integrated science teacher’s guide 1 integrated... · 1 winmat publishers limited teacher’s...

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winmatPUBLISHERS LIMITED

Teacher’sGuide

AuthorsS.A. AliJ.W. EssiahJ.A. KwartengE.C. Saka

AdvisorDerek MacMonagle

GAST Editorial AdvisorsT.K. ArbohS.A. MohammedE.O. Ocquaye

Integrated Science

GAST

Junior

FIRE

WATEREARTH

AIR

Ghana Associationof Science Teachers

JHS INT SCI TG 1.indd 1 06/10/2017 5:43 PM

First published in 2017 by

WINMAT PUBLISHERS LTD

P.O. Box 8077

Accra North

Ghana

[email protected]

www.winmatpublishers.com

Text © Winmat Publishers Ltd. 2017.

Design and Illustrations © Winmat Publishers Ltd. 2017.

All rights reserved. No reproduction, copy or transmission of this

publication may be made without written permission. Any person who

does any unauthorised act in relation to this publication may be liable to

criminal prosecution and civil claims for damages.

ISBN 978-9988-0-4646-0

Designed and typeset by Francis K.N. Nunoo

Illustrated by Seth Attipoe

The publishers have made every effort to trace all copyright holders but if

they have inadvertently overlooked any, they will be pleased to make the

necessary arrangements at the first opportunity.


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ContentsINTRODUCTION 1

PART 1 4

I. OVERVIEW OF INTEGRATED SCIENCE YEAR 1 CONTENT 4

II. SKILLS 7

III. SAFETY ISSUES 9

IV. TEACHING METHODOLOGY 12

V. MULTI-ABILITY LEARNING 15

VI. ASSESSMENT 18

PART 2 35

SECTION 1: INTRODUCTION TO SCIENCE 35

UNIT 1 INTRODUCTION TO INTEGRATED SCIENCE 35

UNIT 2 MEASUREMENT 48

SECTION 2: DIVERSITY OF MATTER 56

UNIT 3 MATTER 56

The kinetic theory ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 59

Solids .... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 59

Liquids .. ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 60

Gases .... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 60

Cells...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 61

UNIT 4 THE NATURE OF SOIL 66

Soil particle size ... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 68

Soil organic matter..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 69

Soil colour.... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .. 70


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UNIT 5 HAZARDS 75

Warning signs ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 77

Other safety signs ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 78

SECTION 3: CYCLES 85

UNIT 6 THE LIFE CYCLE OF FLOWERING PLANTS 85

Pollination.... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 87

Seed dispersal ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 88

UNIT 7 VEGETABLE CROP PRODUCTION 93

The Growing Connection (TGC) ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 95

Staple foods . ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... 96

SECTION 4: SYSTEMS 102

UNIT 8 FARMING SYSTEMS 102

Farming in Ghana ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....103

Farming in Northern Ghana ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....104

UNIT 9 RESPIRATORY SYSTEM OF HUMANS 110

The need for gaseous exchange ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....112

Gaseous exchange in humans .. ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....112

Respiration ... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....114

Aerobic respiration ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....114

Anaerobic respiration . ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....115

SECTION 5: ENERGY 118

UNIT 10 SOURCES OF ENERGY 118

Historical perspective on energy...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....120

Energy sources for the future.... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....121

UNIT 11 CONVERSION AND CONSERVATION OF ENERGY 124

UNIT 12 LIGHT ENERGY 131


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UNIT 13 BASIC ELECTRONICS 138

Evolution of the electric cell...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....140

Voltaic pile ... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....140

Daniell cell ... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....140

Leclanché cell...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....140

Current and potential difference ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....141

SECTION 6: INTERACTIONS OF MATTER 145

UNIT 14 ECOSYSTEMS 145

Ecology. ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....147

Biotic factors in ecosystems ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....148

Abiotic factors in ecosystems.... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....148

UNIT 15 AIR POLLUTION 154

The evolution of the Earth’s atmosphere ...... ...... ...... ...... ...... ...... ...... ...... ...... .....155

Global warming .. ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....156

The greenhouse effect ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... .....157

UNIT 16 PHYSICAL AND CHEMICAL CHANGE 162


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1

IntroductionThis series of books has been written to provide teachers in Ghana with a course which delivers the new syllabus for Junior High School Science.

This Teacher’s Guide is designed to support the teacher in lesson planning and delivering for the Year 1 syllabus, both in terms of factual content and the development of a range of both practical and critical thinking skills.

In Part 1 of this Teacher’s Guide the teacher will find:

• an overview of the Integrated Science Year 1 syllabus

• a discussion of the various skills that it is hoped pupils will develop as a result of following this course

• a review of safety issues with a view to providing a safe environment for pupils to learn

• suggestions on how the teacher may use a variety of different approaches to deliver the course. There are suggestions on how the teacher may organise teaching for pupils of different abilities including those who are disabled in some way

• advice on how and when to assess the progress of pupils.

Part 2 of this Teacher’s Guide will consider the content of the Integrated Science syllabus. Within each unit of this book the teacher will find:

• an introduction

• a list of specific objectives from the syllabus

• cross-references to the Pupil’s Book

• a suggested teaching plan

• additional background information which will allow a broader approach to lessons

• a list of resources with suggestions for using low- or no-cost materials for practical activities where possible

• suggestions where critical thinking skills might be developed

• diagnostic exercises which can be used to identify problematic areas within a unit

• answers to the exercises and activities in the Pupil’s Book.


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The relevant section of the Teacher’s Guide should be read well in advance of teaching a unit so that the teacher has time to plan his or her approach, gather equipment and materials required for activities, and write suitable lesson plans.

Part 1 Effective science teaching i. Overview of Integrated Science Year 1 content

ii. Skills

iii. Safety issues

iv. Teaching methodology

v. Multi-ability learning

vi. Assessment

Part 2 Teaching notes

Section 1: Introduction to scienceUnit 1 Introduction to Integrated Science

Unit 2 Measurement

Section 2: Diversity of matterUnit 3 Matter

Unit 4 The nature of soil

Unit 5 Hazards

Section 3: CyclesUnit 6 The life cycle of flowering plants

Unit 7 Vegetable crop production

Section 4: SystemsUnit 8 Farming systems

Unit 9 Respiratory system of humans

Section 5: EnergyUnit 10 Sources of energy


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Unit 11 Conversion and conservation of energy

Unit 12 Light energy

Unit 13 Basic electronics

Section 6: Interactions of matterUnit 14 Ecosystems

Unit 15 Air pollution

Unit 16 Physical and chemical change


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PART 1

i. Overview of Integrated Science Year 1 contentThere are sixteen units in the Year 1 Integrated Science course. Each unit consists of a series of topics which can be delivered in part of a lesson, or in one or more lessons according to their length.

Section 1: Introduction to science

Unit 1 Introduction to Integrated Science

Meaning of science

Natural sciences and applied sciences

Integrated science

How scientists work

Science and technology

Effects of science and technology on society

Negative aspects of science and technology

Unit 2 Measurement

Common physical quantities

Measuring instruments

Units

Prefixes in relation to units

Measuring area and volume

Reading volume in graduated containers

Determining the volume of irregular solid objects

Measuring temperature

Measuring time

Determining density


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i. Overview of Integrated Science Year 1 content

Section 2: Diversity of matter

Unit 3 Matter

Matter

States of matter

Characteristics of solids, liquids and gases

Changing state

Plant and animal cells

Unit 4 Nature of soil

Nature of soil

Uses of soil

Physical properties of soil

Soil profiles

Unit 5 Hazards

Meaning of the term ‘hazard’

Warning and safety signs

Safety precautions

Section 3: Cycles

Unit 6 The life cycle of flowering plants

Stages in the life cycle of a flowering plant

Conditions for germination

Life cycle and crop production

Unit 7 Vegetable crop production

Crop production

Vegetable crops

Vegetable crop production

Tomato and cabbage production

Importance of vegetable production

Section 4: Systems

Unit 8 Farming systems

Different farming systems

Crop rotation

Unit 9 Respiratory system of humans

Respiration

The respiratory system

Aerobic and anaerobic respiration


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i. Overview of Integrated Science Year 1 content

Section 5: Energy

Unit 10 Sources of energy

Nature of energy

Renewable and non-renewable sources

Energy from renewable sources

Unit 11 Conversion and conservation of energy

Forms of energy

Potential and kinetic energy

Energy transformations

Energy conservation

Unit 12 Light energy

Rectilinear propagation of light

Pinhole camera

Shadows

Eclipses

Reflection

Refraction

Unit 13 Basic electronics

Nature of electronics

Electronic components in circuits

Charging and discharging capacitors

Section 6: Interactions of matter

Unit 14 Ecosystems

Ecosystem

Habitat

Adaptation

Energy transfer

Threats to an ecosystem

Unit 15 Air pollution

Names and sources of common air pollutants

Harmful effects of air pollution

Unit 16 Physical and chemical change

Physical change

Chemical change


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ii. Skills

ii. SkillsIn delivering an Integrated Science course, there are a range of skills that a teacher seeks to engender in his or her pupils. A good course will be seamless in the sense that all of these skills will be woven into the subject content so that pupils will acquire them within the context of a variety of topics.

Knowledge and understandingKnowledge requires pupils to remember and recall facts. It is considered to be the lowest level of learning because it requires no more than a good memory and indicates nothing about how well the facts are understood.

Pupils need to remember facts but they must also demonstrate an understanding of the significance of facts, and how facts link together in order to explain observations and concepts.

Critical thinking skillsIf skills are limited to knowledge and understanding, pupils will learn something of science. However, it is only when pupils start to think about and question what they are learning that real progress is made. Beyond this, pupils should apply what they have learnt to new situations and offer their own explanations of what they have observed based on scientific principles.

The following table outlines higher cognitive skills or critical thinking skills. It is highly desirable that pupils are provided with opportunities to develop such skills during the course.

Critical thinking skill Interpretation

Application The ability to apply general scientific principles to specific situations.

The ability to take knowledge and understanding from a familiar context and apply it to another unfamiliar context.

Analysis The ability to break something down into its component parts and to test the validity of each part.

The ability to compare and contrast by looking for similarities and differences. continued


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ii. Skills

Critical thinking skill Interpretation

Synthesis The ability to create something new by drawing together what has been learnt and what is consistent with scientific principles.

Evaluation The ability to look critically at an exercise, a practical project or some other scientific work and to make critical judgements based on given criteria. Pupils should be encouraged to evaluate their own work with a view to improvement.

In each of the topics in this book, some suggestions are made as to where critical thinking skills may be introduced; or where a topic may be extended to provide a suitable vehicle for delivering and practising such skills.

Science process skillsScience is a practical subject and, as such, a good science course should provide many opportunities for pupils to gain and practise a range of skills which are related to the scientific method. These skills are both mental and practical and can conveniently be described as process skills. Here are some examples of process skills.

Process skill Interpretation

Lesson planning The ability to plan a strategy to solve a defined problem or to carry out a given process, using the enquiry method.

Observing The ability to use all of the senses to make accurate observations.

Measuring The ability to make accurate measurements using suitable instruments.

Manipulating The ability to handle apparatus and equipment correctly and safely.

Communicating The ability to describe findings in words, both orally and in writing.

Data handling skillsMany of the experiments and activities that pupils undertake will provide either qualitative or quantitative data.


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iii. Safety issues

As part of a good science course, students should learn how to record data, in the form of tables, for example, and to display the data in appropriate forms, such as pictographs, bar graphs, line graphs and pie charts.

iii. Safety issuesScience is an exciting subject which should stimulate the curiosity of pupils and increase their desire to learn more. A good science course should provide many opportunities for pupils to carry out practical activities. However in doing so the teacher must be mindful of the potential hazards associated with such work.

Practical work which is not well planned and carried out sensibly may result in injuries such as cuts, burns, irritation to the eyes and nose or even poisoning. The teacher should consider the following information in relation to practical activities.

Laboratory rulesAll pupils should be made familiar with a set of laboratory rules designed to make science lessons safe. A small number of rules which are easily remembered will have a greater impact than a long list which pupils will forget.

Here is an example of laboratory rules which are easily remembered and which will prevent accidents.

DO

• Follow instructions

• Tell your teacher if you have an accident or break something

• Wipe up spillages immediately

• Wear protective clothing when carrying out experiments

DON’T

• Run about the laboratory

• Leave coats and bags where others may trip over them

• Touch apparatus or chemicals without being told to do so

• Eat, drink or taste things in the laboratory

Impress upon pupils that it is their responsibility to provide a safe working place in the laboratory, both for themselves and for other pupils working around them.


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iii. Safety issues

Risk assessmentBefore contemplating carrying out a practical activity the teacher must first assess the risks involved and devise ways of working which will either eliminate or reduce these risks to an acceptable level.

Here is an example of a procedure that pupils may be asked to carry out in the Year 1 course:

• cut up an onion

• remove a piece of onion skin

• place the onion skin on a microscope slide

• stain the onion skin with iodine solution

• place a cover slip over the onion skin

• examine the stained onion skin using a microscope.

What are some potential risks and how may the teacher deal with them?

Potential risk Dealing with the risk

Pupils may cut themselves on sharp knives.

Provide the pupils with pieces from an onion which has already been cut up, or warn pupils when using a knife to cut down onto a board and not cut towards themselves.

Onion releases chemicals which cause the eyes to water.

Tell the pupils not to put their faces near the onion when cutting, and not to put their fingers anywhere near their eyes afterwards until they have washed them with soapy water.

Iodine solution stains clothing. Warn pupils that iodine solution will permanently stain their clothing so they should take extra care when using it and wipe up any spillage immediately.

If the tube of the microscope is wound down while the pupil is looking through the eyepiece it may go down too far and break the cover slip and slide. The broken glass may damage the objective lens.

Warn pupils to wind down the tube of the microscope while observing from the side so that they can see when the objective lens approaches the cover slip. They should look through the eyepiece and move the tube away from the cover slip in order to focus the microscope.


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iii. Safety issues

If the teacher is in any doubt as to whether an experiment is safe, or indeed will give the desired results, he or she should work through it prior to the lesson and, if necessary, modify the procedure so that it can be completed safely by pupils of the class age group.

Pupils should wear eye protection and wear laboratory coats when carrying out practical work. If laboratory coats are not available, use old shirts to protect the body from splashes and spillages.

If experiments are likely to produce obnoxious fumes they should be carried out in a properly ventilated fume cupboard. If such a cupboard is not available, such experiments should be carried out by an open window in a well-ventilated laboratory or outside the laboratory.

