chemical changes
that take place
when two or more
compounds react
and form new
substances
• cells – smallest
units of living
organisms
• chlorophyll –
green pigment
in plant cells that
absorbs radiant
energy
• potential energy –
energy that is
stored in an object
or system
2
The need for energy drives interactions
between living organisms
Living organisms interact with one another and are interdependent.
This means that they rely on each other. The most important way that
organisms interact is in their search for energy or food. For example,
gemsbok eat grass, and lions eat gemsbok. In other words, the interactions
and interdependence between organisms in an ecosystem is driven by the
need for energy to sustain life. This unit will explain where the energy in
ecosystems comes from.
The Sun is the ultimate source of energy
The Sun is the ultimate source of energy for all living things. The Sun
provides this energy in the form of light and heat, which is known as
radiant energy.
All living organisms depend on energy
to sustain life. However, organisms
cannot use the radiant energy from
the Sun directly. The energy must be
changed into a form that can be used.
You should remember that energy
cannot be created or destroyed, but
it can be converted from one form
into another. During a process called
photosynthesis, green plants convert
radiant energy into a form of energy
that living organisms can use.
Figure 2 The Sun
The process of photosynthesis
Photo means ‘light’ and synthesis means ‘to make’. So, during
photosynthesis, plants make food in a series of chemical reactions.
Plants require the following resources in order to photosynthesise:
• Sunlight – plants appear green because they have a green pigment in
their cells. This pigment is called chlorophyll. It absorbs the radiant
energy from the Sun.
• Water – plant roots absorb water from the soil.
• Carbon dioxide – plants absorb carbon dioxide from the atmosphere.
Gases are absorbed and released through the plants’ leaves.
Term 1
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Plants use radiant energy to produce glucose from sunlight and water.
Oxygen is released as a waste product. Glucose is a simple sugar that is
used by the plant for food. The equation for the process of photosynthesis
is shown below:
carbon dioxide + water
chlorophyll
sunlight
glucose + oxygen
radiant energy
oxygen released
into the air
CO2 (factory)
CO2 + H2O
glucose + O2
CO2 in air enters
leaf through
stomata
water absorbed by plant roots
Figure 3 A simple representation of photosynthesis
The radiant energy of the Sun is now converted into potential energy. The
potential energy is trapped in the glucose. This potential energy is the fuel
that plants use to do their work.
When animals eat plants, they consume the energy that the plants have
made during photosynthesis.
Topic 1: Photosynthesis and respiration
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Plants convert glucose into other compounds
Plants change glucose into many other chemical compounds. These
compounds are required by plants for different processes such as growth
and reproduction.
Plants change glucose molecules into starch because this is the chemical
compound that plants use to store energy. Many glucose molecules join
together to form a molecule of starch. For example, the sugars and starch
produced during photosynthesis are stored in the leaves and other parts
such as apples, potatoes, rice and carrots. You can see this in figures 4 to 6.
Sugar and starch is food for animals and humans. It is the most important
energy source that is needed to sustain life.
Glucose is also converted into the chemical compound cellulose. Cellulose
is part of the cell walls of plant cells. Cellulose is a structural material that
provides plants with support – it is the reason why trees can grow so tall
without falling over.
Figure 4 Photosynthesis takes place in
the leaves.
4
Figure 5 Starch is stored in the carrot.
Figure 6 We take in energy in the form of starch
when we eat the carrot.
Term 1
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Activity 2
Write about the requirements for, and products of,
photosynthesis
Look at Figure 7 and answer the questions below.
1
2
3
4
Figure 7 How photosynthesis takes place
1. What type of energy is represented by the part numbered 1?
2. Identify the gases numbered 2 and 3. Where does the gas numbered 3
come from?
3. What is the part numbered 4?
4. What happens in the cells when the parts numbered 3 and 4 meet in
the cells?
5. Write down the word equation for photosynthesis.
6. The sugars that are produced during photosynthesis are transformed
into other chemical compounds. Give the names and functions of TWO
examples of these chemical compounds.
7. Explain in your own words what happens to the plant at night.
8. What is the biological importance of photosynthesis for the ecosystem?
Key concept
Plants change
radiant energy
into potential
energy by
means of
photosynthesis.
This potential
energy is in the
form of starch,
which is used
as food for the
plants, as well as
by the animals
that eat the
plants.
Topic 1: Photosynthesis and respiration
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Skills focus: Variables and fair tests
What are variables?
Key words
• variable – any
factor that has
an effect on an
investigation
• independent
variable – the
factor that you will
purposely change
• dependent
variable – the
variable that you
will measure
• controlled
variable –
variables that are
kept the same
• fair test – an
investigation
where all of the
variables are
controlled
A variable is anything or any factor that has an effect on an investigation.
Examples of some variables include mass, temperature, time, volume and light.
When you plan an investigation you will need to identify all of the variables
that may affect your investigation. There are three different kinds of variables:
• The variable that you will purposely change is called the independent
variable.
• The variable that changes as a result of the independent variable and
the variable that you will measure is called the dependent variable.
• Variables that you will purposely keep the same are called controlled
variables. Controlling variables allows you to conclude that the
changes in the dependent variable are due only to changes that you
made to the independent variable.
What are fair tests?
A fair test is an investigation where all of the variables are controlled. All
of the variables are kept the same and only one variable is changed. This
means that if there is a change to the dependent variable (the variable that
you will measure) it must be caused by the independent variable.
How to identify variables
When you plan an investigation you will make
observations of something happening around you.
You will make an hypothesis which is a statement
where you attempt to explain what you have observed.
The hypothesis will include the independent variable
and the dependent variable. Here is an example
of an hypothesis: Seeds need low temperatures to
germinate. The independent variable is temperature
and the dependent variable is germination of the seed.
Activity 3
Figure 8 When carrying out an investigation only one
variable is changed
Practise identifying variables
For each of the following identify the dependent and the independent variables.
1. Tembela noticed that when the temperature was increased in the greenhouse tomato plants
produced more tomatoes.
2. Bean seedlings were taller when they received more intense sunlight.
3. Look at Figure 8. Suggest the independent variable and dependent variable.
6
Term 1
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Skills focus: Carry out practical investigations
What is a practical investigation?
Key words
Practical investigations are experiments and tests that we conduct to
find out more about the world around us and how it works. To conduct the
experiments and tests, we follow a series of steps in a logical order to make
sure the results of an investigation are valid. These steps are also known as
the scientific method. You learnt the steps of the scientific method in earlier
grades. They are given again to refresh your memory.
How to carry out practical investigations
Step 1: Observe the world and ask questions
Observe the world around you and ask questions about how things work or
why things happen in a certain way.
Step 2: Write a hypothesis
• practical
investigations –
scientific
experiments and
tests conducted
to find answers to
questions
• hypothesis –
possible
explanation or
answer to the
question you are
investigating
A hypothesis is a statement that gives a possible explanation or answer to
the question you are investigating. It is a prediction of what you think the
answer is.
Step 3: Plan your investigation
You have to plan how you are going to test your hypothesis. Think about the
variables that could cause the results of your investigation to change. Make
a list of all materials and equipments you need. Devise a method for a fair
test that you can follow to collect data or results.
Step 4: Conduct your investigation and record your findings
Follow your plan and record all your observations, measurements and other
results in an organised manner.
Step 5: Analyse your results and draw conclusions
Process your results to make it easier to interpret. Use tables and graphs to
make it easier to see trends and patterns.
Draw a conclusion based on the analysis of your results. Compare your
conclusion with your hypothesis to determine whether further testing is
necessary.
Step 6: Evaluate your investigation
Think about how easy or difficult is was to draw a conclusion. Decide
whether there might be a better way to get results. Ask yourself whether
your test was fair and accurate.
Skills focus: Carry out practical investigations
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Activity 4
Practise conducting an investigation
Plan and conduct an investigation to find out whether green leaves produce
starch.
You will need: plant with soft green leaves, such as a geranium • Bunsen
burner • a 500 ml glass beaker • a small glass beaker • tile
• tripod stand • dropper • pair of tweezers • pair of tongs
• spoon • safety goggles • 250 ml water • 50 ml ethanol or
methylated spirits • 50 ml iodine solution
Work through the following points. Write the answers in your workbook.
1. Ask a question
Write down the question you
are trying to answer in this
investigation. Make sure your
question is testable.
2. Write a hypothesis
Write a hypothesis for this
investigation by choosing the
correct option in the brackets:
Green leaves (produce/do not
produce) starch.
Figure 9 The apparatus required to conduct your investigation
3. Plan your investigation
a ) How can you test if green leaves produce starch?
b ) Write down the variables that will affect the results of your
investigation.
c ) Write down the dependent and independent variables.
d ) Explain how you will make sure your test is fair.
e ) Look at Figure 9, which shows the equipment you need. Pay special
attention to the following information before you conduct the
investigation:
• Iodine solution turns blue-black in the presence of starch.
• Ethanol or methylated spirits extracts chlorophyll from
plant cells.
• Boiling water breaks cell walls and stops chemical reactions in
the cells.
• A small glass beaker is used to put ethanol into a water bath.
Ethanol is highly flammable. Ethanol is never put onto an open
flame.
8
Term 1
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4. Conduct your investigation
Work in pairs. If your school does not have the equipment, you can follow
the photos and the steps as follows:
Step 1
• Pick a leaf from the plant.
• Put a beaker of water over the
Bunsen burner to boil.
• Put the leaf into the boiling water
for one minute. What happens in
the cells?
Step 4
• Hold the small glass beaker with the
pair of tongs.
• Place the small beaker into the large
beaker with very hot water for ten
minutes. What is this large beaker
with water called?
• Why is the ethanol placed into this
large beaker of water?
Step 2
• Take the leaf out of the boiling water with a
spoon or a pair of tweezers.
• Put the leaf on the tile and let it cool down.
Turn off the Bunsen burner or heat source.
Step 3
• Pour the ethanol into the small
glass beaker.
• Put the leaf into the ethanol.
Step 5
• Do you see any changes in the leaf?
Explain.
• Take the leaf out of the small glass
beaker with a pair of tweezers or a
spoon. How does the leaf feel?
• Rinse the leaf in warm water. The
warm water softens the leaf.
Step 6
• Spread the soft leaf on the tile.
• Use a dropper to cover the leaf with
iodine solution. Do you observe any
colour change?
Skills focus: Carry out practical investigations
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Skills focus
5. Analyse your data and draw conclusions
a ) What did you notice about the results in the leaf?
b ) What can you conclude from your investigations?
c ) How do your conclusions compare with your hypothesis?
6. Evaluate your investigation
a ) Were you able to answer your testable question from this
investigation?
b ) If not, can you explain what went wrong? What changes could you
make to improve your investigation?
7. Communicate your findings
Write a scientific report using the following headings: Aim; Hypothesis;
Method; Results; Conclusion and Discussion.
Safety
• Do not put the beaker with ethanol near or on an open flame because it will
catch fire.
• Before you begin working with chemicals, put on your safety goggles.
• Hold the ethanol away from your face to avoid boiling water spilling into
your face.
10
Term 1
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Unit
2
Respiration
Respiration releases energy from food
Key word
Living organisms require energy to survive. You learnt in the previous unit
that green plants produce glucose or food during photosynthesis. This food
has potential energy. This energy can be released from the food in a series of
chemical reactions. This process is called respiration. Note that while only
green plants photosynthesise, all living organisms respire. Although plants
make their own food, they also have to break down glucose to release
energy when it is needed.
• respiration –
process in cells
where glucose is
broken down and
energy is released
Oxygen is a resource required for respiration. Plants absorb oxygen from
the atmosphere while animals breathe it in. During respiration, plants and
animals break down glucose and oxygen to produce carbon dioxide, water
and energy. Plants release the carbon dioxide back into the atmosphere and
animals breathe it out. The chemical equation for respiration is shown below:
glucose + oxygen
energy + carbon dioxide + water
Look at Figure 10. The cow is eating grass. Grass contains starch and
other chemical compounds produced during photosynthesis. The grass
is digested by the cow’s alimentary canal. It is broken down into glucose
molecules. The glucose molecules are transported in the bloodstream from
the alimentary canal to the
cells where respiration takes
plant produces
oxygen
place. The cow breathes in
the oxygen that is required
for respiration. The cow uses
the energy that is released
by respiration for growth and
other life processes.
plant takes
plant uses
carbon to
make sugar
molecules
in carbon
animal takes
dioxide
Overall, photosynthesis and
in oxygen
respiration can be thought of
as opposite processes:
• During respiration, food
is broken down and
animal releases
carbon dioxide
energy is released.
• During photosynthesis,
animal breaks down
sugar molecules
plants use the energy
from the Sun to produce
food.
Figure 10 The energy released during respiration is produced during photosynthesis.
Topic 1: Photosynthesis and respiration
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Key word
• clear lime water –
solution of calcium
hydroxide and
water
Activity 5
Write about the requirements for, and products
of, respiration
Look at Figure 11 and answer the questions that follow.
1
3
2
Figure 11 Diagram for Activity 5
1. Name the process that takes place in the cells of the organisms labelled 3.
2. Name the two processes that take place in the cells of the organisms
labelled 2.
3. a ) Write down the word equation for the process mentioned in
question 1.
b ) What does the arrow in the equation indicate?
c ) Describe where each reactant required for this process comes from.
d ) Describe what happens to each of the products.
e ) Explain why this process is important for life.
4. Explain how the energy used by the organisms labelled 3 ultimately
comes from the object labelled 1.
12
Term 1
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Activity 6
Test for the presence of carbon dioxide in
exhaled air
You will need: clear lime water • glass container, such as a beaker or a
drinking glass • drinking straw
Instructions
1. Clear lime water is a solution of calcium hydroxide and water. Pour the
lime water into a glass container.
2. Place the straw in the lime water and exhale (breathe out) through the
straw. You should see bubbles floating up to the surface.
3. Clear lime water turns milky when carbon dioxide is dissolved in it. This
is because the carbon dioxide reacts with the calcium hydroxide to form
calcium carbonate. Calcium carbonate makes the solution cloudy or
milky.
Questions
4. Explain where the carbon dioxide came from.
5. What will happen to a glass of clear lime water if you leave it uncovered
on a cupboard for a few days? Explain your answer.
Figure 12 Clear lime water
turns milky in the presence of
carbon dioxide.
rubber stopper
Activity 7
Test if carbon dioxide is released by
germinating seeds
test tube
germinating bean
seeds
1. Name the gas that turns clear lime water cloudy.
2. Explain why the test tube is closed with a rubber
stopper.
3. Do you expect to see any change in the clear lime water? Explain your
answer.
Key concepts
Respiration is the process in plants and animals where glucose
is broken down to carbon dioxide and water with the release of
energy.
foam rubber
clear lime
water
Figure 13 Carbon dioxide is
released by germinating seeds
during respiration.
Respiration takes place in all living organisms.
Energy can be released from food by a series of chemical
reactions.
Topic 1: Photosynthesis and respiration
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Topic 1 revision
Science language practice
1. Give ONE word for each of the following:
a ) Two or more things that depend or rely on each other
b ) A green pigment in plant cells that absorbs radiant energy
c ) A substance that takes part in a chemical reaction
d ) Plants that produce their own food
e ) The process during which glucose is broken down and energy
is released
f ) A short representation of a chemical reaction
Test yourself
F
A
1. Study Figure 14 which represents the relationship between
photosynthesis and respiration. Answer the questions that follow.
a ) What process takes place in the part labelled F?
(1)
b ) What is the name of the pigment that plays a role
E
in this process?
(1)
c ) Give the names of the TWO inorganic components that
B
are used during this process mentioned in question (a).
(2)
d ) Give the name of the organic food that is produced
during this process.
(1) C
e ) Give the letters of the parts where food is stored.
(2)
f ) Give the letters of the places where the gases and
D
water enter and exit the plant.
(2)
g ) Supply labels for the parts labelled A and D.
(2)
Figure 14 The relationship
h ) What process takes place in cells of all animals and plants?
(1) between photosynthesis and
2. Look at Figure 15. This air pump lets air flow in the direction indicated respiration
by the arrows. Air flows into the first flask on the left side. Sodium
hydroxide in the first flask dissolves carbon dioxide. This means that
the air reaching the locust contains only oxygen. Note that the locust
is not harmed. It receives the necessary gas for respiration. The locust
is released unharmed after the investigation. Answer the questions
that follow.
a ) Will the clear lime water
Air flows into the first flask on the left side
in the second flask turn
cloudy or will it remain
clear? Explain your
answer.
(3)
b ) Why is the carbon dioxide
in the inflowing air
removed?
(2)
c ) Will the clear lime water
NaOH dissolves clear lime water
clear lime water
in the last flask turn cloudy
carbon
dioxide
or will it remain clear?
Explain your answer.
(3) Figure 15 Apparatus to test whether locusts release carbon dioxide during
Total: 20
14
respiration
Term 1
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Term 1: Life and living
Topic
2
Interactions and interdependence within
the environment
Starting off
Plants and animals live together and interact in
ecosystems. They interact with one another and
with the non-living parts of the ecosystem such as
light, temperature, wind and water. Organisms rely
on the ecosystem to satisfy their need for shelter
and food, and space for breeding and hiding from
enemies. There are different relationships between
living things, for example, some organisms eat other
organisms. We show these feeding relationships
with a food chain.
(a)
Activity 1
Identify interactions in an
ecosystem
1. Look at Figure 1(a) and describe the non-living
conditions in this environment.
2. List the living things that you can see.
3. Suggest different relationships between the
living organisms that you have listed.
(b)
(c)
Figure 1 (a) Plants and animals interact in ecosystems; (b) and
(c) show relationships between things
Topic 2: Interactions and interdependence within the environment
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Unit
1
Introduction to ecology
Key words
• ecology – study
of interactions
between living
things and with
their physical
and chemical
environment
• ecosystems – all
of the living and
non-living things
in an environment
and the different
ways in which they
interact with each
other
• protists – single
celled organisms
that may be free
living or living in
colonies
• population –
group of
individuals of
the same species
living in the same
ecosystem at the
same time
• community –
different
populations that
interact with one
another in the
same ecosystem
• biosphere – all
of the different
ecosystems on
Earth
• habitat – place
where organisms
live
16
What is ecology?
Ecology is the study of interactions between living things and their
interaction with their physical and chemical environment. The environment
is made up of different ecosystems. Animals, plants, bacteria, protists and
fungi make up the living parts of the ecosystem. The non-living parts are
the conditions the organisms need in order to survive. These include the
amount of light and water, air, the right temperature and soil.
Interactions between living things
When scientists study the living things in an ecosystem, they classify the
interactions at four different levels: populations, communities, ecosystem
and biosphere.
Populations
A population is a group of
individuals of the same species
or type that live in the same
ecosystem at the same time. An
example of a population is all
of the dandelions on a lawn, all
of the rhino in uMkhuze Game
Reserve or all of the locusts on a
bush.
Communities
Figure 2 A population of locusts
In an ecosystem, there are many
different populations of plants,
animals, fungi and bacteria.
The different populations that
interact with one another in
the same ecosystem form a
community. For example, a
wetland community might have
a population of fish, a population
of frogs, a population of algae
and a population of reeds.
Ecosystems
Figure 3 Wetland community
An ecosystem is all of the living and non-living things in an environment and
the different ways in which they interact with each other. An ecosystem is
made up of two parts: the non-living part called the habitat and a living part,
consisting of the community. A habitat is the place where organisms live.
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Biosphere
The biosphere includes all of the areas on Earth where life exists. This includes
the parts of the lithosphere, the hydrosphere and the atmosphere, living
organisms and dead or decaying organic matter. It is the largest biological
system on Earth. It consists of smaller units called ecosystems.
Biosphere
Ecosystem
Community
Population
Figure 4 Photographs to show the different levels in ecological interactions
Activity 2
Explain and order ecological interactions
1. Explain the meaning of biosphere and ecosystem.
2. Look at Figure 4.
a ) Give an example of each of the following: a population, a
community and a habitat.
b ) Arrange the following words about levels in ecological interactions
in order from the largest to the smallest:
population biosphere community ecosystem
3. Suggest one example of an interaction between living things.
Key concept
An ecosystem is
all of the living
and non-living
things in an
environment
and the different
ways in which
they interact
with each other.
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Unit
2
Ecosystems
Key words
• biotic factors –
all the plants
and animals in
an ecosystem,
as well as their
interactions
• abiotic factors –
all of the nonliving things in an
ecosystem
There are many different kinds of ecosystems found on land and in
water. For example, there are forest, desert, grassland, river and coastal
ecosystems. All of Earth’s ecosystems make up the biosphere.
The non-living parts of an ecosystem influence which living organisms can
live there. In other words, ecosystems contain different types and numbers
of living organisms because they have different environmental conditions.
The living and non-living parts of an ecosystem interact as a system. A
system consists of different parts that work together for a common purpose.
Network of interactions between organisms
and between organisms and their environment
The different populations in a community will depend on each other for
food. Feeding relationships are shown in a food chain or a food web. If the
population of one organism changes, it will affect the numbers of other
organisms in the food web. Examples of interactions between organisms
include the pollination of certain plants by animals like mammals, insects
and birds, and some plants rely on animals to spread their seeds.
Figure 5 Grassland ecosystem
Biotic and abiotic parts of ecosystems
An ecosystem consists of two parts:
• a living part or biotic factors
• a non-living part or abiotic factors.
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Biotic factors
Living organisms and their different interactions make up the biotic factors
present in the ecosystem. Organisms will compete with one another for
food, light, water, space and mates. Look at figures 6 to 9. Some plants rely
on other organisms to pollinate their flowers or spread their seeds. Feeding
relationships between living things are other particularly important biotic
factors in ecosystems. You will learn more about feeding relationships in Unit 3.
Figure 6 Caterpillars compete with
elephants for food.
Figure 9 Barnacles compete for space
on a rock.
Figure 8 Animals like zebra fight for mates.
Figure 7 Plants compete with each other
for light.
Activity 3
List biotic and abiotic factors
Look at figures 10 and 11, which show a desert ecosystem and a forest ecosystem.
Figure 10 Namib Desert
Figure 11 Subtropical forest
1. List the abiotic factors in each ecosystem.
2. List the biotic factors in each ecosystem.
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Abiotic factors
Figure 12 Wind can help
plants to disperse their seeds.
•
•
•
•
Abiotic factors form the non-living part of the ecosystem. Abiotic
factors include temperature, wind, water, light intensity, soil and
slope. They affect living organisms in the following ways:
• Temperature describes how hot or cold an area is. Most
organisms live in temperatures between 0 °C and 40 °C.
Temperatures will vary with the seasons, as well as with day
and night.
• Wind can stunt plant growth and affect animal activities. Wind
is used by some plants for pollination and the distribution of
seeds.
Water is needed for organisms to survive. In areas where water is limited,
plants and animals must be able to reduce water loss. Water is constantly
recycled through the biosphere in the water cycle.
Plants need light for photosynthesis. Some plants grow better in shade
while others grow best in full sunlight. The amount of sunlight received
by plants will vary during a single day and from season to season.
Soils are classified as sandy, loamy or clayey. Each type of soil has
different properties. These properties influence the kind of plants that
can grow in them.
Slope describes how steep the land is. Water runs off steep slopes quickly
and there is little soil because of erosion. Few plants can grow in these
conditions.
Figure 13 Ferns and mosses grow in shady
areas.
20
Figure 14 Quivertrees (kokerboom) need
full sunlight to survive.
Figure 15 A steep rock face supports few
plants.
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Size of an ecosystem
The size of an ecosystem varies. An ecosystem may be
large like a forest or grassland, or it can be small like a
rotting log or a puddle of water. Some scientists see an
ecosystem as encompassing the entire planet.
Survival of individuals and
populations
For plants and animals to survive in an ecosystem, they
need to be able to cope with changes to the habitat.
Changes can be sudden, for example, when a habitat is
suddenly destroyed by fire or people, or more gradual,
such as changes in temperature in the seasons. Some
organisms have the ability to cope or adapt quickly to
these changes. This may be because they feed on a large
variety of foods or because they can survive in a range
of different habitats. Examples of organisms that can
survive rapidly changing conditions and can live in a
variety of habitats are rats, starlings and weeds.
Figure 16 A rotting log is a small ecosystem.
Figure 17 A forest is a large ecosystem.
Figure 18 An insect feeds on nectar in a flower and
also pollinates the flower.
Figure 19 Weeds are tough plants that can survive under difficult conditions.
Key concept
An ecosystem consists of a living part and a non-living part that interact
and affect each other.
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Unit
3
Feeding relationships
Key words
• producers – green
plants that can
make their own
food
• herbivores –
animals that eat
plants, carnivores
are animals that
eat other animals
• carnivores –
animals that feed
on other animals
that are living or
dead
• consumers –
organisms that
rely on other
organism for their
energy and good
supply
• predator –
carnivore that
hunts other
animals
• prey – animals
hunted and eaten
by the predator
22
Organisms can be classified into groups according to what they eat. This
helps us determine the feeding relationships between living things in an
ecosystem.
Producers
Green plants are able to trap sunlight and use it to make food during
the process of photosynthesis. Plants and algae are called producers
because they can make their own food. This food may be used by the plant
immediately or it can be stored as starch in different parts of the plant
for use at a later time. Plants are also important to people for a variety of
reasons. Read the case study below about the marula tree.
Figure 20 Marula fruit are harvested and sold to make skin products and juices.
Case study: The marula tree
The marula tree is indigenous to South
Africa. ‘Indigenous’ means that it occurs
naturally in an area. The Northern Sotho
people believe that the tree was given to
the people by spirits, so it is considered
to be sacred. Therefore, it is one of the
trees that is left standing when all others
have been cut down to make room for
agriculture.
In rural areas there are very few jobs
and many people, especially women, are
unemployed. A company called Marula
Natural Products in the Bushbuckridge
area of Limpopo has employed rural
women to harvest the fruit of the marula
tree, which they then sell to the company.
The company has community-based
values and ensures that the women are
paid a fair price for their goods so that
they can build a sustainable business.
This adheres to the principles of fair
trade. The fruit pulp is extracted and used
to make drinks. Oils from the nut are
used to make skin products. The company
ensures that the fruits are harvested in a
sustainable way and the community is
encouraged to protect their trees because
they are a means of earning money. It also
promotes good environmental practices
and sustainability.
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Activity 4
Read and write about sustainable use
Read the case study on the previous page and answer the following questions.
1. Explain how both the women and the marula trees benefit from this
relationship.
2. Suggest what you think is meant by ‘fair trade’ and ‘harvesting in a
sustainable way’.
Consumers
Animals cannot make their own food. Some animals (herbivores)
get food containing energy by eating plants. Other animals
(carnivores) get food indirectly from plants – they eat other
animals that have eaten plants. Organisms that rely on
other organisms for their energy and food supply are called
consumers. There are different types of consumers that are
grouped according to the kind of food that they eat.
Figure 21 Consumers rely on other organisms
for energy and food.
Herbivores
Animals that feed on plants are called herbivores. Examples
of herbivores are aphids, locusts, giraffes, sparrows, elephants
and cows.
Figure 22 Herbivores feed on plants.
Carnivores
Carnivores are animals that feed on other animals that are living or dead.
There are different kinds of carnivores: predators, scavengers and insectivores.
A predator is a carnivore that hunts other animals. The animals that they
eat are called their prey. Examples of predators include leopards, eagles and
ladybirds. The prey of leopards includes zebra and wildebeest, eagles prey
on meerkats and other small mammals and ladybirds feed on aphids and
other small insects.
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Key words
• scavengers –
carnivores that
feed on dead
animals or
decaying meat
• insectivores –
carnivores that
feed on insects
• omnivores –
animals that eat
plants and other
animals
(a)
(b)
(c)
Figure 23 Examples of predators that hunt and kill their prey are (a) leopards, (b) ladybirds and (c) eagles
Scavengers are carnivores that feed on dead animals or decaying meat.
Examples of scavengers are vultures, hyenas and jackals. Some predators like
lions, will scavenge if the opportunity arises and if they are hungry. Some
scavengers, like hyenas and wild dogs, will also hunt and kill their own prey.
(a)
(b)
(c)
Figure 24 Examples of scavengers are (a) vultures, (b) hyena and (c) seagulls
Insectivores are carnivores that feed on insects. For example, the aardwolf,
which feeds almost exclusively on termites. Bat-eared foxes also feed mainly
on insects such as ants, beetles and grasshoppers, and especially termites,
but they will also eat berries. Pangolins feed only on ants and termites.
Many bird species are insectivores.
Figure 25 The aardwolf is an insectivore.
24
Figure 26 Pangolins locate their prey
using their sense of hearing.
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Omnivores
Animals that eat plants and animals are called omnivores.
Examples of omnivores are humans, pigs, warthogs and
baboons. Many birds eat plant materials and insects, so they
are considered to be omnivores.
Activity 5
Classify organisms into their feeding
groups
1. Classify the following organisms into two groups:
producers and consumers. Present your answer as a table.
mouse leopard marula tree donkey grass algae bee
Figure 27 Warthogs eat roots, bulbs, fruit,
earthworms, scorpions and centipedes.
2. Look at the different animals below:
(a) Ladybird
(d) Vulture
(b) Lion
(c) Zebra
(e) Pangolin
(e) Geckoe
Copy and complete the following table to classify each animal in its
correct feeding group.
Herbivore Predator Scavenger Insectivore Omnivore
Example
3. Give an example of each of the following from the school grounds: a
producer, a predator and a carnivore.
4. Look at the pictures of carnivores and herbivores on pages 23 and 24.
a ) What do carnivores eat?
b ) What do herbivores eat?
c ) Suggest how carnivores and herbivores are suited to catching and
eating their food.
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Key words
• decomposers –
organisms that
break down or
decompose the
remains of dead
plants and animals
and their wastes
• digestive
enzymes –
substances made
by an organism
that break down
food
Decomposers
Decomposers are organisms that break down or decompose the remains
of dead plants and animals and their wastes. Examples of decomposers
include bacteria, fungi, millipedes, beetles and earthworms. Look at
figures 28 to 30. Decomposers vary in size: some are microscopic and
cannot be seen with the naked eye, while others are larger. Decomposers
break down dead matter into simpler substances, which are released into
the soil. These nutrients can be taken up by the roots of plants. In this way,
nutrients are recycled in the ecosystem by the decomposers.
Dung beetles are decomposers that feed only on the dung of large
herbivores. They break down the large parts of dung during their activity.
Broken-down dung mixes with soil, enriching it and improving plant
growth.
• sewage – human
and domestic
waste from
people’s homes
Figure 28 Millipedes eat rotting plant
matter in the soil.
Figure 29 Beetles eat the bodies of
dead animals.
Figure 30 Dung beetles roll dung into food
balls or brood balls where they lay eggs.
Fungi are decomposers that feed by releasing chemicals called digestive
enzymes onto the dead matter. The digestive enzymes break down the
leaves, branches and dead matter into simpler substances or nutrients.
Fungi help to recycle important nutrients by releasing nutrients back into
the soil. Plants can use these nutrients from the soil. Examples of fungi
include mushrooms and moulds.
Figure 31 Mushrooms grow
on decaying plant matter.
26
Bread mould is a fungus. It is made up of a network of strands called
hyphae. In the next activity, you will investigate bread mould.
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Activity 6
Investigate bread mould
You will need: two plastic bags or two glass jars with lids • one slice of dry
bread • one slice of moist bread • magnifying lens
Figure 32 Moist bread in a
sealed plastic bag.
Figure 33 Dry bread in a
sealed plastic bag.
Method
1.
2.
3.
4.
5.
6.
7.
Put each slice of bread into one of the plastic bags or jars.
Seal the bags and label the containers ‘dry’ and ‘moist’.
Place the containers in a dark place for a few days.
Write a hypothesis for this investigation.
State the independent and the dependent variables.
Is this test fair? Explain your answer.
Predict the results in each container.
Observation and results
Key concepts
Living things
can be classified
according to
how they get
their food.
8. Describe the results.
9. Examine the bread with a hand lens and draw a labelled diagram of
your observations.
Producers are
plants and can
make their own
food.
Conclude and evaluate
Consumers are
animals.
10. Describe what you think has happened.
11. Do your results support your hypothesis?
Importance of decomposers
There is a limited supply of materials and nutrients on Earth, and if they are
not recycled by decomposers they will be lost forever. They will be locked
up in the bodies of plants and animals. If there were no decomposers, then
after a while, there would be so few nutrients in the soil that plants would
die. Animals that depend on plants for food would also probably die.
Decomposers and people
Decomposers are important to people because they are used to treat
human sewage. Sewage contains human waste, bits of food and other
chemical wastes. Bacteria break down sewage into simpler substances.
This produces purified water and fertilisers.
Herbivores are
animals that eat
plants.
Carnivores eat
other animals.
Omnivores eat
both plants and
animals.
Decomposers
break down
the remains of
dead plants and
animals and
their wastes, and
recycle nutrients.
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Unit
4
Food chains and food webs
Key word
• food chain –
number of steps
in an ecosystem
showing the
transfer of
energy between
organisms
Role of plants in the ecosystem
Plants and algae play an important role in an ecosystem. Plants and algae
are producers. They capture light energy from the Sun and use that energy
to produce food. This occurs during the process of photosynthesis. Plants
make food that contains energy from the Sun. Only a small amount of the
Sun’s energy is used by living things. This energy is passed along a food
chain in an ecosystem.
What is a food chain?
Food chains show the feeding relationships between living things.
A food chain always starts with producers (green plants or algae)
because they can make their own food. The food chain ends
with decomposers, which release nutrients back into the soil.
Decomposers are not always shown on simple food chains such as
the one below.
Figure 34 Kelp is a producer that uses
energy from the Sun to make food.
agapanthus makes
its own food
agapanthus is eaten
by snails
snails are eaten
by hornbills
Figure 35 A simple food chain from a garden ecosystem.
Energy flow in a food chain
A food chain shows the flow of energy from one organism to the next. The
arrows in the food chain show the direction of the flow of energy.
Energy is passed through an ecosystem along a food chain from the
producers to the consumers. Animals are consumers because they eat
plants or other animals. For example, in a grassland ecosystem, a food chain
might consist of a producer such as grass that is eaten by a herbivore such
as an impala. Energy that was stored in the grass is transferred to the impala.
The impala is, in turn, eaten by a carnivore such as a lion. Decomposers are
the last link in this transfer of energy. Decomposers also break down plants
and animals in each link of a food chain.
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Figure 36 Energy flows along a food chain.
Scavengers and decomposers are also important in a food chain. Scavengers
get their energy by feeding on dead plants and animals. They break down
dead material, which can further be broken down by decomposers such
as bacteria and fungi. Decomposers such as millipedes eat rotting plant
matter in the soil, and they in turn are eaten by predators such as lizards.
Decomposers help return nutrients into the ecosystem.
Activity 7
Identify food chains in an ecosystem
You will need: keys or identification guides on plants and birds
1. Find an ecosystem in or near the school grounds where you can observe
the organisms.
2. Identify some of the plants and animals using the keys.
Observe and record results
3. Observe the activities of the organisms and what they feed on. Record
your observations in a table like the one below.
Date
Name of
producer
Description Name of
and
consumer
observation
Description Herbivore/
and
carnivore/
observation omnivore
4. Use the data that you have collected to create a few possible food
chains from the ecosystem that you observed.
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Key word
• food web – group
of interconnected
food chains
Food webs
There are many food chains in an ecosystem. Most animals do not eat
only one kind of food. For example, a locust does not eat only the leaves
of the acacia tree, it also feeds on grasses and shrubs. The hornbill feeds
on many kinds of insects and small animals, as well as fruit and berries. To
help us understand what an animal eats, we can show how food chains
connect with one another. A group of food chains connected together
is called a food web. Food webs tell us about the different kinds of food
eaten by different kinds of animals. They show how animals and plants in
a community are linked. Look at the food web below. You can see that it
consists of a number of food chains.
leopard
hornbill
eagle
serval
caterpillar
baboon
purple-crested
turaco
earthworm
duiker
mouse
green plant
locust
shrub
Figure 37 A forest food web
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Activity 8
Write and draw food chains and food webs
1. a ) Look at the observations that you recorded on the ecosystem in the
school grounds or nearby area in Activity 7.
b ) Write a food web that shows the different food chains in your
ecosystem and how they are linked together.
2. Look at Figure 37 and give an example of:
a ) a producer
b ) a herbivore
c ) a carnivore
d ) an omnivore
e ) a decomposer.
3. Write down two food chains from the food web in Figure 37.
4. State what decomposers feed on.
5. Describe the important role that decomposers have in the ecosystem.
6. Draw a food web using the following organisms: killer whale, tuna,
phytoplankton, zooplankton, dolphin, sardine, seal, penguin. If you do
not know what these organisms are or what they eat, then do some
research to find out!
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Key word
Activity 9
• trophic level −
steps in a food
chain or food web
Figure 38 shows the different feeding relationships that can be found in a
pond.
Identify food chains in a pond food web
fruit gnat
hippo
kingfisher
dragonfly
reeds
duck
heron
water plants
snail
tadpole
frog
fish
crocodile
Figure 38 Pond food web
Look at the figure and answer the following questions.
1. What do the arrows in the food chain mean?
2. Explain why food webs and food chains always start with producers.
3. Explain why a food web is more accurate than a food chain.
4. Draw two food chains that contain organisms found in Figure 38.
5. Design a food web including as many of the organisms found in
Figure 38 as possible.
6. Label the producers, herbivores and carnivores.
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Trophic levels
Each stage or step in a food chain or food web is called a trophic level.
The first trophic level is made up of the producers. Herbivores, or primary
consumers, make up the second trophic level. The third and higher trophic
levels are made up of secondary or tertiary consumers. These are the
carnivores. Each consumer depends on the trophic level below it for energy.
Energy transfer and energy loss
Only a small part of the energy that is stored in one trophic level is
passed on to the next level. This is because most of the energy is used
by the organisms for life processes such as movement, respiration and
reproduction. Some energy is also lost as heat. Only about 10% of the
energy that is available is transferred to the next trophic level.
We use energy pyramids to represent the amount of energy in each trophic
level and the amount of energy that is transferred from level to level. The
producer trophic level always contains the most energy. Because energy is
lost at each level, the size of each level becomes smaller. This is why these
diagrams are pyramid shaped. Most energy pyramids have a maximum of
three or four trophic levels.
Energy is measured in kilojoules (kJ). The energy pyramid in Figure 39 of
a grassland ecosystem shows the amount of energy transferred from one
trophic level to the next. In one year, 50 000 kJ/m2 of energy is transferred
to the locusts from the producers. The locusts pass on 6 500 kJ/m2 per year
to the striped field mice. If the locusts got 50 000 kJ/m2 from the plants,
but only passed on 6 500 kJ to the striped field mice, what happened
to the other 43 500 kJ? The plants will have used it up moving around,
and lost some of it in their waste. The only energy passed on to the mice
is that which the plants have used in growing. The striped field mice
pass on 310 kJ/m2 per
year to the owl. Only
38 kJ/m2 of energy from
tertiary
consumers
2
the 310 kJ/m of energy
38 kJ/m2 per year
in the striped field mice
becomes energy in the
secondary
flesh of the owl. The
consumers
shape of the energy
310 kJ/m2 per year
pyramid is not affected
by the size or the number
primary
of organisms.
consumers
6 500 kJ/m2 per year
producers
50 000 kJ/m2 per year
Figure 39 Energy pyramid of a grassland ecosystem, showing the amount of energy in kJ/m2 per
year transferred from one trophic level to the next
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Activity 10
Draw and analyse energy pyramids
Look at Figure 40 and answer the following questions.
Figure 40 An energy pyramid
1. Name the trophic level that is always found at the base of a food chain
or food web.
2. Explain what a trophic level is.
3. Explain why there is less energy available at the top of an energy
pyramid.
4. a ) Draw and label an energy pyramid that shows the amount of
energy at each trophic level for the following food chain:
tadpoles
small fish
heron
algae
The algae have stored 67 000 kJ/m2 per year of energy that they
trapped from the sun. The tadpoles store 5 000 kJ/m2 of energy, the
small fish store 450kJ/m2 of energy and the heron stores 57 kJ/m2 of
energy.
b ) Explain what happens to the energy at each trophic level and as it is
transferred from trophic level to trophic level.
Key concepts
Food chains show the feeding relationships between living things.
A food web is a group of interconnected food chains.
Energy pyramids show the amount of energy in each trophic level and the
amount of energy that is transferred from level to level.
34
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Unit
5
Balance in an ecosystem
In an ecosystem, living organisms and the environment that supports them
are in a fine balance. The number of organisms an ecosystem can support
depends on the resources available. These include food, water and shelter.
In general, if there are plenty of resources, an ecosystem can support many
individuals and large populations. If resources are scarce, the numbers of
individuals and the size of the populations will be small.
For example, if food is in short supply, then organisms compete with
each other for access to food. The stronger plants or animals are most
likely survive. When there is a shortager of food, the number of organisms
decrease. When there is more food available, more organisms survive and
the number of organisms increase. In this way, the ecosystem is kept in
balance.
Activity 11
Evaluate impact on a food web when one
organism is removed
Look at the food web in Figure 37 on page 30.
1. Suggest what would happen in the food web if all of the producers died
suddenly.
2. Suggest what would happen if all of the baboons were removed.
All living organisms in an ecosystem interact with one another. So, what
happens to one population affects the whole community. For example, if
the population of mice in a woodland ecosystem increases rapidly because
there is a lot of food available, then the population of owls that eat mice
also increases. If the number of mice, the prey, decreases then the number
of owls, the predators, also decreases. There is a balance between predators
and prey. The size of the populations change so that they are in balance. If
an ecosystem does not remain in balance, it will fail.
The balance in an ecosystem can be disrupted by:
• natural factors
• human factors.
Topic 2: Interactions and interdependence within the environment
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Key words
• disruptions –
something that
interferes with a
process
• pollution – harm
done to the
environment by
the release of
harmful materials
and substances
produced by
human activities
• pollutants –
chemicals or
wastes that
contaminate the
water, air or soil
[author, please add
def here]
• fossil fuels –
energy-containing
compound such as
coal, oil or natural
gas that was
formed millions of
years ago
• poaching –
illegally removing
animals or plants
from the wild
Natural factors that disrupt the balance
Sometimes there are changes or disruptions to an ecosystem that are too big
and the ecosystem is unable to cope. A disruption is something that interferes
with the normal, orderly process of how an ecosystem functions. If there is a
disruption, the ecosystem does not function properly, and the fine balance
between plants, animals and the environment is lost. If this disruption lasts
for a short period of time, the ecosystem will recover. But if the disruptions
are severe, the damage can be so bad that the ecosystem cannot recover
completely. In this case, plants and animals may be permanently lost and
become extinct.
Disruptions that can affect an ecosystem badly include fires, changes in
weather patterns and climate, such as drought and floods, and extreme and
sudden changes in temperature.
Human factors that cause disruptions
Human-induced pollution
Pollution is the harm done when toxic (poisonous) substances and
materials are released into the environment. These substances are usually a
result of human activities.
Pollutants include household and industrial waste, such as plastics, toxic
(poisonous) chemicals from factories, and smoke and gases produced from
burning fuels in power stations, factories and cars.
Farmers add fertilisers, which are made of nitrogen, sulfate and phosphate,
to the soil. The nutrients contained in fertilisers help crops to grow well.
However, the nutrients that are not used by the plants get washed into rivers
by rainfall. This pollutes the water and harms aquatic organisms.
Pollutants from burning fuels, such as petrol, release toxic or harmful gases
into the air that can affect people’s health. Some of these gases, such as
sulfur dioxide, which is produced when fossil fuels are burnt, dissolve in rain
water to make sulfuric acid droplets, known as acid rain. Acid rain damages
buildings, crops and trees, and also changes the pH in rivers and lakes. Acid
water that enters lakes and rivers lowers the pH of the water.
Some species of invertebrates and fish living in these ecosystems
are not able to survive in water with a low pH. As a result, these
animals die and the biodiversity of the water decreases.
Figure 41 Droughts can result in many organisms
dying
36
Water temperature increases when outflows of warm water are
released from factories and when vegetation that overhangs
water is removed. This increase in water temperature leads
to a reduction of water quality, which is called thermal
pollution. The effects of an increase in water temperature are
a change in the amount of oxygen dissolved in the water and
death of some organisms that live in the water. Raising water
temperature also leads to an increase in the rate of decay in the
water, which decreases the oxygen content of the water.
Term 1
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Poaching
Poaching is the illegal removal of animals and plants from
the wild. Many of South Africa’s diverse range of plants and
animals are under threat from poaching. Species of orchid and
cycad, tortoises, lizards and perlemoen, are caught and illegally
exported to countries where they can be sold for thousands of
rands. Rhinos and elephants are killed for their horns or tusks,
which are sought after in Asia. Read about rhino poaching on
page 38.
Figure 42 Floods wash away soil and destroy
plants and animals.
Figure 43 Perlemoen is a delicacy in the Far East and is poached
from South Africa’s rocky shores. It is now almost extinct in the wild.
Figure 44 Reptiles like tortoises and lizards are sold in the pet
trade.
If poaching continues for a long time, and populations do not have a chance
to recover, it can eventually result in a species becoming extinct. This can
affect the balance in ecosystems. For example, if a species of herbivore is
removed from an ecosystem, the numbers of plants increase. If a species of
carnivore is removed, then populations of herbivores increase. This in turn
would result in a decrease the plant populations grazed by the herbivores.
Activity 12
Evaluate the impact of various factors
Look at the ecosystem in your school grounds.
1. Write a paragraph to evaluate and explain what would happen to the
ecosystem under the following situations:
a ) a loss of habitat
b ) a loss of species, for example, certain plants die out or an animal
species no longer lives in the ecosystem
c ) a change in weather or climate such as rainfall or temperature
d ) a factory is built nearby which causes acid rain to fall.
Key concepts
Organisms and the
environment in which
they live are in a fine
balance.
The balance in an
ecosystem can be
disrupted by natural
factors and human
factors.