After assessing the risks involved in carrying out an experiment using his or her professional judgement, a teacher may decide that a particular experiment is not suitable to be carried out by pupils although it might form an important part of a topic. Under these circumstances, the teacher should demonstrate the experiment, taking whatever steps are necessary to ensure the safety of the pupils watching it.

First AidEven after carrying out risk assessment and making adequate provisions for safety, the teacher should anticipate that occasional accidents may happen, because pupils are young and make mistakes or errors of judgement.

It is desirable that a First Aid kit containing items such as cotton wool, eye wash, antiseptic cream, bandages and plasters is available in the laboratory. The contents should be inspected regularly and items replaced as they are used up.

In the event of serious injury, the teacher should seek medical help as quickly as possible. However it is likely that most accidents in the laboratory will result in minor injuries which can be treated provided the teacher is familiar with some basic First Aid procedures.

• Chemicals in the eyes – place the pupil in a horizontal position, either on a table or on the floor, and rinse the eyes with clean water for 10 minutes.

• Chemicals in the mouth – spit out as much of the chemical as possible, then rinse out the mouth with clean water which should also be spat out.

• Chemicals on the skin – wash the area of skin with clean water for several minutes.


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• Burns – cool damaged skin in cold water for 10 minutes then cover with a clean plastic bag or cling film; anti-burn cream is not recommended as it can cause heat to be retained and worsen the burn.

• Minor cuts – wash the wound and remove any dirt; apply antiseptic cream and either a plaster or a bandage as appropriate.

Safety equipmentA blanket should be kept for smothering fires. In the event of a pupil’s clothing catching fire, the area of clothing should be smothered with the blanket immediately to prevent air reaching the flame.

A bucket of dry sand should be kept in the laboratory. In the event of a fire, the sand should be sprinkled or poured on the fire to smother it. Sand is particularly useful where a fire involves an organic liquid like kerosene or fat. Water should never be used to extinguish such fires.

iv. Teaching methodologyScience is a practical subject and the teacher should take advantage of every opportunity to carry out practical work. Where this is not possible, alternative approaches which stimulate pupils should be sought. Courses based entirely on note- taking and written exercises will not deliver either the ethos or the practical skills required by pupils.

Practical activitiesHumans learn by exploring from a very early age so a teaching method that makes use of a pupil’s natural curiosity is likely to be well received.

When lesson planning a practical activity, the teacher must give consideration to factors such as the availability of equipment and materials, the difficulty of the planned procedures, the amount of time available and the potential risks involved. The teacher will then be in a position to make decisions such as:

• Should pupils work individually or in groups?

When there is sufficient equipment and materials, and time is not an issue, it is best if pupils work on their own as this will allow them to develop practical skills. If equipment or materials are in short supply, or the practical activity is likely to take too long for an individual, pupils should work in small groups. A maximum of four pupils per group is often considered to be appropriate. When pupils work in groups,


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it is essential that the teacher ensures that every member of the group contributes to the work and has an opportunity to manipulate equipment and collect data as appropriate. Mixed groups of pupils in which boys carry out all of the practical procedures while girls only record data are not acceptable.

• What level of support should be provided for pupils?

At one extreme an activity may be totally prescriptive and provide a pupil with little opportunity for an individual approach. Conversely, a completely open-ended activity allows a pupil a great deal of opportunity to develop their own ideas, but these may not be compatible with issues such as availability of equipment and materials, safe practice or time restraints. Within any science course there will be opportunities to provide practical activities of different levels of structure.

• What use can be made of locally available equipment?

Scientific equipment is generally expensive. Sometimes it is possible to make use of locally available alternatives. For example, an empty jam jar can take the place of a beaker if it is not necessary to heat a liquid. Similarly, a small teaspoon provides a good alternative to a spatula.

It may also be possible for the teacher to make simple pieces of apparatus from locally available materials. For example, a rain gauge can easily be made from an empty soda bottle.

Class demonstrationAlthough practical activities are desirable, there may be instances where a class demonstration is more appropriate. If an activity requires a particular piece of equipment which is only available in limited numbers, then the teacher has no alternative but to carry out the activity for the class to observe.

There may also be practical activities which are considered too dangerous to be carried out by individuals within the classroom. If safety is an issue then the teacher must not allow pupils to put themselves at risk.

The teacher should also consider limiting activities that produce unpleasant fumes to class demonstrations. It is not sensible to allow pupils to carry out activities that will fill the laboratory with unpleasant and perhaps poisonous gases.

There may be a few instances where it is impossible for the teacher to provide even a class demonstration. For example, some industrial processes require expensive and complex equipment which is impossible to replicate in the laboratory. Under these circumstances, the teacher must refer to the Pupil’s Book but it is essential that such processes are fully explained. Pupils should not be left to read through a process without being given any explanation.


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BrainstormingBrainstorming provides a useful way to start a unit of work. It gets pupils thinking about the topic in hand while, at the same time, it provides the teacher with some insight into the level of pupil understanding.

An appreciation of pupil understanding will allow the teacher to pitch lessons at the correct level. If lessons are pitched too low, pupils become bored and distracted because they don’t believe they are learning anything new. Conversely, if lessons are pitched too high, pupils soon lose touch and do not understand what they are being told.

DiscussionDiscussions in which both the teacher and the class exchange knowledge and ideas are an essential part of any course and are not restricted to science lessons. It is only through discussion that pupils can gain the fullest possible appreciation of the lesson content. At the same time, questions asked by pupils alert the teacher to those parts of a topic which have not been well understood, and to those misconceptions which occasionally arise.

Without discussion, there is a danger that the teacher becomes regarded as the fount of all wisdom of pupils while they receive knowledge without comment.

A free atmosphere should pervade the classroom or laboratory. Pupils should be encouraged to speak out about things without fear of being thought stupid. Pupils should be taught to listen to the opinions of their peers without interruption and wait patiently for their turn to voice their opinions.

Drama and role playOpportunities for drama and role play may be limited in science courses although they are a valuable alternative strategy for dealing with the course content. Role play is particularly useful in dealing with social issues related to science, such as pollution and environmental protection.

Role play is also a useful skill for pupils to develop for use outside the classroom. It can help when dealing with real situations in everyday life.

Question and answerAsking questions about lesson content provides a useful way of identifying those parts of a lesson that have been understood and those which are causing problems


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for pupils. Asking questions can provide a means of initiating class discussion when pupils are reluctant to ask questions themselves.

There is also a role for written questions within a lesson plan.

v. Multi-ability learningIn any large class it is likely that the teacher will be presented with a range of abilities and perhaps also disabled pupils. It is impossible to provide pupils of differing abilities with the teaching they require simply by standing in front of a class and dictating notes or writing on the board.

The teacher must devise strategies whereby pupils can receive group or even individual attention. In order to achieve this, there must be a shift from teacher-centred learning towards pupil-centred learning. In this section the teacher will find some suggestions as to how this can be done.

DiscussionIt is often better to discuss topics with pupils rather than to lecture them. Discussion provides all pupils with the opportunity to contribute and to ask questions about things they do not understand. To some extent, discussion also provides the lesson with an appropriate tempo; the teacher can move quickly through things which are well understood and pause to spend more time on those things which are not.

The teacher should have a list of things which are to be covered in the lesson and should use this to guide the discussions and move on when they believe sufficient time has been given over to a particular issue.

Discussion also gives the teacher immediate feedback on how well, or how badly, particular aspects of a topic are understood. If, after discussion, the teacher thinks that certain things have not been well understood, some remedial action can be taken. This might be going back over some of the work or perhaps approaching the work from a different direction or in a different way.

Group workApart from the educational advantages of group work, it is appropriate that pupils should learn to work together in groups as much of life is about working in harmony with others.


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Group work is often desirable when carrying out practical activities due to a lack of resources, or where an activity is likely to overrun the time available if carried out by an individual. However, group work should not be restricted to practical activities.

Groups may consist of pupils of similar abilities. In this way, groups of more able pupils can be asked to get on with a task while the teacher provides extra help for those groups of less able pupils. It is essential that all pupils contribute equally to the work of the group.

Groups may also consist of a mixture of abilities. The less able pupils in a group can learn from the more able by peer teaching. More able pupils may express themselves in ways which are different from the teacher’s and may sometimes be easier for the less able pupils to understand. It is essential that the more able pupils appreciate their role and are genuinely prepared to help rather than to show off to their less able friends.

Group work frees the teacher from having to stand in front of the class for the whole lesson so that he or she can pass around the class working with different groups of pupils and providing different levels of support as appropriate.

Open-ended tasksIt is impossible to write exercises or set tasks which are satisfactory for every pupil in a multi-ability class. If the work is too easy, the more able are not stretched and will finish very quickly. If the work is too difficult, the less able will not be able to do it and will gain nothing from it.

One way of getting around this is to make work open-ended so that each pupil can do as much or as little as they are able to. For example, in an exercise there may be relatively easy questions at the start but questions become more difficult as the pupil works through it.

In a practical activity, less able pupils may be asked to collect the minimal amount of data while those more able may be expected to collect as much data as possible.

In assessing open-ended tasks, it is important that the achievements of the less able are given equal prominence and praise as those of the more able. Pupils should be made aware that each has his or her own strengths and weaknesses. A pupil who is less able in science may have to work harder to achieve less than a pupil who is more able and finds the subject very easily.

Extension (enrichment) activitiesAnother way to occupy and stretch the more able pupils in a class is to provide extension activities.


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This could take the form of an exercise or task in which all pupils are expected to reach a certain point, but additional questions or materials are provided for those who are able to go beyond that point. In this way, less able pupils are able to work at their own pace without feeling that they are being pressurised to achieve more than they are able.

It is important that all pupils undertake work essential to understanding the topic content. Any extension work should contain material which provides additional practice or perhaps goes a little beyond the syllabus content.

Pupils with a physicall disabilityThere may be pupils who have some form of physical disability, particularly to their limbs, which makes it difficult for them to partake in practical activities where they need to move around and manipulate apparatus.

It is impossible to give advice on all possible forms of physical disability but the following general points should be borne in mind:

• Pupils may need more room to move about so they must have adequate working space.

• Equipment and apparatus must be user-friendly so that the pupil can handle it with ease.

• Pupils may need assistance in setting up apparatus.

• Pupils may need additional time to complete tasks.

• There may be additional safety issues that must be taken into account.

• It may be necessary to modify activities in order that they can be completed.

Pupils with impaired HearingAny pupil who has impaired hearing may find it difficult to hear what the teacher is saying. Depending on the degree of hearing loss, the teacher should consider:

• Sitting the pupil at the front of the class so that he or she may hear better.

• Using illustrations to teach concepts.

• Providing written instructions for practical activities.

• Providing notes on the lesson content.


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vi. Assessment

Pupils with visual impairmentVisual impairment may include colour blindness, sensitivity to light, an inability to interpret illustrations and an inability to see clear images. Depending on the nature of the impairment, the teacher should consider:

• Sitting the pupil at the front of the class so that he or she can see the board more clearly.

• Describing structures in terms of colour and labelling diagrams with the colours.

• Warning pupils in advance when any bright light may be produced, such as when burning magnesium.

• Talking pupils through diagrams rather than assuming that they are self-explanatory.

Other conditionsThere are a myriad of other physical and behavioural conditions which the teacher may need to deal with over time. It is impossible to provide advice beyond saying that the teacher must get to know his or her pupils well, be aware of those who may need extra help in some way, and be prepared to make special provisions for them.

vi. AssessmentIt is very important and useful for a science teacher to assess pupils of different levels in various ways and settings. Therefore, in the course of guiding pupils to learn science effectively, the teacher needs to plan and design assessment tools. The tools will be used to collect evidence about teaching and learning.

Assessment information will help the teacher to make decisions about pupils’ learning. It will also allow the teacher to evaluate his or her lessons and to improve their teaching practices.

The word ‘assessment’ is used to mean the process of identifying, obtaining and providing information about teaching and learning, usually with reference to expected outcomes or criteria. Assessment is about direct measurement of performance.

Assessment refers to all those activities which measure performance of pupils and, by outcome, of the teacher. Therefore, assessment is a task that provides information which may be used to modify the teaching and learning activities. Assessment of learning is an on-going (continuous) process.


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vi. Assessment

Evaluation is the process of making value judgments about overall teaching and learning. These judgments are made on the basis of information gathered through assessment and monitoring. Thus assessment and evaluation are closely related.

Relationship between assessment and evaluationAssessment data is used to make evaluation in the sense that, after administering a test of any kind, it is important to mark it and obtain scores. The next task will be to interpret the scores in order to determine the number of pupils whose performance is poor, average or high, i.e. valuation. This may be done either on a summative or formative basis.

Continuous assessment is a formative evaluation. It is an on-going process which is done from the beginning and continues throughout the school year.

Summative evaluation is the process of judging the totality of all learning that the learner has undergone during a period of time. This is frequently carried out in the form of a test at the end of a unit, term or year.

Formative assessment is often about finding out if particular knowledge and skills have been acquired by pupils. These are often criterion-referenced tests which measure the pupil’s performance in relation to specific instructional objectives. The questions on the tests are directly related to specific knowledge and skills.

Summative assessment is often carried out to determine order so that grading, placement and selection can be made by the teacher. An assessment that compares the performance of a pupil to other pupils is described as norm-referenced. Schools commonly use norm-referenced tests. Summative assessment might also be criteria-referenced in terms of whether given competencies have been mastered or not.

Informal assessmentAssessment may be informal when the teacher moves around the class during a science lesson, talking to, listening to and watching pupils at work.

Informal assessment does not require a formal or defined reference group or a task. More often it includes idiosyncratic information obtained in a setting that is natural to the pupils’ daily experience and ordinary classroom interactions.

Informal assessment data may also include subjective opinions that reflect either the teacher’s teaching style and needs, or the pupil’s learning style and needs. Informal assessment encompasses information that is on-going and cumulative rather than information that is drawn from a fixed point in time.


20

vi. Assessment

Informal assessment data guides the practices of the teacher in the following ways:

• It helps the teacher to check on the general participation of pupils in science lessons. This occurs when pupils are effectively monitored as they carry out their work.

• Talking to and listening to pupils’ ideas and contributions during science lessons will help the teacher to discover any learning difficulties. Once alerted, he or she can start to deal with the problems immediately. This may include pupils with problems in learning science concepts, slow learners, pupils with language problems and those with a negative attitude to learning science. A pupil who spends hours in completing classroom activities produces a myriad of clues as to his or her motivation, ability and needs.

After gathering informal assessment data, the teacher should use it to identify the problems of particular pupils and devise methods of dealing with them. For example, there may be a pupil or group of pupils who are having problems visualising an abstract concept, such as the structure of molecules. The teacher can address this by the use of suitable diagrams, wall charts or models.

The teacher’s skills in gathering and interpreting data on a daily basis will help him or her to gain some insight into the specific problems and requirements of each individual pupil. Such data allows the teacher to devise more appropriate teaching strategies and set more appropriate goals which will, in turn, result in an overall improvement in classroom management.

Formal assessmentIn general, the information obtained through informal assessment is used to interpret the data gathered through formal assessment. For example, the scores of pupils who were less keen to explain and describe concepts will be low in a written test meant to measure such a competence.

Both informal and formal assessment procedures are used in most evaluation situations.

The teacher can assess their pupils formally through oral or written tests, quizzes, examinations and other performance-based tasks and investigations. The teacher should plan and administer at least one of the above to their pupils at regular intervals. For example, a formal assessment might be carried out at the end of each unit.

The teacher may plan with pupils to have a regime of regular formal assessment consisting of a variety of different assessment methods to assess their performance and prepare them for end-of-year examinations.


21

vi. Assessment

Planning for assessmentInformal assessment may be on-going. A teacher may assess each pupil at regular intervals by monitoring their work in the classroom. It is neither possible nor desirable to assess each pupil in each lesson. The teacher should aim to assess each individual once over a given period of time, such as on a weekly basis. In addition, pupils’ work may be assessed by marking exercise books at regular intervals.

There are a number of factors to be considered in planning for assessment. The teacher can devise a suitable strategy based on the following questions:

• Why do we need assessment in science?

• How do I assess?

• Who will be assessed?

• What will be included in the assessment?

• How will I ensure reliability and validity?

Assessment requires the teacher to:

• Identify the purpose.

• Select a suitable activity.

• Prepare the learners for assessment.

• Plan and design the assessment tasks.

The teacher should bear in mind that the nature of the assessment tasks will depend on the nature of subject matter, and the purpose of the assessment, and should reflect the required knowledge, skills and attitudes. The tasks set by the teacher for his or her pupils should be challenging, interesting and enjoyable for pupils.

Reliability and validity are basic concerns of all assessment tasks. In teacher-made tests, the responsibility for reliability and validity rests with the teacher.

Good reliability requires the teacher to provide enough test items so that an individual’s chance errors and misconceptions do not result in an inaccurate picture of their actual ability.

Good validity requires that the assessment is carried out on the appropriate part of the syllabus, the assessment tool is written in such a way that it can easily be understood by all pupils, and the assessment tasks can be completed in the time available.


22

vi. Assessment

Question writingThe following show how different types of questions can be developed around an experiment in which the growth of seedlings is monitored over a period of time. These questions could be used in a topic on the growth of plants.

1 Multiple choice question

A B C D

Q: Four similar-sized plants were grown for 7 days under different conditions. Which plant grew strongest?

A B C D

2 Sentence completion question

A B C D


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vi. Assessment

Q: Four similar-sized plants were grown for 7 days under different conditions.

Plant C grew the .................................... . strongest weakest

Plant C grew two more pairs of leaves than ............................... .

3 Data extraction question

Q: Different amounts of fertiliser were applied to six similar-sized plants and their heights were measured after seven days.

A B C D E F

25 cm

20 cm

15 cm

10 cm

5 cm

0 cm

0 g 5 g 10 g 15 g 20 g 25 g

Tabulate the information given in the diagram in the following table.

Plant A B C D E F

Growth / cm

Fertiliser / g m-2

In this question, pupils must interpret information in the diagram and complete the table.

4 Data presentation question


Draw a bar graph / line graph to present this data.


24

vi. Assessment

Plant A B C D E F

Growth / cm 4 9 15 19 23 16

Fertiliser / g m-2 0 5 10 15 20 25

In this question pupils are given a table of data and can be asked to draw a bar graph or a line graph.

5 A data analysis question


The following graph shows the heights of the plants after seven days.

30

25

20

15

10

5

0

Gro

wth

/cm

Fertiliser/ g per square metre0 5 10 15 20 25

Comment of the pattern of growth shown in the graph.

In this question, pupils are given a graph and asked questions about it.


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vi. Assessment

In addition to not being related to the part of the syllabus being taught, questions may also be invalid for a number of other reasons. Here are some examples of bad practice.

1 Which of the following is an insect?

A ant B mosquito C mouse D snake

Ant and mosquito are both insects. There should only be one correct answer in a multiple choice question.

2 Arrange the following fish according to size starting with the largest.

dzaflafa nile perch shark whale yalefo

The science in this question is incorrect. A whale is not a fish but a mammal.

3 Which planet do you think is the biggest?

Whatever the pupil writes will be correct because it is what he or she thinks. The question should be ‘Which planet is the biggest?’

4 The following table shows how the mass of five pupils varies with their height.

Mass (kg) 5 8 10 12 14

Height (cm) 20 40 55 63 65

Use this data to draw a graph of height against mass.

The data in this question is totally unrealistic. Any data used in a question should be sensible in terms of what it represents.

5 It takes a car 3 hours to travel from Accra to Kumasi. What was its average speed for the journey?

This question cannot be answered because insufficient data has been given. In order to calculate the average speed, the pupil needs to know the distance from Accra to Kumasi.


26

vi. Assessment

Planning exercises, tests, quizzes, examination and performance-based assessment

ExercisesExercises may consist of a few short, straightforward questions covering the instructional objectives. The teacher should write down the correct responses, allocate appropriate time, and decide the particular stage of the lesson where the exercise will be done.

HomeworkIn planning homework, the teacher can prepare a task that engages pupils in brainstorming, revising, and practicing the ideas, skills and theories from the topic recently covered. The types of questions to be included in the homework may depend on pupils’ responses to class exercises and the competencies the teacher wishes to focus on.

A homework assignment for pupils who perform well in class exercises may include extra and more demanding questions. Those who did not do well in the class exercises may be required to work on the same questions again or others of the similar nature. Pupils with special needs and slow learners may be given a separate set of questions.

Weekend exerciseExercises should be given to pupils to solve during the weekend. These should be exercises based on the learning objectives treated during the week and some questions to get pupils reading around.

QuizzesA quiz can be in the form of a series of short and challenging questions which are answered by each individual learner under the supervision of the teacher. It should be allocated a shorter time, and in contrast to exercises and homework, a quiz should be completed without reference to exercise books and other texts for clues or answers.

Class testsTests can be planned in advance. These should be different from exercises and homework, and may contain test items of several types. The teacher should describe the format of a test and its purpose to pupils in advance of administering it.

Written tests may be used to test knowledge and understanding but also to assess skills like application, data handling analysis and decision making. Practical tests such as investigations may be used to test manipulative skills, as well as some higher cognitive skills such as synthesis, evaluation and problem solving.


27

vi. Assessment

School-based assessmentEnd-of-term (terminal) and end-of-year (annual) examinations can be set to include more questions than are in a test. A good examination ought to test all levels of the cognitive domain. It should contain various types of questions and pupils should be advised of the format prior to the examination. The time allocated for completing the examination should be moderately longer than it is thought will be required. The results of the examination can be analysed to provide information for grading and selection.

Designing assessment toolsPupils should not be assessed just for the sake of it. Unnecessary testing:

• Adds to the workload of the teacher.

• Reduces class time that can be spent in covering the syllabus content.

• Results in a loss of impact.

In designing an assessment tool the teacher should take into account the nature of the learners, the subject matter and the instructional process. For example, if pupils have been taught an extended topic it is very likely that the teacher will need to administer a number of exercises and/or tasks to enable pupils to demonstrate mastery of all of the required knowledge, skills and competencies. The teacher should also vary the level of demand of test items within a task, according to the range of abilities of pupils.

The design of assessment tools requires the teacher to make a number of decisions. He or she needs to decide exactly what is it that they wish to assess and thereafter to design the assessment tool accordingly. The assessment tool needs to be:

• Focused on the particular part of the syllabus to tested.

• Focused on the knowledge, skills and competences to be tested.

• Sufficiently demanding to stretch pupils, i.e. not too easy.

• Accessible to all pupils, i.e. not too difficult.

• Clearly set out with instructions that are easily read and understood.

• Written at a language level that can be understood by all pupils.

• Able to be completed by all pupils in the designated time.

A well-designed and fair test will help both the teacher and the pupil to identify those areas of the syllabus and those skills and competencies which require remedial work.


28

vi. Assessment

A teacher needs to use his or her creativity to come up with new and challenging questions. They should not get into the habit of only reproducing or copying exercises which are found in the textbooks and past examination papers. This is because such exercises may not reflect the knowledge, skills and competencies that the teacher wishes to assess. However, questions from textbooks and past papers can be used to improve the teacher’s writing skills in creating their own test items.

Designing good assessment tasksTasks should be based around the knowledge, skills and competencies to assessed. An assessment task should enable the pupils to demonstrate what they know and what they can do.

Initially, the teacher should decide the number of questions which will be included in the task. For example, if there are to be five questions in the task, the ratios can be two fill-in-the-blanks type questions, one multiple choice, and two short answer questions. The mark scheme should provide all of the possible correct answers that pupils may offer.

During the course of teaching science, it is important that the teacher designs different types of tasks. These could include multiple choice tests, short answer tests, open-ended questions, problem solving tasks, group work and short research projects.

Multiple choice questions should have four alternative answers: one key and three distracters:

1 The sense organ used for feeling is the:

A ear

B eye

C nose

D skin

An open-ended question allows the pupil to write what they know:

1 Explain the effects of poor nutrition on children less than 5 years old.

In some of the topics it may be necessary to design tasks that engage pupils in conducting research work or field projects:

1 In the area where you live:

a) Find examples of seeds which are dispersed in different ways.

b) For each type of seed, explain how it is dispersed.


29

vi. Assessment

The teacher should also design a project which can be done as group work, and where the contribution of each pupil can be assessed:

1 In groups of five, conduct interviews with youths who have just recovered from drug addiction and collect the following information:

a) the practices/factors/conditions that influenced them to use/take drugs;

b) the types of drugs they have been using:

c) the effects of the drugs on their body/health, career, family and community;

d) the practices that helped them to stop using drugs.

The assessment can be arranged so that each pupil is assessed by the teacher and at least one colleague. The contribution of each pupil will determine the score of the whole group in this task.

The teacher can also design other tasks that can help pupils to be good inquisitors. Such tasks develop an inquiring mind and help teaching to be a two-way process, and not just the teacher talking all of the time. For example, before getting pupils to investigate the conditions necessary for seed germination, the teacher may encourage pupils to ask themselves several questions about germination of seeds such as:

• What happen to the seeds which have been planted in the soil?

• Some seeds have been planted in wet soil and some in dry soil. Which ones will germinate better?

• Do seeds need air to germinate?

• Do seeds only germinate in the dark?

• Will seeds germinate if you plant them upside down?

• What are the conditions necessary for seeds to germinate?

The central consideration when designing any assessment task is to match the task to the expected pupils’ outcomes in terms of knowledge, skills and competencies.

This means that the tasks the teacher designs for his or her class should target the instructional aims, while allowing pupils to demonstrate their progress and capabilities.

Sources of ideas for good assessment tasks may be:

• brainstorming with colleagues

• looking at textbooks and other publications

• television or newspapers

• looking at local industry or the surrounding environment

• listening to pupils.


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vi. Assessment

Task descriptionAnother important consideration is the need to describe each assessment task in detail. A task description helps the teacher to identify the learning domain and provides for the possibility of writing other assessment tasks from it. It also allows the teacher to review their work and identify problems before they are set for pupils.

Irrespective of the nature of the assessment task, the teacher will need to specify the following:

• The intended use of the results obtained from a task

Specify whether the results will be used in grading and/or selection processes or not. Prior knowledge about the purposes of assessment allows the teacher to select the most appropriate types of tasks.

• The syllabus content upon which the task is based

Specify whether the assessment task is intended to cover several units or the current unit only. Identify the syllabus reference number for the specific objective that the task intends to address.

• The nature and format of questions in the task and whether all questions will be attempted by all pupils

Specify whether all pupils in the class will answer all questions or not. For example, the teacher may instruct slow learners to answer some of the questions and fast learners to answer all of the questions. Also, the teacher may restrict pupils with special learning needs to answering only a few questions.

• Specify whether the task is to be group work or individual work. Where it is group work, specify the roles to be assumed by each member in the group.

Assessments carried out in class often involve individual tasks such as exercises, while assessments carried on field work are more often group tasks.

• The nature of the questions in the task

An assessment task may include questions of several different types. Pupils should be instructed to answer each type of question in the appropriate way.

• The resources needed by pupils to complete the task

Specify any materials, apparatus or other resources which will be needed by pupils to complete an assessment task.


31

vi. Assessment

• The order of tasks

Where there is more than one part to a task, the teacher may need to specify in what order the parts should be attempted.

• The mark scheme and procedure that will be used

At the same time as designing an assessment task, the teacher should also be constructing a suitable mark scheme.

Keeping records and monitoring of pupils’ progress

Meaning and purpose of monitoringMonitoring refers to activities that are pursued by teachers to keep track of pupils’ learning for the purposes of making instructional decisions and providing feedback to pupils on their progress.

Teachers should move around the classroom during group work and engage in one-to-one contacts with pupils about their work. Monitoring individual work will make the teacher aware of how well pupils are progressing with their assignments and working with pupils on a one-to-one basis.

Classroom monitoring largely involves posing questions to pupils during classroom discussions in order to check their understanding of the material being taught.

Questioning provides the teacher with information on pupils’ levels of understanding so that he or she can vary the pace of instruction, either decreasing or increasing the pace of the lesson as appropriate.

Monitoring can alert teachers to situations where pupils do not understand the lesson content and where it may be necessary to break material down into smaller parts to review what has already been taught.

Other monitoring activities include marking and correcting homework. When carefully administered and monitored, homework assignments bear a significant and positive relationship to achievement. Homework also increases pupils’ learning time. Homework should be given frequently as a means of extending pupils’ practice time with new material that is clearly understood by pupils and parents.

The teacher should look to involve parents in monitoring homework. Let them be aware of what needs to be done and encourage homework completion. Homework should be returned to pupils marked, graded and commented on as quickly as possible.


32

vi. Assessment

Learning can also be monitored through administering and correcting tests. Classroom testing is one of the essential elements in monitoring science learning and shows a positive correlation with later pupil achievement.

Effective monitoring of classroom testing will have beneficial effects on learning. This is especially true when tests are administered regularly, collected, scored and returned to pupils promptly so that they can correct errors of understanding before these become ingrained.