Topic 2: Interactions and interdependence within the environment
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More resources
Rhino poaching
Trade in illegal rhino
horn continues
Rhinos are targeted by poachers for their horns. Some
people living in Asia believe in the cultural myths that rhino
horn has medicinal properties. According to these beliefs,
rhino horn can be used to treat just about every illness from
colds to cancer.
The number of rhinos killed in South Africa has increased
rapidly as a result of the continued demand for rhino horn. In
2009, 122 rhino were poached, while in 2012, 455 rhino were
poached. These figures are alarming and could lead to the
extinction of rhino in South Africa.
er threat.
s are und
o
in
h
R
5
Figure 4
Rhino poaching in South Africa
Rhino horn fetches high prices in Asia. Rhino horn is sold for R400 000 per kilogram. It is more
expensive than gold. Rhino horn is made of a substance called keratin, which is similar to the
substance that makes up our hair and nails. It has no magical or healthy properties. In fact, chewing
your fingernails would give you the same benefits!
KNP (SANParks)
South Africa
MNP (SANParks)
GP
LIM
MP
NW
EC
FS
KZN
WC
NC
0
50
100
150
200
Number of rhinos
250
300
Total 333 448 455
2010 2011 2012
Figure 46 Bar graph of rhinos poached from 2009 to 2012
38
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Rhino poaching and crime syndicates
The poaching happening today is not carried out by a poor
man trying to feed his family. Instead, it is run by organised
crime syndicates. These groups use sophisticated tools such as
helicopters, veterinary guns, night vision equipment and assault
rifles. They operate at night and can locate a rhino and remove
its horn in a matter of 15 minutes.
What can you do?
Figure 47
The work
o
f poache
rs
There are many organisations that raise money and awareness
about the plight of rhino that you can join. People need to be
educated so make sure that you are aware of the situation and
that you stay up-to-date with the available data. The solution
to this problem is to try to educate people who believe in the
powers of rhino horn as a medicine to understand that rhino
horn has no medicinal qualities at all. Perhaps writing to political
leaders in these countries can make a difference.
More resources: Rhino poaching
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Unit
6
Adaptations
Key words
• adaptation –
characteristic
that helps a living
thing survive in its
environment
• variations –
differences
between
individuals in a
population
• extinct – there
are no more of
a species left on
Earth
What is an adaptation?
An adaptation is a characteristic that helps a living organism survive
in its environment. Adaptations may occur when there is a change in
the structural, behavioural or functional characteristics of an organism.
Plants and animals must be adapted or suited to the conditions of their
environment.
• A structural or physical adaptation is a special feature of the body, for
example, birds have different shaped beaks that are adapted for eating
different foods.
• Many desert animals rest or go underground where it is cooler to escape
the heat of the day. This is an example of a behavioural adaptation.
• Functional adaptations relate to the way in which the body works. For
example, leaves of erica plants are rolled under at the edges to reduce
water loss. Another example is that people sweat to cool their bodies
down.
Changing environmental conditions and adaptations
Conditions in an environment may change. For example, the environment
may be become hotter and drier, or there may be a shortage of resources.
Living things that adapt to the changes in the environment are most likely
to survive. Organisms that are better adapted will have a better chance to
get the resources that they need. These organisms are more likely to survive
and reproduce.
Living things adapt by chance or by accident. Adaptations are passed on
from parents to their young, and cannot happen in one life time. In any
population, each individual is slightly different. These differences are called
variations. For example, the zebra in Figure 48 is almost black. This is an
example of a variation.
Sometimes a variation can help an
individual to survive better. It is likely
that this individual will reproduce and
pass on its beneficial characteristics
to its young. Eventually, more and
more of that kind of animal or plant
have the characteristic that enables
them to survive. Over time, the whole
population adapts.
Figure 48 This zebra is darker than the rest of the population.
40
Not all variations turn out to be useful
to an individual. A variation can make
it difficult for an animal to survive and
sometimes it can have no effect at all.
Term 1
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Lack of adaptation causes extinction
Some organisms are unable to adapt when change occurs in an
environment. Adaption is more difficult when a change is very sudden.
Organisms that are unable to adapt will eventually become extinct.
Extinct means that there are no more of a species left on Earth.
The dodo was a flightless bird found on the island of Mauritius. It
had no natural predators. When sailors landed on the island, they
hunted the dodo for food. The sailors introduced rats and pigs that
ate the dodo’s eggs and young. The dodos had no way of escaping
from these predators. The sudden arrival of predators caused dodos
to become extinct.
Adaptations of plants
Some plants are adapted to hot, dry environments, while others are
adapted to living in water or to environments where conditions are
moderate. South Africa is a hot, dry country, so many plants here
are adapted to these conditions. Examples are shown in the figures
below.
Figure 49 The dodo, a flightless bird, is
extinct.
Plants that live in water may have the following adaptations:
water lilies have more breathing pores on the top side of the leaf
than the lower side.
Plants that live in deserts may have the following adaptations:
the gazania has grey, hairy leaves to reflect sunlight. The hairs
also trap moisture to reduce moisture loss. The yellow flowers
attract insects for pollination.
Activity 13
Figure 50 Water lilies
Draw and label plant adaptations
Go onto the school grounds and look for different species of
plants.
1. Select two different plants and draw a diagram of each.
2. a ) Describe the environment in which the plant grows.
b ) Label the different parts with annotated labels to
describe the adaptations of the plant.
Figure 51 Gazania plants are adapted to living
in hot, dry environments.
Topic 2: Interactions and interdependence within the environment
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Animal adaptations in extreme environments
Key words
• camouflaged –
colours and shapes
help animals blend
in well with the
environment
• mimicry –
harmless species
copies another
poisonous species
Animals are adapted to living in their habitats. Figure 52 shows how camels
are adapted to live in a hot, dry climate. Figure 53 shows how polar bears
are adapted to live in cold habitats.
thick eyelashes provide
protection from sand and sun
hair lines the ears to prevent sand
from entering
nostrils close to
keep sand out
fat stored in the
hump can be a
source of food when
it is scarce
thick fur provides
insulation during cold
nights
kidneys
concentrate urine
to reduce water
loss
sand-coloured
fur provides
camouflage
broad flat pads
beneath their feet
help camels to
spread their weight
on the sand
Figure 52 Camels are adapted to live in deserts
ears are small to
reduce heat loss
thick layer of body
fat under the skin
insulates the body
and stores energy
thick white fur
provides insulation
and camouflage
large feet
distribute their
weight on the ice
sharp claws and
teeth help polar
bears to catch their
prey
fur on the soles of
feet provides better
grip and insulation
Figure 53 Polar bears are adapted to survive in the Arctic
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Predator adaptations
Sharks and cheetahs are examples of predators. They have adaptations that
enable them to catch and hold their prey.
• Cheetahs have good eyesight and can run very fast for short distances.
They are well camouflaged, which means that they blend in with their
environment. This helps them get close to their prey. They have strong,
sharp claws and teeth to hold onto, kill and tear the flesh of their prey.
• Sharks have a good sense of smell and can swim fast to catch their prey.
They have a streamlined shape and a muscular tail to propel themselves
through the water. Sharp teeth are used to hold prey and they shake
their heads from side to side to rip the flesh into pieces.
Camouflage and mimicry
Animals use different methods to avoid
predators. Some are well camouflaged,
such as many lizards and insects. They have
colours and shapes that are similar to their
environment. They keep still when enemies
are near.
Some animals resemble other animals or
plants in colour or behaviour. This protects
one or both of the organisms. For example,
the African monarch butterfly tastes bad
(unpalatable) and is avoided by birds.
Another species of butterfly resembles the
Monarch butterfly in appearance but it is
edible. It too is avoided by birds. This is an
example of mimicry, where one harmless
species copies another poisonous species.
Activity 14
Figure 54 The butterfly on the left is unpalatable but the one on the
right is not
Read and write about animal adaptations
1. Write a paragraph to describe how the camel and the polar bear are
adapted to the extreme environments in which they live.
2. Describe how the shark and the cheetah are adapted to being good
predators.
3. Explain what camouflage and mimicry are. Use an example to illustrate
your answer.
Key concept
Organisms are adapted so that they can survive in their environment.
Topic 2: Interactions and interdependence within the environment
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Unit
7
Conservation of the ecosystem
Key words
• biodiversity –
total variety of
species in an area
• monocultures –
single crop species
planted over large
areas
• alien species –
species that is not
indigenous to a
specific area
• conservation –
wise management
and use of natural
resources that
protects habitats
and wildlife
• sustainable use –
using resources
wisely so that they
are not depleted
Figure 57 Over-harvesting some
plants like wild ginger has led to its
disappearance in the wild.
44
Many ecosystems are destroyed as a result of the activities of people.
Human populations are continuing to increase and we are using more and
more of the Earth’s resources.
As ecosystems are lost, species become extinct. This means that
biodiversity decreases, upsetting the balance in the ecosystem. Biodiversity
is the total variety of species in an area.
Of course, this has been happening for many hundreds of years, but recently
scientists have noticed a rapid increase in the number of species becoming
extinct each year. Some scientists believe that about half of the species alive
today could be extinct by the end of this century.
Human activities
Activities that cause extinction and reduce
biodiversity include:
• replacing natural habitats that are usually
quite diverse with monocultures of
single crop species planted over large
areas
• overharvesting of plants or animals; for
example, indigenous medicinal plants
such as wild ginger have been almost
completely removed from the wild
• using pesticides to kill animals that cause
disease, such as mosquitoes and rats that
eat our stored grain
• polluting the environment with
emissions from cars and factories
• introducing exotic, alien species
that compete for resources with the
indigenous plants and animals.
Figure 58 Burning fossil fuels pollutes
the atmosphere.
Figure 55 Monocultures have very
low biodiversity.
Figure 56 The isiZulu believe wild
ginger provides protection from
lightning. It is also used to treat
asthma, colds, coughs and flu.
Figure 59 The Indian myna is an
introduced species that outcompetes
indigenous species.
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Why conserve species?
Conservation means the wise management and use of natural resources
that protects habitats and wildlife. Natural ecosystems carry out many
important processes such as:
• regulating the atmosphere and the climate (temperature
and rainfall)
• filtering, cleaning and retaining water
• forming and improving the quality of soil
• providing homes to pollinators of plants, including those
that provide us with food
• recycling of wastes, for example, decomposers that break
down dead plants and animals, and release nutrients
back into the soil
• production of wood, food and fuel.
Sustainable use of resources
Sustainable use means using resources so that they are not depleted. For
example, when collecting bark from trees or fishing in wetlands, only a
certain quantity of the resource should be taken. Enough of the resource
needs to remain so that the population can re-grow and provide resources
the following year. The pepper bark tree that naturally occurs in northeastern KwaZulu-Natal, eastern and northern Limpopo and Mpumalanga
was overharvested and as a result is no longer available to traditional
healers in the wild.
How environmentalists conserve
ecosystems
Setting aside large areas of land in areas that are rich in
biodiversity is important for ecosystem conservation. For example,
the creation of the Kgalagadi Transfrontier Park, which is 3,6
million hectares, means that large areas can be managed in an
ecologically sound way.
Legislation can be used to stop activities such as poaching,
collecting wild plants and clearing land. However, it is often
difficult to enforce such legislation.
Figure 60 The Kgalagadi Transfrontier Park
Controlling alien vegetation
Plants from places such as Australia and South America were introduced
to South Africa for use as wind breaks, fuel and sometimes as decorative
garden plants. Since these plants came from areas that have a similar
climate to that of South Africa, they are already adapted to the conditions
here. No natural predators or enemies of these plants live in South Africa
and as a result their populations were able to increase rapidly.
Topic 2: Interactions and interdependence within the environment
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Because they are tough, quick-growing plants, alien plants outcompete
indigenous vegetation and rapidly take over an area. It is not possible to
eradicate alien vegetation but control methods have been introduced.
These include:
• Biological control – Living things are used to control
the population of a pest. The natural enemy of the plant
pest, such as insects or fungi, is introduced from its native
country and used to control the alien plant. For example,
a weevil was introduced which feeds on red sesbania and
the results have been good. A lot of research must first be
carried out before the organism is released.
• Chemical control – Chemical poisons or herbicides
are sprayed onto alien plants. This method is expensive
and has to be repeated every year. It also can harm the
environment when the poisons enter the ecosystem.
• Mechanical control – This is also expensive and involves
burning, cutting down or uprooting alien plants. It needs
to be repeated every year as young seedlings germinate.
Invasive aliens are controlled successfully when a combination of these
three methods are used. The use of aliens for firewood and to make
furniture and household objects is another method of controlling alien
vegetation from which people can earn a living.
Preservation of wetlands
Wetlands include marshes, floodplains, lakes and
estuarine systems. In South Africa, more than 50% of
our wetlands have already been lost. It is important
that we protect wetlands as they play important
roles in ecosystems.
They filter and clean water, store water, and prevent
flooding and soil erosion. Wetlands have a rich
biodiversity – many serve as breeding grounds for
animals, are used for grazing by farmers and are used
for recreation such as fishing and boating. Plants
such as reeds are used by people for thatching and
making baskets.
Figure 61 Mechanical control of aliens
46
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Activity 15
Write about maintaining biodiversity and
sustainable use
1. Explain what biodiversity and sustainable use mean.
2. Explain why we need to use natural resources carefully.
3. Suggest things that can be done to maintain biodiversity and to use
resources sustainably.
4. Recently, there has been much concern from scientists about fish stocks
in the sea. Some fishing methods catch fish of all ages.
a ) Suggest a way in which immature fish are not caught so that they
get the opportunity to reproduce.
b ) Explain why this is important to fish stocks.
Individuals can contribute to conservation
Every person can be involved in conservation. If everyone did something each
day then much of the Earth’s resources could be conserved. Materials such
as plastic, paper, glass and metal can be recycled. Municipalities can set up
the collection of different materials that can be taken to depots for recycling.
Organic wastes can be collected in gardens and used to make compost.
Recycling means that people produce less waste, which means less waste
to fill landfill sites. It also means that energy consumption is reduced and
damage to the environment reduces as less waste is created. Furthermore,
raw materials are saved.
Activity 16
Write about irresponsible human practices
1. What happens to the waste in your household? Where does it go?
2. a ) Describe different ways in which wastes are inappropriately
disposed of by humans.
b ) Describe the impact of these methods of waste disposal on
ecosystems.
3. Describe what could be done to reduce the amount of waste, and
explain the benefits to people and to the environment.
Key concepts
Human activities may destroy ecosystems.
Resources need to be used in a sustainable way and all people must be
involved in conservation.
Topic 2: Interactions and interdependence within the environment
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Practical Task
Project
Select and study an ecosystem
You will need: thermometers • hand lenses • string and pegs • rulers or
meter sticks • sieves • field guides to identify plants and
animals
Method
1. Select an ecosystem in the school grounds. Examples are the sports
field, the area around a tap, a flower bed or the bank of a stream.
(a)
(b)
(c)
(d)
Figure 62 Examples of ecosystems on the school grounds: (a) sports field, (b) area around a tap,
(c) flower bed, (d) bank of a stream
2. Mark off an area that measures one meter by one metre with a ruler or
metre stick. Use the string to mark the area. Secure the corners with
pegs.
48
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Make observations and record results
3. List and describe each of the abiotic factors in your ecosystem. For a
period of one week, observe and record the following observations in a
table each day:
a ) The amount of sunlight during the day. Is there full sun, half
sunlight or complete shade?
(3)
b ) Water: is there any source of water in the area, such as a
stream or a tap? Has it rained?
(2)
c ) Wind: describe the wind. Is it strong or gentle? Is your ecosystem
protected from or exposed to wind?
(2)
d ) Temperature: use the thermometer to measure the temperature
and record it in your table.
(3)
e ) Soil type: describe the colour of the soil. Is it sandy, clayey or
loamy? Is it light or dark?
(2)
f ) Slope: is the area steep or flat?
(2)
4. Describe how the abiotic factors of the ecosystem affect the plants
and animals. Think about the behaviour of the organisms and their
structure.
(5)
5. a ) Name, count and describe the plants and animals (biotic factors)
in the ecosystem. Use a field guide to help you identify the plants
and animals.
b ) Record your answers in a table.
(8)
6. Describe the relationships (such as feeding relationships) that
also make up the biotic factors in the ecosystem.
(5)
7. a ) Identify any human interference in the area, for example litter,
pathways, or evidence of plants that have been cut down.
(2)
b ) Describe the effect of human interference on your ecosystem. (2)
8. a ) Study a small sample of soil from your ecosystem with a hand lens.
b ) Identify any remains of plants or animals in the soil.
(2)
c ) Decide if the soil is suitable for plant growth.
(2)
[40 × __34 = 30]
Total: 30
Project: Select and study an ecosystem
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Topic 2 revision
Science language practice
1. Match the terms in Column A with their correct meaning in Column B. Write only the correct number
(1–4) next to the letter ((a)–(d)).
Column A
a) Producer
b) Consumer
c) Insectivore
d) Omnivore
Column B
1. Feeds on plant and animal matter
2. Feeds on insects
3. Able to make its own food
4. Unable to make its own food
Test yourself
1. In the Umfolozi Game Reserve, zebra feed on grass, and lions hunt and kill zebra.
a ) Write this information down as a food chain.
(3)
b ) Label the producer and the consumers.
(2)
2. The baobab tree is a useful plant. The leaves can be eaten as spinach or used to feed animals. Fibre
from the bark is used to make rope, baskets and hats. The fruit can be mixed with water to make
a refreshing drink. All parts of the tree have medicinal properties. The leaves and fruit pulp have
been used to treat malaria. Products made from the bark are sold at roadside craft markets.
This table shows the animals counted and identified in a baobab tree:
3.
4.
5.
6.
Bats
(sip
nectar)
Yellowbilled
hornbills
Lizards
6
3
4
Snake Eagles Caterpillars
1
2
500
a ) Explain the meaning of the following words: producer, decomposer, population,
ecosystem.
(8)
b ) Use the information given in the table above to draw a food web to show the feeding
relationships in this ecosystem.
(6)
c ) If the numbers of caterpillars decreased, how would this affect the hornbills and
the lizards?
(1)
d ) During October, young leaves appear on the baobab and by May, the last of the
leaves have fallen. What effect would this have on the population of caterpillars?
(1)
e ) Explain what a community is. Name one member of the community of the baobab tree.
(4)
f ) Give the population number of the caterpillars.
(1)
g ) Describe how the baobab could be food for people.
(2)
You might have noticed that there are fewer carnivores than herbivores in a food web. Suggest
why this is so.
(2)
Write a food chain that starts with dead leaves and has four links.
(3)
Decomposers are organisms found in ecosystems. What are decomposers and what
important role do they play? Include examples in your answer.
(10 )
Suggest two benefits to people of protecting ecosystems.
(2)
Total : 45
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Term 1: Life and living
Topic
3
Micro-organisms
Starting off
Many living organisms, such as plants and animals,
are large enough for you to see with the naked
eye. Micro-organisms, however, are far too small
for you to be able to see unless you use a special
magnifying instrument such as a hand lens or a
microscope. The word ‘micro’ means very small
and ‘organism’ refers to living things. These microorganisms occur almost everywhere but usually you
are unaware of them as you cannot see them. It is
only when they make you sick or have some other
effect, such as making food decay, that you notice
that they are there. The study of micro-organisms is
called microbiology.
Activity 1
Figure 1 Micro-organisms as seen under a microscope
Revise what you know about
micro-organisms
1. Explain what the term ‘micro-organisms’
means.
2. Why are we usually unaware of microorganisms even though they are around us all
the time?
3. Name two instruments that can be used to
observe micro-organisms.
4. Give two ways in which we may become aware
of the presence of micro-organisms in our
immediate environment.
5. a ) List three illnesses that children suffer from
that are caused by micro-organisms.
b ) Do some research and find out what type
of micro-organisms cause the diseases that
you named in question 5(a).
6. People often use micro-organisms to
manufacture certain types of food. Make a list
of as many foods that you can think of where
micro-organisms are used in some part of the
manufacturing process.
Topic 3: Micro-organisms
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Unit
1
Types of micro-organisms
Key words
• magnify – to make
something appear
larger than its
actual size
• unicellular –
consisting of
one cell
• multicellular –
consisting of
many cells
Before the invention of the microscope people had no idea that microorganisms existed. They did not know that micro-organisms caused:
• grape juice to turn into wine
• milk to turn into cheese
• bread to rise
• beer to ferment.
The invention of the first microscope allowed biologists to observe objects
and organisms that no-one had ever seen before.
Activity 2
Observe small objects
You will need: a hand lens or micro-viewer (bio-viewers)
Walk into the school grounds and collect three objects from nature, for
example a leaf, a flower petal and some tree bark.
1. Draw a simple line drawing of each object.
2. Look at the objects that you have collected using the hand lens or
micro-viewer. Discuss what you notice about the objects with a partner.
You should see that when using the hand lens or micro-viewer, the
object appears bigger. We say that we magnify the object. When an
object is magnified you are able to see details on the object that were
not visible to the naked eye.
3. Draw a simple drawing of what each of the objects looks like using the
hand lens or micro-viewer.
There are many different kinds of micro-organisms. They include bacteria,
protists, fungi and viruses, although viruses are generally considered to be
non-living. Most micro-organisms are unicellular, which means that they
consist of a single cell. Some micro-organisms are multicellular.
Micro-organisms
Virus
Bacteria
Fungi
Protists
Figure 2 The different types of micro-organisms
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Viruses
Viruses are microscopic particles that attack the healthy cells of other
living organisms. They are not placed in any of the five kingdoms of
living organisms that you learnt about in
Grade 7. This is because they are generally
considered to be non-living. They do not
carry out the essential life processes that
other living organisms do. They do not break
down food for energy nor do they have an
organised cell structure. They are also not
able to reproduce on their own. They are
only able to reproduce by using materials
from the host cell that they have infected. In
the process of this type of reproduction, they
destroy the host cell.
Figure 3 Diagram of a virus
Bacteria
Bacteria are living things that are neither plant nor
animal. They belong to a group all by themselves. This
capsule
group or Kingdom is called the ‘Monera’. All bacteria
cell wall
are unicellular although some of them live together in membrane
cytoplasm
colonies that are multicellular.
cilia
plasmid
ribosome
DNA
flagellum
Figure 4 Diagram of a typical bacterial cell
There are many different types of bacteria. They are grouped and classified
according to the shape of the bacterial cell.
(a)
(b)
(c)
Figure 5 Groups of bacteria: (a) rod-shaped bacteria are called bacilli (b) round bacteria are called cocci and (c) spiral-shaped bacteria are
called spirilli.
Topic 3: Micro-organisms
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Protists
Protists belong to the kingdom
Protista. This group of organisms is
separate from plants, animals, monera
and fungi. The organisms that are
classified into this group are usually
unicellular. Organisms that occur in
the Protista kingdom include amoeba,
red algae, dinoflagellates, diatoms,
and slime molds.
Figure 6 A diagram of an amoeba, which is a
typical example of a protist.
Coleps
Lextilaria
Achinophrys
Trypanosoms
Dittulgia
Textularia
Trichomonas
Stentor
Vorticella
Eualena
Paramecium
Figure 7 There are many different types of protists.
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Fungi
Fungi are living organisms that are related to both plants and animals but
are also different from these groups. They may be unicellular, such as yeasts,
or multicellular, such as mushrooms. Most fungi grow on their food source
by forming a spreading network of branching filaments called hyphae.
These filaments secrete enzymes that digest the food. The filaments then
absorb the pre-digested food. Examples of fungi include bread mould,
mushrooms, yeast and bracket fungi.
Figure 8 Bread mould is an example of a fungus.
sporangium
spores
sporangiophore
stolon
rhizoids
Figure 9 Most fungi form a network of filaments.
Figure 10 There are many different
types of fungi.
Key concepts
Micro-organisms are living organisms that are too small to see with the
naked eye.
Bacteria, fungi and protists are all types of micro-organisms. Viruses are
included as micro-organisms even though they are non-living.
Topic 3: Micro-organisms
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Skills focus: Measure length and use a scale
Key word
• micrograph –
photograph of
an object that is
viewed under a
microscope
Did you know?
Some common units
that are used to
measure the size of
micro-organisms are
nanometres (nm) and
micrometres (μm).
The following
comparison gives
you an indication of
how small these
measurements are.
What is a micrograph?
As you know, most micro-organisms are not visible to the naked eye. The
only time that we are able to see them is when we look at them using a
microscope or in a micrograph. The micrograph is a magnified image of the
micro-organism. A micrograph allows us to see what the micro-organism
looks like up close, but it makes it difficult to imagine how big the organism
actually is. In many cases, a scale bar is given with a micrograph. This scale
can be used to calculate the actual size of the organism in the photograph.
How to use a scale to estimate the size of a
micro-organism in a micrograph
Look at the micrograph provided below. A scale bar is provided below the
micrograph that indicates by how much the image has been enlarged.
• 1nm = 1 × 10−6 mm
= 0,000001 mm
• 1μm = 1 × 10−3 mm
= 0,001 mm
Figure 11 Micrograph of bacterial cells
The scale bar looks like this:
200 nm
This means that the length of the bar is actually equal to 200 nm in real
life. So if the bar is 8 mm long, then anything that is 8 mm long in the
micrograph is 200 nm long in real life.
So, to get the real length of an organism from a micrograph, follow these
steps:
Step 1: Measure the length of the scale bar in millimetres.
Step 2: Measure the length of the organism in millimetres.
Step 3: Divide the length of the organism by the length of the scale bar.
Multiply your answer by the length printed on the scale bar.
Step 4: Add the unit of the scale bar to your answer.
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Worked example
Step 1: Use your ruler to measure the length of the scale bar that has
been provided with the micrograph in Figure 11.
Measure the bar in millimetres. In this case, the scale bar measures 8 mm.
This scale means that 8 mm on the photograph is equal to 200 nm in real life.
Step 2: Use your ruler to measure the length of the bacterial cell in the
micrograph.
Make sure your measurement is in the same unit as your measurement of
the scale bar. In this case the cell measures 57 mm.
Step 3: Calculate the actual length of the cell by using simple
mathematical principles.
For example: 8 mm = 200 nm, therefore how many nm is 57 mm?
57 mm
× 200 nm
OR: x =
8 mm
= 1 425 nm
Activity 3
Estimate the actual size of a micro-organism
1. Use the technique explained above to estimate the actual size of the
micro-organism in the micrograph provided below. Calculate the length
and width of the cell by measuring along the lines that are indicated.
Skills focus: Measure length and use a scale
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Practical task
Investigate the factors that affect the growth
of yeast
You will need: six packets of dry yeast • six recycled plastic litre bottles
• white table sugar • water • small balloons of different colours
• string or clips for tying off balloons • large, clear, metric
liquid measuring cup • permanent marker
Background information
Yeast is a fungus that uses simple sugars as a food source. Yeast breaks
down sugar to release energy. A by-product of this process is carbon
dioxide. In this investigation, you will grow yeast in different conditions to
see which of the conditions cause the yeast to be the most active. You will
use balloons to trap the carbon dioxide that is released by the yeast. The
more carbon dioxide produced, the faster the yeast cells grow. Once the
experiment is complete, you will submerge the balloons under water and
use water displacement to measure the amount of gas collected in each
balloon.
Method
1. Wash each water bottle thoroughly and remove any labels. Then label
each bottle A to F using the permanent marker.
2. Add one packet of yeast to each bottle and then add sugar to the
bottles according to the following table. Redraw the table below in your
workbook so that you can record your results.
Bottle Condition
A
B
C
D
E
Observations Balloon Water
Water
Displacement
colour before (ml) after (ml) (ml)
No sugar at room
temperature
15 ml sugar at room
temperature
25 ml sugar at room
temperature
15 ml sugar and
place fridge
15 ml sugar and
place in warm area
3. Fill each bottle with 300 ml warm water, replace the lid, and shake
thoroughly to dissolve all of the ingredients.
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4. Remove the lid and stretch a balloon over the opening of each bottle.
Use a different colour balloon for each condition and write the colour in
your data table.
5. Leave the bottles for 1 hour then look at the balloons. Observe any
differences in the balloons. Record your observations in your data table.
6. Now tie a piece of string tightly around the base of the balloon to seal
the balloon so that no gas can escape. Once tightly sealed, remove the
balloon from the top of the bottle.
7. Fill the large measuring cup with enough water so that you are able
to fully submerge the balloon. Record the amount of water in the
measuring cup.
8. Dunk the balloon in the water. Once the balloon is fully submerged,
record the water level again.
9. Subtract the water level before from the water level after to get the
volume of gas produced by the yeast.
10. Repeat steps 6 to 9 for each bottle.
Questions
11. Was the yeast able to grow when there was no sugar present in the
bottle? Give an explanation for this.
(3)
12. Compare the results for A, B and C and describe the effect that
increasing the amount of sugar in the bottles had on:
a ) the size of the balloons.
(2)
b ) the rate at which the yeast was growing.
(2)
13. State an aim for the investigation that involved:
a ) bottles A to C.
(1)
b ) bottles B, D and E, F.
(1)
14. Describe the effect that;
a ) cold temperatures have on the rate at which yeast grows.
(2)
b ) higher temperatures have on the rate at which yeast grows.
(2)
15. Write a scientific report for this investigation in which you include the
following:
a ) a hypothesis
(1)
b ) the aim of the investigation
(1)
c ) your table of results
(3)
d ) a conclusion.
(2)
Total: 20
Practical task: Investigate the factors that affect the growth of yeast
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Unit
2
Harmful micro-organisms
Although many micro-organisms are beneficial to humans
there are others that are harmful. In 1876, Robert Koch, a
German doctor, discovered that micro-organisms cause
diseases. He discovered that if cattle were infected with
anthrax then their blood always had large numbers of a
bacterium called Bacillucis anthracis in it. He realised that
it was these bacteria that were making the cattle sick.
Common diseases caused by
micro-organisms
Figure 12 Robert Koch discovered the bacterium
Bacillucis anthracis and realised that it was the cause of
the disease called Anthrax.
Many diseases or illnesses such at tuberculosis, Aids,
diarrhoea, meningitis and malaria are caused by microorganisms. Disease-causing organisms occur almost
anywhere. Everything you touch (including ATMs,
handrails, doorknobs and toilets), eat or drink has
thousands of micro-organisms on it. It is possible that at
least some of these organisms can make you sick.
Tuberculosis
Tuberculosis (TB) is a bacterial infection that usually affects
the lungs. It can also affect other parts of the body but this
is less common.
The TB bacteria are spread through the air when people
who are already infected cough or sneeze. Droplets of
mucous and saliva containing the bacteria float in the air
and are inhaled by other people. Those people are then
infected.
Figure 13 Turberculosis is caused by the bacterium
called Mycobacterium tuberculosis.
60
One of the first symptoms that you may have if you are
infected with TB is a cough that lasts for more than a few
weeks. You may also cough up blood and have a fever.
Other symptoms include weight loss and night sweats.
A doctor will order X-rays to diagnose TB if he or she
suspects that this is the problem. When the condition has
been confirmed it is then treated with a long course of
antibiotics that can last for six months or more.
Term 1
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Acquired immunodeficiency syndrome or Aids
Aids is caused by the human immunodeficiency virus or HIV. Once
introduced into the body, the virus infects the cells of the immune system
and destroys them. As the immune system is destroyed, the
patient is unable to fight off normal day-to-day infections.
HIV is transmitted through contact with the bodily fluids of a
person who is infected. Infection with HIV occurs as a result of:
•
•
•
•
sexual contact
sharing hypodermic needles
contact with infected blood
transfer from mother to child during pregnancy and
breastfeeding.
It is important to remember that there is no cure for AIDS and
HIV infection. The infection can, however, be managed by
leading a healthy lifestyle and taking antiretroviral medicines
or ARVs. It is essential to avoid activities that may put you at
risk of being infected with HIV.
Figure 14 The human immunodeficiency virus or
HIV that causes Aids.
Initially, if you are infected with HIV, you may experience
fever, aching muscles and joints, a sore throat and swollen glands. These
symptoms soon disappear and you may remain symptom free for many
years. During this time the virus is destroying your immune system so that
eventually you become very ill with everyday infections. You now have Aids.
Malaria
Malaria is caused by a tiny parasitic micro-organism called a plasmodium.
When a mosquito that is carrying the parasite bites you, the parasite is
injected into your blood. The parasite then travels to your liver where it
lays eggs which hatch into more parasites. These go back into your blood
and enter your red blood cells. This destroys the red blood cells. If you are
infected with malaria, you may experience a high fever, chills, shaking,
sweating, headaches, muscle aches and vomiting.
The best treatment for malaria is not to be infected at all. Malaria only occurs
in the parts of the world where the Anopheles mosquito is found. If you are
travelling to a malaria area, you should take medicines call prophylactics
before you go and while you are there. These medicines immediately kill any
parasites that enter your blood if you are infected.
Topic 3: Micro-organisms
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Waterborne diseases
Waterborne diseases include any illness that is caused by drinking water
that is contaminated with micro-organisms. There are many different types
of micro-organisms that can cause severe diarrhoea and vomiting. These
include many species of protozoa, parasites and bacteria.
Diarrhoea is the biggest cause of childhood deaths in most third world
countries. Severe diarrhoea can be dangerous especially if you are vomiting
as well. You can become dehydrated and if you do not receive medical
treatment then this can be fatal.
The following two species of bacteria can cause severe diarrhoea:
• Escherichia coli (E. coli) is a bacterium that occurs naturally in your
large intestine. E. coli is beneficial to humans when it is living in
the large intestine. It digests certain foods so that we can absorb
the nutrients. However, if E. coli is ingested or eaten, it enters the
stomach and small intestine where it causes severe cramps and
diarrhoea. It also causes fever, nausea and vomiting.
• Cholera is caused by the bacterium Vibrio cholerae. The bacteria
releases a toxin that causes the cells in the intestines to release water,
which produces severe diarrhoea.
Figure 15 Escherichia coli causes
severe diarrhoea if it enters the upper
alimentary canal.
Activity 4
Infection with both bacteria usually occurs as a result of eating foods that
are contaminated with faecal matter. The best way to prevent this type of
infection is to thoroughly wash all fruits and vegetables that are going to
be eaten raw. The infection is treated with antibiotics and steps are taken
to ensure that you do not become dehydrated.
Analyse statistics about cholera
South Africa experienced a cholera outbreak in 2001. The statistics for the outbreak are provided in the
table below. Study the table then answer the questions that follow.
Table 1 Cholera cases and deaths reported to the World Health Organization on 20/9/2011
Province
Cases
reported in
24 hours
Eastern Cape
Free State
Gauteng
KwaZulu-Natal
Mpumalanga
Northern Cape
Northern Province
North West
Western Cape
62
0
0
0
5
0
0
0
0
0
Total cases Deaths
Total number Date of Case
to date
confirmed in of deaths
last case fatality rate
past 24 hours
9
1
65
105 708
127
0
793
6
1
0
0
0
0
0
0
0
0
0
0
0
4
228
4
0
2
0
0
06/05/01
Nov/00
04/06/01
19/09/01
0/07/01
Free
14/05/01
08/03/01
25/01/01
0,00%
0,00%
6,15%
0,22%
3,15%
0,00%
0.25%
0,00%
0,00%
Term 1
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1.
2.
3.
4.
5.
Calculate the total number of cholera cases that were recorded.
Which three provinces were least severely affected by the cholera outbreak?
Which province had the highest fatality rate?
Which province had the most deaths as a result of cholera?
KwaZulu-Natal had the most cases of cholera but had the lowest fatality
rate. Suggest TWO reasons why the fatality rate was so low.
6. Write a short paragraph in which you include the following information:
a ) What is cholera?
b ) How is cholera spread?
c ) How can people prevent being infected with cholera?
d ) How is cholera treated?
Preventing infection with micro-organisms
Disease-causing organisms occur almost anywhere. Everything you touch,
eat or drink has thousands of micro-organisms on it. It is possible that at
least some of these organisms can make you sick. It is better to prevent
being infected with these micro-organisms than to treat the infection.
Figure 16 shows ways in which you can reduce your risk of being infected
with a micro-organism.
Practise safe sex.
Wash your hands thoroughly
with soap.
Wash fruit and
vegetables carefully.
Figure 16 Reduce your risk of
an infection caused by a microorganism by following simple
precautions.
Wear gloves when dealing with
bodily fluids such as blood.
Keep food in the fridge to prevent the
rapid growth of micro-organisms.
Don’t share personal
items.
Boil or chemically treat water to
kill any micro-organisms that
may be present.
Cover your mouth
when you cough or
sneeze.
Topic 3: Micro-organisms
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Key words
• vaccines –
preparation of a
weakened or dead
form of a diseasecausing microorganism
• vaccinations – use
of a vaccine to
prevent infection
with specific
diseases
• pasteurisation –
process of heating
food or a liquid
to kill any diseasecausing microorganisms that
may be in it
The role of modern scientists in the cure of
diseases
In the early 1900s the average life expectancy
of a person was about 47 years. Today,
one hundred years later, the average life
expectancy has increased to around 78 years.
The increase in life expectancy is due to the
development of vaccines and medicines
used to treat diseases. Many diseases which
were previously considered incurable are now
prevented by vaccinations or cured by using
modern medicines.
Modern scientists such as Louis Pasteur,
Jonas Edward Salk and Sir Alexander Fleming
made critical discoveries that led to new
treatments and new ways of preventing
infectious diseases.
Louis Pasteur
Figure 17 Vaccinations prevent
people becoming sick from many
different diseases.
Louis Pasteur was born in France on
27 December 1822. He was a chemist and a microbiologist. He is best
known for developing a method that prevents milk, beer and wine from
causing illness in humans. Pasteur’s research showed that it was microorganisms growing in these liquids that caused them to spoil, and when
people drank the liquids the micro-organisms would make them ill. He
invented a process that heats the liquid so that most of the micro-organisms
are killed. This process is called pasteurisation. These days, liquids such as
milk, wine and beer are routinely pasteurised.
Activity 5
Figure 18 Louis Pasteur
64
Investigate diseases caused by micro-organisms
1. Choose a disease that is caused by a micro-organism. Do some research
to make sure that this disease is caused by a micro-organism.
2. Find out the following information about the disease you have chosen:
a ) the name of the micro-organism that causes the disease
b ) the group of micro-organisms to which the organism belongs
c ) the effects and symptoms of the disease
d ) how the disease is treated
e ) how to prevent being infected with the disease.
3. Arrange the information that you found into a poster or pamphlet that
could be used to educate people about the disease. Make your poster
or pamphlet as attractive as possible.
Term 1
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Beliefs about the causes of diseases
Before the invention of the microscope and the discovery
of micro-organisms, each culture had its own beliefs about
what caused people to become ill. Most cultures believed
that diseases were caused either by witchcraft, demons,
the influence of the stars or by the gods. Many cultures had
beliefs that combined two or more of these aspects.
Activity 6
Discuss cultural and historical
beliefs about diseases caused by
micro-organisms
Figure 19 In medieval times, people who were
believed to be witches were burnt at the stake.
Read the case study below and then use the information to answer the
questions that follow.
1. Briefly explain the miasmatic theory of disease.
2. a ) Explain what is meant by the term ‘corrupting matter’.
b ) List four examples of corrupting matter.
3. a ) What is a nosegay?
b ) Explain how someone from the Victorian Era would use a nosegay.
4. Was the miasmatic theory of disease correct? Explain your answer.
5. Write down a list of at least four different beliefs that you, your family
or your friends may have about how diseases are spread. You should
discuss this topic with your friends and family before making your list.
Case study: Preventing infectious diseases
in the Victorian Era
During the Victorian period most
people believed in the ‘miasmatic’
theory of disease. According to this
theory most, if not all, diseases were
caused by inhaling air that was infected
by being exposed to ‘corrupting
matter’. This matter could be rotting
corpses, air that had been exhaled by
sick people, sewage or any other rotting
material. People therefore believed
that diseases were caused by bad
smells or miasma’s. They would carry
small posies of herbs or flowers called
nosegays. When they smelt a bad smell
they would hold the nosegay under
their nose to prevent them inhaling
any miasmas. They believed that this
would protect them from infections.
Key concepts
Some microorganisms cause
diseases such
as tuberculosis,
Aids, cholera and
malaria.
We can take
precautions
to prevent
being infected
with microorganisms.
There are many
myths about
what it is that
makes people
sick.
Topic 3: Micro-organisms
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Unit
3
Useful micro-organisms
Micro-organisms or microbes are essential for the maintenance of healthy
ecosystems. They perform various functions such as decomposing dead
organic material and assisting with the cycling of nutrients. In addition
to this, micro-organisms are used by humans in various manufacturing
processes and to make certain types of food as well as medicines.
Decomposers
You learnt in Topic 2 that when an organism dies, micro-organisms such as
bacteria and fungi start to digest the dead or decaying body. This process of
digestion is called decomposition.
nutrient cycle
dead leaves,
plant and
animal matter
water and air
penetrate soil
minerals and
other nutrients
released into soil
decomposers
break down
organic matter
rocky subsoil
Figure 21 Micro-organisms ensure that nutrients are recycled back into the soil
so that they can be reused by new plants and animals.
Figure 20 Organic substances decay as micro-organisms
like bacteria and fungi digest them.
The process of decomposition releases
nutrients that were stored in the
organism’s body back into the soil. The
addition of these nutrients helps to keep
the soil fertile and new plants can use
these nutrients to grow big and strong.
If there were no micro-organisms, then
dead plants and animals would not
decompose. Nutrients would not be
released and soils would become infertile.
Using micro-organisms to make medicines
Sir Alexander Fleming
Sir Alexander Fleming was born 6 August 1881. Fleming discovered the
antibiotic substance called penicillin by accident when he noticed that a
bacterial culture had been contaminated with a fungus. He saw that the
bacteria immediately surrounding the fungus had all been destroyed. He
realised that the fungus was producing a substance that killed the bacteria.
The discovery of penicillin changed the course of history as many previously
incurable diseases could now be treated with a course of penicillin.
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Using micro-organisms to make foods
Humans have been using micro-organisms to make food since ancient
times. Yeast has been used to make bread rise, as well to brew wine and
beer. Certain types of bacteria are used to make yoghurt and cheese. Some
cheeses need moulds to grow on them to cause them to ripen and mature.
The moulds are added to give cheese such as camembert and brie their
special flavour.
Yoghurt originated in Turkey and is made by adding a bacterial culture to
milk and allowing it to ferment. The partial digestion of the milk by the
bacteria during the fermentation process makes the yoghurt easy to digest.
Activity 7
Make your own yoghurt
You will need: 1 litre of milk • 1 small tub of live yoghurt • 1 pot with a lid
to boil the milk in • containers with lids that seal to put your
yoghurt in
Method
1. Pour the milk into the pot and heat it. Remove the pot from the heat
when the milk is just about to boil.
2. Allow the milk to cool to room temperature.
3. Scoop out some of the cooled milk and add three tablespoons of the
live yoghurt to it. Mix well.
4. Pour the milk and yoghurt mixture back into the rest of the milk and stir.
5. Put the lid on the pot and allow it to stand in a warm place overnight.
You can wrap it in a blanket to keep it warm
6. In the morning you will have a pot of yoghurt. Pour the yoghurt into the
sealable container and place it in the fridge to stop the fermentation
process.
7. Add fruit, sugar or any other flavouring that you prefer.
Key concept
Micro-organisms can be used for the benefit of humans. They can be
used to make food and produce medicines. They are also useful in natural
ecosystems where they decompose dead organic matter and return the
nutrients to the soil.
Topic 3: Micro-organisms
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Topic 3 revision
Science language practice
1. State whether each of the statements in the first column applies to ONLY A, ONLY B, BOTH A AND
B or NONE of the items in the second column.
Statement
1
Consists of very small organisms that cannot be seen with the naked eye
2
Consisting of a single cell
3
Examples of types of micro-organisms
4
Forms a network of spreading filaments
5
Microscopic particles that cause diseases
6
A photograph taken from a microscope
7
A disease caused by bacteria
8
A disease that is treated with ARVs
9
The organism that transmits malaria from person to person
10
An example of a protist
Items
A : Macro-organisms
B : Micro-organisms
A : Unicellular
B : Multicellular
A : Protists
B : Bacteria
A : Fungi
B : Plasmodium
A : Viruses
B : Bacteria
A : Micro-view
B : Micrograph
A : Cholera
B : Tuberculosis
A : Malaria
B : Anthrax
A : Mosquito
B : Bacteria
A : Amoeba
B : Diatom
Test yourself
1. Name four types of micro-organisms and give one example of each.
2. Draw and label diagrams to show the three shapes that are used to group or classify bacteria.
(8)
(6)
3. a ) Give the scientific name for the parasite that causes malaria.
b ) If you wanted to visit Australia and India, is it necessary for you to take anti-malarial
medication? Give an explanation for your answer.
(2)
4.
5.
6.
7.
8.
9.
(4)
List two types of fungi.
(2)
Explain why viruses are not placed in any of the five kingdoms of living organism.
(3)
List three ways in which you can reduce your risk of becoming infected with a micro-organism. (3)
Explain the role played by Louis Pasteur in preventing the spread of diseases.
(6)
List and explain three ways in which micro-organisms are beneficial to humans.
(9)
One of the pupils at Thandi’s school is HIV positive. She is worried that she may become infected
with HIV if she shares a classroom and school equipment with this person. Write a paragraph in
which you explain:
a ) what HIV positive means
(2)
b ) why there is very little risk of Thandi becoming infected with HIV.
(5)
Total: 50
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Term 1 Practice test
1. Multiple choice:
Four options are provided as possible answers to the following questions. Each question has only
ONE correct answer. Select the correct answer and write only the letter (A–D) next to the question
number ((a)–(e)).
a) Energy that is stored in an object or system is called ...
A radiant energy
B electrical energy
C potential energy
D electromagnetic energy
b) The waste product formed during photosynthesis is ...
A glucose
B carbon dioxide
C oxygen
D energy
c) The study of the interactions between living things and their environment is called ...
A ecology
B a habitat
C an ecosystem
D a population
d) Organisms that break down dead organic matter are known as ...
A producers
B consumers
C herbivores
D decomposers
e) Micro-organisms that are generally considered to be non-living are ...