Keeping pupils’ recordsTo monitor learning effectively the teacher needs to keep complete records of pupils’ performances. Generally, record keeping refers to consistent and on-going documentation of pupils work and progress. Record keeping will enable the teacher to make decisions and to plan follow-up work. It will allow them to communicate pupils’ progress to parents and other stakeholders and support their comments with evidence of achievement.

There are several types of pupils’ records that can assist the teacher to monitor science pupils effectively. These may include a checklist of observed behaviour.

A checklist can identify different kinds of observable behaviour. It may contain both negative and positive comments. For example:

o Dislikes science.

o Is uncooperative with teacher.

o Often does not attend science lessons.

o Has fights or arguments.

o Contributes regularly to class discussion.

o Can be trusted to work independently.

o Demonstrates high levels of skill in two or more areas.

o Always completes assignments.


33

vi. Assessment

• Individual pupil progress record folders

It is important to have a folder in which the results of all of the assessments carried out in science are stored.

• File of tasks

The teacher can create a file in which he or she retains copies and/or details of the science tasks including the nature of the task, how long the task will take to complete, instructions for the pupil, scoring criteria, a list of resources needed, and dates when the task was set and when it was completed.

• Progress chart

The teacher can place a chart showing the progress of each pupil on the wall of the classroom. When pupils perform a science task well they can be given a coloured star or some other token which indicates their progress.


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35

PART 2

Section 1: Introduction to ScienceAfter studying this section, pupils will be able to:

1. develop an awareness of the relationship between various scientific fields and their interconnectedness

2. develop a scientific approach to problem solving

3. be aware of the influence of science and technology on the development of society

4. recognise the need for humans to quantify their interaction with the environment

5. show an appreciation of scientific attitudes such as precision and accuracy in making measurement

6. recognise the need for humans to quantify their interactions with the environment through estimation and accurate measurement of physical quantities.


IntroductionThis unit is concerned with the meaning of science and the different branches of both natural sciences and applied sciences. Pupils will learn how scientists work and complete activities which illustrate the stages in scientific investigation. In the final part of the unit, pupils will discuss the relationship between science and technology and consider some negative issues to do with their application.

Specific objectivesAfter studying this unit, the pupil will be able to:

1. explain what is meant by the term ‘science’

2. outline the subjects that make up natural science and applied science

3. explain the term ‘integrated science’

4. describe how scientists work


36


5. distinguish between science and technology

6. explain how science and technology affect society

7. outline some negative uses of science and technology, e.g. warfare and computer fraud.

Pupil’s Book cross-references

Syllabus topicSection in Pupil‘s Book

Pupil’s Book Page

Pupil’s Book Activities

Pupil’s Book Page

Meaning of science 1.1 2

Natural sciences and applied sciences

1.2 2 1.1, 1.2, 1.3 6, 7

Integrated science 1.3 8 1.4 9

How scientists work 1.4 9 1.5, 1.6, 1.7, 1.8, 1.9, 1.10

12, 13, 14, 15, 16

Science and technology 1.5 16 1.11, 1.12 18

Effects of science and technology on society

1.6 18 1.13, 1.14, 1.15

20, 24, 25

Negative uses of science and technology

1.7 25

Lesson planningThe syllabus provides a logical order of work on natural and applied sciences and the relationship between science and technology. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Ask pupils to say what they think science is about. Make a list of points on the board.

2. Explain to pupils that science consists of both natural sciences and applied sciences.

3. Discuss the natural sciences and mention some branches of each.

4. Discuss the applied sciences and explain to pupils what makes them different from the natural sciences.


37


5. Discuss some examples of applied sciences and identify the natural science components in them.

6. Pupils should work through Activity 1.1 identifying some scientific fields.

7. Facilitate Activity 1.2 by chairing a debate amongst pupils in which they are encouraged to express their views on certain issues relating to science. Each pupil should be allowed sufficient time to express his or her opinions, while other pupils listen to them without interruption.

8. Pupils should work through Activity 1.3, relating questions to natural science or applied science.

9. Discuss how different areas of science are related and how there is often overlap between areas in applied science. For example, if pupils consider a farmer spraying a pesticide on his crops to prevent insect damage, then here are some possible links:

• Biology – the growth of plants and the life cycle of insects

• Chemistry – the development and synthesis of effective pesticides

• Physics – design of the spray nozzle to atomise the spray for effective coverage.

10. Use the idea of overlapping areas of science to introduce the concept of integrated science and holistic science.

11. Pupils should work through Activity 1.4, choosing two appropriate topics from the list given.

12. As an opportunity for developing critical thinking skills, pupils could be asked to identify and analyse the components of certain branches of science.

13. Ask pupils to describe how they think a typical scientist works. Explain that a scientist doesn’t randomly select materials and mix them together or start taking lots of measurements without some plan of action. Emphasise that there is a scientific method which is applied to all scientific investigations, no matter which branch of the natural or applied sciences is involved.

14. Discuss the scientific method and explain the need for each of the following steps:

• Identifying the problem

• Formulating a hypothesis or suggesting what should be done

• Carrying out experiments

• Making observations using all of the senses

• Collecting and analysing data

• Making deductions and drawing conclusions from observations and/or data


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collected.

15. Make the point that not every experiment will involve making observations and collecting data. For example, examining the structure of a plant cell is about making visual observations, while measuring the temperature of hot water at regular intervals as it cools down is about collecting data.

16. Pupils should work through Activity 1.5 to ensure that they have understood the nature and importance of the different stages.

17. Pupils should work through Activity 1.6 to ensure that they know how to apply the scientific method.

18. Make pupils aware of the importance of recording scientific investigations accurately, and in a logical way, so that other scientists are able to follow what has been done and replicate experiments if necessary.

19. Discuss the way in which scientific investigations are to be recorded.

20. By way of drawing the scientific method and scientific recording together, ask pupils to suggest some features of a good scientist. Write a list on the board and discuss them with the class.

21. Pupils should work through Activities 1.7 to 1.10 applying what they have learnt about the scientific method and recording. After each activity the teacher should have a brief review session so that pupils can comment on what they have done and raise any questions they may have.

22. Introduce the term ‘technology’ and explain the difference between science and technology. Pupils may find it useful to remember technology and ‘the appliance of science’. Discuss the historic development of technology and identify some examples of modern technology.

23. Pupils should work through Activity 1.11 identifying the differences between science and technology.

24. Pupils should work through Activity 1.12 identifying and discussing how technology impinges on their everyday lives.

25. Discuss the impact of science and technology on society within the contexts of:

• Health • Communication

• Education • Provision of energy

• Agriculture • Obtaining water

• Food preservation • Building


39


• Transport • Clothing

26. Explain to pupils that within any society there are certain superstitions and taboos which originated in history when people knew very little about science but were guided by their experience. For example, in some countries certain foods are not eaten or are taboo. These are often foods that go off very quickly and can make people very ill if not eaten fresh. The safest way is not to eat them at all.

27. Pupils should work through Activity 1.13. Some of the work will have to be done at home.

28. Pupils should work through Activity 1.14 drawing on what they have learnt so far about technology.

29. Ask pupils to suggest what advances technology may make in the future. Stimulate their imaginations by asking questions like:

• Will there be cars that also fly through the air?

• Will mobile phones become small enough to wear on the wrist like a watch?

• Will someone invent a machine that does children’s homework?

30. Discuss some ways in which technology may impact on life in the future.

31. Pupils should work through Activity 1.15 suggesting how science and technology might be able to solve some local problems.

32. Explain to pupils that breakthroughs in science and technology are not always used to benefit people. Discuss some of the negative aspects of science and technology including:

• nuclear weapons

• pollution

• computer fraud.

Additional information for the teacherThe term ‘science’ has been used in different ways throughout history.

At the time of the Ancient Greek philosophers, such as Aristotle, science referred to a body of reliable knowledge that can be logically and rationally explained, but there was no notion of experimentation as a means of providing proof.

Since classical antiquity, science has been closely linked with philosophy. Prior to the evolution of modern science the terms ‘science’ and ‘philosophy’ were sometimes regarded as interchangeable.


40


By the beginning of the seventeenth century, ‘natural science’ was considered a branch of philosophy but the term science was still used in a much broader sense than it is today. It indicated reliable knowledge about a topic, such as we might use the term ‘political science’ today.

In a more modern parlance, the term ‘science’ came to refer not just to knowledge itself, but also to the pursuit of that knowledge. At the time of Kepler, Galileo and Newton, the term was treated as synonymous with ‘natural and physical science’ thus taking in physical science but not biological science.

Through the nineteenth century, the term ‘science’ became increasingly associated with the scientific method and was related to the whole of the natural world including biology, chemistry, geology and physics. The term ‘science’ did not include the study of society and of human thought but this was eventually classified as ‘social science’.

During this period, in 1834, the term ‘scientist’ was coined by the naturalist and theologian William Whewell to distinguish those who sought a knowledge of nature from those who sought knowledge in other disciplines.

A scientific method seeks to explain natural events in a way which is reproducible. An explanation or hypothesis is put forward to explain a particular event. As a result of this explanation, predictions may be made and an experiment carried out to confirm these predictions or not. Disproof of an explanation should be regarded in a positive light since it provides some progress towards ultimate understanding.

Natural sciences are commonly divided into life sciences and physical sciences.

Life sciences include: botany, zoology

Physical sciences include: astronomy, chemistry, physics, materials science, earth science

The distinction between individual natural sciences is not always clear cut. There are a number of what may be termed ‘cross-discipline’ fields in which two natural sciences may be combined, such as astrophysics (astronomy + physics) and biochemistry (biology + chemistry). Environmental science is a multi-discipline field that draws on a number of natural sciences since it has physical, chemical and biological components.

Applied sciences are the result of applying scientific knowledge and principles to a physical environment. There are many branches of applied sciences. These include:

Applied engineering Applied linguistics Applied mathematics

Applied physics Applied chemistry Archaeology

Artificial intelligence Ceramic engineering Computing technology


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Electronics Energy technology Energy storage

Engineering physics Engineering technology Environmental technology

Fisheries science Forensic science Forestry science

Medicine Microtechnology Nanotechnology

Nuclear technology Optics Security engineering

Resources• Access to the Internet or reference books

• Hand lens

• Filter funnel

• Containers

• Filter paper

• Cotton wool

• Clean white cloth

• Pond water

• A variety of leaves

Opportunities to encourage critical thinking skillsPupils could be asked to identify and analyse the different strands of pure and applied sciences which are associated with some branches of science; and to display the results of their analysis in some attractive and easily understood way.

Diagnostic assessment exercisesThese diagnostic assessment exercises will help gauge to what extent the specific objectives of this unit have been achieved. You should be honest in your appraisals since the outcomes will assist you in improving your teaching in the future. If, on reflection, you feel that certain parts or aspects of the unit have not been well understood, some remedial work should be undertaken before moving on.

1 Review the lesson spent introducing natural sciences and applied sciences. Did the pupils understand the difference between the two and could they provide examples of each with confidence?


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2 In terms of carrying out experiments this unit is not typical of what pupils might expect of a science course. Were there any particular topics in the unit where it was difficult to hold the interest of pupils? Can you think of more interesting ways to deliver these topics in the future?

3 Activities 1.7 to 1.10 required pupils to apply the scientific method. Were these activities generally done well, or is there a need to go back and review the scientific method again to ensure that pupils have a thorough understanding of it?

Answers to revision questions in the Pupil’s Book

1 C

2 D

3 C

4 B

5 A

6 B

7 C

8 C

9 D

10 a, d, c, b

11 a. Observations and experiments

b. It would ensure that the truth but nothing else will be recorded

c. Other scientists may want to repeat the experiments to find the truth.

d. Pure and Applied sciences

12 Science and technology have made the world into a global village.

Scientists study the environment not only to understand the happenings around us but also to improve the quality of life in every possible way. By so doing, they have found answers to many questions, but still there are unfound answers to many other questions.

Taking a good look around us, it could be observed that science has done so much for mankind. Scientists have applied and developed scientific ideas to produce new materials, tools and machines, medicines, improved forms of transport and communication, improvement in agriculture and in many other fields.

Not very long ago, one had to travel either on foot or by the use of the beast of burden (camel, donkey, horse) for days just to cover a few kilometres of journey but today one only needs to cover the same distance.

The advent of various forms of aircrafts (supersonic jet airliners, intercontinental jumbo jet aircrafts, huge transport aircrafts, etc.) has made travelling very


43


comfortable and easy. One can move conveniently from one place to another; intercontinental travel times have been drastically reduced; vehicles have also helped to improve the transport system tremendously.

Currently, on the high seas, are huge vessels of all kinds (some conveying only passengers and others carrying all sorts of goods across the great oceans of the world). This has helped to boost inter-continental trade so that goods may be obtained from anywhere in the world.

Some fast moving vehicles have also been built, such as comfortable electric trains, connecting one country to another; there are also streamlined and flashy automobiles, fitted with many electronic gadgets which make it possible for one to communicate with relatives and business partners outside the country.

The designing of computers, mobile phones, fax machines, artificial satellites, video conferencing television sets, Internet facilities, etc. have led to an astronomical improvement in the field of communication. For instance, one can travel abroad and still carry out conversations at home, either by use of the telephone or computer.

What is even more amazing is the use of video conferencing facilities. This wonderful opportunity makes it possible for two people located at two different places in the world to see each other and talk to each other.

Obviously, we owe all these facilities to science and technology. These scientific endeavours have made life very easy; now you can talk to anybody anywhere in the world. If the need be, you can travel to anywhere in the world without experiencing any difficulties.

With the help of television, we can observe any incident happening anywhere in the world. We can also be provided with news of incidents anywhere in the world through radio and the media. All these indicate that, indeed, the world has become a global village where everybody knows everybody and can deal with one another on a one-to-one basis.

13 The five products which show how science has contributed to my life are:

(i) A pair of spectacles

(ii) Needle for sewing

(iii) Electricity

(iv) Sewage system

(v) Car


44


A pair of spectacles

As we advance in age, our ability to see accurately diminishes gradually. And in order to regain our power of sight, we have to resort to the use of spectacles. If, in the past, reading became a difficulty, wearing of the appropriate pair of spectacles would bring back smiles ... now you can read so well, thanks to science.

Sewing needle

On a particularly memorable day, I had to put on a special shirt tailored to suit a special occasion. After putting it on, I saw that two of its buttons had torn away. It therefore become impossible to use the shirt. Luckily, after being able to fasten the buttons to their places with the help of a needle, I was able to wear the shirt to celebrate the occasion. Thanks to science for discovering the needle.

Electricity

By pressing a button on the wall darkness disperses to be replaced with bright rays emanating from electric bulbs. Electrical currents coming from a distant source and passing through specially designed wires cause the sparkling light to radiate from a hanging electric bulb.

Without electricity, televisions, fans, radios, air conditioning gadgets etc. cannot operate. Many other machines require electrical energy to function. Electricity provides energy to make life comfortable. Thanks to science.

Sewage system

Scientific ideas have been used to design sewage systems fitted to our toilets in the home. The system is made up of various components: we have the cistern into which water flows and is stored; then the water closet which receives the solid and liquid wastes. Both the cistern and the bowl on which we sit are connected with a pipe. When the handle attached to the cistern is pressed down, water flows, descending with great force to wash the contents of the bowl away into receiving containers situated outside our homes. The whole process is totally dependent on various degrees of pressure. Through their research, scientists have made it possible for the system to operate and perform perfectly; this prevents the unpleasantness of disposing of untreated sewage.

Car

A car has an engine fitted to a hollow iron casket. When the engine is provided with one of its basic requirements – fuel (petrol) – it can convey you to many places. The car has made travelling very easy. This is a scientific achievement which has helped in making our transportation easy and convenient.

14 Any one scientific invention which has helped to make work easier:

The advent of Information and Communication Technology, popularly called ICT, has brought, in its wake, an exciting epoch of tremendous and amazing revolution which has culminated in unparalleled and infectious communication systems. Indeed, ICT is the building block which gave birth to the idea of the ‘global village’.


45


ICT has given birth to the creation of a myriad of information and communication devices, notably computers of all sorts and varied electronic equipment. For the purpose of this study, we will confine ourselves only to computers. The computer may, no doubt, be classified as one of the modern wonders of the world. We can use them to solve most of our problems. In our offices we use computers to store large quantities of information on small tapes and keep in drawers; this makes retrieval of information very easy and convenient.

For the purpose of communication, we have various devices designed specifically for different events and occasions. We have e-mail, Facebook, Twitter, etc. Through these, data are relayed from one person to another easily everywhere in the world. From the Internet, one can obtain almost any information one wishes to have; from scientific data to social information through to all manner of entertainments. This is the source of pornographic materials which attract many young people, especially young male students.

Now, we have Google Earth and others……… which provide invaluable information for, mainly, research scholars. If at any moment a research officer is uncertain about anything, all he/she does is to turn to the computer for the requisite data – and it is there. One of the most recent and exciting developments is the ‘video conferencing’ device. It facilitates communication between two people at two completely different locations anywhere in the world to view each other and talk to each other.This is an impressive scientific feat, initiated and created by scientists. This device can be utilised by students during lectures. Physics students from Legon can listen in to physics lectures in, say, Bristol University in the UK. The setting would be such that the Legon students can see the physics lecturer delivering lectures in the UK and ask him questions.

In the same manner, a medical specialist in Korle Bu can obtain medical data from a sister hospital anywhere in the world to enable him to complete a surgical operation in progress in Accra through video conferencing; while the surgical operation is going on, in Korle Bu, Accra, the specialist in a hospital in London may convey the required data to the doctor in Accra through person-to-person contact via the video conferencing device.

Currently, some knowledgeable businessmen use the ‘on-line’ device to trade with their partners anywhere in the world. All they need to do is to send their prescriptions through ‘on-line’ to their suppliers, and the goods will be delivered to them. Computers are used for international trading.

Here are some facts about computers:

• We have different kinds of computers.

• There are desk-top computers installed in offices.

• Then, there are lap-top computers which are placed on the thigh when using them, or you can place them on a table.


46


• We also have pocket-size computers which are put into a pocket.

• Recently, we have tablet computers meant for holding in the hand.

15 The importance of questioning in the work of a scientist:

• It allows the scientist to think critically.

• It enhances the scientist’s creative thinking.

• It enables the scientist to activate prior knowledge, focus learning efforts and elaborate on their knowledge.

• It enables the scientist to identify problems and outline clear ways to solving the problem.

16 The areas of science listed in this question can be divided into the three branches of science in this way:

Physics Chemistry Biology

Engineering Pharmacy Pathology

Meteorology Chemical engineering Cardiology

Astronomy Botany

Aquatic biology

Zoology

Agriculture

Radiography

17 Science and Technology:

Science is a continuous process of investigation and experimentation in order to widen people’s understanding of the natural world. It involves the gathering and recording of knowledge to find answers to the questions and challenges that life poses everyday.

Science uses methods involving logical investigation, experimentation and questioning that lead to acquisition of reliable knowledge. The knowledge gained is stored and can be used to help further investigation and understanding. Scientists use systematic and reliable methods to collect information. These methods are all bound together and known as the scientific method.

Generally, science is divisible into:

• Pure science – deals with information derived from research.

• Applied science – uses knowledge obtained from pure science which is applied to solve problems in our daily lives.


47


Technology is the practical application of scientific knowledge to improve life and satisfy the needs of people. Technology is applied to develop scientific ideas to produce new materials, tools and machines and many communication gadgets.

On the whole, science and technology are interrelated. Technology starts from where science stops. In other words, ideas obtained from scientific research are used or applied by technology to develop and produce new materials, tools, machines, etc.

Science and Technology Similarities

Science Technology

Involved with materials found in the environment

Deals with materials also in the environment

Aims at improving life in society Also aims at improving life and satisfying the needs of people

Science and Technology Differences

Science Technology

Obtains data from scientific research directly only

Depends on ideas formulated by science

Uses structured and systematic laid down scientific methods to acquire data

Does not follow any laid down methods to obtain its data

Science is ‘know – why’ Technology is ‘know how’


48

Unit 2 Measurement

IntroductionThis unit is concerned with units and making measurements. It should be used to introduce pupils to the S.I. based and derived units for a small number of common physical quantities. Pupils should practise measuring some physical quantities using appropriate apparatus, and deriving others from the results obtained.


1. list some common physical quantities

2. identify and use appropriate instruments to measure different physical quantities accurately

3. identify and use the appropriate units for different physical quantities

4. relate and use the appropriate prfixes (milli-, centi- or kilo) in relation to the units of length and mass

5. measure the area and volume of objects

6. read the volume of liquids in graduated containers accurately

7. determine the volume of irregular solids using appropriate instruments

8. measure temperature using a thermometer

9. measure time using watches and/or clocks

10. determine the densities of regular and irregular objects.


Syllabus topicSection in Pupil’s Book

Pupil’s Book Page


Pupil’s Book Page

Common physical quantities 2.1 32

Measuring instruments 2.2 33 2.1, 2.2, 2.3, 2.4

35, 36, 37, 38

Units 2.3 39

Prefixes in measurement 2.4 40 2.5, 2.6 41, 42

Measuring area and volume 2.5 42 2.7, 2.8 45, 46


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Unit 2 Measurement


Pupil’s Book Page


Pupil’s Book Page

Reading volume in graduated containers

2.6 47 2.9 48

Determining the volume of irregular solid objects

2.7 49 2.10 50

Measuring temperature 2.8 51 2.11 52

Measuring time 2.9 52 2.12 52

Determining density 2.10 53 2.13, 2.14, 2.15

53, 54, 55

Lesson planningThe syllabus provides a logical order of work on measurement. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Explain what is meant by a physical quantity and identify mass, length, time and temperature as common physical properties.

2. Examine and discuss the instruments used to measure mass, length, time and temperature. Pupils should be shown how to use each instrument.

3. Pupils should work through Activity 2.1 considering the importance of accuracy in taking measurements.

4. Pupils should work through Activity 2.2 on estimating and measuring length.

5. Pupils should work through Activity 2.3 on measuring mass.

6. Pupils should work through Activity 2.4 on measuring temperature.

7. Explain the significance of S.I. units and identify the base units of mass, length, time and temperature. Explain how other units, such as those for area, volume and density, are derived from the base units. Advise pupils that some derived units, like energy, have been given special names.

8. Explain how a series of prefixes can be used to alter the value of any S.I. unit by certain multiples of ten. Pupils should be given plenty of practice in converting between units of the same physical quantity, e.g. grams and kilograms, centimetres and metres.

9. Pupils should work through Activity 2.5 on converting units of length.


50

Unit 2 Measurement

10. Pupils should work through Activity 2.6 on converting units of mass.

11. Demonstrate to pupils how to find the areas of common two-dimensional shapes (square, rectangle, triangle, circle) and the volumes of regular-shaped three-dimensional objects like cubes and cuboids. Pupils should be given suitable shapes and objects and asked to find their areas and volumes as appropriate.

12. Pupils should work through Activity 2.7 on measuring area.

13. Introduce pupils to the measuring cylinder as an instrument for finding the volume of a liquid. It is important that pupils are shown how water forms a meniscus in the measuring cylinder and they should be told to take the volume from the lowest point of the meniscus. Pupils should practise measuring the volumes of liquids using measuring cylinders.

14. Pupils should work through Activity 2.8 on measuring volume.

15. Pupils should work through Activity 2.9 on measuring the volumes of liquids.

16. Demonstrate the technique for finding the volume of an irregular-shaped object, such as a stone, by displacement. This can be done without the need for a eureka beaker simply by recording the volume of water in a measuring cylinder before and after the introduction of the object. An object will displace its own volume of water; therefore the volume of the object will be equal to the apparent increase in volume of the water. Pupils should have plenty of practice of this technique.

17. Pupils should work through Activity 2.10 calculating the volume of an irregular solid.

18. Demonstrate and explain how a simple mercury-in-glass thermometer works. Warn pupils that thermometers are both fragile and expensive. They should be handled with great care. In the event of any breakage, they should advise the teacher straightaway so that any spilled mercury may be cleared up. Pupils should practise taking the temperature of containers of water, and of their bodies.

19. Pupils should work through Activity 2.11 on measuring temperature.

20. Show pupils examples of analogue and digital watches/clocks and discuss how they are used to measure time. If a stop watch is available, explain how it should be used. If not, explain to pupils how they can measure the length of time taken by recording the time at the start and at the end of a process. Pupils should practise measuring time to the nearest second for different processes.

21. Pupils should work through Activity 2.12 measuring time.

22. Pose the question ‘Which is heavier, lead or aluminium?’ Pupils may say that it is lead. Point out that a large block of aluminium is much heavier than a small block of lead. Use this example to introduce the idea of mass per unit volume or density. Explain that we can only make a fair comparison if we compare


51

Unit 2 Measurement

the density of aluminium and the density of lead, i.e. the masses of equal-sized blocks of the two metals.

Introduce the equation:

density = mass / volume.

Explain that to find the density of a material we must know both its mass andits volume. Pupils should practise finding the density of liquids and of regularshaped solids.

Point out that to find the density of a material which does not have a regularshape we must measure its volume by the displacement method described earlier.Pupils should practise finding the density of a material which is an irregularshape.

23. Pupils should work through Activity 2.13 comparing the densities of different substances.

24. Pupils should work through Activity 2.14 finding the densities of materials in the form of regular solid objects.

25. Pupils should work through Activity 2.15 finding the densities of materials in the form of irregular solid objects.

26. Explain to pupils that the density of water is taken as 1 g/cm3. Any material, such as cork, which has a density less than this will float in water; while any material, such as aluminium, which has a density more than this will sink.

27. As an opportunity for developing critical thinking skills, pupils could be asked to investigate how the density of water varies with temperature and evaluate whether it is a reasonable approximation to take the density of water to be

1g/cm3 across the temperature range over which it is a liquid.

Additional information for the teacherScientific measurements are taken in S.I. units. S.I. is short for Système International d’Unités. This system was devised in 1960 so that scientists around the world could work in the same units and thereby avoid conversions between units used to measure the same physical quantities.

There are seven base units in the S.I. system. These are shown in Table 2.1.

Physical quantity Quantity symbol Unit name Unit symbol

length l metre m

mass m kilogram kg

time t second s


52

Unit 2 Measurement


temperature T kelvin K

electric current I ampere A

luminous intensity Iv candela cd

amount of substance N mole mol

Table 2.1 S.I. base units

Only the first four of these units will be needed by pupils. Notice that although the S.I. unit for temperature is the kelvin, temperature is commonly expressed in degrees centigrade or Celsius.

The units for all other physical quantities are derived from the seven base units. Table 2.2 shows some common derived units. Only the first three of these units will be needed by pupils.


Area A square metre m2

Volume V cubic metre m3

Density ρ kilogram per cubic metre

kg/m3 or kgm-3

Velocity V metre per second m/s or ms-1

Acceleration A metre per second squared

m/s2 or ms-2

Force F newton NPressure P pascal PaEnergy E joule JPower P watt WFrequency F hertz HzElectrical charge Q coulomb CElectrical resistance R ohm Ω

Electrical potential difference

p.d. volt V

Table 2.2 Derived S.I. units

Notice that some derived units are rather complicated and have been given special names. For example, the derived unit for energy is the kilogram square metre per second squared, kgm2s–2, but this is called the joule.

Notice also that the derived unit symbols should be written in upper case but the names should start in lower case. For example the correct symbol and name for force is N and newton, and not n and newton or N and Newton.


53

Unit 2 Measurement

The S.I. (International System) is a decimal system just like a metric system. There are certain prefixes which are used to show decimal sub-multiple or multiples of units.

Prefix Symbol Meaning

Mega M x 1 000 000 or 106

Kilo k x 1000 or 103

Deci d x 0.1 or

110

Centi c x 0.01 or 1

100

Milli m x 0.001 or 1

1000

Micro μ x 0.000 001 or 1

1000000

Table 2.3 Prefixes for S.I. units

It is often more sensible or convenient to express quantities using prefixes in conjunction with base or derived units. For example, if pupils are asked to find the density of wood from a small block they are likely to measure the mass in grams and the dimensions in centimetres. They will thus find the density in gcm-3 rather than in kgm-3.

When prefixes are used with units, it is essential that correct use is made of upper and lower case letters. For example, the symbol for milligram is mg and not Mg (which would indicate megagram). Similarly, kilogram should be represented by the symbol kg and not Kg.

ResourcesIn order to make measurements pupils will need access to:

• an electronic or beam balance

• a ruler, a metre rule and perhaps a measuring tape

• a clock with a second hand or a stop watch

• a thermometer (range -10 to 110 ºC is appropriate).

If stop watches are not available, reasonably accurate timing can be achieved using a clock provided it has a second hand or, if it is digital, has a second function.

In order to measure in metres, a metre rule or a measuring tape should be used. If these are not available, sticks exactly one metre long can be measured and cut. A measuring tape can be made from string by tying a knot every metre. Pupils can find the distance by counting the knots and subtracting one.