A viruses
B protists
C bacteria
D fungi
(5)
2. Give the correct term for each of the following statements. Write only the question number and
your answer.
a)
b)
c)
d)
e)
Energy that is absorbed by plants to make food
The substance that is used to test for the presence of carbon dioxide
A group of interconnected food chains
The disease that is caused by Plasmodium vivax
A preparation of a weakened or dead form of a disease-causing micro-organism, which
is given to prevent disease
3. Look at the diagram on the right, which shows the process of
photosynthesis.
a) Name the gases labelled 2 and 3.
(2)
b) Name the substance labelled 4.
(1)
1
2
c) Thandi investigated the rate of photosynthesis
of the tree for 24 hours. Suggest a reason why,
for about half of this time, the rate of
3
photosynthesis dropped suddenly.
(1)
d) Suggest when most oxygen would be released
into the air.
(1)
4
e) Suggest when most carbon dioxide would be
released into the air during the 24 hours. Support
your answer with a reason.
(2)
Term 1 Practice test
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(5)
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4. Study the food chain shown below.
Cricket
Grass
Robin
Black eagle
a) Explain what the arrows in the food chain represent.
b) Explain why the:
i. cricket is an example of a primary consumer
ii. grass is an example of a producer
iii. black eagle is an example of a carnivore.
c) Draw a possible energy pyramid to represent this food chain.
d) Explain why you have drawn the energy pyramid in (c) in this shape.
5. The graph below shows recent HIV statistics for pregnant South African women.
(1)
(1)
(1)
(1)
(2)
(2)
Percentage of pregnant women between
15–24 years that are HIV positive
% that are HIV positive
30
28
26
24
22
20
0
2004
2005
2006
2007
Year
2008
2009
2010
Pie chart showing the number of people living with HIV by region
a) Name the type of micro-organism that causes HIV.
b) Differentiate between being HIV positive and having Aids.
c) Predict whether or not it is possible to be infected with HIV by shaking hands
with an infected person. Give an explanation for your answer.
d) Analyse the graph and answer the following questions:
i ) Describe two trends that you see in the graph.
ii ) Give a possible reason for the trend that you see in the graph.
iii ) Suggest why it is easier to determine HIV numbers for pregnant women than for men.
iv ) Calculate the difference in the highest and lowest percentage of HIV positive
pregnant women.
(1)
(2)
(2)
(2)
(1)
(1)
(1)
Total: 35
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Term 2: Matter and materials
Topic
4
Atoms
Starting off
In Grade 7, you learnt that elements and
compounds are pure substances. All the elements
that we know about are arranged in the Periodic
Table of Elements. You will find a Periodic Table at
the back of this book. Elements form the basis of all
natural and human-made materials.
In this topic, you will investigate what elements are
made up of. You will use a scientific model to help
you understand things that are too small to see,
even with a microscope.
Figure 1 These water pipes are made of copper.
Figure 2 Charcoal briquettes made of carbon are sometimes
used to braai food.
Activity 1
Revise what you know about
elements
1. The elements in the Periodic Table are arranged
into three main groups. Name the group that
each of the elements in the photographs (and
named below) belongs to.
a ) Copper
b ) Carbon
c ) Silicon
2. List two differences between copper and
carbon.
3. Write down the symbols for copper and carbon
that are used in the Periodic Table.
4. In what way is the group that silicon belongs to
in the Periodic Table special?
5. If copper reacts with oxygen, is it still an
element? Explain your answer.
6. If we mix carbon powder with sulfur powder,
are they still both elements? Explain your
answer.
7. In your own words, explain what you think an
element is made up of.
Figure 3 Silicon was used to produce the silicone that these
containers are made from.
Topic 4: Atoms
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Unit
1
Atoms - the building blocks of matter
Key word
• atoms – smallest
units that elements
are made of
From earlier grades, you know that everything around us is made of matter.
A chair, a desk, the clothes you wear or the air that you breathe is all made
of matter. Matter is anything that has mass and takes up space.
All matter is made up of tiny particles called atoms. Atoms are extremely
small. Single atoms are much too small to see with our eyes. The radius of
a typical atom is about 0,0000000001 m. So, if you tightly
packed about 50 million atoms in a straight line, the line
would only be 1 cm long! We can only see atoms when
there are enough of them together in one place and if we
have a microscope like the one in Figure 4.
Elements are made up of atoms
Figure 4 When we study atoms, we use a powerful
scanning electron microscope, which can magnify
things so that very small details appear relatively big.
In Grade 7, you learnt that all the elements that we know
about are organised in the Periodic Table. Currently there
are about 115 different elements. Most of them occur
naturally, but some of them are human-made.
An element is made up of the same type of atoms. All the
atoms of an element are the same, so all copper atoms are
the same and all oxygen atoms are exactly the same.
Look at the photograph of the copper water pipes on the previous page.
The pipes are made up of billions and billions of identical copper atoms. The
charcoal on that page is made up of billions and billions of identical carbon
atoms. Carbon atoms can also arrange themselves in a different way to the
way that they are arranged in charcoal. When this happens, the product is
diamond and not charcoal!
Elements cannot be
broken down into simpler
substances
Figure 5 Diamonds are made
from the element carbon.
The atoms are identical to the
atoms in charcoal, but they are
arranged in a different way.
The French chemist, Antoine Lavoisier
(1743–1794), conducted some research on air
and water, which at the time were thought
to be elements. He discovered that water
was made up of the elements hydrogen and
oxygen. He concluded that elements are pure
substances that cannot be split up into simpler
substances by chemical reactions.
Did you know?
A nuclear reaction
can change the
atoms of certain
elements, but it
requires enormous
amounts of energy.
72
Figure 6 Antoine Lavoisier
Term 2
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Elements are unique
An element cannot be changed into another element by a chemical
reaction. This is because each element is made up of only one type of atom.
We say that each element is chemically unique. The atoms of one element
are different from the atoms of all the other elements. No two elements
have the same atoms.
Elements are listed in the Periodic Table
In Grade 7, you learnt that a Russian chemist called
Dmitri Mendeleev (1834–1907) arranged the elements
in a pattern called the Periodic Table of Elements. You
should remember the following facts about the Periodic
Table of Elements:
• Each element has its own name.
• We represent elements using internationally
recognised symbols. This makes it possible for
scientists all over the world to work together.
• We use one capital letter, or one capital letter and
one lower case letter, to represent an element.
• The Periodic Table is arranged in a grid. There are
Figure 7 Dmitri Mendeleev
seven horizontal rows and 18 vertical columns.
• The elements are arranged in three main groups: metals, non-metals
Did you know?
and semi-metals.
Activity 2
Recall knowledge about atoms
1. Define the term ‘element’.
2. If you break down each of the following, how many different substances
would you be able to recover?
a ) Mercury
b ) Sodium chloride
c ) Water
d ) Carbon dioxide
e ) Oxygen
3. Say whether the following statements are true or false. If a statement is
false, correct it.
a ) All matter is made from elements, so there must be thousands of
different elements.
b ) There is no other element with atoms that are identical to iron
atoms.
c ) A piece of aluminium is made up of billions of identical aluminium
atoms.
The element with the
symbol Au is called
‘gold’ in English,
‘igolide’ in isiZulu and
isiXhosa, ‘gauta’ in
Sesotho, and ‘goud’
in Afrikaans.
Key concepts
All matter is
made up of tiny
particles called
atoms.
An element
cannot be
broken down
into simpler
substances.
The atoms of
one element are
different from
the atoms of all
other elements.
Topic 4: Atoms
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Unit
2
Subatomic particles
Atoms are the basic building blocks that make up elements. Scientists have
spent many years trying to discover what makes up an atom. Each new
discovery has added to our knowledge of atoms. The timeline below shows
the main events in the development of the scientific theories about atoms.
British scientist, Joseph Thomson (1856–1940), also saw the atom at a
sphere. He said that tiny electric charges, called electrons, are spread out
and arranged like layers in an onion inside the sphere. As atoms are neutral
The Atomic Theory timeline
Figure 8 Timeline of scientists’ discoveries about the atom
74
Term 2
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1950 A.D.
1870 A.D.
1850 A.D.
1803 A.D.
1800 A.D.
1780 A.D.
1750 A.D.
0 A.D.
400 B.C.
John Dalton (1800–1850):
Atoms are solid spheres. This was
Joseph Thomson (189
Tiny electric charges c
electrons are randoml
spread throughout th
inside of an atom.
1900 A.D.
The Greek
philosopher
Democritus (470–380
BCE) developed the
first idea of atoms. He
said that if we cut
matter into smaller
and smaller pieces,
we eventually will not
be able to continue.
He called this
smallest unit of
matter the ‘atom’,
from the Greek word
‘atomos’, which
means ‘uncuttable’.
1898 A.D.
Did you know?
In the 1800s, a British chemist and physicist, John Dalton (1766–1844),
developed the first atomic theory. He suggested that an atom was a solid
sphere. His model of the atom looked like a billiard ball.
(do not have a charge) the sphere itself has a positive charge. This model is
called the ‘plum pudding model’ as the electrons are placed like raisins in a
Christmas pudding.
Ernest Rutherford (1871–1937) was a scientist from New Zealand. In 1911,
he conducted some experiments in which he discovered new things about
atoms. He discovered that there is a small centre in an atom with a positive
charge that has almost all the mass of the atom. The centre was called
the nucleus. The space around the nucleus is almost empty except for the
negatively charged electrons.
A Danish scientist, Niels Bohr (1885–1962), discovered that electrons move
in orbits around the nucleus.
2000 A.D.
1964 A.D.
1950 A.D.
1931 A.D.
1913 A.D.
1909 A.D.
James Chadwick (1931):
The nucleus contains
particles with no charge
called neutrons.
1950 A.D.
Thomson (1898): Ernest Rutherford (1909): Niels Bohr (1913):
ctric charges called The mass of an atom is a Negatively charged
ns are randomly
small positively charged electrons ,move in
throughout the
sphere at the centre of
orbits around the
of an atom.
the atom.
positive nucleus.
1900 A.D.
In 1932, a British scientist, James Chadwick, discovered that there were
some particles that did not have a charge. These are called neutrons.
Topic 4: Atoms
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Atoms are made of subatomic particles
Key words
• nucleus – central
region of an
atom consisting
of protons and
neutrons
• protons – positively
charged particles
found in the
nucleus of an atom
• neutrons – neutral
particles found in
the nucleus of an
atom
• electrons –
negatively charged
particles spinning
around the
nucleus of an atom
• model – idea of
how something
works, based on
patterns that
scientists observe
The nucleus of an atom is extremely small compared to the size of the electron
cloud. If you picture the whole atom as the sports stadium at Soccer City
in Johannesburg, the nucleus would be like a marble in the middle of the
stadium.
Activity 3 Revise your knowledge about subatomic particles
1. If you could look inside an atom, what would you see?
2. Which subatomic particle has:
a ) a positive charge
b ) a negative charge
c ) no charge?
3. Draw a picture of an atom with three protons, four neutrons and three
electrons.
4. If an atom has five protons, how do you know that it has five electrons
as well?
Making models of atoms
-
-
Today we know that atoms are made up of smaller subatomic particles. Here is
a list of the main points that scientists agree on about the structure of an atom:
• The central region of the atom is called the nucleus.
• The nucleus is made up of positively charged particles called protons
and electrically neutral particles called neutrons.
• A cloud of negatively charged particles called electrons spin in orbits
around the nucleus.
• Atoms are neutral because the number of negatively charged particles
(electrons) is equal to the number of positively charged electrons (protons).
-
+ +
+ + +
+
-
-
Figure 9 The nucleus contains
positively charged protons and
neutral neutrons. Negatively
charged electrons move in
orbit around the nucleus.
A scientific model is an idea of how something works. Scientists base
models on what they observe. A model helps us to understand something
better. Sometimes a model is a smaller and simpler version of the real
thing. You built a model of Earth in earlier grades. In some models, we
enlarge something we cannot see and represent it in the way that we think
it works. The diagram at the top of the page is an example of this type of
model. Based on what we observe about the behaviour of elements, we can
represent what an atom looks like.
In Grade 7, you learnt that each element has its own block in the Periodic
Table. A block gives us information about the atoms that make up that
element.
How to determine the number of subatomic particles in an atom
We can use the information in the Periodic Table to determine the number
of subatomic particles in one atom of any element.
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•
•
Number of protons = atomic number
Number of electrons = atomic number
(atoms are neutral, so the number of
positive and negative charges must be
equal)
Number of particles in the nucleus = mass
number
Number of neutrons = mass number –
atomic number
•
•
For example, these are the subatomic particles
in one sodium (Na) atom:
• Number of protons = 11
• Number of electrons = 11
• Number of particles in nucleus = 23
• Number of neutrons = 23 – 11 = 12
Figure 10 The nucleus and electron cloud of an atom can be compared
to a marble in the middle of the stadium at Soccer City.
Activity 4 Determine the number of subatomic
particles
1. a ) Copy the table below into your books.
b ) In the first column, write down the names of the first
20 elements.
c ) Use the Periodic Table at the back of this book to
complete the table.
11
Na
23
Atomic number: the number of
protons in the nucleus; this number
identifies the element; no two
elements have the same atomic
number.
Symbol for the element
Mass number: The number of protons
and neutrons in the nucleus
Figure 11 Atomic information about sodium
Element Symbol Number of Number of Number of Number of
protons
electrons
protons and neutrons
neutrons
2. The diagrams below show models of certain elements.
a ) Write down the number of protons, electrons and neutrons for each
element.
b ) Identify each element.
1
2
Figure 12 Diagrams for question 2
Topic 4: Atoms
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Activity 5 Make a 2-dimensional model of an atom
You will need: beads • dried lentils or dried peas • paper plates • glue
1. Choose an element from the first 20 elements in the Periodic Table. Do
not choose any of the elements from question 2 of Activity 4.
a) Determine the number of protons, neutrons and electrons in the atoms
of the element.
b) Use beads to represent the nucleus. Glue beads of the same colour for
each proton in the middle of the paper plate. Use different coloured
beads for the neutrons.
c) Use lentils or dried peas to represent the electrons. Draw an orbit
around the nucleus and glue lentils onto the orbit.
You can see an example of a model of oxygen in Figure 13.
Figure 13 A model of the element oxygen
Key concepts
All atoms are made up of sub-atomic particles: protons, neutrons and
electrons.
Protons are positively charged particles and neutrons are negatively
charged particles. There are always the same number of protons
and neutrons in an atom and together they make up the nucleus.
Negatively charged particles called electrons move around the nucleus.
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Unit
3
Pure substances
We classify matter as either a pure substance or a mixture of different
substances. You will learn more about mixtures in Unit 6.
A pure substance consists of only one type of particle.
• Elements are pure substances, because all the atoms of a specific
element are identical.
• Compounds are pure substances, because all the molecules of a specific
compound are identical. Some compounds consist of particles that are
arranged in the same pattern all the way through.
A pure substance is the same all the way through. Figures 14 to 17 show
some examples of pure substances.
Figure 14(a) Gold
nugget
Figure 14(b) Diagram
of gold particles
All the pieces of gold are identical.
Figure 16(a) Table salt
Figure 15(a) Water
Key words
• pure substance –
substance that is
of made up of one
type of particle
throughout
• mixture – two
or more different
substances that are
mixed together
Figure 15(b) Water
particles
All the particles in a glass of water are identical.
Figure 16(b) Table salt
particles
Figure 17(a) Carbon
dioxide blown into a
balloon
The same particles are arranged in the
same way in a spoon of table salt.
Figure 17(b) Carbon
dioxide particles
All the carbon dioxide particles are identical.
Topic 4: Atoms
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Pure substances have specific properties
You can investigate a pure substance by asking questions about its properties.
• Phase: Is the substance a solid, a liquid or a gas at room temperature?
• Conductivity: Can the substance conduct electricity?
• Solubility: Is the substance soluble or insoluble in water?
• Density: Does the substance float or sink in water?
• Magnetism: Is the substance magnetic?
• Melting point: At what temperature does the substance melt or freeze?
• Boiling point: At what temperature does the substance boil or condense?
Figure 18 This sulfur sample
melts at 119 °C and boils at
445 °C. It is a pure sample.
In real life, very few elements or compounds occur in a pure form. If we
know what the melting or boiling point of a substance is, we can determine
whether a sample is pure. For example, Table 1 below shows some of the
information that we know about the element sulfur and the compound
water at standard atmospheric pressure.
Figure 19 This water melts at
0 °C and boils at 100 °C. It is a
pure sample.
Table 1 The melting and boiling points of sulfur and water
Substance
Boiling point (°C)
Melting point (°C)
Sulfur
Water
445
100
119
0
Activity 6 Identify pure substances
Figure 20 This is tap water. This
sample melts at –0,5 °C and
boils at 101 °C. There are other
elements, such as chlorine and
sodium, mixed in the water, so
it is not a pure sample.
Figure 21 Iron nails
1. For each of the substances in the photographs below, decide whether it
is a pure substance or a mixture. If it is a pure substance, decide whether
it is an element or a compound.
Figure 22 Mixed herbs
Figure 23 Sugar cubes
Figure 24 Balloons
filled with helium
Figure 25 Copper sulfate
Key concept
Elements and compounds are pure substances. A pure substance consists
of only one type of particle.
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Unit
4
Elements
An element is a pure substance because it is made up of only one type of
atom. All the elements that we know about are listed in the Periodic Table.
From Unit 1, you know that there are only a limited number of elements.
Elements combine in different ways to build up all matter that you see
around you. You saw examples of the elements copper, carbon and silicon
on the first page of this topic. Hydrogen, sodium and chlorine are also
elements.
Diatomic elements
Look at the picture of gold on page 79 again. A gold nugget is made up of
millions of gold atoms packed together. Some elements are not made from
single atoms. They are made up of molecules. A molecule is two or more
atoms that are bonded together to form a unit. A molecule that consists of
two atoms is called a diatomic molecule. The elements hydrogen, nitrogen,
oxygen, fluorine, chlorine, bromine and iodine are made up of diatomic
molecules and not atoms. So, for example, all the atoms of hydrogen are still
identical, but they exist in pairs and not as single atoms.
Molecule
Chemical formula
Hydrogen
H2
Nitrogen
N2
Oxygen
O2
Fluorine
F2
Chlorine
Cl2
Bromine
Br2
Iodine
I2
Key words
• molecule – two or
more atoms that
are chemically
bonded together
• diatomic
molecule –
molecule that
consists of exactly
two atoms
Model
Topic 4: Atoms
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Elements form compounds
Sometimes, atoms of different elements react together chemically. They
form molecules of compounds. For example, two hydrogen atoms can
bond with an oxygen atom to form water. There are millions of different
compounds. This table shows some common compounds and their
chemical formulae.
Name of
compound
Elements in the
compound
Formula of
compound
Water
Hydrogen and oxygen
H2O
Carbon
dioxide
Carbon and oxygen
CO2
Salt
Sodium and chlorine
NaCl
Model
Activity 7 Make models to show the atoms that make up
molecules
You will need: white, red, black and blue playdough or modelling clay •
beads • adhesive putty
1. Build models of each of the following molecules. Draw your models in
your book.
a ) Oxygen
b ) Hydrogen
c ) Nitrogen molecules
d ) Water
e ) Carbon dioxide
Key concepts
All the elements that we know about are listed in the Periodic Table.
Some elements are not made from single atoms. They are made up of
molecules.
A molecule is two or more atoms that are bonded together to form a unit.
A molecule that consists of two atoms is called a diatomic molecule.
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Unit
5
Compounds
A compound is a pure substance formed by a chemical reaction of two
or more different elements. In Unit 4, you built models of the compounds
water (H2O), carbon dioxide (CO2) and salt (NaCl).
The ratio of atoms in a compound
French chemist, Antoine Lavoisier, conducted experiments to find out how
elements join together to form compounds. He discovered that the atoms
in a compound are always combined in a fixed ratio. For example, in a water
molecule, there are always two hydrogen atoms (H) and one oxygen atom (O).
In water, the ratio of hydrogen to oxygen is 2:1.
Key word
• compound –
pure substance
formed by a
chemical reaction
between two or
more different
elements
Figure 26 Atoms in a compound always join together in a fixed ratio.
Activity 8 Identify the ratio of atoms in compounds
1. For each of the compounds listed below, write down how many atoms
of each element is in one molecule of the compound.
a ) Hydrogen chloride (HCl)
b ) Sulfur dioxide (SO2)
c ) Ammonia (NH3)
d ) Carbon monoxide (CO)
2. For each of the compounds in question 1, draw a model of one
molecule of the compound.
Topic 4: Atoms
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Key words
• decomposition
reaction –
a chemical
reaction in which
a compound is
broken down
into simpler
compounds or
elements
Chemical bonds and chemical reactions
The atoms in a molecule are held together by chemical bonds. A chemical
bond is a strong force of attraction that holds atoms together.
A compound is formed by chemical reactions. When the element hydrogen
and the element oxygen undergo a chemical reaction, the compound water
is formed. The chemical bonds in the hydrogen molecules and the oxygen
molecules break. Then the hydrogen and oxygen atoms form new chemical
bonds to make water molecules. Figure 27 shows this reaction.
• electrolysis –
a chemical
reaction in which
an electrical
current is used
to decompose a
compound
2 hydrogen molecules and
1 oxygen molecule
2 water molecules
Figure 27 A compound is formed by chemical reactions in which bonds break and are made
Decomposing compounds
Compounds consist of different elements, so we can break a compound
up into the elements that it is made of. Compounds are formed by
chemical reactions, so we need chemical reactions to break them up
again. This type of chemical reaction is called a decomposition reaction.
A decomposition reaction is the opposite of what happened when the
compound was formed. The diagram below shows the decomposition
of water. In this unit, you will learn about two types of decomposition
reactions: electrolysis and heating.
2 water molecules
2 hydrogen molecules and
1 oxygen molecule
Figure 28 The decomposition of water
Electrolysis
Electrolysis is a decomposition reaction in which we use electrical energy
to split up a compound into the elements it is made from. One way to
see how electrolysis works is to connect electrodes made of graphite to a
battery. Then place the electrodes in a solution of the compound that you
want to split up. An element will form at each electrode.
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Figure 29 shows an easy method for the electrolysis of water. First, fill a
see-through container about three-quarters full with tap water and add
half a teaspoon of table salt. Cut a piece of cardboard big enough to close
the container. Sharpen two pencils on both sides. Push them through the
cardboard so that their ends hang in the water. Make sure that the pencils
do not touch the sides of the container or each other. Connect three 1,5 V
cells in series, or use a 6 V battery. Use conducting wire and sticky tape to
connect the pencils to the battery. Make sure that the copper ends of the
wires touch the graphite in the pencils properly. Then, wait a while. Bubbles
will form at the ends of the pencils. You will see more bubbles at the pencil
connected to the negative side of the battery. These are hydrogen bubbles.
The bubbles forming at the end of the other pencil are oxygen bubbles.
In the next activity, you will see an example of how a compound can be
broken down into its elements by electrolysis. Copper chloride (CuCl2)
solution decomposes to form copper (Cu) and chlorine (Cl2). Copper is a
brown solid and chlorine is a gas with a characteristic smell.
Activity 9
+–
6
volt
Battery
Figure 29 An easy way
to demonstrate the
decomposition of water
Demonstrate and record observations of how
copper chloride can be broken down into
elements by electrolysis
You will need: copper chloride (CuCl2) solution • a 250 ml beaker •
two connecting wires • graphite electrodes in a holder •
a 4,5–6 V battery
1. Fill the beaker halfway with copper chloride
solution.
2. Place the electrodes so that the holder is resting
on top of the beaker. The electrodes must be
1–2 cm above the bottom of the beaker.
3. Connect the wires to the electrodes. Attach the
wires to the battery.
4. Record what you observe at each electrode.
Describe anything you see, hear or smell.
5. Which element is formed at the negative
Figure 30 Demonstrating the electrolysis of copper chloride
electrode and which element is formed at the
positive electrode?
6. What can you conclude about copper chloride based on this
demonstration?
7. Disconnect one of the wires and wait a while. Record what you observe
and explain why it happens.
Topic 4: Atoms
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Key word
• thermal
decomposition –
a chemical
reaction in which
heat is used to
decompose a
compound
Safety
Wear safety goggles
when doing this
activity. Move the
test tube in and
out of the flame
otherwise some
of the potassium
permanganate may
shoot out from the
boiling tube. Make
sure that the boiling
tube does not point
towards a person.
Heating
Thermal decomposition is a decomposition reaction in which we use
heat energy to split up a compound into the elements it is made of. The
activity below is an easy way to demonstrate thermal decomposition. In this
activity, you will see an example of how a compound can be broken down
by heating. Potassium permanganate (KMnO4) is a dark purple solid. When it
is heated, oxygen gas is released. We test for oxygen with a glowing splint. If
we put a glowing splint in oxygen gas, it re-ignites.
Activity 10
Demonstrate and record observations of
how potassium permanganate decomposes
into elements by heating
You will need: potassium permanganate (KMnO4) solid • a Bunsen burner •
a boiling tube • a test tube holder • a wooden splint • matches
1. Put about half a teaspoon of potassium permanganate in the boiling
tube.
2. Hold the tube with a test tube holder and heat the potassium
permanganate. Move the tube in and out of the flame.
3. Light a splint. Blow out the flame of the splint
and, while it is still glowing, insert it into the
test tube as in the diagram.
glowing splint
4. Record what you observe.
5. What can you conclude about potassium
permanganate based on this demonstration?
6. Stop heating the tube and test with the
glowing splint again. Explain what you observe.
oxygen gas
7. a ) How do you know that there has been a
chemical reaction?
b ) Do you think that the reaction will
continue if you stop heating the tube?
Figure 31 Testing for oxygen gas
Explain your answer.
Key concepts
A compound is a pure substance formed by a chemical reaction of two or
more different elements.
Atoms in a compound are always combined in a fixed ratio.
Compounds are formed by chemical reactions, so we need chemical
reactions to break them up again, for example by heating or electrolysis.
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Unit
Mixtures of elements and compounds
6
In Grade 7, you learnt that we can mix two or more different pure substances
together. When we mix different elements or compounds together, the
particles of the substances move in between each other. There is no chemical
reaction and we can mix the elements or compounds in any ratio.
The substances that are mixed keep most of their own properties. For example,
in a mixture of peanuts and raisins, the properties of the peanuts and the
properties of the raisins remain the same.
We find mixtures of elements and compounds in the air, sea water, rocks
and living things.
O2
N2
Ar
N2
N2
Xe
H2
N2
O2
N2
N2
N2
O2
N2
O2
He
N2
N2
Kr
Ne
N2
N2
O2
N2
N2
CO2
CH4
N2
Figure 32 The air around you
contains many different elements and
compounds
Figure 33 Sea water is a mixture of
water and different salts
Figure 34 Fruit contains many different
compounds, such as sugars, water and
vitamins
Separating compounds and mixtures
In Unit 5, you learnt that we can separate compounds using chemical
reactions. Electrolysis and heating are two methods that we can use to
separate a compound into other compounds or elements. It is not always
easy to separate compounds into elements. When we mine iron, for
example, we need to melt the rocks that contain the iron in a very hot
furnace in order to get the iron out.
In Grade 7, you learnt that we can separate mixtures using physical
methods. Generally it is easier to separate mixtures than it is to separate
compounds. If you want to separate the mixture of peanuts and raisins, you
simply sort the peanuts and raisins into two piles.
Activity 11
Identify methods to separate mixtures
Remember the different methods for separating mixtures: hand sorting, sieving,
using a magnet, filtration, evaporation, distillation and chromatography.
Describe how you will separate the following mixtures.
1. Sand and salt
2. Sand and iron filings
3. Water and ethanol
4. Rice and cake flour
Key concepts
Elements and
compounds
are often found
mixed together.
It is quite easy
to separate
mixtures by
physical means,
for example
separating sand
and iron filings
with a magnet. It
is more difficult
to separate
compounds,
for example
using a chemical
reaction.
Topic 4: Atoms
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Topic 4 revision
Science language practice
1. Complete the following sentences by filling in the missing words:
a ) One element ________ be changed into another element by a
chemical reaction.
b ) The nucleus of an atom is made up of ________ charged
particles called protons, and electrically ________ particles called
neutrons.
c ) Atoms are ________ because the number of electrons is equal to
the number of protons.
d ) Elements are pure substances, because all the atoms of a specific
element are ________.
e ) Some elements, for example, oxygen, do not exist as single
atoms; they are made up of ________.
f ) The atoms in a compound are always combined in a ________
ratio.
g ) When we ________ different elements or compounds together,
there is no chemical reaction.
Test yourself
1. Name the three main groups in which the elements in the Periodic
Table are arranged. Give an example of one element for each
group.
(3)
2. Identify the following as an element, a compound or a mixture:
a ) magnesium oxide
b ) air
c ) hydrogen gas
(3)
3. Use the Periodic Table of Elements to write down the symbol
of an element that:
a ) is a non-metal in Group 13
b ) has five protons in the nucleus of one atom
c ) is in Group 2 and in the second period
d ) has eight electrons in one atom
e ) has 28 subatomic particles in the nucleus of one atom
f ) has seven neutrons in the nucleus of one atom
(6)
4. The boiling point of pure water is 100 °C at sea level. If a certain
sample of water boils only at 101,5 °C, what do you know about
the sample? Give a reason for your answer.
(2)
5. What do we call the chemical reaction that uses:
a ) an electrical current to decompose a compound?
b ) heat to decompose a compound?
(2)
6. Draw a picture to illustrate the decomposition of copper chloride
with an electric current. Use labels to show what is observed.
(4)
Total: 20
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Term 2: Matter and materials
Topic
5
Particle model of matter
Starting off
All substances, such as air, water, wood, metal and
plastic, are made up of matter. These substances
have different properties, but they all have one
thing in common: they are made up of tiny particles.
Figures 1 and 2 show examples of matter that you
should be familiar with. There is a solid, a liquid and
a gas, which we can see only because it is burning.
All matter is a gas, a liquid or a solid, and matter can
change between these states.
In earlier grades, you learnt that water can exist in
three different states: solid, liquid and gas. Even
though ice, water and water vapour look very
different to each other, they are all made up of the
same type of particles. In this topic, you will learn
how we can use the particle model of matter to
understand what matter is and how it behaves.
Activity 1 Revise what you know about
matter
Figure 1 Ice and the river formed from the melted ice
1. Look at Figure 1. Name the matter you can see
that is a:
a ) solid
b ) liquid
c ) gas.
2. What needs to happen for water to change
from a:
a ) solid to a liquid
b ) liquid to a solid?
3. Suggest a reason why the water in the river can
flow, but the water on the frozen banks cannot.
4. Explain why the water in the river and on the
banks is the same substance.
Figure 2 Gas burning
Topic 5: Particle model of matter
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Unit
1
The concept of the particle model of matter
Key word
• particle model of
matter – model
that helps us
understand that
matter is made
from particles and
how they affect
the behaviour of
matter
Did you know?
One water droplet
holds about 0,05 ml
water. There are 1,67
billion trillion water
particles in a droplet!
The particle model of matter
In Topic 4, you learnt that a scientific model is an idea that is used to
explain how something works. You made a model of an atom to help you
understand more about the subatomic particles in an atom.
The particle model of matter is a scientific model that we use to explain
that all matter is made up of particles and to explain the properties and
behaviour of matter. Look at the examples of pure substances on page 79
again. The gold nugget is made up of atoms and the water is made up of
molecules. To make things easier, we refer to an atom or a molecule as a
particle in the particle model of matter. The diagrams below explain the
main points of the particle model of matter.
1. All matter (solids, liquids and
gases) is made up of tiny
particles. These particles are
so small that we cannot see
them, even when we use a
microscope.
Figure 3 All matter is made up of tiny particles
2. The particles that make up all
matter are always moving. The
particles move faster when
they are heated. They move
more slowly when they lose
heat.
Figure 4 The particles that make up matter
move faster when heated.
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3. The particles have spaces
between them. The spaces are
empty. There is nothing in the
spaces, not even air.
Figure 5 The particles that make up matter
have spaces between them.
Figure 6 The particles that make up matter are
attracted to each other.
4. The particles are attracted
to each other. In some
substances, there is a strong
attraction between the
particles and the particles
are close together. In other
substances, there is a weak
attraction and the particles are
further apart.
Activity 2 Examine what matter is made of
Safety
Do not use a knife
You will need: a piece of chalk or soft crayon • a kitchen knife
that is too sharp. Be
1. Take a piece of chalk and cut it into two equal pieces. Take one of those
careful not to cut
pieces and cut it in half again. Keep doing this until the piece you are
yourself.
left with is too small to cut any more.
2. Imagine that you are as small as a mosquito so that the piece
of chalk that you could not cut into smaller pieces looks big to
you. If you were that small, would you be able to cut that piece
of chalk again?
3. If you could become smaller and smaller, and you kept cutting
the piece of chalk into smaller and smaller pieces, what would
Figure 7 Things are small only if you are big.
you end up with? Would you end up with anything? What would For a mosquito, this piece of chalk does not
look small.
that smallest thing be?
When you cut the piece of chalk into smaller and smaller pieces, you would
have had to stop at some point because your knife was not sharp enough
or small enough to carry on. If you could become very small, you could have
kept cutting the chalk until you had a particle that could not be cut into a
smaller piece. That particle would be so small that it would be invisible. Even
a powerful microscope would not be able to see it. We cannot see particles,
but that does not mean that they do not exist. Sometimes you know that
particles are there because you can smell them.
Topic 5: Particle model of matter
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Key words
• solid – matter
that has a specific
shape and size
• liquid – matter
that flows and
does not have a
specific shape, but
takes the shape
of the container it
is in
• gas – matter that
moves freely; it
does not take on
any shape and
spreads to fill a
space evenly
• states of matter –
the three forms in
which matter can
be found: solid,
liquid or gas
• vibrate – shake
backwards and
forwards
Solids, liquids and gases explained by the
particle model of matter
Water exists in three forms. When it freezes and becomes ice, it is a solid.
When ice melts, the water becomes a liquid and starts to flow. When the
liquid is heated and starts to evaporate, it becomes a gas. We call these
three forms the states of matter.
The particle model of matter explains why matter can occur in different
states, even though the particles themselves stay exactly the same.
Based on observations about the behaviour of
matter, scientists believe that the particles
are arranged differently in the different
states of matter.
The particle model of matter explains the
different states of matter. In a solid, the
particles:
• are packed closely together and
arranged in an organised pattern
• do not move around freely, but vibrate
around fixed positions
• are held together by the strong forces of
attraction between them
• have small spaces between them.
In a liquid, the particles:
• are still close together, but are arranged
more loosely, rather than in a rigid
pattern
• can move faster than in a solid and slide
past each other
• are not held as strongly by the forces
of attraction between them because
the particles are moving faster and are
further apart
• still have small spaces between them,
although the spaces are a bit larger than
in a solid.
In a gas, the particles:
• have no particular arrangement
• move around very quickly
• have so much energy that they move
around freely and fill any space evenly
• have very large spaces between them,
compared to solids and liquids.
92
(a)
(b)
(c)
Figure 8 (a) Solids hold a fixed shape
and have a specific size. (b) Liquids
flow and take on the shape of the
container they are in. (c) A gas does
not take on any shape and fills the
space it is in evenly.
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Activity 3 Draw a table comparing the particles of solids, liquids and gases
1. Copy and complete the table below to compare the particles in solids, liquids and gases.
Arrangement of
particles
Movement of particles Effect of attractive
Space between
forces between particles particles
Solids Packed closely together;
Held together strongly
arranged in an
organised pattern
Liquids
More freely than in solids;
slide past each other;
movements are rapid
Gases
Very large
Diagrams to represent the states of matter
When matter changes from one state to another, the particles themselves do not change. It is only the
arrangement of the particles that changes. Figure 9 shows the different states of water. All the water
particles in the three states are exactly the same. They are just arranged differently.
Ice
Liquid
Gas
Figure 9 (a) In ice, the water particles are arranged in an organised pattern; (b) in liquid water, the particles can
flow and take on the shape of the container; (c) in water vapour (gas), the particles fill the container evenly
Activity 4 Draw diagrams to represent particles in a solid, liquid and gas
(b)
(a)
(c)
Figure 10 Examples of a (a) solid, (b) liquid and (c) gas
1.
2.
3.
4.
Draw a box for each substance above and use dots to represent the particles in each one.
Make sure that you show the correct arrangement, movement and spacing.
Give each box a suitable title.
Write a sentence for each substance that explains why you arranged the particles the way you did.
Topic 5: Particle model of matter
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Key words
Diffusion
• diffusion –
spontaneous
spreading of
particles from
an area of high
concentration
to an area of low
concentration
The particle model of matter explains diffusion. Diffusion is a process in
which the particles in liquids and gases move from a place where there are
many particles (a higher concentration) to places where there are fewer
particles (a lower concentration). An example of this is perfume particles
spreading through the air. Near the perfume bottle there are many perfume
particles, but further away there are only a few. Another example is a drop
of dye in a glass of water. Look at Figure 11. The particles of dye spread
slowly away from where there are many particles and eventually spread
themselves evenly throughout the glass of water.
• kinetic energy –
energy that an
object has because
of its motion
Figure 11 A drop of food
colouring diffusing through
water
Activity 5 Observe solid particles diffusing through water
You will need: one large glass beaker with water in it • one crystal of
potassium permanganate or a drop of food colouring
1. Leave the beaker with water in it to settle, so that there are no currents
in the water.
2. Carefully drop the crystal of potassium permanganate into the beaker.
Do not move the beaker or disturb it in any way.
3. Observe what happens. It will take a long time, so watch the progress
throughout your lesson. Come back during the day and answer
question 4 the next day.
4. How long does the diffusion process take?
The potassium permanganate particles spread between the water
particles. It took a long time for the permanganate crystals to diffuse
evenly between all the water particles. Figure 12 shows what the particles
were doing.
Figure 12 Particles of one substance can diffuse between particles of another substance.
Compare rates of diffusion in liquids and gases
Different substances diffuse at different speeds or rates. Generally, diffusion
takes place faster in gases than in liquids.
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Activity 6 Investigate the rate of diffusion of a gas compared to a liquid
Your teacher will demonstrate this activity to you.
You will need: a substance like ether, methylated spirits or deodorant • tissue paper
Close all the windows and doors of the classroom so there is no wind blowing. Everyone in the
classroom should sit still. Your teacher will throw a substance called ether onto the chalkboard. As soon
as you smell something, put up your hand.
1. Did you notice a pattern in the way that you the class could smell the ether?
2. Could you see what you smelled?
3. What spread from the front of the classroom to your noses?
4. How long did it take learners at the back of the classroom to smell the ether?
5. Compare the amount of time the ether took to diffuse to the time it took for the potassium
permanganate in Activity 5 to diffuse. What can you conclude?
Activities 5 and 6 show that diffusion is faster in gases than in liquids. Particles in a gas move faster than
particles in a liquid. The forces of attraction between particles in a liquid are stronger than those in a gas.
We say they that gas particles have greater kinetic energy. This means that gas particles in a room will
spread out quickly to fill that space evenly.
Case study: Passive smoking and diffusion
Smoking is not healthy for anyone.
Cigarette smoke can cause cancer and other
serious illnesses. This is because cigarette
smoke contains many harmful chemicals.
Some supporters of smoking say people
should be able to have the choice to smoke
or not. However, this is still not fair to the
people who choose not to smoke. Scientific
research shows that just breathing in other
people’s cigarette smoke is harmful. We
call this ‘passive smoking’. Many people
are affected by passive smoking because
the particles of cigarette smoke diffuse
through the air just as easily and quickly
as other gas particles.
South Africa has created antismoking laws to try and reduce passive
smoking. These laws state that you cannot
smoke in a public space that is enclosed or
partially enclosed. You also cannot smoke
outside if you are close to a window or
entrance to a public space, or if you are
in an outside space where people will be
Figure 13 Diffusion causes the
problem of passive smoking.
standing or sitting close together.
Key concepts
Matter is made of particles.
We use the particle model of matter to help us understand how matter behaves, how particles
are arranged and move, and what happens to particles when matter changes between gas,
liquid and solid states.
We also use the idea of particles to help explain the spread of particles through a gas or liquid,
which we call diffusion.
Topic 5: Particle model of matter
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Unit
2
Change of state
Key words
• melt – when a
solid turns into a
liquid
• evaporate – when
a liquid turns into
a gas
• condense – when
a gas turns into a
liquid
• solidify – when a
liquid turns into a
solid
• freeze – when a
liquid turns into a
solid
Heating or cooling can cause a material to change state. We use the particle
model of matter to explain how a material changes state.
Change state by heating
When we heat a solid, we add energy
to the particles. The particles gain
energy and begin to move more. This
movement overcomes the forces of
attraction between the particles, so the
particles move further apart and begin
to move past each other. The organised
arrangement between them collapses. This
causes the substance to melt, forming a
liquid. The substance has changed state
from a solid to a liquid.
If we keep on heating a liquid, we give the
particles more energy. The particles then
move even faster and overcome almost all
of the forces of attraction between them.
The particles move much further apart and
escape from the body of the liquid. The
spaces between them become larger as
they spread into the air or fill the container
they are in. This means that evaporation
has taken place. The liquid has changed
state and become a gas.
Solid
Liquid
Figure 14 If we add energy to a solid,
the particles will start moving faster,
and it will melt and become a liquid.
Liquid
Gas
Figure 15 If we add energy to a
liquid, the particles will start moving
even faster. Eventually, the particles
will evaporate and the liquid
becomes a gas.
Change state by cooling
When we cool down a gas, energy is
transferred from the gas particles to the
surroundings. The particles have less
energy, so they move more slowly. This
means the forces of attraction between
them are able to pull them closer together
again. The spaces between them decrease
and eventually the gas changes state to a
liquid. Condensation has occurred.
96
Gas
Liquid
Figure 16 If we remove energy from
a gas, the particles will start moving
more slowly, and it will condense and
become a liquid.
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If we keep on cooling a liquid down, the particles have even less
energy, so they move even slower. This allows the forces of attraction
between them to pull them closer together and eventually they settle
into a fixed pattern. The particles can no longer move past each other
and only vibrate around a fixed position. The spaces between the
particles decrease until they are packed close together. The liquid has
changed state to a solid. Solidifying or freezing has taken place.
Activity 7 Investigate a change of state
Liquid
Solid
Figure 17 If we remove energy from
a liquid, the particles will start moving
even more slowly, and it will freeze or
solidify and become a solid.
You will need: a spirit burner • a small empty tin • a stand • a candle
• a teaspoon
1. Break up a candle, remove the string and place the wax in the tin.
2. Gently heat the tin until the candle wax melts. Do not overheat the wax
as it releases fumes when it gets hot, and these fumes can ignite.
3. Switch off your burner and watch what happens to the candle wax.
Figure 18 Set up your
apparatus like this.
Figure 19 Gently heat the tin
until the candle wax melts.
4. Record and follow these instructions to explain your activity:
a ) Draw wax particle dots to show the wax in its solid state.
b ) Draw wax particle dots to show the wax in its liquid state.
c ) Write a paragraph that uses sentences like these: ‘Energy was added
to the solid candle wax. This caused …’
d ) Write another paragraph that uses sentences like these: ‘Energy was
removed from the melted candle wax. This caused …’
Key concepts
Matter can change state when we heat it or cool it.
We use the particle model of matter to explain what happens to the
arrangement and movement of particles when it changes state.
Topic 5: Particle model of matter
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Unit
3
Density, mass and volume
Key words
Mass and volume
• mass – measure
of the amount of
matter of an object
Mass is a measure of the amount of matter that an object is made of. Mass is
measured in units such as grams (g) and kilograms (kg). The three blocks in
the picture below all have a mass of 10 kg.
• volume – amount
of space an object
takes up
• density – amount
of mass in a given
volume of matter
Iron
Wood
Sponge
Figure 20 Blocks of iron, wood and sponge foam that all have a mass of 10 kg.
Volume is the amount of space an object occupies. Volume is normally
measured in units like litres (l) and millilitres (ml). It is also measured in units
like centimetres cubed (cm3) or decimetres cubed (dm3). A block that is
10 cm × 10 cm × 10 cm in size has a volume of 1 000 cm3. This is the same
as one litre. The volumes of the three blocks shown in Figure 21 all have the
same volume: 1 litre, or 1 000 cm3.
Iron
Wood
Sponge
Figure 21 Blocks of iron, wood and sponge foam that all have a volume of 1 000 cm3.
Density
The blocks in the Figure 20 all have different sizes, but their mass is the
same. This is because the particles in iron are more closely packed together
than the particles in wood. It is as if the same amount of matter is squeezed
into a smaller volume in iron than in wood. In sponge foam, the particles are
much further apart, so that the same amount of matter takes up much more
space compared to iron.
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In Figure 21, all the blocks have the same volume, but the iron block is
much heavier than the sponge foam block, even though they are the same
size. More iron particles are packed into this volume than in the case of the
wood or sponge foam particles. We say iron is more dense than wood. In
a substance with a higher density, the particles are more closely packed
together. The density of a material is described as the mass in a certain
volume of that material. We write it as follows:
density = mass ÷ volume
Activity 8 Find objects of the same volume with different
mass and compare them
You will need: small blocks of foam, polystyrene, wood and metal that are
the same size
Foam
Polystyrene
Wood
Metal
Figure 22 These blocks have the same volume but different mass.
1. Pick up each block in turn and compare how heavy they feel.
2. Arrange them on your desk in order from heaviest to lightest.
3. Fill in a table like this one.
Blocks arranged in order from
lightest to heaviest
Material block is made from
Heaviest block
Next
Key concepts
Next
Matter occupies
space, so it has
volume.
Lightest block
4. Use the particle model of matter to explain your results.
In Activity 8, you will have seen that blocks of the same size have different
masses. Some are heavier than others. This is because the materials have
different densities. Some materials have a lot of mass in a small space;
others have a smaller amount of mass in the same space. This is because of
the particles they are made of. Some materials have small or light particles
and their particles might be more spread out than in denser materials.