54

Unit 2 Measurement

For the purposes of determining an area, suitable shapes can be cut from cardboard boxes and used by pupils to practise taking measurements.

For the purposes of determining volume, small boxes such as those used for food packaging can be used by pupils to practise taking measurements.

Pupils will also need access to a measuring cylinder for work on the volume and density of liquids and the density of irregular-shaped objects.

Other resources are a source of heat, graduated bakers, assorted containers (tins, bottles, etc., some with labels), labelled soft drinks bottle, efffervascent antacid tablet (or powder), fruits, stones, pens, ice cubes, beakers, paper clips, erasers, coins, set squares, bricks, sugar cubes, soap bars, soup tins, thread, sand, sawdust and blocks, of different materials.

Opportunities to encourage critical thinking skillsPupils are told that:

• density = mass / volume

• the density of water is 1 gcm-3

• when a thermometer is placed in hot water the mercury expands and it is forced up the capillary tube.

Clearly if mercury expands when it is heated, i.e. its volume increases, and density = mass / volume then density must decrease with temperature.

Pupils could be given the task of investigating how the volume of a given mass of water varies with temperature and decide from their results whether taking the density of water to be 1 gcm-3 at any temperature is a reasonable approximation.

Diagnostic assessment exercisesThese diagnostic assessment exercises will help to gauge to what extent the specific objectives of this unit have been achieved. You should be honest in your appraisals since the outcomes will assist you in improving your teaching in the future. If, on reflection, you feel that certain parts or aspects of the unit have not been well understood, some remedial work should be undertaken before moving on.

1 Did pupils understand the need for a common set of units for use in science? Did they appreciate the advantages of having units and symbols that are used by scientists in all countries so that information can be shared more easily, or does this need to be re-emphasised?


55

Unit 2 Measurement

2 Were pupils able to convert commonly encountered examples of units incorporating prefixes such as between grams and kilograms, centimetres and metres, millilitres and litres? If this is not the case, pupils should work through some examples and be given appropriate support.

3 On those activities involving measurement, were pupils obtaining sufficient accuracy with the instruments used or does something further need to be said about reading scales, etc.?

4 Do pupils understand the concept of density as mass per unit? If the answer to this question is ‘no’ then density needs to be reviewed.

5 This unit contains several different calculations. Overall, how successful were pupils in dealing with these calculations? Was there any particular calculation which caused problems for most or all of the pupils? If so, this indicates that some more examples of that particular calculation should be worked through and discussed before moving on.


1 C2 A3 C4 D5 C6 Basic units have a single unit such as metre for length, second for time, kilogram for

mass.

Derived units are multiples of the basic unit, as m2 for area, m3 for volume, Nm or joules for work.

7 All measurements should be verified because of the inaccuracy of the human mind, inaccuracy of measuring instruments, parallax error and zero error of measuring instruments. Verification helps to correct errors arising from the human senses and the instruments used.

8 A body floats when it displaces a weight of water which is equal to its weight or when the relative density of the substances into which it is immersed is greater than its own density.

9 Trace the leaf on squared paper (graph sheet).

1. count all the full squares and write the figure

2. count all half-squares and divide it by 2 and add it to the full squares

3. identify the three quarter-squares and add them to the quarter-squares and to the full and half-squares.

10 Mass in:a milligrams: 145 g x 1000 = 145000 mgb kilograms: 145 kg ÷ 1000 = 0.145 kg


56

Section 2: Diversity Of Matter After studying this section, pupils will be able to:

1. recognise the variety of living and non-living things in nature and their connectedness

2. develop a scientific approach to problem solving

3. understand the nature of matter in its various forms

4. be aware of the physical properties of soil in relation to its uses

5. be aware of hazards in the community and during the teaching/learning of science.

Unit 3 Matter

IntroductionThis unit is primarily concerned with the three different states of matter – solid, liquid and gas – and how their physical properties are related to the distribution and motion of particles.

In this unit pupils will also consider the structure of animal and plant cells. This will include the functions of the various parts of the cells and the differences between plant cells and animal cells.


1. explain the term matter

2. describe the nature and states of matter

3. outline the characteristics of the states of matter

4. demonstrate how matter is changed from one state to another

5. distinguish between plant and animal cells.


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Unit 3 Matter



Pupil’s Book Page


Pupil’s Book Page

Matter in the form of solids, liquids and gases

3.1, 3.2 60, 62 3.1, 3.2, 3.3, 3.4

62, 63

Properties of solids, liquids and gases related to the distribution and motion of particles

3.3 64 3.5 66

Changes of state 3.4 69 3.6, 3.7 69, 73

Cell structure 3.5 74 3.8 75

Comparing plant and animal cells

3.5 77

Lesson planningThe syllabus provides a logical order of work on matter and cell structure. However, if it is more convenient, the topic on animal and plant cell structure could be completed first. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Pupils should discuss the nature of matter and the idea that all matter is composed of indivisible particles which may be atoms, ions or molecules. Explain that this is not a new concept and was proposed by the Ancient Greeks over two thousand years ago, although they had no scientific evidence to support this idea.

2. Pupils should work through Activity 3.1 building models of atoms and molecules.

3. Pupils should work through Activity 3.2 looking at particles of different substances with a hand lens.

4. Pupils should work through Activity 3.3 considering the relationship between atoms, molecules and ions.

5. Explain that all matter may exist as a solid, a liquid or a gas using ice, water and steam as an example.

6. Pupils should work through Activity 3.4 looking at examples of solids, liquids and gases.


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Unit 3 Matter

7. Pupils should discuss the properties of a solid, like a block of wood, a liquid, like water, and a gas, like air. They should pay particular attention to whether each state:

• has a fixed shape

• will take the shape of its container

• can be poured from one container to another

• can be easily compressed.

8. Pupils should work through Activity 3.5 investigating the properties of solids, liquids and gases.

9. Discuss the different properties of solids, liquids and gases in terms of the position and motion of the particles in each. The term ‘kinetic theory’ should be used only if the teacher is confident that it will not cause confusion.

10. Explain that a substance can be changed from one state into another either by heating or cooling. Students should consider the processes of melting, boiling, condensing and solidifying. Introduce the terms melting point and boiling point.

11. Pupils should work through Activity 3.6 investigating changes of state.

12. As an opportunity for developing critical thinking skills, pupils could be asked to investigate the energy changes that take place when a substance changes state.

13. Explain that, in addition to boiling, a liquid may become a vapour below its boiling point by another process called evaporation. Discuss the differences between evaporation and boiling.

14. Explain that some substances are able to change from solid to gas, and from gas to solid without becoming liquids and that both processes are called sublimation. Set up an experiment to show sublimation.

15. Pupils should work through Activity 3.7 investigating sublimation.

16. Explain that cells are the building blocks from which living things are made.

17. Pupils should work through Activity 3.8 looking at cells.

18. Describe the structure of a typical animal cell, explaining the role of the nucleus, cytoplasm and cell membrane.

19. Describe the structure of a typical plant cell, explaining the role of the large vacuole, the chloroplast and the cell wall.

20. Summarise the work on animal and plant cells by asking pupils to make a comparison between the two.


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Unit 3 Matter

Additional information for the teacherThere are traditionally three states of matter – solid, liquid and gas – which exist under normal conditions on the Earth. However, much of the Universe consists of material in a fourth state of matter called plasma. This state consists of a mix of positively charged ions and negatively charged electrons.

The kinetic theoryThe kinetic theory accounts for the physical properties of solids, liquids and gases and explains what happens when a substance changes state. According to the kinetic theory:

• all matter is composed of tiny particles (atoms, molecules or ions) which are in constant motion

• the particles possess potential energy, associated with their position, and kinetic energy, associated with their motion

• the differing properties of the three states of matter are due to differences in total energy, affecting both the position and motion of particles.

SolidsIn solids, particles are closely packed together and held firmly in place by forces of attraction. These may be strong ionic, covalent or metallic bonds in giant structures, or they may be much weaker hydrogen bonding or van der Waals forces between molecules in simple covalent compounds. The stronger the forces of attraction, the greater the energy needed to overcome them – hence the higher the melting point of the solid.

Although the particles in a solid are not able to move position they do vibrate continually about fixed points so they are not entirely stationary. As a result of particles being held in fixed positions, solids:

• have a definite fixed shape and volume

• cannot easily be compressed

• cannot flow.

When a solid is heated its particles gain more energy and vibrate with greater and greater amplitude. Eventually, at a temperature called the melting point, Tm, the particles have sufficient energy to overcome the forces of attraction that hold them in place and the solid melts to become a liquid.


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Unit 3 Matter

LiquidsThe particles in a liquid remain very close to each other and there are still forces of attraction between them. The particles have more kinetic energy than those in a solid and this is sufficient for them to change position, but not to separate.

As a result of the position and movement of particles, liquids:

• are difficult to compress into smaller volumes

• take the shape of the container in which they are placed

• can flow or be poured from one container to another.

At any temperature, there is always a proportion of particles in a liquid which have sufficient kinetic energy to overcome the forces of attraction with other particles and escape from the surface of the liquid. This process is called evaporation.

When a liquid is heated its particles gain more kinetic energy, and a larger proportion of them have sufficient energy to escape from the liquid to become vapour. Eventually, at a temperature called the boiling point, Tb, the liquid boils and becomes a gas.

There are two important differences between evaporation and boiling:

1. Evaporation takes place at any temperature, whereas boiling takes place at one specific temperature.

2. Evaporation only occurs from the surface of a liquid, whereas boiling takes place throughout the liquid.

GasesThe particles in a gas are large distances away from each other compared with those in a solid or liquid, and the gas particles have greater kinetic energy. The attractive forces between particles are very weak – thus they are free to move in random directions at very high speeds.

As a result of the position and movement of particles, gases:

• can easily be compressed into smaller volumes

• take the shape of the container in which they are placed

• can flow or be poured from one container to another

The particles in a gas will occupy all of the space available to them. The spreading out of gas particles due to random motion is called diffusion.


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Unit 3 Matter

CellsCells are the building blocks from which tissue is formed. A simple animal cell consists of a nucleus contained in cytoplasm, which is surrounded by a cell membrane. A plant cell also has these features but also contains a large vacuole and a cell wall made of cellulose. A common mistake made by pupils is to think that a plant cell has a cell wall in place of a cell membrane rather than in addition to it.

Cells in parts of the plant above the ground, i.e. the stem and leaves, also have structures called chloroplasts which contain the green pigment chlorophyll. Chlorophyll is always present in leaves although the green colour may be masked by the presence of other pigments. During photosynthesis, chlorophyll traps sunlight and uses the energy to convert water and carbon dioxide into glucose. Excess glucose is then stored in different parts of the plant as the storage polymer starch. Root cells do not contain chloroplasts since they are not exposed to sunlight.

In a large organism, such as a plant or an animal, there are many different kinds of cells, each adapted to carry out a specific function within the organism.

ResourcesIn order to explore the physical properties of solids, liquids and gases pupils will need:

• different shaped containers • syringes

Syringes are used to show that gases can easily be compressed. If they are not available, this can be shown with a bicycle pump. The end should be closed off with the finger and the plunger pushed down so that air is compressed in the barrel of the pump.

Models representing solids, liquids and gases can be made using common items like seeds to represent particles and thin sticks.

To investigate changes of state pupils will need:

• access to a freezer or the freezing compartment of a refrigerator

• apparatus to bring water to the boil or access to an electric kettle.

Sublimation can be demonstrated using a sealed jar containing a few crystals of iodine or naphthalene (moth balls). On standing on a window ledge overnight, the solid will sublime from the bottom of the jar and recrystallise at the top of the jar or on the underside of the lid.

In order to observe plant cells and animal cells pupils will need:

• access to a microscope

• prepared slides of animal cells and plant cells.

Slides of animal cells (cheek cells) and plant cells (onion skin cells) can be easily prepared in the laboratory using the follow procedures.


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Unit 3 Matter

Wash out the mouth with clean water and then the inside of the cheek with a tea spoon or similar instrument. Place the material gathered onto a microscope slide, spreading it out. Add a couple of drops of methylene blue stain onto the sample and place a cover slip over it. Leave the sample to stand for a few minutes. Place a filter paper at the edge of the cover slip to draw off any excess stain. Examine the specimen under a low-power microscope to identify cheek cells, which should be stained blue.

Carefully peel the outer layer from an onion and remove the thin skin, which is one-cell thick, from the inside of the layer which has been removed using forceps. Place a small piece of the skin onto a microscope slide, spreading it out as much as possible. Add a couple of drops of iodine stain onto the sample and place a cover slip over it. Leave the sample to stand for a few minutes. Place a filter paper at the edge of the cover slip to draw off any excess stain. Examine the specimen under a low-power microscope to identify onion cells, which should be stained yellow.

Othe resources needed are chalk, sugar cubes, bricks, knives, hand lenses, retort stands and clamps, metre rules, string, balloons, potassium permanganate, beakers, glass bottles, matches, mirrors/sheets of metal and shallow dishes.

Opportunities to encourage critical thinking skillsNo mention has been made of the energy changes that take place when a substance changes state. Pupils could plot a graph using the data below to see how the temperature of liquid naphthalene changes as it turns from liquid to solid.

They can analyse the shape of their graph and can deduce that solidifying is an exothermic process, i.e. heat is given out. They can also find the melting point of naphthalene.

Provide pupils with the following:Naphthalene was heated until it was liquid and then allowed to cool and solidify. The temperature was recorded every 30 seconds as it cooled. See Table 3.1.

Time / minutes Temperature / °C Time / minutes Temperature / °C

0 92.0 8 81.0

1 90.0 9 81.0

2 88.0 10 80.5

3 86.5 11 80.0

4 85.0 12 79.0

5 83.5 13 78.0

6 82.5 14 76.5

7 81.5 15 75.0

Table 3.1


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Unit 3 Matter

1. Draw a graph of temperature on the y-axis against time on the x-axis.

2. From your graph, estimate the temperature when the graph is horizontal.

3. Explain the significance of this temperature, and why the graph becomes horizontal for a short time.


1 Review the lesson relating the distribution and motion of particles in solids, liquids and gases to their properties. Did the pupils understand why solids, liquids and gases have different physical properties? Was it necessary to explain the properties of any or all of these states of matter more than once?

2 Are pupils able to explain the difference between boiling and evaporation or will this need more explanation in the future?

3 How did pupils perform in the practical activities which involved using microscopes? These are expensive items of equipment. Were pupils given sufficient instruction before these practical sessions to ensure that microscopes were used properly or should more instruction be given in the future?