Some matter
occupies more
space than other
matter with the
same mass. This
means it is less
dense.
Topic 5: Particle model of matter
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Unit
4
Density and states of matter
Solids, liquids and gases have different densities. In general, gases are less
dense than liquids, and liquids are less dense than solids. There are some
exceptions to this, for example, wood is a solid but it is less dense than
water. However, the order of density from least dense to most dense is
usually: gas, liquid, solid.
The reason why different states of matter have different densities is easily
explained using the particle model of matter.
Solid
Liquid
Gas
Figure 23 A diagram showing the arrangement of particles in a gas, liquid and solid
Particles in a gas are spaced far apart, particles in a liquid are spaced closer
together and particles in a solid are much closer together. This means that in
the same amount of space, gases have much less matter, liquids have more
matter in the same space and solids have the most matter in the same space.
Activity 9 Use the particle model of matter to explain the
density of states of matter
1. a ) If you placed a solid into a liquid, what would usually happen?
Explain your answer.
b ) Would what you described in part (a) happen for all solids? Explain
your answer.
2. Draw three particle diagrams to show a gas, a liquid and a solid in three
separate boxes. Use these boxes to show the differences between the
three states of matter.
3. Write a sentence to explain why gases are generally less dense than
liquids, and liquids are less dense than solids.
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Case study: Solid water is less dense than
liquid water
Ice floats on liquid water. This means
that ice (a solid) is less dense than
water (a liquid). This is very unusual.
Normally, the solid state of a substance
is more dense than its liquid state. Its
particles are closely bound together
and move around less. This is because
energy has been removed from the liquid
state.
When water (liquid) cools down, its
particles start moving closer together.
However, as water starts to freeze, the
particles move apart again very slightly.
You can think of it like a crowd of
people standing close together, pushing
outwards slightly with their elbows. The
people are still packed closely together,
but they are pushing each other slightly
apart. So, when water starts freezing it
floats again. This layer of ice keeps the
water underneath it slightly warmer so
it does not freeze. What do you think
would happen if ice froze from the
bottom upwards in lakes and rivers?
Figure 24 Ice is very unusual because it is less dense than liquid water.
Key concept
Generally, gases are less dense than liquids, while liquids are less dense
than solids. However, this is not always true. For example, wood usually
floats on water.
Topic 5: Particle model of matter
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Unit
5
The density of different materials
Some materials have a low density and some have a high density. For
example, a loaf of bread has a lower density than a clay brick of a similar size.
Activity 10
Compare the densities of different materials
You will need: paper or plastic disposable cups of identical size • different
substances like water, sand and flour
Figure 25 Feel how heavy each cup is.
1. Make sure the cups you use are the same size. Fill each cup to the same
level with a different substance and line them up next to each other.
2. Pick up each cup in turn and compare how heavy each one is. Sort the
materials in the cups from most dense to least dense.
3. Write down the materials in order, from most dense to least dense in the
table below.
Most dense
Least dense
4. a ) In earlier grades, you learnt what a fair test is. Explain how this
investigation was a fair test. Which variables were kept the same?
Which variable was changed?
b ) The instruction asked you to feel how heavy each cup was. Explain
how this was actually a measurement of the density of each
substance and not only the mass.
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Why some materials are denser than others
In Activity 10, you compared densities of different materials by comparing
the masses of the same volume of each material. It was a fair test because
you kept all the variables constant, except for the type of material in the
cups. The density was different for each material.
In Unit 3, you saw that density is the mass of a substance in a certain
volume. This means that the greater the mass of the material in a certain
volume, the more dense the material is. In Units 3 and 4, you saw that
materials in which the particles are packed close together are more dense
than materials in which the spaces between the particles are larger.
Another reason for different the densities of materials is the mass of
individual particles. The larger the mass of the particles that make up a
substance, the more dense the substance is.
Less dense materials float on denser materials
Any material that is less dense than a liquid material will float on it. If it is
more dense than the liquid, then it will sink. Less dense liquids also float on
more dense liquids. An example of this is oil floating on water.
A small amount of oil can spread over a large area of water, making it a very
bad pollutant. You can see this in Figure 26. You should never pour oil down
a stormwater drain, because these drains all lead to rivers.
Figure 26 Oil is less dense than water, so it floats on water.
Topic 5: Particle model of matter
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Activity 11
Mix oil and water to compare densities
You will need: a glass beaker • water • cooking oil
Figure 27 Items you will need in this experiment
1. Pour some water into your beaker. Add one or two drops of food
colouring to the water to make it easier to see.
2. Predict what will happen: will the oil sink below the water or will it float
on the surface?
3. Pour a small amount of oil slowly into the beaker. It is easier to do this
if you allow the oil to run slowly down the inside of the beaker. If your
water becomes messy after putting oil on it, pour it away and use fresh
water.
4. Was your prediction correct? What does this tell you about the density
of oil and water?
5. Discuss what would happen if you poured old engine oil into a river.
Key concepts
Different materials have different densities. This is because of the way in
which their particles are arranged and the mass of the individual particles.
Substances such as oil are less dense than water, so will float on water.
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Skills focus: Raise questions about issues
What are questions about issues?
Scientists must be able to think about problems, issues and natural
phenomena. They should be able to raise questions and communicate them
to the public or to government.
How to raise questions about issues
1. Gather information about an issue you are concerned about.
2. Ask specific questions about:
•
the origin of the problem or issue
•
advantages that might be related to the origin of the issue
•
disadvantages caused by the issue
•
future actions related to the issue.
3. Write down your questions in simple, short sentences.
Case study: The Deepwater Horizon oil disaster
A massive oil drilling accident happened in the Gulf of
Mexico in April 2010. The Deepwater Horizon drilling
rig exploded and caused oil to flow from the bottom of the
ocean. The spill caused extensive damage to marine life
and on shore. Oil floated up from the sea floor and spread
out across the sea onto many kilometres of beaches and
wetlands. Even a small amount of oil can spread out and
pollute a large body of water.
The oil released from that disaster is only a small part
of the amount of oil that enters rivers, lakes and oceans
every day, for example, from cars leaking oil or people
pouring waste engine oil down drains. This has a very
negative impact on the environment.
Figure 28 Oil pollution from homes and factories causes
damage around the world every day.
Activity 12 Practise raising questions about an issue
Read the case study above.
1. The first question you could ask is: ‘Are there any advantages to offshore
drilling?’ Write down your own answer to question.
2. Think of three more important questions about this disaster that you
think the public and governments should be asking. Discuss them with
a partner and in your class.
Skills focus: Raise questions about issues
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Unit
6
Expansion and contraction of materials
Key words
• contract – become
smaller, shrink
• expand – become
larger, swell up, to
increase in size
The particles in any material move around all the time. We say that they are
in constant motion. In solids, the particles just vibrate in the same position.
In liquids, they move around past each other. In gases, the particles are far
apart and move around quickly.
When any material gains energy, its particles move faster. This means that
the forces of attraction between the particles can no longer hold them
together as strongly, so they move further apart from each other. When
materials lose energy, such as when hot wax cools down, the particles slow
down and move closer together.
When particles move closer together or further apart in this way, it causes
materials to contract (grow smaller or decrease in size) or expand (grow
larger or increase in size). The number of particles stays exactly the same, it
is just the spaces between them that changes.
During contraction, the spaces
between the particles get smaller.
During expansion, the spaces
between the particles get bigger.
Figure 29 How particles in a substance change when energy is added or removed
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Activity 13 Use a ball and ring to demonstrate expansion
and contraction
You will need: a ball and ring apparatus • a spirit burner or gas flame • a
beaker almost full of water
Figure 30 The ball and ring apparatus
1. Test the ball and ring by moving the ball through the ring. It should pass
through easily.
2. Heat up the ball in the flame for about one minute.
3. Now test the apparatus again by moving the ball through the ring.
4. What do you notice?
5. Now cool the ball in the water.
6. Test the ball and ring again. What do you notice?
When the apparatus was at room temperature, the ball fitted easily through
the ring. When you heated the ball, it did not pass through the ring. This is
because you added energy to the particles in the ball so that the particles
started moving faster, and therefore they moved further apart. The ball
expanded and became too large to fit through the ring.
When you cooled the ball, energy was removed from the ball. This meant
that the particles slowed down and so the ball contracted. The ball could fit
through the ring again.
Topic 5: Particle model of matter
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Expansion and contraction in real life
Expansion and contraction can be useful, but can also be a problem in real
life. In some countries, the weather can become very cold and pipes can
freeze. You know that water, unlike most other materials, expands when
it freezes. Inside pipes, this can be a big problem, because the pipes can
burst. Figure 31 shows a pipe in which the water has expanded, causing the
pipe to burst.
In cold climates, pipes have to be protected to prevent them from freezing
and bursting.
Engineers can fit metal parts together without welding by using shrink
fitting. The diagrams in Figure 32 on the next page show how this works.
Figure 31 The water in this pipe expanded, causing it to burst.
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(a) The rod is too large
to fit through the hole
when both are at room
temperature.
(b) The outer section is heated up,
so that it swells, making the hole
slightly bigger. At the same time,
the rod is cooled so that it can
fit inside the hole.
(c) The rod is placed in the
hole; it expands and gets
stuck there very tightly.
It has been shrink-fitted.
Figure 32 How shrink-fitting works
Activity 14
Draw and explain expansion and contraction
1. Look at the diagrams in Figure 32 that show shrink-fitting. Draw
diagrams to explain what is happening to the particles in the rod that
allows the engineers to do this.
2. Explain why the particle model of matter, although it is only a model, is
very useful in explaining how matter behaves.
3. What happens to the forces between particles in matter when energy is
added or removed from the matter?
Key concept
The particles in matter move all the time. If we add energy to them, they
move faster and move further apart. This means that the material expands.
If we remove energy, the particles move slower and move closer together.
This means that the material contracts.
Topic 5: Particle model of matter
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Unit
7
Pressure
Key word
• gas pressure –
force created
by gas particles
hitting the walls of
their container
Gas particles inside a container move around very quickly, and collide or
bump into each other and the sides of the container they are in. When gas
particles hit the walls of the container, they apply a force to it. This is what
we call gas pressure. The more particles that collide with the walls in a
certain amount of time, the greater the pressure.
Gases exert pressure outwards. This is why the pressure in a tyre or balloon
goes up when you pump more air into it. If you add more air to the tyre or
balloon, the greater number of particles increases the number of collisions
inside and this increases the gas pressure.
Figure 33 A flat tyre occurs when there is not enough air
pressure inside the tyre.
If there is not enough air inside a car tyre, we say that you have a flat tyre.
There is not enough gas pressure inside the tyre to keep it pumped up
and to keep the metal part of the wheel from riding on the road. If there
is not much gas inside a balloon, it will be limp and floppy. As you blow in
more air, it becomes tighter and larger, until eventually it will be difficult
to blow any more air in, or the balloon will burst.
Both the flat tyre and the floppy balloon are caused because there are
not enough particles moving around inside them. This means that there
are not enough collisions between the gas particles and the inside of
the tyre or balloon, so the tyre or balloon is not pushed outwards very
strongly.
Figure 34 Balloons with enough
air pressure inside them
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Figure 35 Gas particles hit the walls of their container and exert
pressure outwards.
Activity 15
Demonstrate what happens when we blow up
a balloon
You will need: balloons
1. Blow up a balloon. At first it will
be difficult because the rubber is
new and needs to stretch.
2. Notice how much effort you need
to put in to continue blowing up
the balloon.
3. What do you notice when the
balloon gets very big?
4. Discuss what is happening using
the ideas of particles and gas
pressure.
Figure 36 Blowing up a balloon
Key concept
Gas particles move around quickly. Inside a container, gas particles collide
with each other and with the walls of the container. This applies a force to
the walls, which we call gas pressure. If we add more particles by blowing
up the object, a tyre or balloon, for example, the gas pressure increases
because there are more collisions with the wall of the container.
Topic 5: Particle model of matter
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Practical task
Use the particle model of matter to explain
changes in state, density and pressure
1. Figure 37 shows wax in its solid and liquid states. If you heat wax
enough, it will evaporate and become a gas. Draw pictures using
dots as wax particles to show wax in its three states.
(6)
Figure 37 Solid and liquid wax.
If you heat wax enough, it will
turn into a gas.
2. The three boxes in Figure 38 show three different states of matter.
A
B
C
Figure 38 These boxes show three different states of matter.
a ) What happened to the way forces pulled the particles when the
state changed from A to B?
(1)
b ) What is different about the shape of the matter in A and B?
(2)
c ) In which box are the particles moving very quickly?
(1)
d ) The particles in C are in a small box. What would happen to
them if you opened the box in a closed room?
(2)
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3. Arrange the three blocks in Figure 39 in order of decreasing density.
Explain why they have different densities using particle model
diagrams.
(4)
Iron
7,86 kg
Wood
4 kg
Sponge
30 grams
Figure 39 Blocks of iron, wood and sponge foam that all have a volume of 1 000 cm3, but not the same mass.
4. The balloon in the first photograph in Figure 40 was too soft, so you
decided to blow more air into it. Use the idea of particles moving
around inside to explain what happened to the pressure inside the
two balloons.
(4)
Figure 40 A soft balloon and a blown up balloon
Total: 20
Practical task: Use the particle model of matter to explain changes in state, density and pressure
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Topic 5 revision
Science language practice
1. Use the following words to complete this paragraph.
stuff
particles
bits
matter
atoms
mass
Everything around us is made of __________. Matter is the
__________ around us. It has __________ and takes up space. Matter
is made of __________ that are so small that we cannot see them.
We sometimes call these bits __________ and molecules, but we will
simply call them __________.
2. Match the terms in Column A with their correct meaning in Column B.
Write only the correct number (1–4) next to the letter ((a)–(d)).
Column A
Column B
a) Particle
b) Matter
c) Liquid
1. Something that has mass and takes up space
2. Matter that flows and does not have a specific shape
3. A very small piece of something, such as a grain of sand
or something even smaller
4. The spreading of one substance through another substance
d) Diffusion
Test yourself
1. Which unit is mass usually measured in?
(1)
2. Which is heavier, a kilogram of iron or a kilogram of feathers?
Explain your answer.
(2)
3. Make a table with the headings ‘Gases’, ‘Liquids’ and ‘Solids’ to
compare the particles and their behaviour within these three
states of matter.
(7)
4. Railway lines are made of steel, which expands and contracts when
the temperature changes. Draw a diagram and use the particle
model of matter to explain what happens to the railway tracks
when the temperature increases and decreases.
(2)
5. You burn some toast in the kitchen. A minute later your friend
calls out from the bedroom ‘What is burning?’ Use the particle
model of matter, with diagrams, to explain how your friend knew
something was burning even though they could not see it and
did not hear you.
(4)
6. If there are five people in a shop and then 10 more people come
in, has the store become more or less dense with people?
(1)
7. Which two things affect density?
(2)
8. You heat up water in a pot. Write a paragraph to describe what
happens to the water using the following words: energy, particles,
move/moving, position, state, gas.
(6)
Total: 25
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Term 2: Matter and materials
Topic
6
Chemical reactions
Starting off
Everything around us is made up of very tiny
particles called atoms. These atoms can mix
together to form mixtures, or they can join together
to form bigger substances. Atoms join together in
chemical reactions. We call this process bonding.
In this topic, you will learn about the substances
that react with each other. You will also learn what
to look out for so that you know when a chemical
reaction is taking place.
Activity 1
Figure 1 A chemical reaction
Describe a chemical reaction
1. The photograph in Figure 1 shows aluminium
powder reacting with iron oxide in a chemical
reaction.
a ) Describe what you see in the photograph.
b ) Write down everything you can see that
proves that a chemical reaction is taking
place.
c ) Which two substances are reacting with
each other?
d ) Do you think any of the original substances
are left over after the reaction, or has
something new formed?
2. Can you think of any other chemical reactions
that you have seen before?
Topic 6: Chemical reactions
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Unit
1
#
Reactants and products
Key words
• products –
substances that
are produced in a
reaction
• bonds – forces
that hold atoms
together
Chemical reactions
The elements that you learnt about in Topic 4 can join together to form
compounds. This is called a chemical reaction. During a chemical reaction,
substances react to form completely new and different substances, which
have different properties to the substances that reacted together.
The substances that react with each other are called reactants. The new
substances that form during a chemical reaction are called the products.
carbon + oxygen
carbon dioxide
reactants
product
Figure 2 Carbon and oxygen react to form carbon dioxide.
For example, carbon and oxygen will react together to form the product
carbon dioxide:
Inside a compound, there are forces that hold the atoms together. These
forces are called chemical bonds. In a chemical reaction, the bonds in the
reactants break and new bonds form when the products are made. This causes
a chemical change. This means that the products have completely new and
different properties to the reactants, because a new substance has formed.
bonds between
atoms break
new bonds form in
new combinations
Figure 3 Bonds in reactants break and new bonds in the products form
In Figure 3, you can see that you still have the same atoms in the products
that you had in the reactants. In a chemical reaction, atoms are not lost or
gained; the starting atoms are just rearranged in new ways to form different
products.
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A display of fireworks is also a chemical reaction. You can hear loud bangs
and see smoke and colours like those in Figure 4.
Figure 4 Fireworks display
You can tell if a chemical reaction is taking place by looking for the following
signs:
• a colour change
• bubbles or fizzing
• it feels hot or cold
• a smell.
Representing chemical reactions
We can represent chemical reactions using equations. All chemical
substances have names, so we can write their names in a word equation.
One of the reactions that takes place when fireworks go off is sulfur reacting
with oxygen to make sulfur dioxide gas.
sulfur + oxygen
reactants reacting
together
sulfur dioxide
to form products
The plus sign and the arrow have specific meanings in the equation.
A chemical equation is different from a mathematical equation. In
mathematics, the two sides of the equation are exactly equal. This is not the
case in a chemical equation, because the product that forms is completely
different from the reactants. This is why we use an arrow in a chemical
equation and not an equal sign.
Topic 6: Chemical reactions
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Activity 2
Investigate a chemical reaction
You will need: white vinegar • an egg • a beaker
The aim of this activity is to find out whether a chemical reaction will take
place if you put an egg into white vinegar. Gather all the equipment that
you will need.
1. Conduct your investigation.
a ) Place your egg carefully into the beaker. Be careful not to break the
eggshell.
b ) Pour the vinegar over the egg so that it covers two-thirds of the egg.
2. Can you see anything happening? Describe your observations.
3. Explain your observations. Why did this happen?
4. Make drawings to show what you observed. Show the reactants and the
products of the reaction.
Figure 5 An eggshell is about 95% calcium carbonate
Useful chemical reactions
Useful chemical reactions are happening all around us. Below are some
examples of these types of reactions.
Neutralisation of stomach acid
Indigestion in the body can make you feel uncomfortable. It happens
when there is too much hydrochloric acid in your stomach. You can buy
indigestion tablets or antacids like Rennie tablets to neutralise or cancel out
the acid. The chemical reaction that takes place in your body is:
hydrochloric acid + magnesium hydroxide
magnesium chloride + water
Burning fuels
When we burn fuels like octane, they release energy. We can use this energy
to power a car. The chemical reaction when octane burns is:
octane + oxygen
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carbon dioxide + water
Term 2
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Fermentation
When we brew beer, the process that
occurs is called fermentation. The main
ingredients in beer are sugar, yeast and
flavourings. Yeast are micro-organisms,
which are small, living organisms. When
yeast is mixed with sugar, it feeds on
the sugar and convert it into alcohol.
Another product in this chemical
reaction is carbon dioxide:
sugar + yeast
dioxide
alcohol + carbon
Fermentation happens slowly, because
it takes the yeast a long time to feed on
the sugar.
Activity 3
Figure 6 Dried yeast
Use the process of fermentation to make ginger
beer
You will need: 2 litres of water • 2 cups of sugar • 5 g of fine yeast • 1 teaspoon
of Jamaica ginger
1.
2.
3.
4.
5.
6.
Heat the water until it is luke warm.
Dissolve the sugar in the luke-warm water.
Mix the ginger into the solution.
Add the yeast (the yeast must be a fine powder).
Pour the solution into bottles.
Leave the bottles open for two days. This is when the fermentation
takes place.
7. Serve your ginger beer cold!
Activity 4
Identify reactants and products
1. For each of the useful chemical reactions described on this page and
the previous one, write down the reactants and the products in the
chemical reaction.
Key concepts
Substances react with each other to form products that have different
chemical properties.
The reactants are the substances that react with each other and the
products are the substances that are produced.
During a chemical reaction, chemical bonds in the reactants break and
new bonds form to produce the products.
Topic 6: Chemical reactions
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Skills focus: Chemical reactions and chemical equations
Key words
What is a chemical reaction?
• chemical
reactions – occur
when a new
substance is
formed
Chemical reactions occur when a new substance is formed. We can tell
when a chemical reaction has occurred because there may be a change
of colour, a gas is released or heat is formed. When you observe chemical
reactions you will look very carefully for these changes. You can record your
observations in drawings. For example, you can observe what happens
when you blow through a drinking straw into clear lime water in a test tube.
• chemical
equation – a way
of representing a
chemical reaction
Look at Figure 7 and Figure 8. You will observe that a colour change has
occurred.
What are chemical equations?
A chemical equation is a way of representing a chemical reaction or a series
of chemical reactions. For a chemical reaction to occur, a new substance
must be formed. Rusting is a chemical reaction that we are familiar with.
Iron reacts with oxygen in the presence of moisture to form an orbage
substance called rust.
How to write chemical equations
We can write out the chemical equation for this reaction in words, or we can
use chemical symbols and formulae to represent the equation. Rusting is
shown as follows:
Figure 7 Before the reaction
iron + oxygen
2Fe + 3O2
moisture
moisture
iron oxide
Fe2O3
The reactants of a chemical equation are always placed on the left-hand side
of the equation. The right-hand side shows the products of the equation.
The products have different properties to the reactants.
Figure 8 After the reaction
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More resources
Careers in chemistry
Chemistry is a very wide subject, so there are many
careers related to chemistry, for example, in mining,
engineering and in the development of materials.
Mining
ing to a blast furnace
Figure 9 Workers attend
We mine minerals from rocks called ores inside the Earth.
We extract and manufacture iron, coal, aluminium and
many other minerals using chemical processes. The
main minerals that are manufactured in South Africa are
platinum, diamond and gold.
A career in mining iron can involve operating big
machinery at very high temperatures. To extract iron, we react rock that contains iron with carbon in
a blast furnace at a very high temperature. At the end of the process, liquid iron is removed from the
oven. The word equation for the extraction of iron in a blast furnace is:
iron oxide + carbon
carbon dioxide + iron
Engineering and developing materials
Chemical engineers are involved in making and designing substances, and developing products.
For example, chemists have used chemical substances and chemical reactions to make the glass
and plastic bottles that you drink cooldrinks from. Plastics are made from chemicals called polymers.
These polymers can be recycled when you have finished with the bottle and used again. Scientists use
chemical reactions to recycle plastic so that we can use it again.
The bio-fuels industry
Bio-fuels are fuels that are made from organic material such as
plants, and are therefore renewable. Two examples of bio-fuels are
ethanol and biodiesel. To make ethanol, a chemist reacts yeast with
a sugar solution. The yeast feeds on the sugar and converts it into
ethanol and carbon dioxide. This is called fermentation. The sugar
comes from sugar cane plants that farmers can continue to grow
to make more ethanol. Chemists use soybeans or other natural oils
to make biodiesel.
tory
Figure 10 A bio-fuel fac
Figure 11 Recy
cling plastics in
volves chemic
reactions
al
More resources: Careers in chemistry
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Topic 6 revision
Science language practice
1. Choose from the list of words below to complete the following sentences. Write the complete
sentence in your workbook.
force
reactants
atoms
products
form
properties
break
In a chemical reaction, the substances that react with each other are called the _________ and
the substances that are produced are called the __________. The substances that are produced
have new and different chemical __________. In reactions, the __________ are rearranged. A
chemical bond is a __________ that holds __________ together. In a reaction, the chemical bonds
in reactants __________ and new bonds __________in the products.
Test yourself
1. The chemical reaction between hydrogen and oxygen is a very vigorous reaction. A balloon
filled with hydrogen gas explodes when you light it in the presence of oxygen, as you can see in
Figure 12. The word equation for this reaction is shown in the figure.
hydrogen + oxygen → water
Figure 12 Hydrogen reacting with oxygen
a ) Use the photograph in Figure 12 to describe what you will observe when you see this reaction
between hydrogen and oxygen.
(1)
b ) Write down the names of the reactants in this reaction.
(2)
c ) Write down the name of the product in this reaction.
(1)
d ) Draw a picture diagram and explain what happens to the atoms of the reactants before
they recombine to form the products.
(2)
2. List four observations that could be proof of a chemical reaction taking place.
(4)
3. In brewing, yeast feed on sugar in the following reaction:
sugar + yeast
a ) Write down a name of this reaction.
b ) Write down the names of the reactants.
c ) Write down the names of the products.
alcohol + carbon dioxide
(1)
(2)
(2)
Total: 15
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Term 2 Practice test
1. Match the terms in Column A with their correct meaning in Column B. Write only the correct
number (1–5) next to the letter ((a)–(e)).
Column A
Column B
a) Bond
1. A substance that is made up of one type of particle all the way through
b) Pure substance 2. To swell up or become larger
c) Compound
3. Spontaneous spreading of particles from an area of high concentration
to an area of low concentration
d) Diffusion
4. A force that holds atoms together
e) Expand
5. A pure substance formed by a chemical reaction between two or more
different elements
(5)
(3)
2. Name the three subatomic particles and the charge of each one.
3. Copy and complete the following table.
Name of
compound
Elements in
compound
Formula of
compound
Ratio of atoms
in compound
H2O
Sulfur and oxygen
1:2
Carbon dioxide
Sodium chloride
NaCl
(5)
4. The beaker in the photograph below contains water and food colouring.
a ) Name the process demonstrated in the figure above.
b ) Use a particle model drawing (a box with dots of two different colours) and labels to
show what is happening in the beaker.
c ) Use the correct scientific words to explain what is happening in the photograph and in
your drawing.
Term 2 Practice test
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(1)
(2)
(2)
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Term 2 Practice test
5. A block of iron and a block of wood of exactly the same shape and size are
standing side by side.
a ) Which block has the greater mass?
b ) Suggest a reason for your answer in (a). Draw and label a particle model diagram of both
substances to illustrate this.
(1)
(4)
6. Look at the photograph of the ball-and-ring apparatus below.
a ) Choose the correct words in these sentences: When we heat the ball, we find that it (can/
cannot) fit through the ring. This means that the ball has (expanded/contracted).
b ) Complete the missing words in this sentence: In part (a), if we allow the ball to cool down
because
.
again we find that
c ) Use particle model diagrams with labels to explain what is happening in parts (a) and (b).
7. If you put a small amount of zinc (Zn) in a bottle, add dilute hydrochloric acid (HCl), and
put the opening of a balloon over the top of the bottle, the balloon will fill up with gas.
If you then remove the balloon and knot the end, it will float.
a ) Write the left-hand side of the word equation to show the reaction that
happens when zinc is added to hydrochloric acid.
b ) If one of the products is zinc chloride, predict what you think the gas could be.
c ) Using what you learnt in part (b), complete your word equation from part (a)
(2)
(2)
(4)
(2)
(1)
(1)
Total: 35
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Term 3: Energy and change
Topic
Topic
#
7
Static electricity
Starting off
All matter is made up of atoms. Atoms are made up
of tiny particles. An atom has an equal number of
negatively charged and positively charged particles.
Therefore, the charges balance each other so that
the total charge of the atom is neutral. Sometimes,
an imbalance occurs between the negative and
positive charges in an atom. Such an imbalance
in the charges can light up the sky, as we see in
Figure 1. This imbalance of charges in a material is
called static electricity.
Activity 1
Figure 1 Lightning
Describe experiences with
static electricity
1. Describe your experiences with lightning.
2. Have you ever heard stories about lightning in
your community? Share some of these with the
class.
3. Describe any experience you have of being
shocked while doing the following:
• walking on a carpet
• putting on a jersey
• combing your hair.
4. Explain why magnets attract each other.
5. Explain why magnets repel each other.
6. Explain why you think your clothes stick
together when they come out of the tumble
dryer.
7. Explain why you sometimes get a shock on a
cold day when you touch a metal.
Topic 7: Static electricity
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Unit
1
Friction and static electricity
Friction transfers electrons between objects
You can charge some materials by rubbing them. Friction caused by rubbing
materials such as plastic, Perspex and glass with nylon, wool or silk, transfers
electrons between the atoms of the two materials. For example, if you rub
a plastic ruler with a cloth, the plastic pulls electrons from the cloth. The
plastic ruler gains a negative charge and the cloth gains a positive charge.
Figure 2 Rubbing does not create a charge, but separates
the charges that are already there.
Activity 2 Rub a plastic ruler to investigate the effects of
charged objects
You will need: a plastic ruler or glass rod • woollen cloth • small pieces of
tissue paper
Method
Figure 3 You can pick up
pieces of tissue paper with an
electrically charged glass rod.
126
1. Sprinkle the pieces of tissue paper on the table.
2. Rub the plastic ruler or glass rod with the woollen cloth.
3. Bring the ruler close to the pieces of tissue paper and observe what
happens.
4. Write down your observations.
5. Explain why the pieces of paper get attracted to the ruler or glass rod.
6. Draw a labelled diagram of the ruler and cloth to show how the electric
charges separate.
Term 3
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Electrons move from one material to another
When electrons move from one material to another, a positive charge is
created on the surface of the first material (where the electrons move from).
A negative charge is created on the surface of the second material (where
the electrons move to). It is only the electrons that are transferred. Protons
and neutrons do not move.
For example, woollen cloth readily gives up electrons to other materials
that it comes into contact with. Rubbing a balloon with a woollen cloth
allows the balloon to gain extra electrons, so
the balloon will eventually become negatively
charged. The rubbed portion of the balloon
will then be attracted to positively or neutrally
charged objects, and repelled by other
negatively charged objects.
If the negatively charged balloon is allowed
to touch an object that is not negatively
charged, some of the extra electrons will be
transferred to this other object and the degree
of attraction will decrease. Therefore, when a
negatively charged balloon is thrown up to the
ceiling of the classroom, and sticks there, it will
fall down eventually as some of the electrons
will be transferred to the ceiling. In this way,
the balloon loses some of its negative charge
and therefore cannot stick to the ceiling forever.
Activity 3
Figure 4 Negatively charged balloons may stick to a positively
charged or neutral ceiling.
Explain electron transfer
You will need: a balloon • piece of string • piece of woollen cloth
Method
1.
2.
3.
4.
5.
6.
Inflate the balloon and tie the neck.
Rub the balloon against a piece of woollen cloth.
Throw the balloon towards the ceiling. It should stick to the ceiling.
Explain why the balloon sticks to the ceiling.
Wait for a few minutes and observe what happens.
Explain why the balloon falls back down after a few minutes.
Topic 7: Static electricity
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Key words
• electric charge –
positive or
negative property
of a particle
• electric shock –
reflex response
to the passing of
electricity through
the body
Charged objects repel or attract each other
Objects with different electric charges attract each other. Attraction is the
tendency of particles with opposite electric charges to move towards each
other. For instance, if you place a positively charged rod next to one that is
negatively charged, the rods will be attracted to each other. If the charges
are great enough and the rods are light and free enough to move, they will
come into contact.
Figure 5 Objects or materials with opposite (unlike) charges
attract each other.
Objects with the same electric charge repel each other. Repulsion is the
tendency of particles with the same electric charge to separate or move
away from each other. For example, a negatively charged rod will repel
another negatively charged rod. Similarly, a positively charged rod will repel
another positively charged rod. Figure 6 illustrates this.
Figure 6 Objects or materials with the same (like) charges repel
each other.
Figure 7 The child's hair has become positively charged, so
the individual hairs repel each other, while all of them are
attracted to the negatively charged plastic surface.
128
Often, when children play inside large plastic tubes,
their movement causes their hair to rub against the
plastic. Eventually, they come out of the tube with
their hair standing up. This is because as they move
through the plastic tube, their hair transfers electrons
to the tube as the individual hairs rub against the
sides of the tube. This means that the individual hairs
become positively charged, and start to repel the other
hairs around them. At the same time, the surface of
the plastic tube becomes negatively charged, so the
positively charged hairs are attracted to the sides of
the tube. If the child had to touch a metal object, she
would experience a static electrical shock. You can
read more about this on page 130.
Term 3
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Activity 4
Demonstrate static electricity
You will need: salt • pepper • table cloth (or any piece of cloth) • woollen
cloth • balloon
Method
1. Pour some salt on the table cloth, then pour some
pepper on top of it and mix with your finger.
2. Inflate the balloon and charge it by rubbing it a
few times on the woollen cloth or on your dry hair.
3. Predict what will happen if you bring the charged
balloon close to the pepper and salt mixture.
4. Bring the balloon closer to the mixture of salt and
pepper.
5. Observe what happens: the pepper particles
should be attracted to the balloon.
6. Hold the balloon in the same position for some
time, until the pepper particles fall back down.
Figure 8 Rubbing a balloon on your hair can charge
the balloon and your hair.
7. Explain your observation.
Activity 5
Investigate repulsion and attraction between like
charges and unlike charges
You will need: 2 balloons • piece of string • piece of woollen cloth
Method
1.
2.
3.
4.
5.
6.
7.
Inflate one balloon and tie the neck.
Rub the balloon against the piece of woollen cloth.
Allow the balloon to stick to a wall.
Inflate the second balloon and tie the neck with the piece of string.
Rub the balloon against the piece of woollen cloth.
Hold it by the string and bring it closer to the balloon sticking to the wall.
Observe what happens and explain why the balloons are repelling each
other.
Topic 7: Static electricity
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Unit X (continued)
Key words
• static electricity –
electricity caused
by the build-up of
electric charges
on the surface of a
non-conductor of
electricity.
• electric spark –
flash of light
produced by
electric discharge
• electric
discharge – flow
of electric charge
through a gas,
liquid or solid
Discharge of electrons can cause shocks
or sparks of static electricity
Static electricity is the build-up of electric charges on the surface of a
material, usually a non-conductor of electricity. It is called ‘static’ because
there is no movement of charge. No current flows because the materials
involved are non-conductors of electricity. There two types of electric
charge. They are called positive (+) and negative (−) charges. The positive
charges are called protons and the negative charge electrons.
A static electric spark is a flash of light caused by the electric discharge
of static electricity. The most common spark you can experience is a small
one that can jump from your finger to some metal object, giving you a
slight shock. These sparks simply startle you and don't cause much pain or
damage, but the small shock that you feel is a reflex response to the passing
of electricity through the body. The slight pain that you feel is from the
heat caused by the electrons jumping through the air gap. The noise made
from such a spark is a snapping sound, and is caused by the rapid heating
of the air. These small sparks usually occur when your body builds up static
electricity due to your dry skin rubbing against your clothing, or after
walking across a carpeted floor.
Figure 9 An electric spark jumps from the hand to the door knob.
Although the spark caused by static electricity cannot harm you, these
sparks can be dangerous if you are near fuel, such as at a filling station. It
could cause a fire or even an explosion. People have been killed or severely
hurt doing something as simple as filling their vehicles' petrol tanks or gas
containers. Such dangerous sparks are sometimes caused by the electric
discharge that comes from the build-up of friction from the fuel being
pumped into a vehicle or container, or by you when you get out of the car
or remove an article of clothing. If static charges are allowed to discharge
through the areas where there is fuel vapour, a fire can occur. This occurs
especially when the air is dry.
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Figure 10 Electric sparks can cause fuel vapour to ignite and start a fire.
Activity 6
Explain the danger of sparks and shocks caused by
static electricity in real-life situations
1. Explain what an electric spark is.
2. Explain why you may experience an electric shock when you climb into
your bed.
3. Describe other activities that can cause an electric spark or an electric shock.
4. Explain how you can prevent yourself from getting shocked by static
electricity when opening a door into your room.
5. Read the More Resources section on the next page and explain how you
can argue against the belief that witchdoctors can cause lightning to
strike a person or their house.
6. Read the More Resources section and explain how you can protect
yourself against lightning.
Key concepts
Friction can cause the build-up of electric charges on the surfaces of
objects.
Electrons can move from one material to another causing some material to
be negatively charged and others to be positively charged.
Unlike charges attract and like charges repel each other.
The discharge of electrons can cause shocks or sparks of static electricity.
Topic 7: Static electricity
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More resources
Lightning
Lightning is a form of natural static electric
discharge. A lightning bolt or spark is a highly
charged form of static electricity that is formed
because of differences in charge between two
electric fields. The sound we hear when we see
lighting is called thunder. Thunder is caused
by a shock wave created in the air, similar to
the sonic boom of a supersonic jet plane. The
lightning occurs first and the thunder occurs a
fraction of a second later.
Figure 11 Li
ghtning can
be dangero
us.
What causes lightning?
Lightning is produced in thunderstorms when liquid
and ice particles collide, and build up large electric fields
in the clouds. Once these electric fields become large
enough, a giant spark (the lightning bolt) occurs between
them or between them and the ground like static
electricity, the lightning spark can occur between clouds,
between the cloud and air, or between the cloud and the
ground. These types of storms are often called electric
storms.
ses dry
ghtning cau
Figure 12 Li
catch fire.
vegetation to
Dangers of lightning
The temperature inside a lightning bolt or spark can be hotter than the surface of the Sun. Objects
that are struck by lightning can catch fire. For example, if lightning strikes dry vegetation, the heat
energy transferred can start a bush or veld fire. Usually, the flash is so brief that objects show little or
no evidence of burning at all.
When a tree is struck by lightning, the liquids inside the trunk and bark turn into gas instantly, leading
to a very high pressure inside the trunk, which explodes anything that is between the gas and the
open air. Usually, the lightning current runs just underneath the bark, down to the ground, and the
tree is scarred by a strip of blown-away bark. The tree usually survives such a strike. Sometimes,
the current may run down near the centre of the trunk, and then there may be little left of the
tree afterwards. This is one of the reasons why it is not safe to stand under or near a tree during a
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thunderstorm. The exploding bark and
timber can create projectiles that can do
harm. It is also not safe to be under a tree
during lightning because lightning may
jump from the tree to the person taking
shelter there.
How to prevent being struck by
lightning
•
•
•
•
•
Stay away from trees: Lightning
strikes tall objects such as big trees
and the lightning may jump from
the tree to the person under the
tree.
Do not run: When you run, you
to turn
e's trunk
e
tr
e
th
e
create friction which increases the
uids insid
es the liq
s
u
a
c
chance of static electricity that can
g
in
.
3 Lightn
the tree
ing out
Figure 1
ry
d
y
link up with the lightning to create a
b
re
, the
into gas
spark and a shock.
Avoid using water (showering, washing your hands or dishes): Water also conducts
electricity, so you could be electrocuted if you are touching water.
Avoid using landline telephones during an electric storm: Electricity follows wiring
and metal pipes, this can lead to you being electrocuted.
Avoid using cellphones or electronic devices during electric storms because lightning
bolts or sparks tend to follow the shortest route to the ground – which may be
through your electronic device.
More resources: Lightning
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Topic 7 revision
Science language activity
1. Copy the following sentences and fill in the blanks.
a) An electron has a n__________ charge.
b) A positively charged particle is called a p___________.
c) L____________ charges repel each other and u___________ charges attract each other.
d) The build-up of electrons in an object is called s___________.
e) F___________ does not create charges, but separates them.
f ) L___________ is a form of natural static electric discharge.
g) Discharge of electrons can cause s_______ or s________ of static electricity.
Test yourself
1. What is the difference between an electron and a proton?
(2)
2. How does friction cause static electricity?
(2)
3. What causes an electric spark?
(1)
4. Why does a rubbed balloon stick to a wall?
(1)
5. Why is it not safe to stand under a tree during an electric storm?
(2)
6. A balloon is rubbed with a woollen cloth and brought closer to an empty can of cold drink,
which is standing on a smooth surface. What will happen to the can when the rubbed
balloon is brought close to it?
(1)
7. What happens when a positively charged object is brought closer to another positively
charged object?
(1)
Total: 10
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Term 3: Energy and change
Topic
8
Energy transfer in electrical systems
Starting off
Energy can be transferred in electrical systems by
the movement of electric charges. Electricity is the
word that we commonly use for electric charge.
Electricity can travel through wires to light up a
city. It can also make small and big things work.
A buzzer, a car and an aeroplane all depend on the
energy transferred by electric charges to function.
Electricity can heat the water we wash with and the
water we use to make coffee. If we are not careful
with our use of electricity, it can hurt or kill us, or it
can burn down our houses.
Activity 1
What do you remember about
electric circuits?
1.
2.
3.
4.
Figure 1 A simple electrical circuit
Label the parts numbered 1 to 5 in Figure 1.
In which part of the circuit is the energy stored?
What is the function of part 2?
Explain what should happen in order for the
bulb to light up.
5. Which of the following particles flows through
the wires?
a ) protons
b ) electrons
c ) neutrons
Topic 8: Energy transfer in electrical systems
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Unit
1
Circuits and current electricity
Key words
• circuit – path
through which
electric charge can
move
• electric current –
flow of electric
charge in a circuit
Figure 2 A simple electrical
circuit
In Topic 7 you learnt that electric charges can be transferred from one object
to another. Electric charges can jump over a gap between two objects to
cause a spark or a shock. A path can be created for electric charge to move
from one object to another. This path is called a circuit. A simple circuit
consists of a source of energy such as a cell, conducting wires for the electric
charges to move on, and a bulb. The flow of electric charge in a circuit is
called the electric current. Figure 2 shows a simple electrical circuit.
A circuit is a system that transfers electrical energy. The cell is the energy
source. Chemical energy from the cell is transferred to electrical energy.
Electrical energy is converted to light and heat energy in the bulb. The cell,
conducting wires and the bulb work together to form a system that transfers
energy. First, the energy source provides the chemical energy, then the flow
of charges (the current itself ) in the conducting wire use kinetic energy
to move, and finally, the energy is transferred again to the device as heat,
light, sound or another type of energy. Another example of a circuit is a
television that is connected to an electric power source. When you switch
on a television set, electric charges move from the power source through
conducting wires to the television. The television converts electrical energy
into light, heat and sound energy.
All electrical appliances function because a circuit is completed when they are
connected to a power source such as a cell, a battery or the electricity mains.
Activity 2
Identify systems that transfer electrical energy
Study the photographs in Figure 3 and answer the questions that follow.
Figure 3 Which of these pictures shows a system that transfers electrical energy?
1.
2.
3.
4.
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Identify a picture that represents a system that transfers electrical energy.
Give a reason for your answer to question 1.
Describe the energy changes that occur in the two other photos.
Explain why the other pictures do not represent systems that transfer
electrical energy.
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A circuit can be open or closed. An open
circuit is one in which electric current
cannot flow. A closed circuit is one in
which electric current is allowed to
flow. A closed circuit is needed to make
a device work. For example, a circuit is
needed to make a torch bulb light up.
A circuit has a number of components,
but in simple circuits, such as in a torch,
only a cell, conducting wires and a bulb
cells
make up the circuit. In Grade 6, you
learnt that electrical energy is stored in
Figure 4 The components of a torch.
a cell. The more cells that are connected,
the greater the amount of electrical energy can be stored. The components
are connected from one terminal of the source of energy (the cell) along
conducting wires (copper wires) through the device (bulb) and back to the
source of energy (cell).
_
+ _
switch
+
A component that opens and closes a circuit is called a switch. A torch has a
switch that opens the circuit, so that there is no flow of charge. In this case,
the torch bulb does not give light. When the switch is closed, there is flow of
electric charge and the torch bulb gives off light.
Activity 3
bulb
(a)
Make a simple circuit
You will need: cell • cell holder • conducting wires with crocodile clips •
torch bulb • bulb holder • switch
Method
1. Connect the cell to the cell holder.
2. Screw the bulb into the bulb holder.
3. Connect a conducting wire from one end of the cell to the open switch
as in Figure 5 (a).
4. Take another conducting wire and connect it from the open switch to
one terminal of the bulb as in Figure 5 (b).
5. Connect another conducting wire from the other end of the bulb holder
to the other terminal of the cell as in Figure 5 (c).
6. Close the switch and write your observation of what happens to the bulb
in Figure 5 (d).
(b)
(c)
Key concepts
A circuit is a system for transferring electrical energy.
(d)
A closed circuit is needed to make a device work.
A circuit is a pathway through which electric charges move.
Figure 5 Steps in making a
simple circuit.
Topic 8: Energy transfer in electrical systems
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Unit
2
Components of an electrical circuit
Key words
• conducting
wires – materials
through which
electrons can flow
• switch – device
that is used to
control the flow of
charge in a circuit
• cell – chemical
system that stores
electrical potential
energy
A circuit has a number of components that are connected together. You
have already learnt about conducting wires, a switch, a cell and a bulb. In
this unit, you will learn more about these components.
Conducting wires
One of the basic components of an electric circuit is the conducting wire.
Conducting wires are materials through which electrons can flow. They are
usually made of metals, because metals are good conductors of electricity.
They carry electricity over short and long distances. Figure 6 shows the
power cables that carry electricity over long distances. Figure 7 shows small
insulated copper wires that are used to carry electricity over short distances
in electrical appliances. If you have an electrical appliance that you want to
use outside the house, such as a lawnmower, you use an extension cord.
• battery – two
or more cells
forming a chemical
system that stores
electrical potential
energy
Figure 6 These conducting wires
carry electricity over long distances.
Figure 7 These conducting wires carry
electricity over short distances.
Switches
The other important component of a circuit is the switch. A switch is
connected in a circuit so that it can break the flow of electric charge in the
conducting wires. Look at Figure 8. When the switch is open, the conducting
wires are separated and a gap is created, so that the electric charges are not
able to flow to the other part of the conductor. When the switch is closed,
the conducting wires allow the electric charges to flow through.
Switches provide a convenient way of controlling electrical circuits, because
they allow you to stop or start the electric current whenever you want.
Figure 9 shows how a switch is represented in a circuit diagram.
(a)
(b)
Figure 8 (a) When the switch is open, there is a gap in the circuit.
(b) When the switch is closed, the conducting wires touch and the
gap is closed
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Figure 9 The circuit symbol for a switch.
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The mains switch in a house or building controls how much electrical
energy flows into the house. The amount of electric charge flowing in the
kitchen stove is different for that allowed in the lights and other plugs.
Switches are also used in electrical appliances such as an electric kettle,
computer, cellphone or television. When you no longer want to view your
television, you use a switch on the television to stop electric charges from
flowing in the television circuit, which switches the television off. A car’s
electric windows are also controlled by a switch. When you press on the
switch to open them, you actually allow electric charges to flow in the
electric circuit that operates the electric windows.
Figure 10 A switch is used in electric car windows.
The cell or battery
A cell or battery is a source of electrical energy. A cell is a chemical system
that stores electrical potential energy. A circuit is not complete without a
cell. When a cell is connected to a bulb, the bulb lights up because chemical
reactions occur inside the battery, and potential energy is transferred to the
kinetic energy of the electric charges. A battery has two terminals: a positive
and a negative terminal.
Electrons move out of the negative terminal of the battery through the
connecting wires to the bulb, and back to enter the battery through the
positive terminal. The electrons transfer energy from the battery to the bulb,
where energy is given off as light and heat.
+
–
Figure 11 A battery has a negative and a positive terminal.
Topic 8: Energy transfer in electrical systems
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Key words
• resistors – devices
that oppose the
flow of current
• filament –
resistant wire
inside a light bulb
that glows to
produce light
• circuit diagrams –
simple diagrams of
an electric circuit
that use standard
symbols to
represent the basic
components of the
circuit
Batteries come in different types
and sizes. They are used in different
appliances to supply energy to the
appliance. Different appliances use
different types of batteries. A cellphone
battery is different from a laptop battery.
A car battery is different for a torch
battery.
Figure 12 Batteries are used in different
appliances.
In a circuit diagram, a cell and a battery are represented as follows:
a cell
Figure 13 The circuit symbol for a cell.
a battery
Figure 14 The circuit symbol for a battery.
Resistors
You already know that electric current is the flow of electric charge. Material
is needed through which charges can flow. Materials that oppose or resist
the flow of charge are called resistors. Such materials offer electrical
resistance. Electrical resistance is a measure of how much an object opposes
or resists the flow of electric charges. Conducting wires such as copper
wires also offer some resistance, which is why they become hot when
charges flow through them. However, copper wires offer very low resistance
compared to other metals such as nichrome wire. Resistors in a circuit
influence the amount of current in a circuit.
Activity 4
Investigate the influence of a resistor on a circuit
You will need: cell holder for 3 cells • 3 cells • 5 cm piece of thin nichrome
wire • torch bulb • switch
Method
1. Connect the three batteries in series to the switch and the bulb.
2. Close the switch and observe the strength of the light bulb. Open the
switch again.
3. Predict what will happen to the bulb if you connect the nichrome wire.
4. Connect the 5 cm piece of nichrome wire to the circuit.
5. Close the switch and observe the strength of the light bulb.
6. Explain your observations.
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A light bulb, such as a torch bulb, contains a resistance wire called a filament.
The filament is made of wire that resists the flow of electric charges. The
filament heats up to be white hot when connected in a circuit, so it gives off
light and heat energy. The resistance wire is connected to two contact points:
one end is connected to the metal casing of the bulb, and the other end is
connected to the solder knob at the bottom. The two contacts are separated
by an insulator. You will learn more about the bulb in Unit 3.
Many household appliances, such as electric heaters, kettles, geysers and
stoves contain resistors. The resistors heat up to provide useful output heat
energy.
Figure 15 The filament in the
bulb has a very high resistance.
Some resistors are specially designed to provide resistance in electronic
appliances, such as television sets and radios, so that the right amount of
current is fed to different components of the appliance to make them work
properly.
Figure 16 shows the circuit symbol for a resistor in an electrical circuit diagram.
Circuit symbols
Electric circuits are represented diagrammatically by circuit diagrams.
The table below provides a list of circuit symbols that should be used when
drawing circuit diagrams.
Figure 16 Resistors can be
shown in these two ways in a
circuit diagram.
Table 1 Examples of circuit symbols
A cell
A closed switch
A battery
A bulb
An open switch
A buzzer
Conducting wire
Topic 8: Energy transfer in electrical systems
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Activity 5
Draw simple circuit diagrams
1. Draw the circuit diagrams of the circuits shown in each case.
a ) Circuit 1:
b ) Circuit 2:
c ) Circuit 3:
Activity 6
Interpret simple circuit diagrams
Study Figure17 and answer the questions that follow.
Figure 17 A simple circuit
1. Which component stores electrical energy?
2. Is an electric charge flowing through the circuit? Explain your answer.
3. Explain what happens in the bulb when it lights up.
4. Explain what would happen if the cell was disconnected from the circuit.
Key concepts
The basic components of an electric circuit are a cell or battery, the
conducting wires, a switch and a resistor.
Electric circuits can be represented by circuit diagrams.
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Skills focus: Draw electric circuit diagrams
What is an electric circuit diagram?
Electric circuit diagrams can be drawn free-hand, but you may use a ruler to make your diagrams look
neat. You also need to know the accepted circuit symbols for the different components of a circuit.
How to draw an electric circuit diagram
Follow the steps below to draw a circuit diagram of the simple circuit in Figure 18.
Figure 18 A circuit diagram shows the components of a circuit in simplified form.
Step 1: Draw the symbol for a cell.
One end of the cell is positive, one end is negative.
When drawing the cell, the positive end is always the
long line and the negative end is the short line.
Step 2: Draw the symbol for a bulb two lines
below the symbol for the cell.
Step 3: Draw a line to represent the conducting
wire from the midpoint of the long line
of the cell to the bulb symbol.
Step 4: Draw a line from the midpoint of the short line of
the cell to the other part of the bulb symbol.
When there are more components than a cell and a bulb in
a circuit, you may draw the cell first, skip two rows in your
exercise book and draw another component directly below
the cell. Then, draw one component on the left and another
on the right. Draw the bulb one line below the additional
components. Connect the components with lines. Figure 19
shows this connection using the example of a house alarm
system. The circuit in an alarm system consists of a cell, a
switch, a bulb for lighting and buzzer for making noise when it
is triggered at the switch.
Activity 7
1.
Figure 19 The circuit diagram of an alarm system.
Practise drawing a circuit diagram
Draw the circuit diagram to represent the circuit in a torch that works
with two cells.
Skills focus: Draw electric circuit diagrams
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Unit
3
Effects of an electric current
Key words
• short circuit –
electric circuit that
allows current
to flow in an
unintended circuit
• magnetic field –
lines of force
surrounding
a permanent
magnet or a
moving charged
particle
You have already learnt that when electric charges flows through a
circuit, energy is transferred from the battery or source of energy to the
components in the electrical circuit. But an electric current has other effects
as well. Some of these effects are discussed in this unit.
A current can heat a resistance wire
When electric charge flows through a resistor, electrical energy is converted
to heat. In an incandescent light bulb, electricity runs through the filament,
which is made of tungsten. Tungsten has a high resistance to electricity and
the filament is very thin so that it offers even more resistance. This resistance
turns electrical energy into heat energy. The heat is enough to make the
filament white hot, and so produce light.
Short circuits
Electricity flows through a closed circuit to make an electrical appliance
work. However, electricity tends to take the easiest path through a
circuit. The current encounters resistance due to the construction of the
components of a circuit. If you accidentally connect a conducting wire so
that there is a direct path through the wires from the positive terminal to
the negative terminal of the battery, the electric charges will not flow to
the light, but will go directly back to the battery, because that is the path of
least resistance. This is a short circuit.
Activity 8
Create a short circuit
You will need: conducting wires • cell holder • switch • bulb • bulb holder
Figure 20 An incandescent
light bulb.
Method
1. Connect the circuit so that the bulb lights up.
2. Open the switch so that there is no current flowing through the circuit.
3. Connect another conducting wire from one terminal of the cell to the
other terminal.
4. Close the switch to allow the current to flow, and observe if the bulb
lights up.
5. After 2 minutes, touch the conducting wires to feel which is warmer.
6. Explain why the conducting wire that does not pass through the bulb is
hotter.
Figure 21 The wires create a
short circuit.
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The conducting wires from the cell will heat up quickly. This usually happens
with short circuits, since more electrons can crowd through the wires than
when they had to ‘work’ to operate the light bulb. If the amount of energy
supplied is high enough, such as in a house or car, a short circuit like this can
cause the wires to melt. This is the cause of many house and car fires.
Electric current causes a magnetic field
When electric current passes through a wire, it causes a magnetic field.
Magnetic fields are the regions of force surrounding a permanent magnet
or a moving charged particle. The existence of a magnetic field around a
conductor that is carrying electric charge can be demonstrated by putting
iron filings on a piece of card or paper, as shown in Figure 22.
Figure 22 Iron filings indicate the magnetic field around
a conducting wire.
Activity 9
Investigate the effect of a current-carrying
conductor
You will need: piece of light cardboard • iron filings • 3 batteries • long
conducting wire • 4 compasses • switch
Method
1. Pierce a hole through the middle of the cardboard.
2. Feed the conductor through the hole.
3. Connect the conductor to the switch and the first battery. Then connect
the second battery, and lastly, the third battery.
4. Hold the conducting wire with the cardboard in a vertical position, so
that the cardboard acts as a tray.
5. Spread some iron filings on the cardboard around the conductor.
6. Close the switch to allow current to flow in the conductor. Observe
what happens to the iron filings.
7. Open the switch and remove the iron filings.
Topic 8: Energy transfer in electrical systems
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Key words
• electromagnet –
magnet in which
the magnetic field
is produced by
a flow of charge.
The direction of
the magnetic field
can be determined
by placing one or
more compasses
on a card and
observing the
directions that
they indicate
• ionic solution –
solution with
positively and
negatively charged
particles
• anode – electrode
where current
flows in from
outside
• cathode –
electrode where
current flows out
• electrode –
electrical
conductor used to
make contact with
a non-metallic part
of a circuit
146
8. Put four compasses around the conductor on top of the cardboard and
note the directions indicated by the compasses.
9. Close the switch again and observe the directions indicated by the
compasses.
10. Write down your conclusion.
Figure 23 Compasses show the direction of the
magnetic field around a conducting wire.
Electric current can be used for making
electromagnets
The pulling or pushing force of a magnet is because of the magnetic field
around it. Since a current-carrying conductor also produces a magnetic
field, it can be used to make a magnet. Such a magnet is called an
electromagnet.
It is fairly easy to build an electromagnet:
wrap some insulated copper wire around
an iron core, such as an iron nail. If you
attach a battery to the wire, an electric
charge will flow and the iron core will
become magnetised. When the battery
is disconnected, the iron core will lose
its magnetism. Figure 24 shows an
electromagnetic forklift that is used to
move metals from one point to another.
A switch allows current to flow in the
forklift so that it attracts the metal
objects. The objects can then be moved
elsewhere. When the switch is opened to
stop the current flow, the forklift loses its
magnetism and then the metal objects
are released.
Figure 24 Useful effects of electric
current in an electromagnetic crane for
scrap metal
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An electric current can cause a chemical
reaction in a solution
When electricity is passed through an ionic solution, a chemical reaction
may occur. A chemical reaction occurs when one or more chemicals react to
create a different chemical or chemicals. When electricity is passed through
a solution of copper(II) chloride, an ionic solution is formed.
An ionic solution
If you put copper(II) chloride in water, the copper chloride separates into
copper ions and chlorine ions. The copper ions are positively charged and
the chlorine ions are negatively charged. This makes the mixture of copper
chloride and water an ionic solution. An ionic solution is a solution with
positively and negatively charged particles.
The anode and the cathode
If you connect two metals to a cell and then put the two metals into the
ionic solution, a chemical reaction occurs in the ionic solution. The cell
attached to the metals can be thought of as an electron pump, causing
electrons to move along the wires. This means that one of the metals will
be left with a positive charge, because electrons are being pumped away
from it. The piece of metal that is positively charged is called the anode.
The other metal has electrons being pumped towards it, so it is negatively
charged. The piece of metal that is negatively charged is called the cathode.
The anode and cathode are also called electrodes.
Electrolysis
Now you can understand that when these electrodes are placed in a solution,
the ions will be attracted to either one electrode or the other. The negatively
charged particles will move towards the anode (the positive electrode) and
the positively charged ions will be attracted to the cathode (the negative
electrode). Electrolysis is
the process by which ionic
substances are broken down
into simpler substances
when an electric current is
passed through them.
During electrolysis, the
copper(II) chloride solution
is broken down into copper
metal and chlorine gas.
Copper is deposited on the
cathode and chlorine gas is
formed at the anode.
Figure 25 The electrolysis of copper(II) chloride.
Topic 8: Energy transfer in electrical systems
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Electrolysis of water
Water can be broken down by electrolysis to produce oxygen and hydrogen
gas. You will investigate this in Activity 10.
Activity 10 Investigate the electrolysis of water
You will need: 3 cells • 2 conducting wires with alligator clips • 2 pencils •
beaker • warm water • small piece of cardboard • electrical or
masking tape • pencil sharpener
Method
1. Sharpen both ends of both pencils.
2. Fill the glass with warm water.
3. Connect the cell or battery to the tips of the pencils
as shown in Figure 26. It is important that the wires
make good contact with the graphite in the
pencils. Secure the wires with the masking tape.
4. Punch small holes in the cardboard and push
the pencils through the holes, as shown in
Figure 26.
5. Place the exposed tips of the pencils in the
water, so that the tips are fully submerged but
not touching the bottom. Adjust the cardboard
to hold the pencils.
6. Wait for a minute or so. Small bubbles should
soon form on the tips of the pencils. Hydrogen
bubbles will form on one tip (associated with
the negative electrode, or cathode) and oxygen Figure 26 The electrolysis of
water.
on the other.
Key concepts
An electrical current transfers energy to the particles in a bulb's filament,
producing light that the filament emits.
Fuses are safety devices that reduce the danger when using electricity (see the
More Resources section on the next page).
A short circuit can occur when an electric current takes the path of lowest
resistance.
Electric current can be used for making temporary magnets known as
electromagnets.
Moving charges in a conductor cause a magnetic field around it.
An electric current can cause a chemical reaction in a solution.
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More resources
Fuses
Large power overloads can damage electrical equipment, or in more serious
cases, cause a fire. A fuse serves to protect an overloaded electrical circuit
by breaking the flow of electricity before any damage is caused. A fuse is
made up of a piece of metal that melts when overheated. Fuses must be
replaced after they melt. Figure 27 shows a picture of a fuse.
Key word
• fuse – a device that
is used to protect
components of a
circuit
Figure 27 A fuse serves to protect an electric circuit.
How fuses work
There are many different types of fuses for residential and commercial use,
but the most common type is made up of a filament that is enclosed in a
glass or ceramic and metal casing. In an electrical appliance, such as a radio,
the fuse is typically plugged into a central fuse box through which all the
wiring passes. Electricity passes through the fuse before passing through all
the components of the radio. So, when the electricity is flowing normally,
the fuse allows the electricity to pass across its filament, as the circuit is
closed. If an overload occurs, the filament melts, which disrupts the circuit,
and the flow of electricity stops.
Fuses are also found in cars. They are found in component circuits such as
the lights, the car radio and the electric windows. Once a fuse is blown, it
must be discarded and replaced with a new one.
Figure 28 Fuses come in different forms.
More resources: Fuses
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Practical task
Task
Make and use an electromagnet
You will need: 1 iron nail (15 cm long) • 3 metres of insulated copper wire
• 1 or more cells • a pair of wire strippers • a switch • very
small nails • insulation tape
Figure 29 The equipment needed to make an electromagnet
Method
1. Use a pair of wire strippers to remove about 3 cm of insulation from
each end of the wire. This is necessary because some of the copper wire
needs to be exposed to allow the battery can make a good electrical
connection.
2. Neatly wrap the wire around the nail. Make certain that you wrap the
wire all in one direction. You need to do this because the direction of
a magnetic field depends on the direction of the electric current that
is creating it. If an electric current is flowing directly towards you, the
magnetic field created by it circles around the wire
in a counter-clockwise direction. If the direction of
the electric current is reversed, the magnetic field
also reverses and circles the wire in a clockwise
direction. If you wrap some of the wire around
the nail in different directions, the magnetic fields
from the different sections will fight each other and
cancel each other out, reducing the strength of
your magnet.
Figure 30 Wind the wire around the nail.
150
The more wire you wrap around the nail, the
stronger your electromagnet will be. Make certain
that you leave enough of the wire unwound so that
you can attach the battery.
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3. Use the insulation tape to attach one end of the wire to the positive terminal of the battery
and the other end of the wire to the negative terminal of the battery. If all has gone well, the
electromagnet should now be working.
Do not worry about which end of the wire you attach to the positive terminal of the battery
and which one you attach to the negative terminal. Your magnet will work just as well either
way. What will change is your magnet’s polarity. One end of your magnet will be its north
pole and the other end will be its south pole. Reversing the way the battery is connected will
reverse the poles of your electromagnet.
4. Connect a switch to the circuit by disconnecting the battery or cell. Cut a small piece of
conducting wire in order to connect the switch.
5. Close the switch and bring one end of the iron nail closer to the smaller nails, if they are
repelled, use the other end of the nail. If they are attracted to the nail, attract as many as
possible and move them with your electromagnet to another position in the table. Open the
switch and see them drop off.
Questions
Answer the following questions after you have proved that your electromagnet can work.
6. Explain what an electromagnet is.
(2)
7. Explain why you need to remove a bit of the insulation from the ends of the conducting
wires.
(2)
8. The more wire you wrap around the nail, the __________ your electromagnet.
(1)
9. Explain why all the wire must be wrapped in one direction around the nail.
(2)
10. What device can be used to determine the direction of the magnetic field in the
electromagnet?
(1)
11. What is the purpose of the electric cells in the electromagnet?
(1)
12. What is the function of the switch in the electromagnetic crane?
(1)
13. What should be done in order for the electromagnets to attract the smaller nails?
(1)
14. What should be done to cause the attracted nails to fall from the electromagnetic nail?
(1)
15. Mention two things that can be done to make the electromagnet stronger.
(2)
16. Explain why the electromagnet is a resistor.
(1)
17. Draw a labelled circuit diagram of the electromagnet you have made.
(5)
Total: 20
Practical task: Make and use an electromagnet
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Topic 8 revision
Science language practice
1. Match the terms in Column A with their correct meaning in Column B. Write only the correct
number (1–10) next to the letter ((a)–(j)).
Column A
Column B
a) Electric current
b) Electrolysis
c) Short circuit
d) Fuse
e) Resistor
f ) Magnetic field
g) Anode
h) Cathode
i) Electrons
1. Solution that contains positively and negatively charged particles
2. The electrode where current flows out
3. The electrode where current flows in from the outside
4. Device that opposes the flow of current
5. The regions of force surrounding a permanent magnet or a moving charged particle
6. An electrical circuit that allows current to flow in an unintended circuit
7. Device used to protect the components in a circuit
8. Negatively charged particles
9. Process by which ionic substances are broken down into simpler substances when
an electric current is passed through an ionic solution
10. The flow of charge
j) Ionic solution
Test yourself
1. List four basic components of an electric circuit.
(4)
2. Draw the circuit diagram of an electronic game that uses three cells to give light and sound.
(4)
3. Your electric kettle is not working and you have discovered that the problem is with the light
that indicates when the kettle is on. Draw a circuit diagram to show how you can create a short
circuit to keep the kettle working.
(5)
4. Explain what an electromagnet is.
(2)
5. Label the parts numbered (a) to (e) in Figure 31.
(5)
e)
d)
c)
b)
a)
Figure 31 The electrolysis of copper(II) chloride
Total: 20
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Term 3: Energy and change
Topic
9
Series and parallel circuits
Starting off
In Topic 8 you learnt about how a circuit is a
pathway for conducting electrical energy. There are
many different components that can be connected
in a circuit, for example, an energy source (such as a
battery), resistors (such as light bulbs) and switches,
which can control the current.
Figure 1 Most electrical wires are made of copper.
We can connect these components in different
types of circuits. The main types of circuits that you
will find around your home are either series circuits
or parallel circuits. The current flows in slightly
different ways in each type of circuit, so they can be
used for different purposes.
Activity 1
Revise the components of a
circuit
1. Name a source of energy that can be connected
in a circuit.
2. What material are conducting wires usually
made from?
3. Name the components that are represented by
these symbols:
a)
b)
c)
4. Explain the role of a fuse in a circuit.
5. Why is a light bulb also called a resistor in a
circuit?
Topic 9: Series and parallel circuits
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Unit
1
Series circuits
Key words
• series circuit –
electric circuit
where electrical
components are
connected one after
the other and there
is only one pathway
for the current to
flow through
• resistance –
material’s ability
to block or oppose
the flow of
electricity
• conductors –
materials that
allow electric
current to pass
through them
• insulators –
materials that do
not allow current
to pass through,
or they allow very
little current to
pass through
A series circuit provides only one pathway for the electric current to pass
through it. Think of a hose pipe: there is only one path for the water to flow
through the pipe. If there is anything stuck inside the pipe, such as some
stones, it is more difficult for the water to flow through it. The stones have
blocked or created a resistance to the flow of water. In the same way, a light
bulb or any other resistor in an electric circuit creates a resistance for the
current flowing through the circuit. This means that every time a resistor is
added in series, less current can flow through the circuit. The overall current
in the series decreases. You can see the effect of the reduced current by the
reduced brightness of the light bulbs.
Activity 2
Observe the effects of connecting resistors in a
series circuit
You will need: battery • circuit board or cell
holders • conducting wires •
3 identical LED light bulbs
1. Set up a circuit with one cell and one light
bulb, as shown in figures 2 and 3.
2. Copy this table and record how bright the
light bulb is.
Number of light
Brightness of the
bulbs in the circuit light bulbs
Figure 2 Series circuit with one
light bulb
1
2
3
Did you know?
Even if one resistor is
connected in a circuit,
the current will remain
the same everywhere
in that circuit. Current
does not ‘bunch up’
just before the resistor
and flow smoothly
once it has passed the
resistor. Instead, the
current is reduced
everywhere in the
circuit.
154
3. Connect a second light bulb to the series
circuit and observe the brightness of
the bulbs. Are they brighter or dimmer
than when there was just one bulb in the
circuit? Record your answer in the table.
4. Connect a third light bulb to the circuit.
Observe the brightness of the bulbs and
record your findings in the table.
5. What do you notice about the brightness
of the light bulbs as more bulbs are added
to the circuit?
Figure 3 Circuit diagram of a series
circuit with one light bulb
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Materials that conduct electricity
The metal wires in the circuit are the conductors that allow electric current
to flow through the circuit. Most metals are good conductors of electric
current and you can find wires made out of many different types of metal,
for example, copper, steel, silver and even gold. Materials that do not allow
electric current to pass through
are called insulators. Examples of
insulators are plastic, rubber and
glass.
Although electric current will flow
through different metals, some
metals are better conductors
than others. All conductors have
some resistance, and different
metals have more resistance than
others. The metals that have the
least resistance make the best
conductors.
Activity 3
Figure 4 Copper is an excellent conductor and is
used in a lot of electrical wiring.
Investigate how different metals conduct
electricity
You will need: light bulb • 2 clips • battery • copper wire • steel wool •
nichrome wire
1. Connect the light bulb to the battery using the copper wire.
2. Observe how bright the light bulb is and record your observation in a
table.
Type of
metal wire
Brightness of
the light bulb
Copper
Steel
Nichrome
3. Now connect the light bulb to the battery using the steel wool. Is the
light bulb brighter or dimmer than when you used the copper wire?
Record your observations in the table.
4. Repeat the investigation using the nichrome wire and record your
observations in the table.
5. Which type of metal wire made the best conductor?
Key concepts
A series circuit
provides only
one pathway for
the current to
pass through.
The current
is the same
everywhere in
the series circuit,
but every time a
resistor is added
in series, the
overall current
in the circuit
decreases.
Different
metals conduct
electricity
differently; some
make better
conductors than
others.
Topic 9: Series and parallel circuits
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Skills focus: Predict and write a hypothesis
What is a hypothesis?
A hypothesis is our best guess at the answer to a scientific question that we
want to investigate. It is written in the form of a statement. The hypothesis
does not have to be correct but you must be able to test it using an
experiment. The results of your experiment will prove if the hypothesis is
true or false.
How to write a hypothesis
Writing a hypothesis that can be tested is one of the most important
steps in an investigation. Before you write the hypothesis, you need to
know what the question is that you want to test. Then you should write a
sentence that is a guess at the answer to this question. To turn this guess
into a hypothesis, you need to make sure that it gives us a clear idea of
how to test it.
For example, our test question might be: ‘Do some objects fall more quickly
than other objects?’ We could guess the answer: ‘Some objects fall more
quickly than other objects.’ This guess is not a good hypothesis because it is
not clear how we would test it. A better hypothesis would be: ‘A rubber ball
falls more quickly than a feather.’
Figure 5 You must be able to
test your hypothesis with a fair
experiment.
Activity 4
Practise writing a hypothesis
1. For each example below, fill in the missing test question or hypothesis.
2. Discuss your answers with the class. Note that there is more than one
possible answer in each case.
Test question
1. Do all metals rust at the same rate?
2.
3. What is the best material to make a
roof from, if you want to keep your
house cool?
4. What makes some fires smoky and
other types of fires less smoky?
5.
156
Hypothesis
Packets with small holes will
keep fruit fresh for longer than
cardboard boxes will.
Copper wire will conduct
electricity better than aluminium
wire.
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Unit
2
Parallel circuits
A parallel circuit provides two or more pathways for the current passing
through it. Think of the current as cars and the parallel circuit as roads. There
can be several roads running alongside each other that connect the same
two points together, so there is more than one route for the cars to travel
along. The more roads that connect these points together, the more cars can
travel between them at any one time, and a road block on one road does
not stop the cars from travelling on the other roads. In the same way, in a
parallel circuit the current increases as more resistors are added in parallel,
and if one doesn’t work (for example, a light bulb burns out) then the others
will continue to work.
Activity 5
Key word
• parallel circuit –
electric circuit
where there is
more than one
pathway for the
current to flow
through
Observe the effects of connecting more resistors
in a parallel circuit
You will need: a battery • a circuit board or cell holders • conducting wire •
3 identical light bulbs
1. Connect two light bulbs in parallel, as shown
in the top diagram in Figure 6. Observe
the brightness of the bulbs. Are they as
bright as each other, or is there a difference
between them?
2. Connect a third light bulb in parallel in
the parallel circuit. What happens to the
brightness of the bulbs? Do you observe
a difference between now and when
there were only two light bulbs in the
circuit?
3. Predict what would happen if you added a
fourth light bulb in parallel in the circuit. Would
there be a difference in the brightness of the
bulbs?
4. Write a sentence about what happens when
you connect more light bulbs in a parallel
circuit.
Figure 6 A circuit diagram
for three light bulbs
connected in parallel
Topic 9: Series and parallel circuits
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Activity 6
Compare the effects of resistors connected in
series and in parallel
You will need: 2 sets of conducting wire • 2 circuit boards or cell holders •
2 identical (working) light bulbs • 2 burnt-out light bulbs •
2 batteries
Figure 7 Two light bulbs connected
in series
Figure 8 Two light bulbs connected
in parallel
1. Set up a circuit with two light bulbs connected in series, as shown in Figure 7.
2. Set up a circuit with two light bulbs connected in parallel, as shown in Figure 8.
3. Compare the brightness of the light bulbs in the series circuit with
the brightness of the light bulbs in the parallel circuit. Record your
observations in a table.
Observations in the
series circuit
Observations in the
parallel circuit
Two bulbs in the circuit
Three bulbs in the circuit
Two working bulbs and
a burnt-out bulb in the
circuit
4. Add a third bulb in the series circuit and add a third bulb in the parallel
circuit. What do you notice about the brightness of the bulbs in each
circuit? Record your observations in the table.
5. Replace one of the bulbs in each of the circuits with a burnt-out light
bulb. What do you notice? Complete the table.
Key concepts
A parallel circuit provides two or more pathways for the current passing
through it.
The overall current increases when more resistors are added in parallel.
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Unit
3
Output devices
An output device is something that is connected to an electrical circuit. It
transforms the potential electrical energy in the cells and batteries in the
circuit into another form of energy such as heat energy, sound energy or
light energy.
The light bulb in Figure 9 is an example of an output device. The energy from
the battery is transformed into light energy.
Any resistor in an electric circuit is an output device. Here are some common
examples of output devices:
Output device
Type of output
Light bulb
Light-emitting
diode (LED)
Beeper
Buzzer
Motor
Light energy
Light energy
Key word
• output device –
something that
transforms the
potential energy in
a cell into another
form of energy,
such as heat,
sound or light
Sound energy
Sound energy
Kinetic energy (movement)
Figure 9 The light bulb is an example of an output device.
Activity 7
Identify output devices
There are many different output devices that we use in our homes
every day. A heater is one example. The energy conversion flow diagram
for a heater is:
Input: electrical energy
Output: heat energy
1. How many different output devices can you see in your classroom?
2. Draw energy conversion flow diagrams to show the input and output
for each output device that you identify.
Key concepts
Output devices transform electrical energy into another form of energy, for
example, light, heat or sound.
Examples of output devices include light bulbs, LEDs, beepers, buzzers and
motors.
Topic 9: Series and parallel circuits
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Skills focus: Build electric circuits and draw circuit diagrams
What is a circuit diagram?
Circuit diagrams use standard symbols to represent each component of a
circuit. This allows anyone to build the same circuit accurately. You learnt
about some of these symbols in Topic 8. It is important to know how to
recognise or interpret the symbols used in a circuit diagram, so that you
can build the correct circuit. Interpreting symbols and other types of
information is an important skill that all scientists use.
How to interpret a circuit diagram to build a
circuit
Step 1: Identify each of the components used in the circuit. Use Table 1
on page 141 if necessary.
Step 2: This circuit contains four cells, one switch, three bulbs and
conducting wires. Build the circuit.
a ) Connect the cells in series.
b ) Connect two light bulbs in parallel.
c ) Connect the battery and parallel light bulb in series with the
last light bulb and the switch.
Activity 8 Practise drawing circuit diagrams
1. Draw the following circuit diagrams:
a ) An electrical circuit with three cells in parallel and two bulbs
connected in series.
b ) An electrical circuit with a battery consisting of three cells
connected in series, and three bulbs connected in parallel. Each
bulb has its own closed switch.
2. Describe how you will build the circuit in the diagram below.
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More resources
The history of electricity
Read the information on the timeline and do more research about the history of electricity.
Did you know that there are many different
careers that work with electricity? For
example, electricians, electricity supply
maintenance and electronics engineers, who
assemble the computers that you use, and
many more. Find out what you can about
these different jobs. Would you like to do any
of these jobs when you leave school?
Figure 10
An electr
ic
ian
An
Figure 11
pply
su
y
it
ic
electr
n
nce perso
maintena
Figure 12
An electr
o
nics engin
eer at wo
rk
More resources: The history of electricity
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Topic 9 revision
Science language practice
1. Define each of the following terms:
a ) electric current
b ) series circuit
c ) parallel circuit
d ) resistor
2. What is the difference between a conductor and an insulator?
Test yourself
1. Look at the circuits below.
A
B
C
a ) In which circuit will the light bulbs be the brightest?
b ) In which circuit will the light bulbs be the dimmest?
(2)
(2)
2. In Circuit 1, two bulbs are connected in series using nichrome wire as the conductor. In Circuit 2,
two identical bulbs are connected in series using copper wire as the conductor. In which circuit
will the bulbs be the brightest? Explain your answer.
(4)
3. Name each of these symbols that are used in circuit diagrams.
a)
b)
c)
(3)
4. Draw the following circuit diagrams.
a ) An electrical circuit with two cells connected in parallel, and two cells in series
b ) An electrical circuit with four cells and a switch connected in series, and three light bulbs
connected in parallel.
(2)
(2)
Total: 15
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Term 3: Energy and change
Topic
10
Visible light
Starting off
In Topic 8, you saw that electricity can cause a
bulb to light up. You also learnt that the bulb does
not only radiate light energy, but heat energy as
well. You can tell that the circuit is closed and that
electricity is flowing through the conducting wires
because you can see the light energy radiating from
the bulb. We call this visible light.
Visible light is the term used to describe all the
forms of radiation that you are able to see with your
eyes. Therefore, we can say that, in order for you
to be able to see something, light from that object
must enter your eyes.
In this topic, we will discover the properties and
behaviour of visible light.
Activity 1
Figure 1 The rainbow is a spectrum of the colours that – all
together – make up white light.
Explore what you know about
visible light
1. Look at Figure 1 and answer these questions:
a ) Name three things that you can see in the
picture.
b ) Although you can see many things in the
picture, only one object is a source of light.
Which object is it?
c ) Discuss the following with a partner and
report back to the class: If only one object is
a source of light, how is it possible that we
can see the other objects in the picture?
2. Name three sources of light.
3. How many colours can you see in the rainbow
in Figure 1?
Topic 10: Visible light
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Unit
1
Radiation of light
Key words
• visible light – type
of energy that
comes from a light
source and can be
observed by the
human eye
• luminous – word
to describe an
object that gives
off light or glows in
the dark
• radiation –
process in which
light moves away
from the its origin
• illuminated – lit
up or provided
with light
• ray diagram –
diagram that
uses lines with
arrowheads to
show the path of a
ray of light
Visible light (or light) is emitted from a luminous object such as a star
or a light bulb. A luminous object is any object that gives off light from
its own source, such as the flame of a burning candle or lightning. Light
is transferred by radiation. When you
switch on the light in a room at night,
the whole room becomes illuminated
because light is emitted from the bulb
and radiates in all directions.
Light travels in straight lines. This explains
why you are not able to see light around
corners. When light travels from an object
that is around a corner, the light is unable
to bend around the corner and reach
your eye.
Figure 2 Light travels in straight lines. In
this picture, some light rays from the Sun
are let through a gap in the clouds. We can
see that the rays of light do not bend as
they radiate towards the Earth.
A ray diagram is a simplified way of
showing how light is radiated from
a luminous object. The path and
direction of one ray of light is represented by a line with an arrowhead. But,
remember: light rays radiate in all directions, so a simple ray diagram only
represents a few of the rays of light that are radiated by the luminous object.
The pinhole camera
A pinhole camera also illustrates that light travels in straight lines. This
is a very simple apparatus that is used to form an upside down image of
a luminous object on a screen. The pinhole camera can be constructed
by using a shoebox that is painted black on the inside. At one end of the
box there is a very small hole. At the other end, the side of the shoebox is
removed and fitted with wax- or tissue paper, that will form the screen on
which the image forms.
Figure 3 A pinhole camera that forms an image of a candle
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Although the image on this very primitive
camera is not very clear, you might be able
to see that the image formed on the wax
paper is upside down. A ray diagram can
help to explain why this happens.
Light shines in all directions from the candle.
Some of this light passes through the
pinhole and forms an image on the tissue
paper. The ray diagram is greatly simplified
and only shows two of the thousands of rays
that shines from the candle.
Activity 2
Figure 4 A ray diagram of the object and the object’s image on the
pinhole camera’s screen
Draw a ray diagram
1. Why do we only show a few light rays when we draw a ray diagram?
2. Using the example of the candle and its image on the pinhole camera’s
screen, draw a ray diagram of a simple light bulb and its image on the
pinhole camera’s screen.
3. When a torch shines on a wall, a white circle of light appears on the wall.
a ) Draw a picture of the torch and the image that it makes on the wall.
b ) Draw a ray diagram of the light as it leaves the torch and travels to
the wall.
The speed of light
Light travels from a luminous object through empty space extremely
quickly. The speed of light is approximately 300 000 kilometres per second.
Question: If the distance from the Sun to the Earth is 150 million kilometres,
how many minutes will it take light from the Sun to reach Earth?
150 000 000 km
= 500 seconds
Answer: ___________
300 000 km/s
Since there are 60 seconds in a minute, 500 seconds is the same as
8 minutes and 20 seconds.
Activity 3
Calculate the distance between the Earth and a star
1. If it takes light from a star 20 minutes to reach Earth, calculate how far
away from Earth the star is.
Key concepts
Light is emitted by luminous objects.
Light travels in straight lines.
Light travels very fast through empty space.
Topic 10: Visible light
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Unit
2
The spectrum of visible light
The Sun radiates white light. White
light is actually a combination of all
the different colours of light, which
you can see separately in the bands
of a rainbow. The collection of all the
colours that you find in a rainbow is
called the spectrum of visible light.
Key words
• spectrum of
visible light –
full collection of
colours that make
up white light
• wave – pattern
created by the
repeated up-anddown or side-toside movement
of a medium
(substance) when
energy moves
through it
• wavelength –
length of one wave
pattern
Light is called a wave because
when it travels, it moves in a regular,
Figure 5 A rainbow shows the spectrum of light.
repetitive pattern (up and down).
Water waves form a similar pattern,
but unlike water, you cannot see the pattern that light creates. Each of the
different colours of visible light has a characteristic wave: some colours have
long waves (such as red light) and some colours have short waves (such as
blue light). Wavelength is the term used to describe the length of a wave
pattern. The shorter the wavelength, the more waves will be able to pass a
certain point at a given time. The number of waves that pass a certain point
in one second is called the frequency of the wave.
• frequency –
number of waves
that move past a
certain point in
one second
• refraction – ability
of a wave to
change direction
(or bend) when it
passes from one
medium (such
as air) to another
(such as glass)
• dispersed (light) –
white light that
is broken up into
different colours of
light
• reflected (light) –
light that has
changed direction,
but continues
to travel in the
original material
166
Figure 6 Light is shown as a wave. The different colours are in the same order that they appear in a
rainbow.
The different colours that together make up white light are violet, indigo,
blue, green, yellow, orange and red. Violet has the shortest wavelength and
therefore the highest frequency. On the other side of the spectrum, red has
the longest wavelength and the lowest frequency.
Light refraction
Light can bend and change direction when it moves from one medium to
another, such as from air to glass. We call this bending refraction.
However, the different colours of light that make up white light refract at
different angles. This is why it is possible to see different colours.
To see how light refracts, we use a triangular prism (a three-dimensional
shape) that is made of clear Perspex or glass. When white light enters the
prism, it is refracted as it moves from the air to the glass or Perspex, and
again when it moves out of the prism (from the Perspex or glass to the air).
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Because of the shape of the prism and the effect of refraction, the white
light is split into its component colours when it leaves the prism. We say that
the white light is dispersed so that the different colours are visible.
Activity 4
Observe and record the sequence of colours when
light is shone through a triangular prism
You will need: a ray box or a cardboard shoebox (with a lid)
that has a small slit cut into one side • a torch •
a triangular prism • a piece of white cardboard
Method
1. Place the ray box in front of the prism. If you are using the
cardboard box, place the torch inside the box so that a small
beam of light shines through the slit, and put the box’s lid on.
2. Place the prism in the path of the small beam of light, so that
the light shines on one of the slanting sides of the prism.
Figure 7 Light from the light source in the box
shines on the prism and creates a spectrum of
colours.
3. Place the piece of white cardboard a short distance behind
the prism. Move it around until you see the rainbow colours appear on the
cardboard.
How does a rainbow form?
We see rainbows in the sky during or after it has rained. This is because the
air is filled with very small drops of water, which act like tiny prisms.
Light enters a droplet of water and is refracted. But, when it reaches the
other side of the droplet, it doesn’t leave the medium as it did in the
triangular prism. Instead, it is reflected inside the droplet, but in a new
direction. It eventually leaves the droplet, but is refracted again, and is
dispersed into the different colours of the rainbow.
Key concepts
White light is
made up of a
range of waves
with different
frequencies and
wavelengths.
The seven
colours that
make up white
light are violet,
indigo, blue ,
green, yellow,
orange and red.
Violet has
the shortest
wavelength
and longest
frequency. Red
has the longest
wavelength
and shortest
frequency.
Figure 8 Light from the light source in the box shines on the prism and creates a spectrum.
A rainbow forms
when light
falls on water
droplets in the
air.
Topic 10: Visible light
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Unit
3
Opaque and transparent substances
Key words
• opaque – does not
allow light to travel
through
• absorbed (light) –
light travels to
the material and
is unable to travel
any further
An opaque object is an object that does not allow any light to travel
through it. Examples of opaque materials include metal, clay, bricks, wall
paint and cardboard. Light is either absorbed or reflected by the opaque
object. If light is absorbed, it means that the light is unable to travel any
further once it has reached the opaque object. All black objects absorb light,
so no light will travel from that object to your eye. When no light waves
reach your eyes, your brain interprets this image as black.
However, we can see opaque objects (even black objects) because they
reflect some light onto your eye. Your brain is able to interpret the different
wavelengths of light as different colours and can build a picture of what
you see.
Shadows are darker areas that form behind opaque objects because the
light is unable to travel through the object. Because light travels in straight
lines, an opaque object will either absorb or reflect some light, but will not
allow any light to travel through the object to the wall or area behind it. The
area where light is absent will appear black to the eye. A shadow is cast on
the side of the object that faces away from the light source.
Look at Figure 9, which shows a picture of a torch shining on a cardboard
box. The ray diagram in Figure 10 explains how the shadow in this picture is
formed.
Figure 9 A torch shines on a cardboard box
and creates a shadow.
Activity 5
Figure 10 A ray diagram of a torch shining light onto an opaque
object: Light travels from the torch to the wall, where it is reflected to
your eye. No light reaches the wall directly behind the opaque object
so the eye sees this part of the wall as black.
Draw diagrams to show how shadows are cast by
opaque objects
1. Draw a ray diagram to show how a shadow is formed when a torch
shines light on a book that is standing on the floor, 50 cm away from
a wall.
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Activity 6
Predict the effect of moving an object closer to, or
further away from, the light source on the size of
the shadow that forms
You will need: light source • square piece of cardboard • triangular piece of
cardboard • piece of paper • pencil • measuring tape or ruler
Figure 11 How to set up the apparatus
Method
1. Look at Figure 11. How do you think the shadow will change if the
cardboard square is moved closer to the light source?
2. Set up the apparatus as illustrated in the picture.
3. Measure the distance between the bulb and the cardboard.
4. Redraw the outlines of the shadow on the piece of paper.
5. Calculate the surface area of the shadow.
6. Repeat the experiment, but move the cardboard square closer to the
light source.
7. Repeat steps 3 to 6 using the triangular piece of cardboard instead of
the square piece of cardboard.
8. What conclusion can you draw from this investigation?
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Key word
• transparent – light
is able to travel
through
When the object is far away from the light source, a smaller amount of
light is blocked and therefore the shadow is smaller. When the object is
closer to the light source, more light is blocked and therefore the shadow
is larger.
Figure 12 When an opaque object is further away from the light source, its
shadow will be smaller.
All the light rays that are radiated from the flashlights will be blocked by the
object. No light will reflect from the paper behind the object, and a black
shadow will appear on the paper.
Transparent objects
A transparent object is any object that allows light to travel through it.
Light passes through transparent substances, such as glass, clear plastic,
cellophane and clean water. When a clear image can be seen through the
object, it means that all light has passed through.
In some objects, such as coloured cellophane, some of the light is absorbed,
some is reflected, but most passes through. Sometimes you are able to see
a reflection of yourself in a window. This shows that although most of the
light passes through transparent objects, it is also possible that some light
can be reflected.
Key concepts
Light cannot travel through opaque objects.
Opaque objects casts shadows on the side opposite the one facing the
light source.
Most light travels through transparent objects, although some light can be
reflected and absorbed.
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Unit
4
Absorption of light
Light can be absorbed by surfaces of some materials. In Unit 3, we
discovered that light can be absorbed by opaque objects. When all light is
absorbed, the surface will appear black. This means that all black substances
are examples of materials that completely absorb all light that travels to it.
Light is absorbed differently by different materials. A mirror, for example,
will absorb no light, while a coloured piece of cellophane will absorb all
colours, except its own colour.
A material has colour because it absorbs some of the colours in the
spectrum and reflects other colours. During the day, white light shines from
the Sun on different objects, yet they appear to have different colours. White
light is made up of all the different colours, each with its own frequency.
Let’s assume a wall is able to absorb light of all frequencies, except for red
light. When white light shines on this object, all the frequencies
will be absorbed, but red light will be reflected. Since red light
is the only light that reaches the eye, the wall appears to be red.
You can see this in Figure 13.
Although light is a wave, in order to make it easier to sketch
diagrams, it is usually shown as a straight line.
When you look at an image through a piece of green cellophane,
the image is made up of shades of green and black. Figure 14
should demonstrate why this happens.
Figure 13 Why an object appears to be a
certain colour
Figure 14 Absorption of light through a transparent object
Look at Figure 15 on the next page. When an object is viewed through a
piece of blue cellophane, the white part of the object appears to be blue
and the pink parts of the object, as well as the green parts appear to be
black.
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Figure 15 How a piece of blue cellophane affects the image that we see
A black pot appears to be black because all the frequencies of light are
absorbed and therefore no light reaches the eye. The idea of a black surface
that absorbs radiation was also introduced in Grade 7, when you studied the
radiation of heat and discovered that dark surfaces heat up quickly, because
they are able to absorb heat.
A white or shiny surface (for example, a piece of white paper) reflects all the
light that shines onto it. In Grade 7, you discovered that white and shiny
surfaces also reflect heat waves in the same way.
Activity 7
Explain how absorption helps us to see different
colours
1. Explain why everything appears to be black when you close your eyes.
2. When red and green light combine, they form yellow light. If you look at
a red square with blue dots on it, through a yellow piece of plastic, the
square will appear to be red with black dots on it. Explain why this is so.
3. What will you observe if seven torches, each shining light of only one of
the seven colours of the rainbow, shine their light together on the same
spot?
4. Think about seven cans of paint, each containing paint that represents
one of the colours of the rainbow. What will you observe when all the
paint from the seven different cans are mixed together?
Key concepts
Light can be absorbed by the surfaces of some material.