4 Are pupils clear about the similarities and the differences between a typical animal cell and a typical plant cell and the functions of the various cell parts? Is this confirmed by pupils’ responses to question 11 in the revision questions? If responses to this question were generally poor it suggests that this topic has not been well understood and should be reviewed.


1 D

2 A

3 B

4 B

5 D

6 B

7 B

8 a The smallest particle of iron is an atom.


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Unit 3 Matter

b When an atom gains or loses an electron to gain stability, like the inert or noble gases, it becomes an ion. The noble gases have a fully filled shell. Each has the stable outer electron octet (8 electrons) or duplet (2 electrons in K-shell). In order to be stable and behave like an inert gas, atoms must gain or lose an electron. Usually, atoms become stable when they have two electrons in the outer shell or eight electrons in the outer shell.

When an atom gains an electron, the number of electrons becomes more than the number of protons. When an atom loses an electron the number of protons becomes more than the number of electrons.

As a result, there are two types of ions:

• positive ions and

• negative ions.

Positive ions: A positively charged ion is formed when an atom loses one or more of its electrons to become stable and non-reactive, just like the noble gases. It should be clear that when an atom becomes unstable because it has lost some electrons, it causes this balanced relationship between the positive protons and the negative electrons to be broken. As a result, there would not be sufficient negative electron charges to balance the positive proton charges on the nucleus of the atom. Since the positive charges will be more, the particle assumes an overall positive charge.

Negative ions: On the other hand, a negatively charged ion is formed when an atom gains one or more electrons to become stable. Non-metals form negative ions. The additional electrons gained by the atom cause an unbalanced situation. The increase in the number of electrons creates an unbalanced situation between protons and electrons in the nucleus; so the particle assumes an overall negative charge.

9 a Matter exists in three physical states: solid, liquid and gas. Temperature and pressure are the two factors which determine the state in which a type of matter exists. The increase or decrease in temperature influences the states in which matter exists.

b Solid: the particles of a solid are packed closely together. They are held together by strong forces of attraction. The particles are unable to move position but they are able to vibrate about their fixed positions. Their inter-particle distances are very small. When solids are heated, the particles vibrate more vigorously as the temperature of the solid rises. The vibrations become so violent that the particles partially overcome the forces of attraction which hold them in position and can move about. They are still attracted to each other but the distance between particles increases slightly. The heat energy supplied is used to overcome the attractive forces and therefore increases the distances between particles. Solids have definite shapes.

Liquid: In the liquid state, the particles are able to move about but are still held loosely together. A further rise in temperature increases the kinetic energy of the particles until the bonds between them are totally broken. The liquid changes state into a gas. A liquid takes the shape of a container. A liquid can be poured.

Gas: Particles are further apart in gases than in liquids and solids. Little or no bonding forces exist among particles of a gas, so they are very volatile. In the


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Unit 3 Matter

gaseous state, the molecules of the substance are free to take up any shape. Gases have no definite shape.

10. The distances between particles of a solid are extremely small; they are all bonded tightly together. They do not move at all but they can vibrate. The strong forces of attraction holding the particles together give solids a definite shape and fixed positions. When heating, the particles begin to vibrate; as the temperature increases, the particles vibrate more vigorously. Continuous increase in temperature results in violent vibrations of the particles until they partially overcome the forces of attraction which bind them in that tight position and begin to move about. As this is going on, they still remain attracted to each other. However the distances between particles widen and increase slightly as the temperature increases.

The overbearing heat energy supplied is used to break up and overcome the rigid attractive forces binding the particles together so tightly. Consequently, therefore it forces the distances between particles to widen and increase.

When the temperature continues to move up, the distance between particles of the solid increases, and it melts into liquid. At that temperature, the particles in the liquid move about and collide with each other.

It should be appreciated that not all particles travel with exactly the same speed; some move quickly while others move more slowly. An occasional particle gains sufficient energy to break free and escape from the liquid surface. Escaping particles take a lot of heat energy with them. This happens when inter-particle forces are weak.

11 a i nucleus – it carries the genetic materials of the cell that control the activities of the cell

ii cytoplasm – it is the site for chemical reactions in a cell

iii cell surface membrane – it controls the movement of substances in and out of cells

iv cell wall – it provides rigidity and definite shape to a plant cell

b State four differences between plant cells and animal cells:

Plant cells Animal cells

Have cellulose cell wall Do not have cell wall

Have chloroplast containing chlorophyll No chloroplast

Have large and permanent vacuole Have small and temporary vacuole

Vacuoles are few Vacuoles are many

Have fixed and rigid shape Have irregular shape

Protoplasm is not dense Protoplasm is dense


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IntroductionThis unit is concerned with the composition of soil and how it is used. Pupils will consider some of the physical properties of soil and look at soil profiles as a means of assessing the nature of a soil.


1. describe the nature of soil

2. outline the uses of soil

3. describe the physical properties of soil

4. explain the importance of the soil profile in crop production.



Pupil’s Book Page


Pupil’s Book Page

Nature of soil 4.1 82 4.1 84

Uses of soil 4.2 85

Physical properties of soil 4.3 87 4.2, 4.3, 4.4 88, 91, 93

Soil profile and crop production

4.4 94 4.5, 4.6 96, 97

Lesson planningThe syllabus provides a logical order of work on soil structure. However, if it is more convenient, the topic on the physical properties of soil could be completed before the topic on the uses of soil. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Pupils should examine a sample of soil and suggest what it contains. Pupils should shake the sample in a jar with some water and allow the particles to


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settle. Pupils should observe that the larger particles settle first at the bottom while the smaller particles settle last at the top.

2. Ask pupils to explain why it is that if 50 cm3 of soil and 50 cm3 of water are added together the final volume is less than 100 cm3. From this evidence they should deduce that soil contains air, which is lost when the soil and water are mixed.

3. Ask pupils to explain why it is that if a weighed sample of soil is left somewhere warm overnight, it weighs less the next morning. From this evidence they should deduce that soil contains water, which evaporates and is lost to the air.

4. Explain to pupils that so far they know that soil consists of a matrix of rock particles, air and water. There are also organic components to soil consisting of live and dead plants and animals.

5. Pupils should work through Activity 4.1 exploring the components of soil.

6. Discuss the different uses of soil. This should include:

• the role of soil in supporting plant growth

• the ability of soil to hold water

• the role of soil in providing habitats for living organisms

• the use of soil for building.

7. Discuss the texture of soil and how this is related to the size of the particles.

8. Pupils should complete Activity 4.2 investigating the feel of different soils.

9. Discuss the structure of sandy soil and relate this to its physical properties.

10. Discuss the structure of clay soil and relate this to its physical properties.

11. Discuss the structure of loam and relate this to its physical properties.

12. Explain the importance of soil water, and why it is important for soil to receive enough but not too much water.

13. Pupils should work through Activity 4.3 investigating the water-holding capacity of different types of soil.

14. Pupils should work through Activity 4.4 investigating capillary action of different types of soil.

15. Explain the importance of soil temperature and how this is affected by soil water.

16. Explain the importance of organic matter.

17. Explain the term soil profile and its importance to farmers and other land users. Discuss the significance of topsoil and its role in supporting plant growth.


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18. Pupils should work through Activities 4.5 and 4.6 exploring the profile of the soil in the area near the school. They should make a labelled diagram of this profile.

19. As an opportunity for developing critical thinking skills, pupils could be asked to analyse and compare the properties of samples of soil from different locations in the area around the school.

Additional information for the teacher

Soil particle sizeSoil consists of a matrix of mineral particles which have been altered from the parent rock by the processes of erosion and weathering. The gaps between the particles are filled with air, water and other solid particles. Soil also contains organic material in the form of humus and live organisms.

Most soils have a density in the range 1 to 2 gcm-3.

The composition of a good quality soil, in terms of volume, is 45% minerals, 25% water, 25% air and 5% organic material.

The mineral content of soil consists of a mixture of sand, silt and clay. Sand and silt are formed by physical weathering of the parent rock, while clay is formed by chemical weathering.

Particles Diameter / mm

sand 2.00–0.05

silt 0.05–0.002

clay < 0.002

Table 4.1

Table 4.1 shows that sand has the largest particles while clay has the smallest. The diagram below shows the approximate percentages of sand, silt and clay in the soil corresponding to different soil types.


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silty clay

silty

clay

100

90

80

20

10

70

60

40

30

50

clay loam

loam

sandy clay loam

loamy sandy loam

sandsand

sandy clay

90

100

80

70

60

50

40

30

20

10

silty clay loam

silty loam

Sand (%)

Clay

(%)

Silt (%)

100

90

80 70

60 50 40 30

1020

A soil in which sand predominates is described as a sandy soil, while one in which clay predominates is a clay soil. A soil in which none of the components is dominant is known as loam. The mineral composition of a typical loam might be 40% sand, 40% silt and 20% clay. The proportion of each component determines the nature and properties of the soil including the retention capacity for water and nutrients.

The ability of a soil to retain water is determined by the size of the spaces or pores between particles. Water molecules hold more tightly to the small particles in clay than to the larger particles of sand. Clay soils have a tendency to waterlog in wet weather while sandy soils dry out rapidly in dry weather.

The ability of soil to retain nutrients depends on the surface area of the particles and the unbalanced ionic charges on the particles. Sand is the least active and therefore retains least nutrients. Clay is the most active and therefore retains the most nutrients.

Loam is often considered the ideal soil because there is sufficient sand present to hold the soil open and keep it from waterlogging while there is sufficient clay present to ensure that nutrients are retained.

Soil organic matterOrganic material in soil consists of all dead plant material and all creatures, both live and dead. Soils will typically have a range of dead organic material in various stages of decay. Most of the things that live in soil are dependent on this decaying material for nutrients and energy.


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The final stage of decomposition of organic material in soil is called humus. Humus typically makes up around 5% by volume of soil. In addition to providing nutrients it also improves the texture of the soil and thus its ability to sustain plant growth.

Soil colourThe colour of soil is primarily determined by the minerals present and the oxidation states of the metals they contain. Iron forms minerals which impart a yellow or red colour, while organic material decomposes into black and brown compounds.

Resources• Digging tools, e.g. spade, pickaxe, mattock, shovel

• Tape

• Garden line

• Head pans

• Measuring cylinders x 4

• Filter funnels x 3

• Test tubes x 3

• Holed corks x 3

• Set of crayons

• Large and small containers

• Glass jar, like a jam jar or large clear bottle with a wide opening

• Hand lens

• Electronic balance

• Stop watch or other means of measuring time

• Retort stands and clamps

• Cotton wool

• Topsoil

• Different types of soils, numbered 1, 2, 3, etc.

• Dry samples of different soil types (sandy, loamy and clay)

• White paper

• Filter paper

• Large dish


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Opportunities to encourage critical thinking skillsPupils could carry out a survey in which they obtain samples from three or four different locations within a few miles of the school. For example: the school sports field, a wooded area, a cultivated field and a road. The physical properties of each soil could then be tested.

Physical propertySample

A B C DLocation

Colour

Texture

Water content

Organic matter

Porosity

Table 4.2

Pupils could be asked to analyse their results and to suggest reasons for any differences in the physical properties of the samples.

Diagnostic assessment exercisesThese diagnostic assessment exercises will help you gauge to what extent the specific objectives of this unit have been achieved. You should be honest in your appraisals since the outcomes will assist you in improving your teaching in the future. If, on reflection, you feel that certain parts or aspects of the unit have not been well understood, some remedial work should be undertaken before moving on.

1 Review the lesson spent introducing the different components of soil. Were pupils already aware about the structure of soil and therefore little time was needed dealing with this? Or was this new to most pupils and would they have benefited from additional time?

2 Review the lesson spent on relating the structures of different soils to their properties. Were there any parts of the lesson where pupils appeared particularly interested? Can you say why this was? Were there any particular parts of the lesson where pupils appeared bored? Can you say why this was?

3 This unit involved exploring the soil profile at a location near to the school (Activities 4.5 and 4.6). Was there any difficulty when arranging this work? Were


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the necessary tools readily available or did they need to be sourced in advance? Are there any lessons to be learnt about doing activities like this in the future?


1 A 2 B 3 D 4 D 5 A 6 D 7 B 8 C 9 B 10 B 11 C

12 B 13 D 14 B 15 A

16 a In agriculture soil is described as the top layer of the Earth’s crust which we cultivate and in which crops and other plants sometimes grow.

b The main parts or components of the soil are the mineral fraction, the organic fraction which comes from dead and broken down living things, water, air and living organisms. The mineral fraction is formed when rocks are broken down into very small particles grouped as sand, silt and clay.

c Four functions of the soil in crop production include the following:

1. The soil holds plants firmly. This way the soil provides anchorage or support for plants.

2. The soil contains nutrients which plants take up as food for their growth and development.

3. The soil can hold water needed by plants for growth and other activities.

4. The soil contains air which is necessary for the proper development of roots and other living things in the soil.

17 a Four physical properties of the soil include the soil texture, soil structure, soil air, soil water and soil organic matter. The amounts or proportions of sand, silt, clay and organic matter present in a particular soil give the soil its texture. Soil structure describes how soil particles (sand, silt, clay and organic matter) are arranged or grouped together to form single units called aggregates. Soil air is the air found in soils. It is found in between the soil particles. Soil water refers to the water present in soils. It is found in the spaces between the particles and also attached to the particles.

b Humus is soil organic matter obtained from the waste matter of living things and the decaying bodies of dead things.

c Soil organic matter is important in the soil for crop production in the following three ways:

1. It contains plant nutrients.

2. It binds the soil particles together to improve the soil and reduce erosion.

3. It holds water for plants.


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18 a • It reduces the rate of soil erosion.

• It ensures good drainage system.

• It promotes the activities of soil microorganisms.

• It makes preparation easier.

• It helps in the conservation of soil.

• It promotes easy movement of air in the soil.

b • It is a raw material for photosynthesis.

• It is needed by plants for the transport of soil nutrients to other parts of the plant.

• It dissolves soil nutrients for easy absorption by roots of plants.

• It helps easy tillage of the soil

• It cools the plant through transpiration.

c • It affects the formation of decomposition of soil organic matter.

• It affects the absorption of water and nutrients from the soil.

• It influences seed germination and root development in seedlings.

• It affects the population of soil-microorganisms.

19 a Soil profile is the vertical cross-section of the soil showing a series of distinct layers or horizons and the parent material from which it was derived.

b • The depth of the topsoil helps farmers to decide on what crops to grow on the land.

• It helps farmers to predict the organic matter content of the soil.

• It enables the farmer to know what tillage implements to use.

• It helps the former to determine the drainage status of soil.