Light is absorbed differently by different materials.
A material has a certain colour because it is able to absorb some colours
and reflect others.
The frequencies that are absorbed by objects do not reach the eye.
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Unit
5
Reflection of light
Light is reflected off most surfaces, which is why we can see the objects
around us. While you read this book, light is radiated from a light source,
onto the page where it is reflected back to your eyes. But, light is not
reflected from the black ink on the page, so all the words appear black. Your
brain interprets the absence of reflected light as black.
Key words
• normal –
imaginary line
on a reflective
surface that is
perpendicular to
the surface
• incident ray –
light ray that
travels to the
reflective surface
• reflected ray –
light ray that is
reflected by the
reflective surface
Figure 16 The reflection of light from a book
When you look at a smooth surface (like a polished table or a mirror),
it is possible to see your own image on that surface. Let us carefully
demonstrate how it is possible for you to see yourself in a mirror:
• angle of
incidence – angle
between the
normal and the
incident ray
• angle of
reflection – angle
between the
normal and the
reflected ray
• plane – imaginary
flat surface that
only has length
and width, but no
depth or height
Figure 17 How a mirror works
•
•
•
1 and 2: Light from a light source reflects on you and shines on the
mirror. When light is reflected, it always changes direction.
2 and 3: Light shines on the mirror and is reflected back to your eye.
4: Your brain ‘reads’ that the light ray that just entered your eye travelled
the distance equal to the length of rays 2 and 3 together. Therefore, the
brain forms an image a distance away (the sum of the distance that rays
2 and 3 travelled).
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Sometimes when you look at a mirror at an angle, you see an
image of another object. Figure 18 shows how this happens.
In the diagram, the red light that shines on the mirror is radiated
at an angle. When it is reflected, it is also reflected back at the
same angle.
When the reflected ray reaches your eye, your brain receives a
message that a light ray that travelled a distance equal to the size
of arrows 1 and 2 combined, entered your eye. Your brain then
forms an image this same distance away from the eye.
In order to explain how reflection works in scientific language, it
is important that we use the following terminology:
Figure 18 How an image forms in a mirror when
you look at the mirror at an angle
Normal: The normal is an imaginary line on a reflective surface
that forms an angle of 90° to the surface.
Incident ray: This is the light ray that travels to the reflective surface. You
can think of the incident ray as the ‘incoming’ ray.
Reflected ray: This is the light ray that is reflected by the reflective surface.
You can think of the reflected ray as the ‘outgoing’ ray.
Angle of incidence: This is the angle that is measured from the normal to
the incident ray.
Angle of reflection: The angle that is measured from the normal to the
reflected ray.
The laws of reflection can be summarised as follows:
1. The incident ray, the reflected ray and the normal (to the reflection
surface at the point of incidence) lie in the same plane. A plane is an
imaginary flat area that only has a length and width, but no depth.
2. The angle that the incident ray makes with the normal is equal to the
angle that the reflected ray makes with the same normal.
3. The reflected ray and the incident ray are on the opposite sides of the
normal.
mirror
bull dog
clip
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001
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07
06
05
071
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30
0
20
160
0
01 0
14
0
40
angle of
incidence
0
60
70
0
80
90
100 11
0
12
13
laser pointer
50
angle of
reflection
02
061
03
05
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04
04
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03
protractor
Figure 19 A ray diagram showing how light is reflected
off a reflective surface.
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Figure 20 A protractor and laser pointer can be used to show how and where
the angle of incidence and the angle of reflection can be measured.
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Activity 8
Understand the scientific terminology used for
light reflection
Study Figure 20 on page 174 and Figure 21 below to answer the questions
that follow.
Figure 21 A laser pointer shines laser light onto a mirror.
1. How big is the angle of reflection? Explain how you arrived at this answer.
2. Give the scientific terminology for BC, AB and BD.
Activity 9
Investigate how images form on different surfaces
You will need: piece of tin foil • torch • mirror
1. Place the mirror flat on a table and shine the torch in the mirror. (Do not
look at the image of the light directly.)
2. Place the piece of tin foil on a table and shine the torch on the tin foil.
How does the image that forms differ from the image formed in the
mirror?
3. Crumple the tin foil and straighten it again. Place the tin foil on the table
and shine the torch on the tin foil. What can you conclude about the
relationship between the texture of a surface and the reflection on that
surface?
The reflection of light from smooth and rough
surfaces
A mirror has a very smooth surface. On a smooth surface, all the
light is reflected in the same direction.
On a rough surface, different light rays will shine on different
parts of the surface, so some might shine on relatively flat parts,
and some might shine on parts that are at a greater angle away
from the flat surface.
Figure 22 All the light rays are reflected in the
same direction in a mirror.
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In Activity 9, you experimented with tin foil. Although the
straightened tin foil appeared to be smooth, if you looked
at it closely, you would have found that its surface is not
as smooth as a mirror’s surface.
When light is reflected from a rough surface, not all the
light that is reflected reaches the eye and therefore, the
Figure 23 Reflection of light from a rough surface, such
brain is not able to form an image. The light is scattered,
as crumpled tin foil
which means that it reflects in a number of different
directions with no regular pattern in the reflection. The
smoother the surface, the more the light is reflected in the same direction
and therefore, the clearer the image that forms.
Key word
• scattered (light) –
light that reflects
in different
directions, with
no regular pattern
apparent in the
reflection
On the smooth tin foil, you were almost able to make out an image, but on
the crumpled foil, all you saw (at best) was just a brighter spot.
Activity 10
Draw a ray diagram
1. Draw a labeled ray diagram to illustrate how it is possible to ‘see’ around
a corner with the aid of a mirror. Use Figure 24 to help you.
mirror
Figure 24 How is it possible to see around a corner using a mirror?
2. Explain the following with the aid of a ray diagram: Although a piece
of white paper is able to reflect all the light that shines on it, it is not
possible to form an image of a reflection.
Key concepts
Light is reflected off most surfaces.
Light changes its direction when it is reflected.
The laws of reflection tell us how light is reflected.
On smooth surfaces, light is reflected in the same direction.
On rough surfaces, reflected light is scattered.
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Unit
6
Seeing light
In order to understand how you see, it is important to understand the
functions of the main components of the eye. They are briefly explained
below and are shown in Figure 25.
Key words
• cornea –
protective front
covering of the eye
Cornea: The cornea is the protective front covering of the eye. It is
completely transparent and protects the eye against dust, germs
and other harmful matter.
• retina – sensory
layer at the back of
the eye
Retina: The retina is a sensory layer at the back of the eye where
all the light that enters the eye gathers, and where the image is
formed. The image is formed by specialised receptor cells in the
retina when they are stimulated by specific wave frequencies
(colours).
• pupil – hole in the
centre of the iris
that controls the
amount of light
that enters the eye
Pupil: The pupil is a hole in the centre of the iris. When the pupil
becomes larger, more light can enter the eye; when it is smaller,
less light can enter the eye. Therefore, we say that the pupil
controls the amount of light that enters the eye.
• optic nerve –
part of the eye
that transmits
information from
the retina to the
brain
Optic nerve: The optic nerve transmits information about the
formed image from the retina to the brain.
Figure 25 The main components of the human eye
Light of different frequencies passes through the cornea (because it is
transparent), enters the eye through the pupil and travels to the retina.
Specialised receptor cells in the eye’s retina are stimulated by specific
frequencies (colours). The light energy that forms an image on the retina is
converted to electrical nerve impulses. These impulses travel through the
optic nerve to the brain, which interprets the impulses and tells us what we
are seeing.
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The frequencies that determine the colours of light, and that are absorbed
by the surface of an object, do not reach the eye. If all the colours of light are
absorbed by a surface and no light reflects to the eye, the brain interprets
the absence of light as black and will see that the object is black.
Why objects appear to have a certain colour
Think about a yellow sunflower. Why do the sunflower’s petals appear
yellow?
White light from the Sun shines on the petals of a sunflower. The petals
absorb all the colours of the spectrum, except for yellow, which it is able to
reflect. Since only the yellow light reflects back to the eye, and all the other
colours are absorbed, only yellow light will reach the eye’s retina. Therefore,
the brain will interpret the colour yellow from this information.
If a blue light shines on the yellow flower, the light will be absorbed and no
light will reflect to the eye. The flower will appear to be black.
Figure 26 White light shines on the flower, but only the colour
yellow is reflected to the eye.
Activity 11
Figure 27 When all the light is absorbed and no light reaches the
eye, the brain interprets the absence of light as black.
Explain how your brain forms an image
1. Draw a ray diagram to explain why a blue car will appear blue on a
sunny day.
2. Explain why a blue car appears black at night, inside a dark garage
when the light is not switched on.
3. A green leaf looks green in daylight.
a ) Draw a ray diagram to explain why the leaf appears green in
daylight.
b ) Draw a ray diagram and explain why a green leaf will appear black
in blue light.
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How do we see colours that are not part of the visible
light spectrum?
From the explanation of of how we see colours, it is clear why a blue car
looks blue to us, but what about other colours, like pink, brown, beige and
so on? Do each of these colours also have a unique frequency?
Pink (and all the other colours that
are not part of the seven colours
that make up the spectrum of light)
cannot be represented by a wave
with a specific image. These colours
form when different combinations of
the seven colours that make up the
spectrum reaches the eye. When white
light shines on an object that is able to
absorb green, but reflect all the other
colours, all the colours except green,
will shine on the retina. The brain is
programmed to interpret the presence
of all the colours, except green, as
pink. You can see this in Figure 28.
Figure 28 How the brain interprets the colour pink
The eye is also able to see different
shades of pink. If more blue light and
less yellow light shines on the retina, the brain will interpret a darker shade
of pink. If less blue light and more yellow light shines on the retina, the brain
will interpret a lighter shade of pink.
All images that you see are the result of electrical nerve impulses that sends
messages to your brain. In Unit 4, you learnt that if a mixture of all the
frequencies of light enters your eye, you see white. If no light enters the your
eye, you see black.
Now you understand that this happens because your brain interprets the
frequencies and combinations of frequencies of light in different ways.
Figure 29 When all the colours shine on the retina, the brain
interprets white.
Figure 30 When no light is reflected from a surface of an object,
and the object is not luminous, the brain interprets black.
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The image formed on the retina is actually upside down
In Unit 1, you learnt about the pinhole camera and drew a ray diagram to
explain how the image on the screen of the camera formed. Remember that
the image formed was upside down.
The same thing happens in the eye:
Figure 31 Light from an object travels to the eye and forms an
upside-down image on the retina.
All images that form on the retina are upside down, but when the
information is sent through the optic nerve to the brain, the brain not only
processes the colours and shapes from the information, it also has the ability
to turn these images the right way up.
Activity 12 Explain how the brain forms an image
1. Explain why the image that forms on our retina is not a true image of
what is in front of us.
2. Many colours do not really exist and are made up or imagined by the
brain. Do you agree with this statement? Explain your answer.
3. Now try this:
a) Use an A4-sized piece of paper and roll it into a tube.
b) With one hand, put one end of the tube against your eye. Close
your other eye.
c) Look at something that is about 3 m away for about 10 seconds.
d) Put your other hand about 10 cm away from the closed eye, next to
the tube.
e) Open the eye that was closed. Do you see the hole in your hand?
The apparent ‘hole’ in your hand is a visual illusion. A visual illusion forms
in your brain when the image that you are looking at is presented in such a
way that some information does not go through to the brain. Therefore, the
brain does not have enough information to interpret exactly what the eye is
seeing, and processes the image incorrectly.
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It appears that when light travels from air to glass, the light beam refracts
(bends) towards the normal:
incident ray
normal
light bends towards
the normal due to
refraction
normal
if no refraction occurs, light will continue
along this path
refracted ray
Figure 32 Light is refracted when it enters a rectangular prism.
When light leaves the prism and continues to travel through the air,
refraction occurs again. This time the light beam refracts away from the
normal:
incident ray
normal
light bends towards
the normal due to
refraction
normal
refracted ray
if no refraction occurs at the 2nd surface,
light will continue along this path
Figure 33 Light is refracted when it leaves a rectangular prism.
Key concepts
Objects around us reflect or radiate light with different frequencies that
enter the eye.
Specialised receptor cells in the eye’s retina react to specific frequencies or
colours.
In the eye, light energy is converted to electrical nerve impulses.
Impulses travel to the brain and the brain interprets them as that what
we see.
When all light is absorbed by objects and no light reflects and reaches the
eye, the brain forms a black image.
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Unit
7
Refraction of light
In Unit 2, you learnt that when light travels from one transparent material to
another, it refracts (bends). You have also learnt the scientific terminology
used for light, and have learnt how to draw ray diagrams. In this unit, you
will draw advanced ray diagrams that explain the refraction of light.
Activity 13
Demonstrate the change in direction of a light ray
(beam) through a parallel-sided prism
You will need: torch and a piece of cardboard with a thin slit cut into it, or a
laser pointer • rectangular glass prism • large piece of white
paper • 3 pencils (red, blue and green) • ruler
Method
1. Place the rectangular glass prism on the large piece of white paper that
is on a flat surface, such as a table.
2. The light from the light source needs to be at the same level as the
prism, as light needs to shine on the side of the prism. You may have to
hold the light source, or put it on a chair or another table that will allow
the light beam to line up with the side of the prism.
3. Draw the path that the light beam will follow on the paper. Use a ruler
to do this.
4. Turn the prism approximately 30 degrees, so that the side facing the
light source is not perpendicular to the light beam.
5. Use the red pencil to draw the outline of the prism on the white paper.
6. Switch on the light source. Use a ruler to draw the path taken by the
light beam as it leaves the prism (also with the red pencil).
7. Remove the prism from the paper and draw a line to connect the two
beam paths.
8. Repeat steps 5 to 7 twice, but turn the prism more each time. Use the
blue and green pencils to represent the prism and beam paths on the
paper.
9. In each case, what do you notice about the directions of the beam paths
moving to and from the prism?
10. In each case, what do you notice about the angle of the line that you
drew to connect the two beam paths?
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Activity 14
Predict the refraction of light
1. Complete the ray diagram for the refraction of light in a rectangular
prism:
Figure 34 Light is refracted in a rectangular prism.
2. A pencil appears to be bent if it is placed in water. This is shown in
Figure 35. Redraw the pencil in the water and draw a ray diagram to
show how the light that reflects from the pencil will be refracted in the
water.
Figure 35 The pencil appears to be bent when it
is placed in water.
Refraction of light through a triangular prism
In Unit 2, we discovered that when white light enters a triangular prism, it
disperses the light into the seven colours of the rainbow. Different colours of
light will refract with different angles. Red light will refract the least and blue
light will refract the most. To simplify matters, we will use a laser light source
instead of white light, as laser light has a single frequency.
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Key words
• tangent – straight
line that does not
cross a curve, but
only touches the
curve at a single
point
• convex – outward
curve
Light enters the prism at an angle to the normal and is refracted towards the
normal.
normal
If there is no refraction,
light will continue
along this path.
incident ray
• concave – inward
curve
Figure 36 The refraction of light as it enters a triangular prism
On the second surface of the prism, the light is refracted again. But, the
normal of the second side of the prism is not parallel to the normal of the
first surface (as was the case with the rectangular prism). This is why the light
changes direction completely. Light travels from glass to air and is therefore
refracted away from the normal.
normal
normal
If no refraction occurs
at the 2nd surface,
light will continue
along this path.
incident ray
refracted ray
When passing from glass
to air the light ray refracts
away from the normal.
Figure 37 The refraction of light as it enters and leaves a triangular prism
Activity 15
Draw a ray diagram of white light passing
through a triangular prism
1. How would the ray diagrams for refraction through a triangular prism
for blue light differ from the ray diagrams for red light?
2. Draw a triangular prism and show how each colour that makes up the
white light is refracted in order to obtain a colour spectrum.
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Refraction through a lens
When light travels from air to glass, it refracts towards the normal. In the case
of a curved surface, as in Figure 38, the normal will be perpendicular to the
tangent on the surface.
Look at Figure 38. You can see that, as the parallel light rays enter and leave
the lens, they refract to eventually focus at a specific point.
Figure 38 The refraction of light in a lens
In Figure 39, the rays are focused on a specific point because the lens is
convex (in other words, it curves outwards).
Figure 39 Light rays are refracted by the lens and are
focused on a single point.
Some lenses curve inwards. These are called concave lenses. Using your
knowledge of refraction in lenses from above, how do you think a concave
lens will affect the incident light rays?
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Unit X (continued)
Activity 16 Draw a ray diagram to show refraction of light
through a lens
1. Complete the following ray diagram and show refraction when the light
rays enter and leave the lens.
Figure 40 Light rays strike a concave lens.
Refraction of light around us
Amongst other things, lenses are used in practice to focus or ‘bend’ light, to
enlarge images or to correct eyesight. Lenses are also used in a number of
other applications, such as telescopes, cameras and microscopes.
Key concepts
Light can be refracted by transparent substances.
Light changes direction when it is refracted.
When light travels from air to another transparent medium, the light
changes direction towards the normal in that medium.
When light leaves the transparent medium, it changes direction away from
the normal.
A triangular prism is able to refract and disperse white light into the
colours that are seen in a rainbow.
A lens is able to refract and focus light.
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More resources
Careers in optics
Research in optics
Optics is the branch of physics that involves the
behaviours and properties of light.
A great volume of information is known about the
uses and characteristics of light, but as we continue to
explore the universe, or the behaviour of atoms and
electrons, more information about light is discovered.
This leads to more applications and uses of light, which
creates new opportunities for careers relating to light
and optics. One example of a special type of light that
was discovered is lasers. Lasers are used in medical and
scientific research. Lasers are also used as a tool for
cutting and welding.
Figure 41 A
scientist doin
g research w
ith lasers.
Optical fibre is another example of an important discovery
relating to light. Optical fibres act as a pathway for light,
allowing it to travel around corners. It can also carry
information, which is why telecommunications companies
today use fibre-optic communication to transmit data.
The discovery of optical fibre opened up careers in the
transmission of information and engineering (design of
fibre-optic sensors).
lot
Figure 42 A
s.
optical fibre
s
chnology use
of modern te
None of these applications would be possible if there were
no physicists who do research at universities and leading
companies. A developing world needs informed and
creative students that understand the physics and are able
to come up with new ways of using it to make life easier
and more fun.
Optometrists
Apart from the possibilities in research, there are other
career opportunities that specialise in knowledge of
light. Optometrists specialise in the function and care of
eyesight. They help treat eye diseases and improve the
eyesight of their patients.
Figure 43 O
ptometrists
specialise in
and the trea
eyesight
tment of eye
disorders.
More resources: Careers in optics
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Topic 10 revision
Science language practice
1. Provide definitions for each of the following terms:
a ) Luminous
b ) Wavelength
c ) Frequency
d ) Refraction
e ) Reflection
f ) Transparent
g ) Opaque
2. Give one word to describe the following:
a ) The part of the eye where an image is formed
b ) Light bends when it travels from one material to another
Test yourself
1. Name all the colours in the visible spectrum of light in order of
decreasing wavelength.
(3)
2. Draw a ray diagram to show how a triangular prism is used to
create a spectrum of visible light.
(3)
3. Why is it not possible to write down the frequency of white light? (2)
4. Explain the difference between refraction and dispersion.
(4)
5. Why does green paper with white spots appear to be black with
blue spots when you look at it through a piece of blue cellophane? (4)
6. Explain, with the aid of a ray diagram, why it is possible to see an
image of yourself on a polished table.
(3)
7. Complete the ray diagram in Figure 44.
Show the normal on the surface where
the light ray travels from glass to air.
(3)
8. Given the terms, reflection, refraction and
absorption, choose the term that best
explains the following:
a ) A computer screen that is switched
off is black.
b ) The thick walls of the fish tanks at the
aquarium make fish appear to be
bigger than they really are.
c ) Printing paper looks white.
Figure 44 Incomplete ray diagram
(3)
Total: 25
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Term 3 Practice test
1. Multiple choice:
Four options are provided as possible answers to the following questions. Each question has only
ONE correct answer. Select the correct answer and write only the letter (A–D) next to the question
number ((a)–(c)).
?
a ) The resistant wire inside a light bulb that glows to produce light is called a
A conducting wire
B filament
C resistor
D magnetic field
(1)
b ) The number of waves that move past a certain point in one second is referred to
of the wave.
as the
A wavelength
B dispersion
C speed
D frequency
(1)
c ) Why is it better to drive a white or silver car in a hot climate?
A White and silver cars radiate light and heat better than cars of other colours.
B White and silver cars refract light and heat better than cars of other colours.
C White and silver cars reflect light and heat better than cars of other colours.
D White and silver cars absorb light and heat better than cars of other colours.
(1)
2. Give the correct scientific term for:
a) the build-up of electrical charges on the surface of a material
(1)
b) an imaginary line on a reflective surface that forms an angle of 90˚ to the surface.
(1)
3. Match the terms in Column A with their correct meaning in Column B. Write only the
correct number (1–5) next to the letter ((a)–(e)).
(5)
Column A
Column B
a) A device that opposes the flow of electrical current
1. Electric spark
b) The result of the sudden electrical discharge of static
electricity
c) The process in which light moves away from its origin
2. Refraction
d) The ability of a wave to change direction when it passes
from one medium to another
e) A material that allows electrical current to pass through it
3. Resistor
4. Conductor
5. Radiation
4. State the three laws of reflection of light.
(6)
Term 3 Practice test
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Term 3 Practice test
5. Differentiate between:
a ) a parallel circuit and a series circuit. Use the example of two light bulbs, and draw
sketches to illustrate your answer.
b ) the angle of incidence and the angle of reflection.
6. Look at the diagram below and answer the questions that follow.
a ) Is it possible for the light bulb to glow?
b ) Give the correct term to describe the circuit in the diagram.
c ) Explain what is meant by the term given in question 6 (b).
d ) Give one possible negative effect of such a circuit.
e ) Explain how this problem can be avoided in the case of the electrical circuits
in a house.
7. Draw and label the apparatus that is used to break down copper(II) chloride into
copper metal and chlorine gas. Also label the products formed at each of the electrodes.
(4)
(2)
(1)
(1)
(2)
(1)
(1)
(7)
Total: 35
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Term 4: Planet Earth and beyond
Topic
11
The solar system
Starting off
The universe is so big that we do not know where it
begins or ends, but scientists have found out a lot
about our region of space over the last 300 years.
We know that the Earth, the Sun and the Moon are
in a small part of space. There are also many other
objects in our part of space, such as other planets
and their moons. The Moon and Earth’s distance
from the Sun are also very important for life to exist
on Earth.
Figure 1 Earth’s orbit around the Sun and the Moon’s orbit
around the Earth
Activity 1
Revise what you know about
the Sun, the Earth and the Moon
Look at the picture in Figure 1 and answer these
questions.
1. Point to the following objects in the picture:
a) the Sun
b) the Earth
c) the Moon.
2. Put the Sun, the Moon and the Earth in order of
size from biggest to smallest.
3. Which object is closer to the Earth: the Sun or
the Moon?
4. Is the Sun a planet or a star?
5. On Earth, the Sun seems to move across the sky
during the day. Does this mean that the Sun is
moving around the Earth?
Topic 11: The solar system
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Unit
1
#
The Sun
Key words
• Sun – mediumsized star, which is
the centre of the
solar system
• star – body of hot,
glowing gases in
space that produces
its own energy
• nuclear reaction –
type of reaction in
which the nucleus
of an atom changes
its characteristics
and becomes
something else
The Sun is a star of medium size. It looks bigger and brighter than other
stars we see because it is much closer to the Earth than other stars. Even
though the Sun is an ordinary star, it is the most important star for Earth.
Without the Sun, there would be no life on Earth.
The Sun produces heat and light
Like all other stars, the Sun is a burning ball of gases. The Sun consists
mainly of hydrogen and helium gas. The atoms of hydrogen gas
continuously react with one another to form helium gas. These reactions are
called nuclear reactions and they produce vast amounts of energy in the
form of heat and light.
Heat and light from the Sun travel in all directions in space. Some of this heat
and light eventually reaches the Earth, making life possible on our planet.
H
He
helium
H
H
H
nuclear reaction
energy
hydrogen
Figure 2 Hydrogen atoms in the Sun react to produce helium atoms
and lots of heat and light.
Sun facts
• If the Sun were the size of a soccer ball, the Earth
would be the size of a pin-head.
• The Sun is about 150 million km away from the Earth.
If you travelled at 80 km/h, it would take you 214 years
to get there.
• The temperature of the Sun ranges from about
15½ million °C at its centre, to 5 500 °C at its surface.
Remember that boiling water is 100 °C!
• The Sun has been burning for 4,6 billion years and is
calculated to keep burning for at least another 5 billion
years.
• The Sun is about 333 000 times heavier than the Earth.
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Structure of the Sun
The core of the Sun is its hottest part. This is where hydrogen changes into
helium. Heat and light energy move from the core towards its outer surface
and are then released from there into space.
sunspots:
areas that appear
dark and are slightly
cooler than the rest
of the surface
solar flares:
explosions of gas on
the surface which sends
high-energy particles
into space
core:
hottest part of the
sun where nuclear
reactions take place
prominences:
loops and arcs of gas
suspended above the
Sun’s surface
Figure 3 There is a lot of activity in the core of the Sun, as well as on its surface.
Activity 2
Find out about the Sun
1. Answer the following questions.
a ) What are the main gases found in the Sun?
b ) What is responsible for the vast amounts of heat and light produced
by the Sun?
c ) Is the Sun the biggest star in the universe?
2. a ) Do research at the library or on the Internet to find out more about
solar flares, prominences, solar wind or anything else about the Sun
that interests you.
b ) Make an A3-sized poster to show your findings and display it in
class. Use writing and pictures on your poster.
Key concepts
The Sun is a medium-sized star.
Like other stars, the Sun produces large amounts of light and heat
continuously.
The energy in the Sun comes from powerful nuclear reactions during
which hydrogen gas changes into helium gas.
Safety
• Never look
directly into the
Sun because you
may permanently
damage your
eyesight.
• Too much sunlight
on your skin may
damage your skin
forever or cause
cancer.
Topic 11: The solar system
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Unit
2
Objects around the Sun
Key words
• solar system – Sun
and the planets
and other objects
that move around
the sun
• planet – rounded
body travelling
around a star in a
clear circular path
• orbit – circular
path that a body
in space follows as
it travels around
another body
• terrestrial –
relating to land
• dwarf planet –
body similar to a
planet but that
does not clear its
orbital path of
other bodies
The Sun and the objects in the region of space around it are known as the
solar system. Objects such as planets, dwarf planets, moons, asteroids, ice
and dust are found in the solar system. The Sun is at the centre of the solar
system.
Eight planets
For an object in space to be called a planet, it must:
• travel around the Sun in a regular circular path called an orbit
• be almost spherical in shape
• be able to keep its orbital path clear of other objects.
There are eight planets that orbit the Sun. They are Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus and Neptune. The planets are different sizes,
rotate on their own axis, revolve around the Sun at different speeds and
have their own orbit.
Scientists divide the eight planets into two groups:
1. Inner rocky planets: Mercury, Venus, Earth and Mars, which are all made
up of rock. They are the terrestrial planets.
2. Outer gas giants: Jupiter, Saturn, Uranus and Neptune, which are made
up mostly of gases and liquid. They are all larger than the terrestrial
planets, and are the group of planets furthest from the Sun.
Dwarf planets
A dwarf planet is a planet that is not able to keep its path clear of other
objects. Up until 2006, Pluto was counted as the ninth planet in the solar
system. But the new definition of the term ‘planet’ meant that Pluto was
reclassified as a dwarf planet. Eris, Ceres and Makemake are other examples
of dwarf planets.
Activity 3 Explore the planets of the solar system
1. Which are the terrestrial planets? Explain why they are called this.
2. What type of planets are Jupiter, Saturn, Uranus and Neptune? Why are
they called this?
3. Are the temperatures on the terrestrial planets all similar?
4. Name one similarity between any two of the eight planets.
5. Name one unique fact about each planet.
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Mercury
Venus
Earth
Mars
Mercury is the closest
planet to the Sun.
Temperatures on the
day side of the planet
reach up to 427 °C.
However, Mercury’s very
thin atmosphere cannot
retain the heat, so it is
freezing on the night
side of the planet, where
temperatures can drop to
–180 °C.
Venus has a thick
atmosphere that is
permanently covered
with clouds so that we
cannot see the surface.
The atmosphere contains
mostly carbon dioxide,
which traps the Sun’s heat,
boosting temperatures to
471 °C. This makes it too
hot for life.
Earth has a thick
atmosphere that contains
a large supply of oxygen. It
has abundant water in its
oceans, fresh water on its
surface and underground
water beneath the
surface. On average, the
temperatures range from
–40 °C to 40 °C. Because of
these conditions, Earth is
the only planet in the solar
system able to support
life.
The surface of Mars is like
a cold desert, covered
with red-orange dust and
rocks. Its temperatures
are similar to those of the
Earth’s, compared to the
temperatures of other
planets, but it is still
colder on average. These
low temperatures and
the thin atmosphere of
mostly carbon dioxide do
not allow liquid water to
remain on Mars.
Jupiter
Saturn
Uranus
Neptune
Jupiter is the biggest
planet. Because of its
distance from the Sun, it
gets very little heat and
light. This creates average
freezing temperatures
of –148 °C. Jupiter’s very
thick atmosphere consists
mainly of hydrogen and
helium. Giant storms
occur on Jupiter; one
storm was thought to
have lasted for hundreds
of years.
Like the other gas giants,
Saturn’s very thick
atmosphere is made
mostly of hydrogen and
helium. The average
temperature is –178 °C.
Saturn has the distinctive
rings around it. The rings
consist of small, solid
particles and ice crystals.
Uranus is the only
planet that spins on
its side. Uranus is the
coldest planet, with its
temperatures reaching
–216 °C. Its atmosphere
consists mainly of
hydrogen and helium,
but contains more water,
methane and ammonia
than the other gas giants.
Neptune is furthest away
from the Sun. It takes
165 years to complete
one revolution in its
orbit. It is very cold and
dark on Neptune, and
temperatures reach
–218 °C. Its atmosphere
and structure is similar to
that of Uranus.
Topic 11: The solar system
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Mercury
Earth
asteroids in asteroid belt
Venus
Mars
Jupiter
Saturn
Uranus
Neptune
Kuiper Belt
dwarf planet:
Pluto
comet
Figure 4 Objects in the solar system. The Sun is the biggest object. It is so big that it makes up about 99% of all the matter in the solar system.
Pictures of the solar system do not show the planets and their distances from the Sun correctly to scale. If they were drawn to scale, all the
objects would not be able to fit onto this page.
Sun
dwarf planet:
Makemake
dwarf planet:
Eris
Moons
Key words
A moon is a body that revolves around a planet. Moons do not have their
own source of light. They reflect light from the Sun.
A moon always moves around the same planet. Mercury and Venus have no
moon, Earth has one and Mars has two. The gas giants have many moons,
with Saturn and Jupiter having just over 60 moons each.
• moon – body that
revolves around
a planet and that
shines by reflecting
the light of the Sun
• asteroid – piece of
rock in space
Asteroids and the asteroid belt
An asteroid is one of many rocks found in space mostly between the orbits
of Mars and Jupiter. The area where asteroids are found is called the asteroid
belt. This belt is a huge area in which hundreds of thousands of rock pieces
race around the Sun.
Asteroids are made of a material that is similar to the material of the
terrestrial planets, but they are too small to be called planets. Asteroids have
iron cores, just like the core of the Earth.
• meteoroid – small
piece of rock in
space, smaller than
an asteroid
• meteor –
meteoroid when
it enters Earth’s
atmosphere and
burns up as it falls
• meteorite –
remains of a
meteoroid after
it crashes onto
Earth’s surface
Figure 5 Most asteroids are smaller than 1 km in diameter, but they can have
diameters as large as 900 km.
Meteoroids, meteors and
meteorites
A meteoroid is a solid object in space that is smaller than an asteroid. Most
meteoroids come from the asteroid belt. Sometimes a meteoroid enters the
Earth’s atmosphere and starts to burn up. When this happens, it is called a
meteor, which we often call a shooting star. Sometimes meteors crash into
the ground before burning up completely. These remains are then called
meteorites.
Figure 6 A meteor, or
shooting star
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Key words
• comet – icy
body that releases
gases and dust
when it gets close
to the Sun
• gravity – object’s
natural force that
pulls other objects
towards itself
• Kuiper Belt –
broad region
between Mars
and Jupiter also
containing millions
of asteroids
Comets
A comet is a body made of frozen gases and bits of rock. It comes from
beyond the furthest planets. Comets enter the solar system, travel around
the Sun and then leave the solar system again.
Comets have three distinct parts: a head, an outer circle of light called the
coma, and a tail. The tail of a comet can be up to 10 million km long and it
always points away from the Sun. The head of a comet contains lumps of
rock that are bound together by ice. As the head approaches the Sun, the
ice melts and releases gases and dust. This creates a bright ring of gas and
dust around the head, as well as a very long, bright tail. Every time a comet
passes the Sun, it loses millions of tons of ice, until eventually it is nothing
more than a trail of dust.
coma
head
tail
Figure 7 Halley’s comet passes by Earth every 75 or 76 years. The next time it is due to pass
by is in 2061.
Shape of the solar system and gravity
The solar system looks like a flat disc. The Sun spins at the centre and all the
objects orbit around it in the same direction.
The planets and all the other objects in the solar system are held in their
orbits by gravity. Gravity is the natural force of every object that attracts
other objects to itself. The more mass an object has, the stronger its
gravitational pull. The closer two objects are to each other, the stronger the
gravitational pull between them.
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Neptune
Mercury
Earth
Venus
Mars
Jupiter
Uranus
Saturn
Figure 8 The forces of gravity in the solar system balance in a way that keeps the objects in their
predictable, stable orbits.
Of all the bodies in the solar system, the Sun has the most mass and
therefore the strongest force of gravity. This is why the planets and other
objects in the solar system revolve around the Sun.
Kuiper Belt and Oort Cloud
Outside the solar system, beyond Neptune, is a ring of icy and rocky objects
known as the Kuiper Belt. Scientists think that there may be billions of icy
Kuiper Belt objects.
The Oort Cloud is thought to be even further away than the Kuiper Belt.
It is believed that the Oort Cloud consists of lumps of dust and gases, is
spherical in shape and surrounds the solar system. Scientists think that the
comets that occasionally enter the solar system and orbit the Sun come
from the icy Oort Cloud and Kuiper Belt.
Oort Cloud
solar system
Kuiper Belt
Figure 9 The existence of the Oort Cloud,
where comets are thought to develop,
was proposed by Dutch astronomer Jan
Oort in 1950.
Topic 11: The solar system
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Activity 4
Construct a model of the solar system on the
school grounds
You will need: an area on the school grounds that covers a distance of
600 m • cardboard • paint • paintbrushes • compasses • rulers • scissors
• measuring tape or metre sticks • wool or string • drawing pin • sticks
• sticky tape • marker pens
1. Work in nine groups. Each group will make either the Sun or one of the
planets on cardboard circles.
a ) Use the measurements in Table 1 on page 201 to draw a circle on
cardboard that represents the Sun or your planet.
b ) Cut out the Sun or your planet and paint it or use coloured paper to
show its colour and texture.
c ) Label the Sun or the planet using a thick marker.
d ) Stick the Sun or planet onto a stick using some glue or sticky tape,
as shown in Figure 10. You will push the stick into the ground later.
cardboard circle
sticky
tape
stick
Figure 10 Use cardboard circles
to represent the Sun and planets.
Note: It is not possible to make a
scale model of the solar system in
the exact proportions. Therefore
we use approximate values to
make a scale model.
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Table 1 Sizes and distances from the Sun for planet models
Sun or planet Radius for the model
(mm)*
Sun
695
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
2,5
6,0
6,5
3,5
71,5
60,5
25,5
25,0
Sun
Distance for the model
(m)**
7,5
13,5
19,0
26,5
97,5
179,5
360,0
562,5
Mercury
Venus
Earth
Mars
* About 1 billion times smaller than the actual radii
** About 8 billion times smaller than the actual distances
2. Follow these instructions to put your solar system together:
a ) Push the stick with the Sun into the ground at one end of the area
you chose in your school.
b ) Use a measuring tape or a metre stick to measure the distance
from the Sun for each planet. (Use the metre distances in the
table above.) Then push the stick of each cardboard planet into
the ground at the correct spot.
3. Answer the following questions about the scale model.
a ) Which planet is more or less the same size as the Earth?
b ) How many Earths can fit across the diameter of Saturn?
c ) If the distance from the Earth to the Sun was 1 unit, approximately how
many units would the distance be from Jupiter to the Sun, and from
Neptune to the Sun?
Key concepts
Jupiter
Saturn
Uranus
Neptune
A variety of objects surround the Sun, including eight planets and their
moons, dwarf planets, asteroids, and icy objects in the Kuiper Belt and
Oort Cloud.
Figure 11 Model of the solar
system
All the objects in the solar system have their own special features.
The solar system looks like a flat disc.
The Sun rotates at the centre of the solar system and all other objects orbit
around it in the same direction.
Gravity keeps all the objects in the solar system in their stable orbits
around the Sun.
Topic 11: The solar system
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Practical task
Interpret facts about the solar system and write about the
planets
Part A: Interpret facts about the solar system
Look at Tables 2 to 4 about the solar system and answer the following questions:
1. Order the eight planets from smallest to biggest.
(4)
2. Which two planets have the most number of known moons?
(1)
3. Order the eight planets from those with the coldest temperatures to those with the hottest
temperatures.
(4)
4. a ) Name a planet whose day is shorter than that of the Earth’s.
(1)
b) Name a planet whose year is shorter than that of the Earth’s.
(1)
5. Which two places do scientists think comets come from?
(2)
6. Which of the planets and dwarf planets listed takes the longest to complete one revolution? (1)
7. Is it true that Saturn is the only planet with rings of rock and ice around it? Explain your
answer.
(2)
8. A group of friends are walking home one night and happen to look up at the sky. Answer
the following questions and explain each answer.
a) Pedro points to a light in the sky and says it is Venus. Could he be right?
(2)
b) They see a light flash across the sky. Maryam says it is an asteroid. Could she be right? (2)
20
Total (Part A): __
= 10
2
Table 2 The eight planets
Planet Diameter Distance No. of Composition Surface
Rotation Revolution Rings Visible
(km)
from
known rock/gas/ice temperature (One
(One year)
without a
Sun
moons
(°C)
day)
telescope?
(millions
of km)
202
Mercury
4 880
58
0
Rocky
–180 to 427
59 days
88 days
No
Yes
Venus
12 100
108
0
Rocky
471
243 days 225 days
No
Yes
Earth
12 756
150
1
Rocky
–88 to 58
23 h 56
min
365 days
No
Yes
Mars
6 794
228
2
Rocky
–87 to –5
24 h 31
min
687 days
No
Yes
Jupiter
143 200
778
63
Gas
–148 (average) 9 h 55
min
12 years
Yes
Yes
Saturn
120 000
1 427
63
Gas
–178 (average) 10 h 42
min
29 years
Yes
Yes
Uranus
51 800
2 871
27
Gas
–216 (average) 17 h 12
min
84 years
Yes
No
Neptune 49 528
4 498
13
Gas
–214
(average)
165 years
Yes
No
16 h 6
min
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Table 3 Two dwarf planets
Dwarf Dia- Distance Number Compo- Surface
planet meter from Sun of known sition
temperature
(km) (millions moons
rock/gas/ (°C)
of km)
ice
Rotation Revolution Rings Visible
(One day) (One year)
without
a telescope?
Pluto
2 300
4 400
3
Icy/rocky
–229
6,4 days
248 years
No
No
Ceres
950
446
0
Rocky
–73
9 hours
4,6 years
No
No
Table 4 Asteroids and comets
Other solar
system
objects
Location
Size
(diameter)
Asteroid
Mostly in
asteroid belt
between the
orbits of Mars
and Jupiter
Come from
the Kuiper
Belt or Oort
Cloud
100 m to under Rocky
1 000 km
No
Size changes Ammonia ice,
depending on dry ice, water,
dirt and rocks
closeness to
the Sun
Sometimes
Comet
Composition Visible
without a
telescope?
Note: A planet’s day is the time it takes to spin around on its own axis.
A planet’s year is the time it takes to orbit the Sun.
Part B: Compare and write about the planets
Use information from this topic, as well as from other sources such as the
library or the Internet, to complete this part of the task.
Write a report about the features of, and conditions on, the other planets
in the solar system. Your report should:
• have a cover and be four to five pages long
(1)
• include at least five facts about the conditions on, and features of,
each planet
(40)
• include, for every planet, at least one comparison with any other
planet/s, for example what is similar or different about the planets’
atmospheres, compositions or features
(8)
• include a picture of each planet, with captions
(8)
• be laid out clearly and logically.
(3)
60
= 20
Total (Part B): __
3
Total (Part A + Part B): 30 × __23 = 20
Practical task: Interpret facts about the solar system and write about the planets
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Unit
3
Earth’s position in the solar system
The Earth is the third planet from the Sun. As far as we know, the Earth is the
only planet that can support life.
Temperatures on Earth
Distance from the Sun is the most important factor affecting a planet’s
temperature range, although there are other factors, such as a planet’s
atmosphere.
Scientists say that the Earth is the perfect distance away from the Sun to
allow life on Earth. If the Earth was closer to the Sun, it would be too hot for
life; if the Earth was further away from the Sun, it would be an icy world too
cold for life. The Earth’s average temperature ranges between –40 °C and
40 °C. The graph shows how distance from the Sun affects temperatures on
planets.
Temperature (˚C)
500
100
0
Mercury
Venus
Earth
water boils
water freezes
Mars
Jupiter
Saturn
Neptune
–200
Uranus
Distance from Sun
Figure 12 The further away from the Sun, the lower the temperatures on the planets. Venus is an
exception, as its atmosphere plays a role in its temperature being higher than that of Mercury.
Sunlight and the food chain
The energy produced in the Sun is sent out in all directions in space as heat
and light. Some of this heat and light eventually reaches the Earth. It is this
energy that enables life to exist on Earth. For example:
• Sunlight is necessary for plants to produce food.
• Animals and people in turn depend on plants for food and oxygen.
• Sunlight also heats up parts of the Earth and creates winds and rain that
are necessary for life.
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Sun produces
heat and light
energy
plants use Sun’s energy
Plants use sunlight to make
food and oxygen. This process is
called photosynthesis. The food
is energy for the plant. It stores
the food and uses it to grow.
stored energy passed to animals
Animals eat plants. Energy
stored in plants is passed on
to these animals. Energy that
the animal does not use is
stored in its body.
stored energy passed to other animals and people
Animals and people eat other
animals. Energy stored in the
bodies of animals is passed on
to other animals and people.
Figure 13 The Sun is the source of energy for Earth and all life on it.
Figure 13 shows how the Sun is the source of energy in the food chain.
Activity 5
Explain how the food chain depends on sunlight
Look at Figure 13.
1. How do plants use light energy from the Sun?
2. How do animals use energy from the Sun?
3. Do you agree that the Sun’s energy changes into different forms on
Earth? Explain your answer.
4. Explain the following statement: ‘Without sunlight, there would be no
plant and animal life on Earth.’
Topic 11: The solar system
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Unit X (continued)
Water on Earth
In Earth’s temperature range, water can exist in all its three states as follows:
• Liquid – in oceans, lakes, rivers, swamps and under the ground.
• Gas – as water vapour in the air.
• Solid – frozen as ice in the ice caps of the Arctic and Antarctic.
Water constantly changes between these states in the water cycle. The
water cycle ensures that the amount of water on Earth stays more or less
the same, and that there is fresh water available. The movement of water
through its different states in the water cycle is shown in Figure 14.
other gases 1%
oxygen
21%
nitrogen
78%
Figure 15 Oxygen makes up
21% of the gases in Earth’s
atmosphere.
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Figure 14 Water changes into gas, liquid and solid states in the water cycle.
Oxygen
About 21% of the Earth’s atmosphere contains oxygen. Oxygen is essential
for life on Earth because it is needed in breathing processes and to release
energy in the cells of most living organisms.
Scientists believe that the amount of oxygen in the atmosphere today
was not available when life first started forming on Earth. Early simple life
forms, such as certain kinds of bacteria known as blue-green algae, were
most likely the first to start producing oxygen. As oxygen became available,
this allowed more and more complex life forms to evolve. Today, oxygen is
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produced by photosynthesis in green plants. This is what keeps the high
oxygen levels in the atmosphere.
sunlight
oxygen (O 2 )
carbon dioxide
(CO 2 )
water (H 2O)
CO2+ H2O
sugars + O 2
Figure 16 Plants produce oxygen as a
by-product of photosynthesis. In this way,
they maintain the level of oxygen in the
atmosphere.
Activity 6
Write about why the conditions on Earth are ideal
for life
1. Write a one-page report on the conditions on Earth that make this planet
ideal for life. Use the information in this topic and other sources, such as
the library or Internet to do this task.
Key concepts
Earth is the third planet from the Sun.
Earth is the only planet known to support life.
Earth’s distance from the Sun provides the ideal temperature range.
Water is a liquid, gas or solid in Earth’s temperature range.
Sunlight provides the energy for the food chain.
Oxygen is available for life processes.
Early life forms and algae produced enough oxygen for the evolution of
more sophisticated life forms.
Topic 11: The solar system
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Topic 11 revision
Science language practice
1. Match the terms in Column A with their correct meaning in Column B.
Write only the correct number (1–6) next to the letter ((a)–(f )).
Column A
Column B
a) Sun
1. The circular path that a body in space follows as it travels
around another body
2. A piece of rock in space
3. A body of hot, glowing gases in the centre of the solar system,
which produces energy through nuclear reactions
4. An object’s natural force that pulls other objects towards itself
5. An icy body that releases gases and dust when it gets close to
the Sun
6. A rounded body travelling around a star in a clear circular path
b) Planet
c) Gravity
d) Comet
e) Asteroid
f ) Orbit
Test yourself
1. Place the following in order from biggest to smallest:
asteroid
2.
3.
4.
5.
Jupiter
solar system
(5)
Sun
Earth
Which star is the centre of the solar system?
(1)
Name the eight planets in order from the Sun.
(8)
What is the difference between an asteroid and a comet?
(4)
Figure 17 shows the solar system. Write labels for the parts labelled
A to G.
(7)
F
B
A
G
C
D
Sun
E
Figure 17 The solar system
6. Give two reasons why the Sun is important for life on Earth.
7. Write a paragraph to explain why Earth has the ideal conditions
for life to exist.
(2)
(3)
Total: 30
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Term 4: Planet Earth and beyond
Topic
12
Beyond the solar system
Starting off
Sextans B
Sextans A
NGC
3109
Leo A
Antlia
dwarf
Leo II
Leo I
Canes
Dwarf
Milky
Way
NGC
6822
NGC NGC
185 147
M110
IC 10
Andromeda
Galaxy
Triangulum
Galaxy
Andromeda
Pheonix
II, II and III
Dwarf
Pegasus
IC
Cetus
Dwarf
Tucana
Dwarf 1613
Dwarf
LGS3
WLM
Aquarius
SagDIG Dwarf
Figure 1 Galaxies and star groups in the universe within
5 million light-years
The universe consists of millions of galaxies
of which the Milky Way Galaxy is one. Within
each galaxy there are numerous solar systems.
Our solar system is in the Milky Way galaxy.
Sometimes stars are grouped together and
named, for example Scorpius and Musca. These
are called constellations.
Activity 1
Demonstrate your
understanding of the
universe
1. Draw a simple sketch with captions, to
show your understanding of the universe,
galaxies, solar systems and the Milky Way.
Draw the outline of the universe with a
broken line to indicate that it is expanding.
Show at least two galaxies and two solar
systems, each with two planets and two
moons.
2. Compare your image with one or two
friends in a group and then make a final
group drawing.
3. Prepare to present and explain your picture
to the class.
Topic 12: Beyond the solar system
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Unit
1
The Milky Way galaxy
Key words
• constellation –
grouping of
stars with a
specific name,
for example,
Southern Cross,
Scorpius and
Sagittarius
• galaxy – collection
of stars held
together by their
mutual gravity
Our solar system in the Milky Way galaxy
Copernicus was the person who brought about a much greater
understanding of our solar system. Later, the invention of the telescope
allowed astronomers to discover new planets. Today we have scientific
instruments and spacecraft that allow us to get more close-up views and to
expand our knowledge.
Look at Figure 4 on page 196. In our solar system, Earth is one of eight
planets orbiting the Sun (which is a middle-aged star). Meteors, asteroids
and comets, moons and a lot of ‘leftovers’, including bits of dust, gas, balls
of ice and rock, and debris from disintegrating solar bodies, also form part
of this solar system which is situated about 27 000 light-years away from
the centre of the Milky Way galaxy. Billions of these leftovers are found in
the Kuiper Belt, as well as outside Neptune’s orbit. Some of these leftovers
stayed in orbit in the solar system but others were thrown clear of the solar
system by gravitational encounters with the planet Jupiter. When the orbit
of some of these bodies is disturbed, they fall towards the Sun, where they
become comets with long glowing tails.
A galaxy is a collection of stars
Stars in the universe are mostly found in groups of millions or trillions of
all shapes and sizes, held together by their mutual gravity. Astronomers
found that many of them are spiral-shaped, some are spherical, and some
have irregular shapes. These dense groups of stars are called galaxies. Some
of these galaxies produce new stars, others are living out their lifespan,
while some merge to form even bigger galaxies, sometimes called ‘cities of
stars’. One theory of how galaxies are formed is that small lumps of matter
clump together to form spiral-shaped galaxies. Over time, smaller ones
are consumed by bigger ones which merge together to form even larger
galaxies, called ellipticals. Stars then wrap around the heart of the galaxy in
all directions, looking more like a sphere than a spiral. Some of the smaller
galaxies group together to form dwarf galaxies.
Galaxies contain large quantities of dark matter which does not produce
light but reveals its presence through the gravitational pull it has on the
visible stars and gas. It seems 90% of the Milky Way consists of dark matter,
which forms a halo around the galaxy and extends thousands of light years
into space.
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Our Sun’s location in the spiral-shaped
Milky Way galaxy
Key word
The Milky Way galaxy consists
of a thick bulge of stars in
the middle with four bright
spiral arms, and from above it
looks like a flat disc. Our Sun is
located towards the edge of the
Milky Way galaxy in one of the
spiral arms. The spiral is about
100 000 light years in diameter
and about 2 000 light years
thick, consisting of hundreds of Figure 2 The Milky Way as we see it from Earth,
thousands of stars, all orbiting
a black hole surrounded by stars.
the centre of the disc. On a clear
night the hazy band of light, which is the combined glow of the millions of
stars, can be seen clearly in the night sky. To the ancient Greeks it looked like
spilled milk across the sky.
• black hole –
infinite mass
of nothingness
with immensely
powerful gravity;
able to suck up
everything in its
way
Did you know?
One light year = ten
trillion kilometres =
10 + 12 zeros =
10 000 000 000 000
New inventions over the years such as radio and infrared astronomy, have
provided us with clearer information. These are both forms of energy with
longer wavelengths that pass through the dust, consisting of elements like
silicon, carbon and iron particles from surrounding planets, much more
easily, to reach radio and infrared telescopes on Earth. Radio astronomy
was also the key to a better understanding of the disc of the Milky Way.
They found that everything in the galaxy orbits the centre of the disc.
Objects nearer the centre orbit faster than objects farther out. By measuring
these movements astronomers gained more insight into the structure
and outward expansion of the disc inside the galaxy and eventually the
everlasting expansion of the universe.
Activity 2
Demonstrating the shape of the Milky Way galaxy
with a spiral shape
You will need: medium-sized bucket (or bowl, or mug), 75% filled with
water • milk frother (little battery-operating machine) • little bottle of
food colouring or anything that would colour the water
1. Fill three-quarters of the container with water.
2. Put the milk frother in the water and switch it on. The water will start
swirling (spiralling).
3. Drop a few drops of the colouring in the middle of the water.
4. Explain what you see happening inside the bucket. Look specifically at
the speed of the swirling in the middle of the bowl (mug) and towards
the edge of the bowl.
Safety
Be careful with the
food colouring as it
stains badly – keep
it away from your
clothes.
Topic 12: Beyond the solar system
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Sun
Figure 3 The heart of the
Milky Way – a flat, disc-shaped
object that looks like a
pinwheel
For many years, astronomers such as William Herschel thought that our
Sun (solar system) was at the centre of the Milky Way galaxy. His view and
research was obscured by the hazy dust, as well as other objects which were
released into space. Radio and infrared technology assisted us so that we
now know that our Sun is actually situated 27 000 light years away from the
centre of the Milky Way in one of its spiral arms. We also know that the Milky
Way consists of 200 to 400 billion stars, with a black hole four million times
the size of the Sun in the middle. The black hole is surrounded by giant stars,
clouds of dust and magnetic fields.
Activity 3
Drawing to show the position of our solar system in
the Milky Way
You will need: A4 or A3 paper for drawing • colour crayons • sellotape or
prestik to put pictures up on the wall
1. Make a rough sketch of a spiral galaxy – use the examples in your book
as reference.
2. Include at least four spiral arms and clearly indicate the black hole in the
middle and the billions of stars surrounding it.
3. Indicate the position of our Sun (solar system) towards the edge of the
spiral on one of the arms.
4. When complete, put your picture on the wall and prepare to tell the
class at least three important facts about your picture.
Activity 4
Compare features of a galaxy and a solar system
Read the information given in Unit 1. Draw two columns and compare a
galaxy and a solar system in terms of the following:
1. Location/position in the universe
2. Three important components of each
3. Size
4. Movement
5. One outstanding feature of each
Key concepts
A galaxy is a dense collection of stars, held together by strong gravitational
forces.
Our solar system is in the Milky Way galaxy.
The Milky Way is a spiral-shaped galaxy.
Our Sun is located in the Milky Way galaxy.
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Unit
2
Our nearest star.
The Sun is the nearest star to Earth
Key words
The Sun that we see every day is our nearest star and like all stars it changes
constantly. It looks brighter than other stars because it is so close to us. The
Sun produces its own energy and when this energy is released into space, it
is in the form of visible light. The nuclear reaction happening in its core
(600 million tons of hydrogen atoms fuse to make 596 million tons of
helium) is an ongoing energy-releasing process, which will last for billions
of years before this star will die like many others in the universe.
Powerful magnetic fields encircle the Sun, forming magnetic storms called
sunspots. Sometimes these magnetic fields trigger enormous explosions
called sun flares. These sun flares and sunspots peak every 11 years when
big streamers of hot gas cause further explosions which can be seen on the
Sun’s surface.
• sunspots –
magnetic storms
on the Sun’s
surface
• sun flares –
enormous
explosions on the
Sun’s surface
Although the Sun supports all life on Earth, it is potentially dangerous and
harmful. The Earth’s atmosphere protects us only to a certain extent through
the ozone layer but as we slowly deplete this layer, through production of
carbon dioxide for example, it has become vitally important that we protect
ourselves from the harmful rays of the Sun.
Energy
from the
Sun
We use energy from
the Sun for solar
powered cooking
and heating.
Wind is caused by the Sun. The Sun
heats up the surface of the Earth.
Because the surface of the Earth
is different all over, it heats up
unevenly. The uneven heating of
the Earth's surface causes air to
move and winds to blow.
Animals and humans get
energy when they eat plants
and other animals as food.
Plants use the
Sun’s energy to
make the food
they need to grow.
We use this
energy in
wood, when
we make a fire.
Coal, petrol, gas are
formed over millions of
years from dead plant and
animal matter. We use
this energy for cooking,
heating and lighting, and
to make electricity.
The Sun keeps the water
cycle moving. The Sun's heat
causes water to evaporate.
Evaporation is an important
step in the water cycle.
Winds cause waves
and strong currents
in the seas and oceans.
Figure 4 The Sun is our main source of energy.
Topic 12: Beyond the solar system
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Alpha Centauri is the nearest visible
star to the Sun
Alpha Centauri is our closest
neighbouring star system. It is the
brighter of the two pointers of the
Southern Cross constellation and the
third brightest star visible from Earth.
It can only be seen from the southern
hemisphere and forms part of the
Centaurus constellation.
Alpha Centauri is about 4,2 light-years
away from our solar system, and consists
of three main stars, one small and faint
and the other two brighter and bigger,
about the size of our Sun.
Sun
Centauri A
Centauri B
Astronomers think that there is a
Proxima
good chance that a solar system
(sun and planets), similar to ours, might
Figure 5 A size comparison between the
be found there. So far they have found
Centauri-group and our Sun
one, circling Alpha Centauri B (also
called Hadar) every 3,2 days. It is not yet named but it is now the
closest planet outside our galaxy, circling a star (sun).
Alpha C-A
Southern Cross
Figure 6 Alpha Centauri A (marked with the arrow) and
the Southern Cross towards the east
Figure 7 Alpha Centauri A on the left and Alpha Centauri B on the
right. Proxima Centauri faintly circle south of Alpha Centauri A.
This star system can only be seen by people who live below 29 degrees
north. People living in the southern hemisphere, especially countries like
South Africa, Australia and New Zealand can see it all the time.
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Activity 5
Locating Alpha Centauri using the Southern Cross
Alpha centauri
Southern Cross
Proxima
Figure 8 Use the Southern Cross to identify Alpha Centauri A & B, and Proxima Centauri.
1. Work together with a friend that lives near you.
2. Wait for a cloudless night with clear skies.
3. Determine where south is and look for the four bright stars that form
the Southern Cross.
4. To locate the Centauri 7 system in the night sky, you must draw a line
from the west star to the east star (crossbar of the Southern Cross),
lengthen it towards the west and you will reach Alpha Centauri B
(Hadar) first and then Alpha Centauri A, with Proxima Centauri a little
speck to the south-east of Alpha Centauri A.
5. After locating it answer the following questions:
a ) Which one of the two stars are the brightest?
b ) Why do you think one is brighter than the other?
c ) Why are astronomers positive about finding a planet(s) near Alpha
Centauri?
d ) Why can people of the northern hemisphere not see the Centauri
system?
Key concepts
The nearest star to the Earth is the Sun.
The Sun supports all life on Earth.
Alpha Centauri is the closest neighbouring star system. It forms part of the
Southern Cross constellation.
Topic 12: Beyond the solar system
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Unit
3
Light years, light hours and light minutes
Activity 6
A number exercise
Do this exercise on your own first and then compare your answers with
those of a partner.
Write the following in figures e.g. one hundred = 100.
1. One thousand
2. Hundred thousand
3. One million
4. Thousand million
5. One billion
6. Nine hundred and ninety nine thousand million
7. One trillion
8. One trillion five hundred and ninety billion seven hundred and twenty
million eight hundred thousand five hundred.
Measuring distances to stars and other objects
beyond the solar system
The immense size of the universe resulted in scientists having to find different
ways of measuring distance. Modern telescopes and other techniques enable
us to look at, and get a better view of, our galaxy and other galaxies, making
us even more aware of the incredible distances involved. Our closest star
(besides the Sun), Proxima Centauri, is about 39 trillion kilometres or 3,9 light
years away. All the other solar systems, stars and galaxies are millions, and
sometimes billions, of times further than that; therefore using kilometres or
miles is impractical because the numbers are far too big.
When measuring these vast distances, we use light years, light hours and
light minutes. Even though a light year seems like a unit used for measuring
time, a light year measures distance.
A light year is the distance that light travels in one year at 300 000 km per
second, used for measuring distances such as those between galaxies. The
nearest galaxy to Earth is about 100 000 light years away and Earth is about
27 000 light years from the centre of the Milky Way.
One light hour is the distance light travels in an hour. It is used to measure
shorter distances, for example bodies in and around our solar system. Our
solar system is about 13 light hours in diameter.
Light minutes are used to measure relatively shorter distances, for example
between different planets within our solar system. Earth is about eight light
minutes from the Sun.
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0h
10ly
UV Ceti
8ly
6ly
4ly
2ly
6h
Sirius
Ross 154
18h
Barnard’s
Star
Sun
Proxima Alpha
Centauri
Wolf
369
Lalanda 21185
12h
Figure 9 The star systems within 10 light years (ly) from our Sun (solar system).
Figure 9 illustrates the incredible size of a small section of the universe. Look
at our Sun in the middle, which is part of the solar system. The Sun is
100 000 light years in diameter, and the Earth is 27 000 light years from the
centre of the solar system. Close your eyes and imagine yourself standing
on the Earth in the centre of the solar system and look outwards to the stars
within ten light years from Earth. You would only be able to see two of them
with the naked eye, Proxima Centauri and Sirius, the others are all faint red
dwarf stars. These two stars are outside our galaxy (ten light years away)
and still visible to the naked eye. There are millions of stars inside our own
galaxy, the Milky Way, which we cannot see because they are either too far
away (they could be tens of thousands of light years away – remember our
galaxy is 100 000 light years in diameter) or they are older and do not seem
to shine as clearly as Sirius because they could be dying.
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Activity 7 Getting to grips with distances in the universe
Use the following conversion table to help you answer the questions below:
Unit
Light year
Equivalent distance in km (figures rounded off)
10 000 000 000 000
ten trillion
Light hour
1080 000 000 000
Light minute
Light second
18 000 000
300 000
one billion eighty
thousand million
eighteen million
three hundred thousand
1. Calculate the distance between Alpha Centauri and the Milky Way in
kilometres.
2. The Milky Way is 2 000 light years thick, how many kilometres would
that be?
3. The spacecrafts Voyager 1 and 2 have now, after travelling 18 billion
kilometers, reached the border of our solar system. How many light
hours would that be?
4. Spacecraft Curiosity has reached Mars, the fourth planet from the Sun.
Mars is about 230 million kilometres from the Sun, how many light
minutes would that be?
5. If our solar system is 13 light hours in diameter, how many kilometres
would that be?
6. When we see the Andromeda Galaxy, also called M31, we actually see it
as it was two million years ago, can you explain this?
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Activity 8
Understanding the concept of time and distance in
the universe
1. You may have seen a film where they use a time machine that takes you
back in time.
Read the passage given below on your own. It explains something
about time and distance and going back in time.
Because a light year is directly related to the time light takes to travel
through space, it follows that we look out into the universe we also
look back in time. For example, in about the year 5 250 BCE, a star
in the constellation of Taurus exploded. That star was about 6 300
light years from the Earth, meaning that the light from the explosion
took 6 300 years to cross the intervening space, and finally reached
us in the year 1 054 CE. That was the date observers on Earth finally
saw the explosion that created the Crab Constellation. This 'lag' is a
consequence of the immense distances between the stars. When we
look up at the Crab Constellation today, we see it not as it is now, but as
it was in about 4 300 BCE.
a) Explain your understanding of the passage above to a partner.
What is the writer saying to us?
b) Between the two of you, prepare to give feedback to the class.
Key concepts
We use light years, light hours and light minutes to measure vast distances.
One light year is the distance light travels in one year; one light hour is the
distance that light travels in one hour; one light minute is the distance light
travels in one minute.
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Unit
4
Beyond the Milky Way galaxy
Key word
• mergers – action
of two or more
galaxies being
consumed into
one larger galaxy
The Milky Way galaxy is one of billions
of galaxies
In 1923 Edwin Hubble noticed
a particular type of star inside
a dense cluster of stars that he
thought was part of the Milky
Way. He later discovered that
it was not a star but another
cluster of stars, another galaxy,
outside the Milky Way. This
was the first galaxy, called City
of Stars, found outside the
Milky Way. In the decades that
followed, astronomers found
Figure 10 The Local Group is a group of 45 galaxies that
forms part of the Milky Way.
billions of other galaxies in
all shapes, sizes and colours,
scattered across the universe. About 400 of these galaxies have planets in
their orbits, some with and some without moons.
(a)
(b)
(c)
(d)
(e)
(f)
Figure 11 (a–f) Examples of different galaxies in the universe
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The Milky Way galaxy forms part of a larger group of about 45 galaxies,
called the Local Group. The Andromeda Galaxy (M31) is one of the larger
ones, about 2,5 million light years away. The size of the observable
universe is estimated to be about 28 billion light years. Compare this to the
2,5 million light years of M31 and you will realise the immense size of the
universe. Our nearest galaxy, Sagittarius, is a small one in the constellation.
Sagittarius is about 100 000 light years away, situated behind the Milky Way.
Astronomers say it will one day become part of the Milky Way, like many
other galaxies that in the past have been consumed by the Milky Way.
Galaxies have various shapes and sizes
Galaxies can be classified in many ways, but they are mostly classified by
their shapes. The most colourful galaxies are called spiral galaxies. The Milky
Way galaxy is a perfect example of such a spiral: it looks like a flat disc with a
bulge in the middle and spiral arms that wrap around it.
Galaxies tend to group together, and because of their very strong gravity,
they latch onto one another, forming bigger galaxies, sometimes as massive
as one million light years in diameter. Their shape then usually changes to
look like a sphere. Mergers can take hundreds of millions to billions of years
to complete and in the process, intense bursts of new stars and black hole
formation can take place.
Figure 12 A spiral galaxy, the Milky Way
Figure 13 A merged galaxy
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Activity 9
Identifying galaxies by their names
1. Allocate a name to each one of the list of pictures of galaxies given in Figure 14, below. Use the names
in the word box to help you.
Busy Galaxy
Tangled Galaxy
Collision Course
Bright Companions
Galactic Hat Dance
Fast Exit
(a)
(b)
(c)
(d)
(e)
(f )
Figure 14 Name the galaxies (a) to (f ).
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The immensity of the ever-expanding universe
The universe is estimated to be about 13,7 billion years old and consists of
atoms, dark matter and dark energy. Our solar system is about 4,6 billion
years old. Since the 1920s, when Edwin Hubble discovered that the universe
was constantly expanding, astronomers have been trying to estimate, as
accurately as possible, the size of the universe. Currently, the observable
size of the universe is estimated to be about 28 billion light years. In 1998,
information gathered by the Hubble Space Telescope confirmed that the
universe is expanding at an ever increasing rate. The latest interesting facts
about the universe are as follows:
1. The universe was hot when it was young (at birth) and it cools down as
it expands. Scientists believe that it started losing heat within minutes
after birth.
2. It will be cold when it grows old. Scientists also believe, after
observations made on galaxies farthest from us, that the everexpanding universe will most probably end in a ‘Big Freeze’, after
starting off with a ‘Big Bang’.
3. The age of the universe is (to a 1% precision) 13,7 billion years old. The
credit for this accuracy goes to measurements made by the WMAPteam (Wilkinson Microwave Anisotropy Probe), who gathered all the
information to be able to calculate this number.
4. A huge chunk of the universe is made up of things we cannot see.
Radio waves and visible light allows us to see far into the cosmos,
but unfortunately the larger portion cannot be seen by any of these
frequencies.
5. There is no such thing as the universe’s centre.
The Earth is not in the middle of the universe or the
galaxy, and our galaxy is not the centre of the universe.
Scientists believe that the universe has no centre, and
that all galaxies are expanding away from one another.
6. To gain a deeper understanding of the universe,
scientists find that, as they are trying to investigate
larger and larger structures, they should actually study
smaller and smaller structures – even smaller than the
atom. To achieve this, scientists have finished building
the Large Hadron Collider near Geneva in Switzerland.
This should tell us more about the origin of the
universe, starting with the smallest of particles inside
Figure 15 The Hadron Collider
an atom and expanding at an ever-increasing rate.
Key concepts
There are billions of galaxies scattered across the universe; the Milky Way is
one of them.
The Milky Way forms part of a group of galaxies known as the Local Group.
Galaxies that form part of a group will eventually merge to form one big
galaxy.
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Topic 12 revision
Science language practice
1. Match the terms in Column A with their correct meaning in Column B.
Write only the correct number (1–10) next to the letter ((a)–(j)).
Column A
Column B
a) Galaxy
1. Distance light travels in a year
b) Solar system
2. Galaxies grouping together
c) Constellation 3. A collection of stars held together by their mutual
gravity
d) Ellipticals
4. Curved course of object (e.g. planet) around the Sun
e) Spiral
5. A mysterious force causing the universe to expand faster
f ) Light year
6. Group of stars with a specific name
g) Sunspot
7. The form many galaxies take
h) Sunflare
8. A sun with planets and moons in orbit
i) Orbit
9. Magnetic storms on the Sun’s surface
j) Dark energy 10. Huge explosions on the Sun’s surface
Test yourself
Complete the following sentences using the answers in the box:
star
Pluto
spiral
Alpha
Local Group
Eris
light year
300 000 km/sec or 300 000 km/hour
nuclear
Milky Way
galaxy
1. Our solar system forms part of the galaxy called
the ______________.
2. A cluster of stars kept together by their mutual gravity is called
a ____________.
3. Our Sun is a ___________ that creates energy because of
____________ reactions taking place in its core.
4. Our ninth planet actually consists of two dwarf planets called
_________ and __________, and an asteroid, called Ceres.
5. A light year is the distance light travels at a speed of
________________ for the duration of a year.
6. The third brightest star visible from Earth is __________ Centauri
but Proxima Centauri is the nearest to Earth.
7. The Milky Way galaxy forms part of a group of 45 galaxies called
the __________.
8. Galaxies are mostly classified according to their shapes, of
which the ________ form is dominant.
(1)
(1)
(2)
(2)
(1)
(1)
(1)
(1)
Total: 10
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Term 4: Planet Earth and beyond
Topic
13
Looking into space
Starting off
Telescopes help us to observe objects many miles
away that we otherwise would not be able to
see. In this topic you will be learning about many
different types of telescopes. South Africa has some
of the world’s best telescopes. We will look at the
specific conditions that are needed for good sky
observations.
Before telescopes were invented, people’s
knowledge about the universe was limited. Some
of their observations were amazingly accurate but
some ideas they had were completely wrong. Early
civilisations gave us the idea of constellations, and
different cultures have given us different stories
about the stars.
Figure 1 A telescope
Activity 1
Discuss what you know about
the night sky
Look at Figure 1 and discuss these questions in
groups.
1. What time of day was the photograph taken?
2. Why would a telescope be used at this time
of day?
3. What part of the sky is shown?
4. What would you see in the sky without using
the telescope?
5. What might you see in the sky with the
telescope?
6. What do you think people knew, or believed,
about the night sky before telescopes were
invented?
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Unit
1
#
Early viewing of space
Key words
People see planets and stars in the night sky
• astronomy – study
of bodies in space
The night sky has been a source of fascination and wonder for people for
thousands of years. Rock-art paintings in caves in Europe show that people
observed and recorded the movements of stars and planets, even before
writing was invented.
• astronomers –
people who study
the bodies of
space
From about 5 000 years ago, early civilisations studied the heavens
with great interest. We have records from ancient Babylonian, Egyptian,
Greek and Roman civilisations. Carved stones and clay tablets from
about 1 100 BCE show that ancient people had already identified many
constellations.
The ancient Egyptians were highly advanced in their knowledge of
astronomy. Even before telescopes were invented with very simple
equipment, they made remarkably accurate calculations about the distance
from the Earth to the Sun and even the size of Earth itself. Plato and Aristotle
were amongst many who made important contributions to astronomy.
Ptolemy of Alexandria is famous for his book Almages written in 150CE.
Figure 2 Ptolemy, Greek astronomer
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Figure 3 Famous Kurdish astronomer
and mathematician, Abu Abdullah Al
Battani
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In the early civilisations, many priests were also astronomers. They believed
there was a bond between man and the universe, and that what happened in
the skies affected what happened to people. It was clear to them that the Sun
was very important to the daily lives of people, providing light and helping
crops to grow. This is why a number of cultures had a Sun god. For example,
Re was the Egyptian Sun god and the Aztecs in central Mexico had a Sun god
called Tonatiuh.
In Africa too, the Sun and the Moon played an
important role in cultural beliefs. Even today, the
Swazis hold the Ncwala festival in mid-summer (when
the Sun is at its highest), while in Malawi, ceremonies
and weddings are held when the Moon is full. In San
legend, the Moon is a man who has angered the Sun.
Every month the Sun’s knife cuts away pieces from
the Full Moon until finally only a tiny piece is left.
From this piece, the Moon gradually grows again.
Astronomy did not only develop in the Middle East.
The Chinese, Aztecs and Incas all studied the stars and
tried to predict events from what they saw.
Arranging stars into visible
constellations
Early astronomers tried to count the stars but they
soon gave up trying. It was like counting the grains of
sand on a beach. But they saw that particularly bright
stars appear to make patterns and they called these
patterns constellations.
Nowadays, the sky has been divided up into 88 areas
Figure 4 Chinese astronomer
surrounding, and including, these bright stars. They
are still called constellations. The ancient names of
constellations are still used, for example, Perseus, Centaurus and Orion.
Many, but not all, constellations can be seen from South Africa. We see
different constellations in winter and in summer.
The smallest constellation is the Southern Cross or Crux. Although it is small,
the four stars that make up this constellation are very bright, so we can
easily see it. It can also help us to not get lost because we can use it to find
the direction south.
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Table 1 Times at which constellations can be seen in the southern hemisphere
All year
Spring
Summer
Autumn
Winter
Carina
Centaurus
Southern Cross
Andromeda
Aquarius
Capricornus
Pegasus
Pisces
Canis Major
Cetus
Eridanus
Gemini
Orion
Perseus
Taurus
Bootes
Cancer
Crater
Hydra
Leo
Virgo
Aquila
Cygnus
Hercules
Lyra
Ophiuchus
Sagittarius
Scorpius
Different cultures identify and name certain
constellations
Constellations were identified by early Middle Eastern and Mediterranean
civilisations, and named after mythical heroes, gods and animals. For
example, Centaurus is half-man and half-horse, Leo is a lion and Hercules is
a hero.
Other cultures also identified and named certain constellations. The names
were often linked to a story. The Khoisan people had a story about a girl
child whose magical powers were so strong that when she looked at a
group of fierce lions, they were immediately turned into stars. These are the
three stars of Orion’s belt.
The Tswana had a different story for these stars. They called Orion’s sword
and belt ‘Dintsa le Dikolobe’. They said these were three hunting dogs
chasing three piglets.
Activity 2 Observe, record and compare the appearance of
the Southern Cross
In this activity you will need to go outside in the evening to find the
Southern Cross. Try to go when the sky is dark but when there are few
clouds. You should do this every second week across two consecutive
months.
Make two large copies of the table shown:
Date :
Time :
Date :
Cloud cover :
Cloud cover :
Darkness :
Darkness :
Changes in appearance of the Southern Cross :
228
Time :
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How to find the Southern Cross
The Southern Cross roughly forms the shape of a cross or a kite. The ‘vertical’
piece always points in the general direction of south when followed from
the top of it down to the bottom.
Face the south from a position where you can see the horizon. In winter,
slowly scan the horizon in a circle; in summer scan points higher in the sky.
Search for a group of four bright stars and one faint star that form the shape
of a kite. Depending on the time of the year, the shape they form will not
always be an upright kite. Check that the two very bright pointer stars,
Alpha Centauri and Beta Centauri, point to the top point of the Southern
Cross. If you do not see the pointer stars, you are looking at a different cross,
called the False Cross.
Beta centauri
Southern Cross
Alpha centauri
Figure 5 The Southern Cross and the pointers
Method
1. When you have found the Southern Cross, draw its position on the
semi-circle that represents the full night sky.
2. Take note of how far it is above the horizon, and the angle of the cross.
3. If it is visible, draw in the Moon.
4. Fill in the other details required.
5. When you have done all four sightings, describe the changes in
appearance and position of the Southern Cross.
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The Pleiades are a group of stars in the constellation Taurus. They disappear
for a few months over winter. The Tswana people call them ‘Selemela’, which
means ‘the digging stars’ and the Xhosa call them ‘Isilimela’. When they appear
in spring, it is time to plough and plant seeds. It is a time of new beginnings, a
time for initiation schools and ceremonies to take place. They are considered
friendly and children are taught to stretch their hands out to them.
The Sotho, Tswana and Venda have a name for the Southern Cross and
the Pointers. They are ‘Dithutlwa’. The Pointers are male giraffes and the
Southern Cross stars are female giraffes, which are seen grazing above
the trees.
The constellation Scorpius has a row of curving stars and is famous for
the bright reddish star Antares. The !Xu Bushmen called this star ‘The Firefinishing Star’. It has a reddish colour and it sets late at night, when the camp
fires have died down.
Many civilisations, from Babylonians to Zulus, believed there was a dome
stretched over Earth and the stars and other bodies moved on the surface of
this dome.
Orion’s Belt
Figure 6 Constellation of Orion, showing Orion’s Belt and
sword, which Tswana people call‘Dikolobe’
Key concepts
People have been observing planets and stars since before writing was
invented.
Ancient civilisations were advanced in their knowledge of astronomy.
The heavens played an important part in many cultures, including African
cultures.
Early astronomers arranged stars into constellations.
Different cultures have different names for constellations and different
stories about them.
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Unit
Telescopes
2
People see more when they use a telescope
Key word
It was in 1608 that a Dutch eyeglass maker discovered that, by looking
through two small lenses held in front of one another, a distant object
appeared to be much closer. He had invented the first telescope.
Just one year later, a famous Italian scientist called Galileo Galilei assembled
a telescope that made objects seem 30 times closer. When he looked at the
Moon, he was amazed at the detail he could see. For the first time he could
see craters, mountains and valleys. He also saw the four largest moons
orbiting Jupiter and he saw dark spots on the Sun.
• craters – dents or
hollows made by
rocks that crash
into planets or
moons
When Galileo looked at the Milky Way, his telescope did not seem to bring
the stars closer because they are too far away. But when he looked at the
spaces between the stars, he was very surprised to see many more stars
appear. The number of visible stars had seemed to increase a thousand
times just by the invention of the telescope.
From this time onwards, steady improvements in the quality of telescopes
have allowed astronomers to see more and more detail in space. New types
of telescopes have been invented and they have added to our knowledge of
the universe.
Activity 3
See how telescopes improve visibility
Look at the two photographs in Figure 7.
1. Count how many craters you can see on each photograph of the Moon.
2. Describe how using a telescope allows you to see more detail.
Figure 7 The Moon seen by (a) the naked eye and (b) a small telescope.
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How different types of telescopes work
Telescopes work very much like the human eye. Like the eye,
its main job is to collect light given off from a distant object
and focus that light so that we can see the object.
Optical telescopes
Optical telescopes are telescopes that you look through.
A simple optical telescope consists of a long tube and two
lenses. The lens at the end of the tube nearest the object is
called the objective lens, and the lens nearest your eye is
called the eyepiece lens.
When light enters the telescope, the light is bent, or refracted,
by the objective lens so that it focuses that light, or image, at
a point. The eyepiece lens magnifies the image making the
distant object look bigger and clearer. Because the light is
bent, we say this telescope works by refraction.
Better optical telescopes have larger lenses. Even better
optical telescopes use mirrors, as they are much lighter than
glass lenses. They are also more powerful as they can collect
more starlight. When mirrors are used, the light is reflected up and down
the tube. This increases the focal length of the telescope and allows it to
see objects that are further away. Because the light is reflected, we say this
telescope works by reflection.
Figure 8 A simple optical telescope that refracts
the light.
secondary mirror
primary mirror
eyepiece
light path
telescope tube
light path
Figure 9 A cassegrain optical telescope that reflects the light.
Magnification
The combination of convex and concave lenses or mirrors magnifies the
object. It makes the object seem nearer and more detail can be seen. How
big the telescope makes it look is called the magnification.
If a telescope has a magnification of ten times (x10), the object looks ten
times bigger than without the telescope. If it has a magnification of x100,
the object looks a hundred times bigger than without the telescope. So the
bigger the magnification, the bigger the object looks.
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Activity 4
Calculate the magnification of a telescope
To calculate the magnification of a telescope, you need to know the focal
length of the telescope and the focal length of the eyepiece.
You divide the focal length of the telescope by the focal length of the
eyepiece.
For example, if the focal length of the telescope is 1 000 mm, and the focal
length of the eyepiece is 25 mm then the magnification is:
1 000
= 40 times
25
1. Calculate the magnification of each telescope in Table 2.
Table 2 Calculate the magnification of each telescope
Telescope
Focal length of
eyepiece
Focal length of
telescope
A
20 mm
600 mm
B
24 mm
1200 mm
C
4 mm
800 mm
D
12 cm
120 cm
Activity 5
Make an information poster
Magnification
Research a well-known telescope, like SALT or Hubble, or one in Hawaii such
as Keck, Subaru or Gemini or Hobby-Eberly, or Hale in the USA.
1. Design an information poster that will explain how it is used.
2. Write about what important information this telescope has captured.
3. If you can, say why it is positioned where it is.
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Key word
• atmosphere –
gasses
surrounding Earth
Using optical telescopes to study the universe
SALT
South Africa has one of the world’s largest optical telescopes, called SALT
(Southern African Large Telescope). It is the largest single optical telescope
in the southern hemisphere. It has a mirror 11 metres in diameter and it
weighs 82 tons. It is a reflecting telescope.
SALT is situated near Sutherland in the Karoo in the Northern Cape. The site
was chosen for its dark, clear skies and good weather conditions. This is a
dry part of the country, so the air has low humidity.
SALT is a very powerful telescope. It can detect the light from faint or distant
objects in the universe, a billion times too faint to be seen with the naked
eye.
Figure 10 SALT telescope
Telescopes in space
Even with the best optical telescopes, the Earth’s atmosphere sometimes
stops us from getting the best images of distant bodies in space. The
atmosphere can distort or bend the light coming from stars, and there is
dust and water vapour in the atmosphere. So scientists have sent telescopes
into space on rockets where they now work as satellites. Satellites go
round and round the Earth in an orbit. The telescopes on the satellites take
pictures of bodies in space without looking through the Earth’s atmosphere.
These pictures are sent back to Earth. The results have been spectacular
and have given scientists a different view of the universe. We have views of
distant planets that we couldn’t have seen from Earth. We can see details of
the universe that would be fuzzy blobs if we had seen them from Earth.
Hubble telescope
The most famous of the space telescopes is the Hubble Space Telescope.
It was the first major telescope to be sent into space, in 1990. It has an
unobstructed view of the universe. It has taken nearly 600 000 photographs
of bodies in space and is still sending fantastic pictures back to Earth. Hubble
has to be serviced by astronauts taken into space on a shuttle spacecraft.
Figure 11 A photograph of a nebula
taken by Hubble telescope.
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Figure 12 Hubble telescope
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Radio telescopes
Optical telescopes are not the only kind of telescope. Scientists have
discovered that all bodies in space, like stars, planets, black holes and even
galaxies give out radio waves which we cannot see with our eyes. We need
to use a different kind of telescopes to find and record the radio waves. We
use radio telescopes to do this.
Radio telescopes do not have lenses or mirrors and we do not look through
them. There are many different designs to collect different types of radio
waves, but these designs usually have a metal bowl or dish to receive the
radio waves. Scientists make pictures from the radio waves but in order to
work well, radio telescopes need to be far away from cellphone and radio
networks.
A radio telescope on its own can only collect a small amount of information,
but a group of radio telescopes together can collect much more information.
A group of radio telescopes working together is called an array of
telescopes.
KAT-7, MeerKAT and SKA
South Africa has a number of large radio telescopes. The first was built in the
1960s at Hartebeeshoek in Gauteng but more recently the KAT-7 array was
built in the Karoo. KAT-7 is part of MeerKAT, a larger array still being built.
When finished, it will be the largest and most sensitive radio telescope in
the southern hemisphere, until SKA is completed.
SKA is the Square Kilometre Array. This is a huge radio telescope array with
thousands of individual telescopes. It will be the most powerful telescope
ever built. It will be able to see to the furthest parts of the universe and to
see back to before the first stars and galaxies formed.
South Africa has also been chosen to build SKA because of the expertise
available and because of the weather conditions in the Karoo. The main part,
with most of the receivers, will be constructed in the Northern Cape, near the
town of Carnarvon, where MeerKAT is being constructed. Part of the array
will be built in Western Australia. It should be completed by about 2024.
Figure 13 Radio telescope at Hartebeeshoek
Figure 14 Impression of what SKA will look like
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Good conditions for looking into space
The main task of optical telescopes is to collect light from distant objects.
Anything that stops the light from getting to the telescope will mean the
image received will be poor.
The best conditions for large optical telescopes are:
• The weather must usually be clear – no clouds.
• The air above the telescope must be still, not moving.
• The air should be dry. The amount of water in the air (humidity) must
be low.
• The sky must be dark with no light pollution from street lights or
city lights.
• The telescope should be at a high altitude above sea level. This is
because Earth’s atmosphere distorts or bends the light from stars.
This is why large optical telescopes are built in places where they can
receive the best images possible. Often these places are in deserts or on
mountains.
Some famous places in the world for telescopes are: Mauna Kea, in Hawaii
(4 267m high), a volcano on Canary Islands (2 133m high) and Atacama
Desert, Northern Chile.
Good conditions in South Africa
South Africa also has many locations where conditions for observing the sky
are excellent. Many parts of the country have fine weather, still, dry air and
dark skies. Some time ago a number of telescopes were erected in or near
cities, but after 1972, the Karoo region of the Northern Cape was chosen to
be the astronomical centre. This is why SALT, KAT-7, MeerKAT and SKA will all
be located here, a world-famous centre for astronomical studies.
Key concepts
Telescopes allow people to see much more detail in the sky.
Telescopes gather light, form an image of a distant body and magnify the
image.
Magnifying the image makes it look nearer, bigger and clearer.
Optical telescopes use lenses or mirrors. They focus the light by refraction
(lenses) or reflection (mirrors).
Well-known optical telescopes are SALT and the Hubble Space telescope.
Radio telescopes receive radio waves in metal dishes.
An array (group) of radio telescopes works better than individual
telescopes.
South Africa has MeerKat and will soon build SKA.
Good conditions for looking into space include clear skies, still air and little
light or air pollution. South Africa has many places that have these good
conditions.
The Karoo is the main centre for South African astronomy.
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Skills focus: Draw a scientific diagram
What is a scientific diagram?
A scientific diagram is an accurate drawing of an organism or piece of
equipment, or arrangement of equipment for an investigation. It is an
information-recording skill. It shows you the structure of the organism or
equipment. A scientific drawing is a line drawing. It should be neat, simple,
clear and accurate. It should have labels and a heading.
How to draw a scientific diagram
Here are some tips for doing a scientific diagram:
1. Use white, unlined paper and a sharp HB pencil.
2. Make your drawing large. It should fill about half the page.
3. Leave space on the right of the drawing for the labels.
4. Use single, solid lines for your drawing.
5. Do not sketch, shade in or use feathery lines.
6. Use a clean eraser to make corrections.
7. Draw the lines for your labels in pencil, with a ruler.
8. Make sure that the lines are horizontal and parallel to each other.
9. The lines should all end in the same vertical position.
10. Put all the labels on the right unless putting them all on the one side
would make your drawing cluttered.
11. Write the labels in pen at the end of each label line.
12. Write the labels in lower-case letters. Do not underline labels.
13. Give the drawing a detailed heading that includes:
• what you are showing
• if the drawing is a cross section or longitudinal section
• the magnification or the scale of the drawing.
Activity 6
Practise a scientific drawing
1. Do a scientific drawing of a telescope with labels to explain how the
telescope works. You may use the examples in figures 8 and 9, or
research your own telescope.
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Topic 13 revision
Science language practice
1. Unscramble the letters to make words from this chapter.
a ) tpilaco
d ) ceaps
b ) rryaa
e ) tomosarren
c ) nafyimg
2. Use the words in the word boxes below to complete the following
sentences:
horizon constellation optical satellite magnified astronomy refracted reflected
a)
b)
c)
d)
e)
f )
g)
h)
A group of stars in a pattern is called a
When something looks bigger we say it has been
The study of bodies in space is called
A telescope that we look through is called an
When light is bent, we say it is
When light bounces off a mirror, we say it is
The line where Earth and sky meet is the
An object that goes around Earth in an orbit is a
.
.
.
.
telescope.
.
.
.
Test yourself
1. How advanced were ancient civilisations in their knowledge of the universe?
2. Which civilisations have left us records of their knowledge of astronomy?
3. Give one example of an African story about the stars.
4. Give three examples of constellations.
5. What is the smallest constellation?
6. Why is this constellation so visible?
7. What are the essential parts of a simple telescope?
8. What are the two kinds of optical telescopes?
9. How would you recognise a typical radio telescope?
10. What is SALT ?
11. What is an array?
12. What does SKA stand for?
13. Why has the Karoo been chosen to be South Africa’s astronomical centre?
(2)
(2)
(3)
(3)
(2)
(2)
(3)
(2)
(2)
(2)
(2)
(2)
(3)
Total: 30
238
Term 4
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Practice examination: Terms 1 and 2
1. Multiple choice:
Four options are provided as possible answers to the following questions. Each question has only
ONE correct answer. Select the correct answer and write only the letter (A–D) next to the question
number ((a)–(d)).
a ) This scientist first arranged the elements into a pattern called the Periodic Table.
A. Antoine Lavoisier
B. Ernest Rutherford
C. Niels Bohr
D. Dmitri Mendelev
b ) Carbon dioxide gas is more compressible than liquid carbon dioxide because:
A. molecules of a gas are further apart than the molecules of a liquid
B. molecules of a gas are smaller than the molecules of a liquid
C. molecules of a gas are larger than the molecules of a liquid
D. molecules of a gas are closer together than the molecules of a liquid.
c ) Bacteria are grouped and classified according to:
A. the size of the cells
B. the shape of the cells
C. the colour of the cells
D. the presence or absence of a cell wall.
d ) Louis Pasteur is known for:
A. developing a method that prevents milk from going bad
B. developing a vaccination
C. the discovery of microorganisms
D. the discovery of penicillin.
(4)
2. Give the correct scientific term for each of the following:
a ) Introduced species that are a problem
(1)
b ) Total variety of species
(1)
c ) Illegal removal of animals and plants from the wild
(1)
d ) Non-living factors in an ecosystem
(1)
e ) Group of individuals of the same species.
(1)
3. Explain the meaning of the following terms:
a ) Photosynthesis
(2)
b ) Respiration
(2)
c ) Look at the photograph below of an investigation to find out if leaves produce starch.
Practice examination: Terms 1 and 2
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Practice
examination: Terms 1 and 2
Term 4 test
i. Suggest a reason why the leaf was placed in boiling water.
(1)
ii. Suggest a reason why the leaf was placed in ethanol.
(1)
iii. Describe one safety precaution that you would have taken while carrying out this test. (1)
iv. If the leaf had been producing starch, predict the results that you would have expected. (2)
4. Look at the food web below and answer the questions
leopard
hornbill
eagle
serval
caterpillar
baboon
purple-crested
turaco
earthworm
duiker
mouse
green plant
locust
shrub
a ) Select organisms from the food web and write one food chain with four links.
b ) Name an omnivore.
c ) Suggest a reason why most food chains begin with green plants.
d ) Predict what would happen to the mice if all of the eagles died from a disease.
e ) Energy pyramids are used to show the relationships between living things.
i. Explain what an energy pyramid shows us.
ii. Explain why the trophic levels become smaller at each level as you move
up the pyramid.
5. The table below shows the different gases that are found in dry air.
(3)
(1)
(2)
(2)
(3)
(2)
Nitrogen
Carbon dioxide
Argon
Oxygen
a ) From the table select:
i. a molecule of a compound
ii. an element that normally exists as molecules.
b ) Describe the structure of an atom.
c ) Tabulate two differences between mixtures and compounds.
6. a ) Draw a diagram to show how particles of a liquid are arranged.
b ) Use the particle model of matter to explain what happens when a liquid is heated.
240
(1)
(1)
(4)
(2)
(2)
(5)
Practice examination: Terms 1 and 2
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Practice examination: Terms 1 and 2
7. Two balloons were filled with gases. One balloon was filled with hydrogen gas and the other with
carbon dioxide gas. The balloons were identical and they were each filled to the same volume. After
about 6 hours, the balloon containing hydrogen gas had shrunk but the other balloon containing
carbon dioxide gas did not change its volume.
a ) Is the test a fair test?
(2)
b ) Select the independent variable.
(1)
c ) Select the dependent variable.
(1)
d ) Infer which molecules are larger.
(1)
e ) Use the particle model of matter to discuss what had occurred.
(2)
8. The following volumes of oil, water and paraffin were placed in a 50 ml measuring cylinder: 10 cm3
of oil, 10 cm3 of paraffin and 20 cm3 of water. The density of oil is 0,9 g/cm3, paraffin is 0,8g/cm3 and
water is 1g/cm3.
a ) Explain density.
(2)
b ) Predict which liquid would float on top in the measuring cylinder.
(1)
c ) Select the liquid with the greatest volume.
(1)
d ) Select the liquid with the greatest density.
(1)
e ) Apply your knowledge of the particle model of matter to discuss why liquids are used in
thermometers.
(2)
f ) Explain what happens during a chemical reaction.
(1)
g ) Give one example that indicates that a chemical reaction has occurred.
(1)
9. An investigation was conducted to find out the effect of the amount of sugar and different
temperatures on the growth of yeast.
a ) Name the group of organisms that yeast belongs to.
(1)
b ) Name the independent variables.
(2)
c ) Name the dependent variable and explain how it was measured.
(2)
d ) Suggest reasons why there are ‘holes’ in bread.
(1)
e ) Describe two ways in which fungi are useful to people.
(2)
Total: 70
Practice examination: Terms 1 and 2
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Practice examination: Terms 3 and 4
1. Multiple choice:
Four or five options are provided as possible answers to the following questions. Each question
has only ONE correct answer. Select the correct answer and write only the letter (A–E) next to the
question number ((a)–(e)).
a ) The process of photosynthesis:
A. stores energy taken from the plant
B. uses energy from the Sun
C. releases carbon dioxide into the air
D. causes leaves to become green in colour.
b ) Which one of these best describes the surface temperature of the Sun?
A. 60 000 °C
B. 6 000 °C
C. 600 °C
D. 150 000 °C
E. 150 million °C
c ) An astronomer wishes to measure the distance between two galaxies. Which of the units of
measurement listed below should she use?
A. Kilometers
B. Light hours
C. Light minutes
D. Light years
E. Centimetres
d ) Choose the best phrase to complete this sentence: Lightning is caused in thunderstorms when …
A. liquid and ice particles collide
B. hail stones fall thickly
C. it is raining heavily
D. you can hear thunder
E. there are flashes in the sky.
e ) We can see things because:
A. light reflects off objects
B. reflected light has an incidence ray
C. light is absorbed by our retinas
D. the angle of reflection is equal on both sides of the normal
E. light is made up of a mixture of colours.
(5)
2. Match the terms in Column A with their correct meaning in Column B. Write only the correct
number (1–7) next to the letter ((a)–(g)).
242
Column A
Column B
a ) Electron
1. The flow of electric charge in a circuit
b ) Fuse
2. A negatively charged particle spinning around the nucleus of an atom
c ) Hypothesis
3. A force that holds atoms together
d ) Output device
4. A device that is used to protect components of a circuit
e ) Bond
5. Something that transforms the potential energy in a cell into another form of energy
Practice examination: Terms 3 and 4
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Term 4 test
Practice
examination: Terms 3 and 4
f ) Resistance
6. A possible explanation or answer to the question you are investigating
g ) Electric current
7. A material’s ability to block or oppose the flow of electricity
(7)
3. This diagram below shows an electric circuit that includes a cell, a bulb and a switch.
a ) Redraw this diagram as a circuit diagram, using the correct circuit symbols. Label
each symbol.
b ) You wish to make the bulb glow brighter. Redraw the circuit diagram with correct
labels to show how you could achieve this.
c ) Draw a single circuit symbol to show what you would change in your diagram to
stop the bulb from producing light.
4. You want to test the ability of some substances to have a static electrical charge produced
on them. You decide to test a balloon, a plastic ruler and a piece of white plastic drain pipe.
You rub the objects you are testing and bring each of them close to a gentle stream of water
that is running out of a tap.
(7)
(4)
(2)
a ) What factors or variables would you need to keep the same for this test?
(4)
b ) Name the factor that you will be changing.
(1)
c ) What would you measure to provide hard evidence to compare the three substances?
(2)
d ) A friend comes in and says that, even if you keep all the variables you noted in (a) the same,
your test will not be fair because there is one major problem with the way in which you have
designed it. Suggest what your friend’s reason for saying the test is not fair could be.
(2)
Practice examination: Terms 3 and 4
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Practice examination: Terms 3 and 4
5. Look carefully at this diagram showing refraction of light through a block of glass.
incident ray
normal
normal
refracted ray
a ) Redraw the diagram and show where the ray of light will shine when it emerges on the
other side of the block of glass. Include the normal and the correct label for the ray on the
other side.
b ) Draw and label in the same diagram where the ray of light would go if refraction did
not take place.
6. Describe what happens to white light for an object to appear red in colour.
7. Refer to the diagram of the solar system below and answer the following questions.
a ) What is the name of the group of the first four planets from the Sun?
b ) What is the name of the group of the last four planets from the Sun?
c ) What is the name of the belt of small objects between Mars and Jupiter?
d ) One of the objects in the diagram is an icy body that releases gases and dust when
it gets close to the Sun. What is the name of objects like this?
244
(3)
(2)
(4)
(1)
(1)
(1)
(1)
Practice examination: Terms 3 and 4
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Practice examination: Terms 3 and 4
e ) Planets are kept in their orbits by gravity. Explain in one sentence what gravity is.
(2)
f ) Suggest a reason why all the objects in the solar system revolve around the Sun.
(2)
g ) Write a short paragraph suggesting reasons why Earth is the only planet in this solar system
that is ideal for life.
(4)
h ) Name the galaxy in which this solar system is situated, and state what shape of galaxy it is. (2)
i ) Explain how this galaxy got its name.
(1)
j ) Draw a sketch of this galaxy to show the position of this solar system in it. Label the
following:
•
The Sun
•
The hub of the galaxy
•
A spiral arm of the galaxy
(3)
k ) How far is the solar system from the centre of the galaxy?
(1)
8. Complete the following sentences by filling in the correct word. Write down only the letter
and the correct word next to it.
a ) The
constellation helps people on Earth find their direction at night.
(1)
b ) A cluster of telescopes grouped together, like the SKA, is called an
.
(1)
c ) Radio telescopes operate with radio waves that are received by using huge
.
(1)
d ) Telescopes that we look through are called
telescopes.
(1)
9. a ) Explain in a few sentences why the Karoo was chosen as the astronomical centre
of South Africa. Give at least two reasons.
(2)
b ) Select the key differences between reflective and refractive telescopes, and discus
how this difference means that reflective telescopes can help us see further than
refractive telescopes.
(2)
Total: 70
Practice examination: Terms 3 and 4
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Glossary
A
abiotic factors all of the non-living things in
an ecosystem
absorbed (light) light travels to the material
and is unable to travel any further
adaptation characteristic that helps a living
thing survive in its environment
alien species species that is not indigenous to
a specific area
angle of incidence angle between the normal
and the incident ray
angle of reflection angle between the normal
and the reflected ray
anode electrode where current flows in from
outside
asteroid piece of rock in space
astronomers people who studies the bodies
of space
astronomy study of bodies in space
atmosphere gasses surrounding Earth
atoms smallest units that elements are made of
B
battery two or more cells forming a chemical
system that stores electrical potential energy
biodiversity total variety of species in an area
biosphere all of the different ecosystems on
Earth
biotic factors all the plants and animals
in an ecosystem, as well as their interactions
black hole infinite mass of nothingness with
immensely powerful gravity- able to ‘suck up’
everything in its way
bonds forces that hold atoms together
C
camouflaged colours and shapes help animals
blend in well with the environment
cathode electrode where current flows out
carnivores animals that feed on other animals
that are living or dead
246
cell (electrical) chemical system that stores
electrical potential energy
cells smallest units of living organisms
chemical equation representation of a
chemical reaction
chemical reactions chemical reactions that
take place when two or more compounds
react and form new substances
chlorophyll green pigment in plant cells that
absorbs radiant energy
circuit path through which electric charge can
move
circuit diagram simple diagram of an
electric circuit that uses standard symbols to
represent the basic components of the circuit
clear lime water solution of calcium hydroxide
and water
comet icy body that releases gases and dust
when it gets close to the Sun
compound pure substance formed by a
chemical reaction between two or more
different elements
concave inward curve
condense when a gas turns into a liquid
conductors materials that allow electric
current to pass through them
conducting wires materials through which
electrons can flow
conservation wise management and use of
natural resources that protects habitats and
wildlife
constellation grouping of stars with a specific
name, for example, Southern Cross, Scorpius
and Sagittarius
consumers organisms that rely on other
organisms for their energy and food supply
contract become smaller, shrink
controlled variable variables that are kept
the same
convex outward curve
cornea protective front covering of the eye
craters dents or hollows made by rocks that
crash into planets or moons
Glossary
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D
decomposers organisms that break down or
decompose the remains of dead plants and
animals and their wastes
decomposition reaction chemical reaction
in which a compound is broken down into
simpler compounds or elements
density amount of mass in a given volume of
matter
dependent variable the variable that you will
measure
diatomic molecule molecule that consists of
exactly two atoms
diffusion spontaneous spreading of particles
from an area of high concentration to an area
of low concentration
digestive enzymes substances made by an
organism that break down food
dispersed (light) white light that is broken up
into different colours of light
disruptions something that interferes with a
process
dwarf planet body similar to a planet but
that does not clear its orbital path of other
bodies
E
ecology study of interactions between living
things and with their physical and chemical
environment
ecosystem all of the living and non-living
things in an environment and the different
ways in which they interact with each
other
electric charge positive or negative property
of a particle
electric current flow of electric charge in a
circuit
electric discharge flow of electric charge
through a gas, liquid or solid
electric shock reflex response to the passing
of electricity through the body
electric spark flash of light produced by
electric discharge
electrode electrical conductor used to make
contact with a non-metallic part of a circuit
electrolysis the process by which ionic
substances are broken down into simpler
substances when an electric current is passed
through them
electromagnet a magnet in which the
magnetic field is produced by a flow of
charge. The direction of the magnetic field
can be determined by placing one or more
compasses on a card and observing the
directions that they indicate
electrons a negatively charged particles
spinning around the nucleus of an atom
evaporate when a liquid turns into a gas
expand become larger, swell up, to increase
in size
extinct there are no more of a species left on
Earth
F
fair test an investigation where all of the
variables are controlled
filament resistant wire inside a light bulb that
glows to produce light
food chain number of steps in an ecosystem
showing the transfer of energy between
organisms
food web group of interconnected food chains
fossil fuels energy-containing compound such
as coal, oil or natural gas that was formed
millions of years ago
freeze when a liquid turns into a solid
frequency number of waves that move past a
certain point in one second
fuse device that is used to protect
components of a circuit
G
galaxy collection of stars held together by
their mutual gravity
gas matter that moves freely; it does not
take on any shape and spreads to fill a space
evenly
Glossary
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gas pressure force created by gas particles
hitting the walls of their container
gravity object’s natural force that pulls other
objects towards itself
H
habitat place where organisms live
herbivores animals that eat plants, carnivores
are animals that eat other animals
hypothesis possible explanation or answer to
the question you are investigating
I
independent variable the factor that you will
purposely change
insectivores carnivores that feed on insects
interdependent two or more things that rely
on each other
ionic solution solution with positively and
negatively charged particles
insulator materials that do not allow current
to pass through, or they allow very little
current to pass through
illuminated lit up or provided with light
incident ray light ray that travels to the
reflective surface
mass measure of the amount of matter of an
object
melt when a solid turns into a liquid
mergers action of two or more galaxies being
consumed into one galaxy
meteor meteoroid when it enters Earth’s
atmosphere and burns up as it falls
meteorite remains of a meteoroid after it
crashes onto Earth’s surface
meteoroid small piece of rock in space, smaller
than an asteroid
micrograph photograph of an object that is
viewed under a microscope
mimicry harmless species copies another
poisonous species
mixture two or more different substances that
are mixed together
model idea of how something works, based on
patterns that scientists observe
molecule two or more atoms that are
chemically bonded together
monocultures single crop species planted
over large areas
moon body that revolves around a planet
and that shines by reflecting the light of
the Sun
multicellular consisting of many cells
K
kinetic energy energy that an object has
because of its motion
Kuiper Belt broad region between Mars and
Jupiter also containing millions of asteroids
L
liquid matter that flows and does not have
a specific shape, but takes the shape of the
container it is in
luminous word to describe an object that
gives of light or glows in the dark
N
neutrons neutral particles found in the
nucleus of an atom
normal imaginary line on a reflective surface
that is perpendicular to the surface
nuclear reaction type of reaction in which the
nucleus of an atom changes its characteristics
and becomes something else
nucleus central region of an atom consisting
of protons and neutrons
M
O
magnetic field lines of force surrounding a
permanent magnet or a moving charged
particle
magnify to make something appear larger
than its actual size
opaque does not allow light to travel through
optic nerve The part of the eye that transmits
information from the retina to the brain
orbit circular path that a body in space follows
as it travels around another body
248
Glossary
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output device something that transforms
the potential energy in a cell into another
form of energy, such as heat, sound or light
omnivores animals that eat plants and other
animals
P
parallel circuit electric circuit where there is
more than one pathway for the current to
flow through
particle model of matter model that helps
us understand that matter is made from particles
and how they affect the behaviour of matter
pasteurisation process of heating food or
a liquid to kill any disease-causing microorganisms that may be in it
photosynthesis radiant energy is converted
into potential energy which is stored in food,
and oxygen is released
plane imaginary flat surface that only has
length and width, but no depth or height
planet rounded body travelling around a star
in a clear circular path
poaching illegally removing animals or plants
from the wild
pollutant chemicals or wastes that
contaminate the water, air or soil
pollution harm done to the environment
by the release of harmful materials and
substances produced by human activities
population group of individuals of the same
species living in the same ecosystem at the same
time community different populations that
interact with one another in the same ecosystem
potential energy energy that is stored in an
object or system
practical investigations scientific
experiments and tests conducted to find
answers to questions
predator carnivore that hunts other animals
prey animals hunted and eaten by the predator
producers green plants that can make their
own food
products substances that are produced in a
reaction
protists single-celled organisms that may be
free living or living in colonies
protons positively charged particles found in
the nucleus of an atom
pupil hole in the centre of the iris that controls
the amount of light that enters the eye
pure substance substance that is of made up
of one type of particle throughout
R
radiant energy energy contained in
electromagnetic radiation
radiation process in which light moves away
from the its origin
ray diagram diagram that uses lines with
arrowheads to show the path of a ray of light
reactants substances that react chemically
with other substances to form products
reflected (light) light that has changed
direction, but continues to travel in the
original material
reflected ray light ray that is reflected by the
reflective surface
refraction ability of a wave to change direction
(or bend) when it passes from one medium
(such as air) to another (such as glass)
resistance material’s ability to block or oppose
the flow of electricity
resistors devices that opposes the flow of
current
respiration process in cells where glucose is
broken down and energy is released
retina A sensory layer at the back of the eye
S
scattered (light) light that reflects in different
directions, with no regular pattern apparent
in the reflection
scavengers carnivores that feed on dead
animals or decaying meat
series circuit electric circuit where electrical
components are connected one after the
other and there is only one pathway for the
current to flow through
sewage human and domestic waste from
people’s homes
short circuit electrical circuit that allows
current to flow in an unintended circuit
Glossary
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solar system Sun and the planets and other
objects that move around the sun
solid matter that has a specific shape and size
solidify when a liquid turns into a solid
spectrum of visible light full collection of
colours that make up white light
star body of hot, glowing gases in space that
produces its own energy
states of matter the three forms in which
matter can be found: solid, liquid or gas
static electricity electricity caused by the
build-up of electric charges on the surface of
a non-conductor of electricity
Sun medium-sized star, which is the centre of
the solar system
sun flares enormous explosions on the Sun’s
surface
sunspots magnetic storms on the Sun’s
surface
sustainable use using resources wisely so that
they are not depleted
switch device that is used to control the flow
of charge in a circuit
T
tangent straight line that does not cross a
curve, but only touches the curve at a single
point
terrestrial relating to land
thermal decomposition chemical reaction
in which heat is used to decompose a
compound
250
transparent light is able to travel through
trophic level steps in a food chain or food web
U
unicellular
consisting of one cell
V
vaccinations use of a vaccine to prevent
infection with specific diseases
vaccines preparation of a weakened or dead
form of a micro-organism that causes a
disease
variable any factor that has an effect on an
investigation
variations differences between individuals in
a population
vibrate shake backwards and forwards
visible light type of energy that comes from
a light source and can be observed by the
human eye
volume amount of space an object
takes up
W–Z
wave pattern that is created by the repeated
up-and-down or side-to-side movement of
a medium (substance) when energy moves
through it
wavelength length of one wave pattern
Glossary
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Index
A
abiotic factors 18, 20, 21
absorbed light 166
see also light; visible light
adaptations 38, 39
animal see animals
behavioural 38
functional 38
physical 38
plants see plants
predator see predators
acquired immunodeficiency
syndrome 61
AIDS see acquired
immunodeficiency
syndrome
algae 20
alien
species 42
vegetation 43
control 43–44
Alpha Centauri 212, 212
amoeba 54, 54
angle
of incidence 171–172
of reflection 171–172
animals 1, 3, 15, 40
adaptations 40, 40, 41
anode 144, 145
Anopheles mosquito 61
asteroid belt 193
asteroids 193, 199
astronomers 224–225
astronomy 224, 236
atmosphere 232
atomic theory 74
atoms 72–73, 74, 75–76, 77–78,
82, 83, 123
B
bacteria 53, 62, 65
battery 136, 137–138
biodiversity 42, 45
bio-fuels industry 121
biosphere 1, 16, 17, 17
biotic factors 18, 19, 20
black hole 206, 209
Bohr, Niels 75
bonds 116, 116
see also chemical bonds
brain 178
bread mould 27
burning fuels 118
C
camouflage 38, 41
carbon dioxide 2, 13, 58
carnivores 24
cathode 144, 145
cell walls 2, 3
cells 2, 136, 137
cellulose 3
Chadwick, James 75
change of state 96, 97, 112
chemical
bonds 84, 119
equations 6
reactions 2, 72, 84, 86, 87,
115, 116–118, 120, 144, 145
chemistry 121
chlorophyll 2
cholera 63
statistics 63
circuit/s 134, 135, 151, 158, 160
see also electric circuits
closed 135
components 151
diagrams 138, 140–141, 158
parallel 151
series see series circuits
symbols 139, 141
clear lime water 13
colours 170, 176, 177
comets 193, 194, 194, 199
communities 16, 17
compounds 79, 80, 82, 83,
86, 87
decomposing 84
concave 183
condense 96
conducting wires 136
conductor 144, 153
conservation 42, 45
constellations 206, 224, 225,
226, 228, 236
consumers 22, 23
contract 106
contraction 107–108, 109
convex 183
cooling 96–97
cornea 175
current electricity 134
D
Dalton, James 74
decomposers 27, 28, 29, 29,
30, 66
decomposition 66, 66
reaction 83
Democritus 74
density 98–99, 100, 101,
102–104, 112
different materials 102–103
diarrhoea 62
diatomic
elements see elements
molecule 81
digestive enzymes 26
diffusion 94, 95
rates 95
diseases 64–65
disruption 34, 35
dodo 37, 37
E
Earth 187, 200, 202–203,
204, 211
position 200
temperatures 200, 201
water 201
see also water
Index
mml_9780636140912_plt_nat_g08_lb_eng_zaf.indb 251
251
31/05/13 12:55 PM
ecological interactions 17
ecology 16
ecosystems 15, 16, 17,
18–19, 28, 29, 36, 42, 43,
46–47
balance 34, 35
human factors 35
natural factors 35
conservation 43
interactions 17
size 23
electric
charges 126, 127
like 127
unlike 127
circuits 133, 133, 135, 136, 150
components 136
current 134, 142, 143, 145,
146, 150, 152, 156
discharge 128
shock 126, 128, 130
sparks 128, 130, 132
electrical
conductors 153
energy 134
systems 133
electricity, history 159
electrode 144
electrolysis 83, 84–85, 86,
146, 150
electromagnets 144, 145, 146,
148–149, 150
electrons 76, 77, 124, 125,
128, 132
transfer 125
elements 71, 72, 73, 80–81,
82, 87
diatomic 81
energy 2, 3, 11, 11, 28, 96, 106,
108, 157, 161, 201
flow 28
loss 32
pyramids 32, 33, 33
transfer 32, 133
engineering 121
environment 13, 16
environmental conditions 38
252
Escherichia coli 63
evaporate 96
exhaled air 13
expand 106
expansion 107–109
extinct 38
extinction 39
eye 175
functions 175
F
feeding relationships 22, 25
fermentation 119
filament 138, 139
Fleming, Sir Alexander 67
food 11
chains 28, 28, 29, 30, 31,
33, 200
decay 51
webs 28, 30, 30, 31, 33, 34
fossil fuels 34, 35, 42
freeze 96
frequency 164
friction 124, 128, 132
fungi 53, 58
fuses 146, 147
G
galaxies 205, 206, 207,
218–219, 220
shapes 219
sizes 219
gas
particles 111, 111
pressure 110, 111
gases 92, 95, 100, 101
germinating seeds 13
glucose 3
gravity 194, 197
growth 3
H
habitat 16, 21
heat energy 157
heating 86, 96
herbivores 22, 23
Hubble telescope 232
human
activities 42, 45
immunodeficiency virus 61
human-induced pollution 33
hygiene 65
hypothesis 7, 8, 154
writing 154
I–J
illuminated 162
images 178
immune system 61
incident ray 171, 172
individuals 19
insectivores 24
insulator 153
investigation 7–8, 9
plan 8
ionic solution 144, 145
K
kinetic energy 95
Kuiper Belt 195, 206
L
Lavoisier, Antoine 72
lens 183
life 1
light 13, 162, 164–165, 178–179
see also visible light
absorption 169–170
energy 157
frequencies 177
hours 214
intensity 20
minutes 214
ray 180
reflection 171, 172–173, 184
refraction 166, 180–181,
182, 183
years 214, 222
Index
mml_9780636140912_plt_nat_g08_lb_eng_zaf.indb 252
31/05/13 12:55 PM
lightning 123, 123,
130, 131
liquids 92, 95, 100
living organisms 1, 1, 2,
13, 13
luminous objects 162
M
magnetic field 142, 143
magnets 123
magnify 52
malaria 61, 61
Marula tree 22, 22
mass 98, 99
materials 71, 89, 102,
106, 153
contraction 106
expansion 106
matter 71, 79, 89, 91, 95, 97, 99,
100, 108
medicines 67
melt 96
Mendeleev, Dimitri 73
mergers 218
metals 153
meteor 193
meteorite 193
meteoroid 193
microbiology 51
micrograph 56, 57
micro-organisms 1, 51, 56–57,
61, 66
harmful 60–61
size 56–57
types 52
microscope 51, 52
Milky Way Galaxy 205, 206,
208, 209, 210, 216, 218
mimicry 38, 41
mining 121
mixtures 79, 87
models 76, 77, 82
molecules 81, 82
monocultures 42
moons 187, 193
multicellular 52, 53
N
nanometres 56
neutralisation of stomach
acid 118
neutrons 77, 124
normal 171, 172
nuclear reactions 188, 189
nucleus 76, 77
nutrition 65
O
oil 104
disaster 105
pollution 105
omnivores 25
Oort Cloud 195, 195
opaque
objects 166, 167
substances 166
optic nerve 175
optical fibre 185
optics 185
organisms 16
output devices 157
oxygen 202
P
parallel circuits 155, 156
parasites 61
particle model of matter
89–90, 97, 100, 112
particles 89, 100, 108, 123
negatively charged 123
positively charged 123
passive smoking 95
Pasteur, Louis 65
pasteurisation 65, 65
penicillin 65
Periodic Table of Elements 71,
73, 77, 82
photomicrograph 56–57
photosynthesis 1, 2, 3, 3, 5, 11,
14, 22, 22, 200
process 2
pinhole camera 162–163
plane 171
planets 190–191, 198
dwarf 190, 199
inner rocky 190–191
outer gas giants 190–191
plants 1, 3, 5, 13, 21, 24, 28,
41, 41
adaptations 39
poaching 36, 37
pollutants 34, 35
pollution 34, 35
populations 16, 17, 21
potential energy 2, 3
practical investigations 7
predators 22, 24, 41
adaptations 41
pressure 110, 112
prey 22, 24
producers 22
products 116, 119
protists 16, 53, 54, 55
protons 76, 77, 124
pupil 175
pure substances 79
properties 80
Q–R
radiant energy 2, 3
radiation 161
rainbow 165
ray diagram 162, 163, 174
reactant 6, 116, 119
recycling 43
reflected
light 164
ray 171, 172
reflection 172
laws of 172
reproduction 3
resistance 152
wire 142
resistors 138–139, 153, 155,
156, 160
in parallel 156
in series 156
Index
mml_9780636140912_plt_nat_g08_lb_eng_zaf.indb 253
253
31/05/13 12:55 PM
respiration 1, 11, 12, 13
retina 175, 178
rhino poaching 37, 37
Rutherford, Ernest 75
S
SALT see telescopes
scattered light 173, 174
scavengers 22, 24, 29
scientific
diagram 235
method 7
seeing light 175–176
series circuits 151, 152, 153
sewage 26, 27
shadows 166–167
short circuit 142, 143, 146
slope 18
soils 18
solar system 187, 190, 192,
192, 194, 196, 198, 204, 206,
209, 210, 214, 222
model 196–197
position 210
solidify 96
solids 92, 100
solutions 145
sound energy 157
Southern Cross 214–215, 229,
227, 229, 230
appearance 227
pointers 229
space 223, 224, 234
observation in South
Africa 234
species conservation 41
speed of light 163
stars 188, 211, 212, 214
distances 214
starch 3
test 13
254
states of matter 92, 93, 100,
112–113
static electricity 123–124, 127,
128, 132
sub-atomic particles 74, 76
sugars 3, 58, 59
sun 2, 187, 188–189, 201, 201,
204, 208, 209, 211
gases 189
structure 189
sun flares 211, 222
sunlight 2, 3, 188, 200, 201
sunspots 211, 222
surfaces 173–174
rough 173
sustainable use 23, 42,
43, 45
switches 136–137
U
unicellular 53
universe 205, 215, 215, 221,
223, 236
distances 214, 215
expanding 221
time 217
V
variables 7, 8
variations 38
vibrate 92
viruses 53
visible light 161, 164
spectrum 164, 165, 177, 186
volume 98, 99
T
W
tangent 183
telescopes 223, 229, 230–231,
234
KAT-7 235
magnification 230
MeerKAT 235
optical 230, 232, 234
radio 233, 235
arrays 234
SALT 234
SKA 235
in space 232
temperature 13
changes 19
thermal decomposition 86
Thomson, Joseph 74
time 217
transparent objects 167
substances 166
trophic levels 32
tuberculosis 60, 60
waste 43
water 2, 3, 13, 94, 104, 146
cycle 202, 202
liquid 101
solid 101
waterborne diseases 62
wave 164
wavelength 164, 186
wetlands 45
preservation 45
wind 13
X–Z
yeast 58
growth factors 58
Index
mml_9780636140912_plt_nat_g08_lb_eng_zaf.indb 254
31/05/13 12:55 PM
Acknowledgements
Every effort has been made to trace the copyright holders of material
produced in this title. We would like to apologise for any infringement of
copyright so caused, and copyright holders are requested to contact the
publishers in order to rectify the matter.
Cover design by MML Studio
Typesetting by Diacritech, India
Reproduction by MML Studio
Printed by [PRINTER TO INSERT]
Cover photo by Lawrence Lawry/Getty Images/Gallo Images
Artwork by Will Alves, Tina Nel, Sue Etberg, Claudia Eckard, B R Kruger
Photographs by Thomas Talkner and Helen Stock
The publisher would like to thank the following for the use of copyrighted
images in this publication:
Digital9408/Bigstock (pg. 1); European Space Agency/Science Photo Library
(pg. 2 Fig. 2); Lenka Bigstock (pg. 4 Fig 4); Viki2win Bigstock (pg. 4 Fig. 5);
Gamut Stock Images/Bigstock (pg. 4 Fig. 6); Dirkr/Bigstock (pg. 15); Getty
(pg. 15 Fig. 1(b)); Johan Swanepoel/Bigstock (pg. 15 Fig. 1(c)); Ibogdan/
Bigstock (pg. 16 Fig 2); Yasar/Bigstock (pg. 17 Earth) Focus_on_Nature/
iStockphotos (pg. 17 Quiver tree); EcoShot/Bigstock (pg. 17 Suricate family);
iStock (pg. 18); Hannamariah/Bigstock (pg. 19 Fig. 7); Karimala/Bigstock
(pg. 19 Fig. 9); DmitryP/Bigstock (pg. 19 Fig. 10); larsek/Bigstock (pg. 19
Fig. 11); Wayne Matthews/AfriPics (pg. 20 Fig. 12); Robyn Mackenzie/
Bigstock (pg. 20 Fig. 13); MartinHeigan/iStock (pg. 20 Fig. 14); Slavapolo/
Bigstock (pg. 20 Fig. 15); Vicsa/Bigstock (pg. 21 Fig. 16); Infografick Bigstock
(pg. 21 Fig 17); Awie Badenhorst/iStock (pg. 21 Fig 18); Scamp/Bigstock
(pg. 21 Fig. 19); BirdImages/iStock (pg. 22 Marula tree) Afripics (pg. 22
Marula fruit); Trevkitt/Bigstock (pg. 23 Fig. 21); Africa Media Online (pg. 23
Locust); Ekipaj/Bigstock (pg. 23 Cow); Styve/Bigstock (pg. 23 Giraffe);
Javarman/Bigstock (pg. 24 Fig. 23(a)); AlexStar/Bigstock (pg. 24 Fig. 23(b));
Andreas Resch/Bigstock (pg. 24 Fig. 23 (c)); Life on White/Bigstock (pg. 24
Fig. 24(a)); BrettM82 /iStockphotos (pg. 24 Fig. 24(b)); Micha Klootwijk/
Bigstock (pg. 24 Fig. 24(c)); Getty (pg. 24 Fig. 25); Peter Johnson/CORBIS/
Greatstock (pg. 24 Fig. 26); Iv Nikolny/Bigstock (pg. 25 Fig. 27); AlexStar/
Bigstock (pg. 25 (a)); Anna Omelchenko/Bigstock (pg. 25 (b)); EcoShot/
Bigstock (pg. 25 (c)); Erllre/Bigstock (pg. 25 (d)); GP232/iStock (pg. 25 (e));
Duelune/Bigstock (pg. 25 (f )); Macropixel/Bigstock (pg. 26 Fig. 28); Pixelman/
Bigstock (pg. 26 Fig. 29); Jenny Waterson/Bigstock (pg. 26 Fig. 30); Sharon B/
Bigstock (pg. 26 Fig. 31); SarahEm/Bigstock (pg. 28); Belinda_bw/Bigstock
Acknowledgements
mml_9780636140912_plt_nat_g08_lb_eng_zaf.indb 255
255
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(pg. 36); Photostash/Bigstock (pg. 37 Fig. 42); Africa Media Online
(pg. 37 Fig. 43); EcoShot/Bigstock (pg. 37 Fig. 44); breid/Bigstock (pg. 38
Fig. 45); Peter Nile/Bigstock (pg. 39); Wonderpixel/Bigstock (pg. 41 Fig. 49)
Tihism/Bigstock (pg. 41 Fig. 50); Wonderpixel/Bigstock (pg. 41 Fig. 51);
Tezzstock /Bigstock (pg. 42 Fig. 52); Shariffc/Bigstock (pg. 42 Fig. 53); Nigel
Dennis/Getty Images/Gallo Images (pg. 43); Merrilld/Bigstock (pg. 44
Fig. 55); Shariffc/Bigstock (pg. 44 Fig. 56); Afripics (pg. 44 Fig. 57) Eric1513/
Bigstock (pg. 44 Fig. 58); NorGal/Bigstock (pg. 44 Fig. 59); Bettie’s Photo
Barn/Bigstock (pg. 46); Pei Lin/Bigstock (pg. 48 Fig. 62 (a)); Vladr/Bigstock
(pg. 48 Fig. 62(b)); Scott Bean/Bigstock (pg. 48 Fig. 61 (d)); A. Dowsett, Health
Protection Agency/Science Photo Library (pg. 51); David Scharf/Science
Photo Library (pg. 53 Fig. 5(a) and (b)); Getty images (pg. 53 Fig. 5(c)); Astrid
& Hanns-Frieder Michler/Science Photo Library (pg. 54); Gregory Dimijian/
Science Photo Library (pg. 55 Fig. 8); Whitemay/iStock (pg. 55 Fig. 10);
Dr Gary Gaugler/Science Photo Library (pg. 60 Fig. 12); A. Dowsett, Health
Protection Agency/Science Photo Library (pg. 60 Fig. 13); Steve
Gschmeissner/Science Photo Library (pg. 62); Adisa/Bigstock (pg. 63
supermarket); Monstersparrow/Bigstock (pg. 63 kettle); F Marsicano/
Bigstock (pg. 63 female sneezing); Yastremska/Bigstock (pg. 63
toothbrushes); Razvan Photography/Bigstock (pg. 63 latex gloves); Gina
sanders/Bigstock (pg. 63 washing hands); Eskay Lim/Bigstock (pg. 63 pack of
condoms); Bioraven/Bigstock (pg. 63 washing fruit); Yuri_Arcurs/Bigstock
(pg. 63 smiling lady); Oleg Golovnev/Bigstock (pg. 64 Fig. 16); Alex Raths/
iStock (pg. 64 Fig. 17); Janimal/Bigstock (pg. 65); Colour59/Bigstock (pg. 66
Fig. 20); Mr. Smith/Bigstock (pg. 70 grass); brm1949/Bigstock (pg. 70 insect);
THEGIFT777/iStockphotos (pg. 70 Cape Robin); Kurt Jay Bertels/
iStockphotos (pg. 70 black eagle); PILart/iStock (pg. 71 Fig. 1); mg7/Bigstock
(pg. 71 Fig. 2); Brooke Becker/Bigstock (pg. 71 Fig. 3); LeggNet/iStock (pg. 72
Fig. 4); group/Bigstock (pg. 72 Fig. 5); denisk0/iStock (pg. 72 Fig. 6); Alamy
(pg. 73 Fig. 7); Alamy (pg. 74 John Dalton); Stock Montage/Getty Images/
Gallo Images (pg. 74 Joseph Thompson); Greatstock/Corbis (pg. 75);
TheBiggerPicture/Alamy (pg. 77 Fig. 10); klikk/Bigstock (pg. 79 Fig. 14(a));
Ayala_Studio/iStockphotos (pg. 79 Fig. 15(a), pg. 80 Fig. 20); Chris_Elwell/
Bigstock (pg. 79 Fig. 16(a)); Grafissimo/iStock (pg. 79 Fig. 17(a)); The Bigger
Picture/Alamy (pg. 80 Fig. 18); Jag_cz/Bigstock (pg. 80 Fig. 21); ChinKS/
Bigstock (pg. 80 Fig. 22); Provasilich/Bigstock (pg. 80 Fig. 23); JustASC/
Bigstock (pg. 80 Fig. 24); Iwka/Bigstock (pg. 80 Fig. 25); Warren Goldswain/
Bigstock (pg. 87 Fig. 32); ZambeziShark/Bigstock (pg. 87 Fig. 33); Erem/
Bigstock (pg. 87 Fig. 34); Skeptic/Bigstock (pg. 89 Fig. 1); Farvatar/Bigstock
(pg. 89 Fig. 2); Forwardcom/Bigstock (pg. 92 Fig. 8(a)); Gino Santa Maria/
Bigstock (pg. 92 Fig. 8(b)); Martyn F. Chillmaid/Science Photo Library (pg. 92
Fig. 8(c)); eTrayne/Bigstock (pg. 93 Fig. 9); Mikeledray/Bigstock (pg. 93
Fig. 10(a)); Gino Santa Maria/Bigstock (pg. 93 Fig. 10(b)); Mike Ledray/
256
Acknowledgements
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Bigstock (pg. 93 Fig. 10(c)); Rhambley/Bigstock (pp 94, 123); PH.OK/Bigstock
(pg. 95); Rich Lindie/Bigstock (pg. 101); 1photo/Bigstock (pg. 103);
Greatstock/Corbis (pg. 105); ; Tenor/Bigstock (pg. 110 Fig. 33); Yastremska/
Bigstock (pg. 110 Fig. 34); Paulaphoto/Bigstock (pg. 111 Fig. 36); Liming/
Bigstock (pg. 112 Fig. 37); Nito/Bigstock (pg. 113 Fig. 40 left); Kalina Vova/
Bigstock (pg. 113 Fig. 40 right); Charles D Winters/ Science Photo Library
(pg. 115); Gino Santa Maria/Bigstock (pg. 117); Devon/Bigstock (pg. 118);
Aleksan/Bigstock (pg. 119); Science Photo (pg. 120); Caro/Alamy/Afripics
(pg. 121 Fig. 9); Tornadochaser/iStock (pg. 121 Fig. 10); Flippo/Bigstock
(pg. 121 Fig. 11); Gettyimages (pg. 122); Evgeny_D/Bigstock (pg. 125); IS2/
Bigstock (pg. 127); Barbara White/Bigstock (pg. 128); Intoit/Bigstock
(pg. 129); Pasphotography/Bigstock (pg. 132 Fig. 11); Grisha Grigorov/
Bigstock (pg. 133); AAAAAA/Bigstock (pg. 136 torch); SVLuma/Bigstock
(pg. 136 cyclist); Goodday/Bigstock (pg 136 horse); Dmitry Matrosov/
Bigstock (pp. 138, 161); Kastock/Bigstock (pp. 138, 153); Xzserg/Bigstock
(pg. 139 Fig. 10); Scanrail/iStockphotos (pg. 140 Fig. 12); Martyn F Chillmaid/
Science Photo Library (pg. 145); GIphotostock/Science Photo Library
(pg. 146); Paul Ridsdale Pictures /Alamy/Afripics (pg. 147); 076/Bigstock
(pg. 149 Fig. 27); Garry518/Bigstock (pg. 149 Fig. 28); Thomas Talkner
(pg. 150 Fig. 29); Philip Duff/Alamy/Afripics (pg. 155 Fig. 4); Sashkin/Bigstock
(pg. 159); Michael Jung/Bigstock (pg. 161 Fig. 10, night view of city);
Zhudifeng/Bigstock (pg. 161 Fig. 12); Strick9/Bigstock (pg. 161 dollars);
MartinM303/Bigstock (pg. 161 streetlamp); Marzolino/Bigstock (pg. 161 four
lamps); Neftali/Bigstock (pg. 161 stamp); Elenamiv/Bigstock (pg. 163);
pryzmat/Bigstock (pg. 164 Fig. 2); Hydromet/Bigstock (pg. 166 Fig. 5);
lightpoet/Bigstock (pg. 187 Fig. 41); leaf/Bigstock (pg. 187 Fig. 42);
kenny001/Bigstock (pg. 187 Fig. 43); Science Photo Library/The Bigger
Picture (pg. 192); Plutonius 3d/Bigstock (pg. 195 Mercury); NASA (pg. 195
Venus, Jupiter, Saturn, Uranus, Neptune); t_rust/Bigstock (pg. 195 Earth);
Tristan3D/Bigstock (pg. 195 Mars); DeMango/Bigstock (pg. 197 Fig. 5);
Harvard College Observatory/Science Photo Library (pg. 198 Fig. 7); Peter
Mellows/Bigstock (pg. 211); The Bigger Picture/Science Photo Library
(pg. 214 Fig. 7); Mark Garlic/Science Photo Library (pg. 220 Fig. 10); Science
Faction/Getty Images/Gallo Images (pg. 220 Fig. 11(a), pg. 222 Fig. 15(d));
L. Calcada/European Southern Observatory/Science (pg. 220 Fig. 11(b),
pg. 222 Fig. 15(e)); Stocktrek Images/Getty Images/Gallo images (pg. 220
Fig. 11(c), pg. 222 Fig. 15(a)); The Bigger Picture/Science Photo Library
(pg. 220 Fig. 11(d); pg. 222 Fig. 15(f )); Lynette Cook/ Science Photo Library
(pg. 220 Fig. 11(e), pg. 222 Fig. 15(c)); European Southern Observatory/
Science Photo Library (pg. 220 Fig. 11(f ); pg. 222 Fig. 15(b)); Science Photo
Library/The Bigger Picture (pg. 221 Fig. 12); NASA- ESA/Getty Images/Gallo
Images (pg. 221 Fig. 13); The Bigger Picture/Science Photo Library (pg. 223);
Noel Powell/Shutterstock (pg. 225); The Granger Collection/Topfoto/INPRA
Acknowledgements
mml_9780636140912_plt_nat_g08_lb_eng_zaf.indb 257
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(pg. 226 Fig. 2); Art Directors & TRIP/Alamy/Afripics (pg. 226 Fig. 3);
Bridgeman Art Library/Digitalsource (pg. 227); Daneel/Bigstock
(pg. 231 Fig. 7(a)); David Crehner/Bigstock (pg. 231 Fig. 7(b)); D. Hurst/
Alamy/Afripics (pg. 232 Fig. 8); Shaen Adey/Gallo Images (pg. 234 Fig. 10);
The Bigger Picture/Science Photo Library (pg. 234 Fig. 11, 12); Beeld/
Siddique Davids/Gallo Images (pg. 235 Fig. 13); Reuters/Handout-SKA
Organisation/Swinburne Astronomy (pg. 235 Fig. 14)
258
Acknowledgements
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Period
7
6
7
6
5
4
3
2
1
H
90
58
231
Protactinium
Thorium
232
Pa
91
141
Pr
60
61
(267)
Rutherfordium
Rf
179
Hf
Hafnium
104
72
91
Zr
Zirconium
40
48
Ti
Titanium
22
4
238
U
144
Uranium
92
62
(268)
Dubnium
Db
105
181
Ta
93
Tantalum
73
(237)
Np
Neptunium
93
(145)
95
152
Eu
Europium
63
(271)
Seaborgium
Sg
106
184
W
Tungsten
74
96
96
157
Gd
Gadolinium
64
(272)
Bohrium
Bh
107
186
Re
Rhenium
75
(98)
Tc
55
Molybdenum Technetium
43
Manganese
Mn
25
7
(244)
Plutonium
(243)
Americium
(247)
Curium
Pu Am Cm
150
Samarium
94
42
52
Cr
Chromium
24
6
metals
semi-metals
non-metals
Nb Mo
Niobium
41
51
V
Vanadium
23
5
Nd Pm Sm
(227)
Ac
Actinium
89
139
La
89
Yttrium
Y
Lanthanum
57
39
45
Sc
Scandium
21
3
Praseodymium Neodymium Promethium
59
(226)
Th
140
Cerium
Ce
(223)
Ra
Radium
Fr
88
137
Barium
Caesium
133
Ba
Cs
56
88
Francium
87
55
86
Strontium
40
Rubidium
38
Sr
39
Rb
37
Ca
Calcium
K
20
24
Potassium
19
23
Mg
Magnesium
Na
Sodium
12
9
Beryllium
Lithium
7
Be
4
2
Li
1
Hydrogen
11
3
1
1
Group
(247)
Bk
159
Terbium
Tb
Berkelium
97
65
(277)
Hassium
Hs
190
Osmium
Os
108
76
101
Ru
56
Iron
Fe
Ruthenium
44
26
8
(251)
Cf
Californium
98
163
Dy
Dysprosium
66
(276)
(252)
Es
Einsteinium
99
165
Ho
Holmium
67
(281)
Ds
110
195
Pt
Platinum
78
106
Pd
59
Ni
Nickel
Palladium
46
28
10
(285)
169
Thulium
Tm
101
69
113
204
Tl
115
Indium
In
70
Ga
Gallium
Thallium
81
49
31
27
(257)
Fermium
207
Lead
Pb
Tin
119
Sn
114
82
50
73
Ge
28
Silicon
Si
12
C
Carbon
Germanium
32
14
6
14
209
Bi
Bismuth
115
83
122
Sb
75
As
Arsenic
Antimony
51
33
31
Phosphorus
P
14
N
Nitrogen
15
7
15
non-metals
116
(209)
Po
Polonium
84
128
Te
Tellurium
52
79
Se
32
Sulfur
S
16
O
Oxygen
Selenium
34
16
8
16
117
(210)
Astatine
At
127
Iodine
I
80
Bromine
Br
36
Cl
19
F
Fluorine
Chlorine
85
53
35
17
9
17
18
(222)
Radon
Rn
131
Xenon
Xe
84
Krypton
Kr
40
Argon
Ar
20
Neon
Ne
4
Helium
He
118
86
54
36
18
10
2
102
173
Yb
Ytterbium
70
(284)
(258)
Mendelevium
(259)
Nobelium
(262)
Lr
Lawrencium
103
175
Lu
Lutetium
71
(289)
symbol
period
number
name
atomic
number
group
number
(288)
(293)
2
11
Boron
B
13
(294)
atomic mass
5
(294)
Ununtrium Ununquadium Ununpentium Ununhexium Ununseptium Ununoctium
Cn Uut Uuq Uup Uuh Uus Uuo
201
Mercury
Hg
112
80
112
Cd
65
Zinc
Zn
Cadmium
48
30
12
Al
11
B
Boron
Aluminium
13
5
13
Fm Md No
167
Er
Erbium
100
68
(280)
Rg
197
Gold
Au
108
Silver
Ag
64
Copper
Cu
111
79
47
29
11
Meitnerium Darmstadtium Roentgenium Copernicium
Mt
192
Ir
Iridium
109
77
103
Rh
59
Cobalt
Co
Rhodium
45
27
9
metals
semi-metals