20 a Soil profile picture at www.wikipedia.org

b Horizon Colour Texture Porosity Depth Organic matter

A (Top-side)

Dark Moderate between sandy and clayey soils

Moderate Not so thick High


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B (Sub-soil)

Less dark Mixture of clay and sand particles

It is porous

Thicker than top-soil

Small amount

C (Weathered

rock)

Brown Mostly sand and silt

It is porous

It is relatively thicker than sub-soil

No organic matter due to lack of living organisms

D (Bed rock)

Reddish brown to tan

More clay and bigger rock

Less porous

Very thick No organic matter


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Unit 5 Hazards

IntroductionThis unit is concerned with hazards and safety issues in the laboratory. Pupils will learn to identify potential hazards and recognise the warning and safety signs used in a scientific laboratory. They will also discuss safety procedures to prevent accidents in school and in the home.


1. explain the term ‘hazard’

2. identify and interpret warning and safety signs in the community and laboratory

3. identify safety precautions to prevent accidents in the home and school.



Pupil’s Book Page


Pupil’s Book Page

Hazards 5.1 102

Warning and safety signs 5.2 103 5.1 105

Safety precautions 5.3 108 5.2, 5.3 110

Lesson planningThe syllabus provides a logical order of work on hazards and safety. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Point out to pupils that the laboratory is a potentially dangerous place. Ask them to suggest some sources of danger. Make a list on the board.

2. Introduce the term ‘hazard’ and explain that it is used to describe anything that may cause danger or expose someone to danger.


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Unit 5 Hazards

3. Describe some of the hazards in the laboratory and compliment pupils if they were able to initially identify them. Hazards should include:

• corrosive substances

• flammable substances

• toxic substances.

4. Encourage pupils to discuss the potential dangers associated with these hazards and how these dangers may be avoided.

5. Show pupils a variety of different hazard symbols on packaging, bottles and charts. Ask them if they can guess the meaning of each one by looking at the picture. Some like ‘highly flammable’ are very obvious while others like ‘oxidising’ will need some explanation. Explain that these signs are there to warn people and they should not be ignored.

6. Explain that there are other signs used in the laboratory to do with:

• wearing protective clothing

• prohibited activities

• First Aid.

Discuss each of these, emphasising the importance of them.

7. Pupils should carry out Activity 5.1 and play the safety symbols game.

8. As an opportunity for developing critical thinking skills, pupils could be asked to design a hazard symbol for a fictitious hazard.

9. Point out to pupils that in scientific experiments, burners are sometimes used to heat things. Ask what particular risk is associated with using a burner. If necessary mention fire. Describe the safety precautions in place to deal with a fire. This should include making pupils aware of the location of and discussing the use of:

• a fire extinguisher

• a bucket of sand

• a fire blanket.

10. Explain to pupils that, although there are particular hazards in the laboratory, there are also hazards in everyday life that they need to be aware of. Discuss some examples of everyday hazards.

11. Extend the theme of hazards to the community and home. Discuss some examples of hazards in the home.

12. Pupils should work through Activity 5.2 discussing accident prevention in school and in the home.


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Unit 5 Hazards

13. Explain the need for rules in school in order to keep everybody safe. Either advise pupils of the laboratory rules and explain their importance, or allow the class to draw up their own laboratory rules based on discussion and consensus.

14. Pupils should work through Activity 5.3 playing out some different scenarios centred on accidents.


Warning signsWarning signs are to alert people to hazards. They are printed in black on a yellow background. The signs are triangular but may also be square when shown on bottles, or diamond-shaped when shown on road vehicles. Here is some additional information about common warning signs.

Toxic

This is a poisonous chemical substance. If inhaled or swallowed it can cause severe illness or death of a person. Safety regulations must be followed in handling or dealing with them. They should not be allowed to enter your body, mouth, nose, eye or skin. Always wash the part of your body in contact with these poisonous substances with plenty of water.

Corrosive

A corrosive chemical substance has a burning effect. They can burn the floor, the desk and your skin. Concentrated mineral acids like sulphuric acid, hydrochloric acid, nitric acid and phosphoric acid are corrosive. Likewise, concentrated alkalis such as potassium hydroxide and sodium hydroxide are corrosive substances. When a corrosive substance comes in contact with your body, wash with plenty of water. Water dilutes the corrosiveness of a chemical substance and makes it less reactive.

Explosive

An explosive substance is one that can react rapidly, sending particles in all directions at great speeds. Some substances are spontaneously explosive, and thus can react even in the absence of an external force. Explosive substances should never be brought near heat sources as this may increase the risk of explosion.

Highly flammable

A flammable substance easily catches fire. Such substances should never be heated using an open flame or brought near a flame because of the risk of fire. Flammable substances should be heated using an electric heater or a water bath.


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Unit 5 Hazards

Ethanol, petrol, diesel, kerosene and methylated spirit are common examples of flammable liquids. Flammable liquids readily evaporate so their containers must be stoppered immediately after use. A build-up of vapour of a flammable substance is a fire hazard.

Harmful or irritant

A harmful or irritant substance is the one that can cause discomfort and illness but is not life-threatening in the same way as a poison. These substances should not be inhaled or allowed to come into contact with the skin.

It is good practice to treat all substances as potentially harmful or irritants. A good scientist will protect him or herself from contact with chemicals and immediately wash off any splashes to the skin.

Oxidising

An oxidant is a substance that helps a burning substance to burn faster by providing it with oxygen. In the presence of an oxidising agent a small fire will increase in size and ferocity. Heating a mixture of an organic material with an oxidising agent is potentially dangerous. For example, heating a mixture of potassium permanganate, an oxidant, and sawdust may result in an explosion.

Radioactive

A radioactive substance spontaneously releases radiation. Radiation is invisible but potentially harmful to the body. Radiation may cause illness and even death if a person is exposed over a period of time.

Radiation is a hazard in the nuclear industry and in laboratories which use radioactive elements like radon, uranium and polonium. Workers must wear badges which detect the levels of radiation to which they have been exposed.

High voltage

This sign is used on a cable or appliance to show high electric potential difference or voltage. High voltage may immediately kill a person who touches a bare wire connected to it. It is important that pupils appreciate this before being allowed to use the power supply in the laboratory.

Other safety signsThere are several other groups of signs that are used to maintain a safe environment and reduce the possibilities of accident and injury.


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Unit 5 Hazards

Prohibition signs

Prohibition signs indicate behaviour that is prohibited. On a prohibition sign, the activity is represented in black and white and a red circle and diagonal stripe are superimposed on it.

Common prohibition signs include:

• no smoking

• naked flames prohibited

• not drinking water.

Mandatory signs

Mandatory signs identify particular actions that must be taken. The prescribed action is shown in white on a solid blue circle.

Common mandatory signs include:

• eye protection must be worn

• hand protection must be worn

• breathing mask must be worn

• ear protection must be worn.

Safe condition signs

Safe condition signs tell people of a safety facility. The facility is represented in white on a solid green square.

Common safe condition signs include:

• First Aid

• eye wash

• emergency electricity cut off.

Resources• Cards x 10 with hazard symbols on one side and meanings on the back

• Green, yellow and red cards

• Whistle

• Stop watch


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Unit 5 Hazards

Opportunities to encourage critical thinking skillsPupils could be asked to design a hazard warning sign for a fictitious hazard. For example, they could be told that a certain substance catches fire when it is exposed to sunlight. Their sign must warn people of this hazard.

Pupils should start by analysing the format of existing warning signs, taking note of their shape, colour and format. They should then design an appropriate image for their sign.


1 Was the lesson spent alerting pupils to the potential dangers in the laboratory, pitched at the correct level so that they understood the importance of safety issues but were not put off carrying out practical work in the future? Did pupils get the message that, if they obey the laboratory rules and follow instructions, they are highly unlikely to come to any harm?

2 Review the lesson spent introducing hazard signs. Were there any hazard signs which were universally known/understood by pupils and which could be used to introduce the topic in the future? Were there any hazard signs which were not well known/understood and which would be best looked at after an initial introduction?


1 D

2 A

3 B

4 D

5 A

6 A


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Unit 5 Hazards

7 HIGHLY

FLAMABLE TOXIC FIRST AIDNO SMOKING

(a) (b) (c) (d)

8 a Prohibition signs: These are permanent safety signs used for prohibiting behaviours likely to cause danger.

Examples of behaviour likely to cause danger include smoking at unauthorised places – workplaces, laboratories, classrooms, etc; chatting unnecessarily while operating a machine or working at the laboratory; running or eating at a workplace; U-turning of vehicles at places where this is not allowed, etc.

b NAKED FLAMES

PROHIBITED

(i) (ii) No eating or drinking

9 It is important not to overload electrical sockets by plugging too many appliances into them. This could cause them to overheat and possibly catch fire.

Fire is likely to start if one of the electrical appliances is defective. Contact between flammable materials provided by the defective appliance and of heat energy provided by a naked flame from the electrical source could start a fire.

In such situations, electrical devices can overheat and cause wires to become red hot and melt the plastic insulation that surrounds them. Sparks resulting from a short circuit may be sufficient to start a fire.

Most fires start small and grow bigger if not checked in time. Small fires anywhere must first be fought with fire extinguishers and fire blankets. In the event that this does not stop the fire, and it gets out of control, the fire service should be called in immediately.

10 Three sources of hazards in the workplace are:

• electric shock

• dust

• food contamination and poisoning.


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Unit 5 Hazards

Electric shock as a hazard

When an electric current passes through the human body by mistake, it can cause discomfort and even death. This is what is called an electric shock. The extent of damage depends on how great the current or voltage is.

An electric current produced by a simple torch battery, or even a few of them joined together, would not give a significant electric shock. However, electricity from the mains at 120V or 240V is a serious hazard and a danger to all. Faulty or defective wiring is, in most cases, the cause of electric shocks, particularly where bare wires are exposed. Electric shocks may also come about from fires and explosions and from other disasters such as earthquakes.

The degree of shock to an individual is dependent on the quantity of current which the person is exposed to. Light shocks give no more than a prickling sensation but in severe electric shocks the heart, the muscles, breathing, mental co-ordination and other body functions are impaired and can stop working.

Dust as a hazard

Very often, the potentially serious hazard of dust and its devastating effects are taken very lightly. Particles of various sizes of dust are carried in the air from sources such as deserts, dry earth roads, quarrying, building construction sites, running and rubbish dumps. Other hazardous sources of dust particles are from factories which manufacture items such as cotton, asbestos, cement and chemicals.

Usually, dust particles are so fine they cannot be seen by the naked eye. The finer the particles, the more easily they are inhaled.

People who are unfortunate to constantly inhale dust particles are likely to contract a respiratory disease. Where dust is a hazard, workers should be provided with suitable protective equipment, such as respiratory masks. These masks prevent workers from breathing in dust and so prevent damage to the respiratory system.

Food contamination and toxicity

Naturally, there are foods which contain poisonous or toxic substances. These poisons may be found either in the peel or in the food itself. Bitter cassava, for instance, contains hydrogen cyanide (HCN) in the peel, while some types of yams and cocoyams also contain alkaloids. When some foods are peeled and boiled their poisons get destroyed; in some mushrooms, however, even when they are boiled or cooked, their poisons remain deadly and are not destroyed.

Apart from these, there are many micro-organisms (bacteria and fungal spores) hovering in the air, some of which are useful; but others are extremely poisonous and harmful. They act on both cooked and uncooked foods. Fungal spores can contaminate food and mould grows on the food.

The actions of some micro-organisms produce poisons which may not be detected easily in the taste or scent, colour or quality of the food.


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Unit 5 Hazards

Food poisoning

Food poisoning may occur mainly in the kitchen but also it may be traced to restaurant food and foods bought in the street or produced under hot and unsanitary conditions. Other small animals like rodents, flies, insects, etc., may carry the poisonous substance on parts of their bodies to contaminate food as they roam about in search of food.

Food which is ill-prepared or undercooked or improperly preserved meat, poultry, eggs and dairy products (such as milk) are some of the main causes of food poisoning. Salmonella bacteria cause a severe form of food poisoning.

Some Ghanaian foods such as fish, meat, bean, kontomire, etc. which are kept in warm places for hours create convenient conditions for the multiplication of toxic bacteria and this can lead to food poisoning.

Food poisoning can lead to organ failure, irreparable body damage or even death.

People likely to suffer from food poisoning are those who mostly eat from outside foods kept at normal temperature.

Food poisoning symptoms include fever, stomach ache or cramps, high temperature, diarrhoea, convulsions, headache, nausea, vomiting and dehydration.

11 First Aid

a Blood is life; it is absolutely necessary to stop it from flowing or pouring away from the body. Accidents invariably occur at places far away from hospitals or clinics. To ensure that people do not lose too much blood during accidents, measures are taken to stop the free flow of blood before the victim is conveyed to the nearest clinic or hospital for full treatment.

The initial measures taken at the site of an accident in order to sustain life before a victim is conveyed to hospital are known as First Aid treatment.

In other words, it is basic medical treatment which is given to people as soon as possible after they have been hurt in an accident or when suddenly people become ill.

b How First Aid is catered for in the science laboratory

A specially designed wooden box is tailored to suit the purpose for which it is made. This box is filled with miniature shelves which divide the enclosed space into compartments. A lock and a key are provided to ensure absolute safety of the drugs contained inside. A red-cross emblem is printed on the front of the box to single it out as a First Aid box. The box is placed at a convenient and wholly accessible place in the laboratory. Normally, the entire box is painted white.

The drugs stored in it are those which may be needed immediately in the event of a laboratory mishap or an accident. The usual laboratory accidents involve mostly acid spills resulting in burns and corrosion of skin and scalds; breaking of bottles and test-tubes etc. leading to various cuts; improper handling of highly flammable substances which may cause irritation on contact with the skin; production of toxic fumes which could cause suffocation, etc.


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Unit 5 Hazards

It is important to observe that the skin is a cover for vital tissues in the human body. Damage to the skin must be prevented by all means in the laboratory since it gives the body its beauty and appeal. Failure to achieve this may lead to undesirable consequences, e.g. damage to skin can cause bleeding, scalding and in some cases infections.

In the laboratory, chemicals can harm the skin by burning, scalding, piercing, causing itches and sometimes peeling cells off the body. Substances that burn the skin include fires, toxic sprays, concentrated acids and alkalis. Acids scald the skin and create scars that are unpleasant to see.

It is precisely for these reasons, and to avoid permanent damage to the skin and the body as a whole, that drugs to combat the adverse impact of accidents in the laboratory are safely kept in the First Aid box.

Materials which may be kept in a good First Aid box include: iodine lotion, cotton wool, various bandages, clips to assist in holding bandages in position, safe painkillers, gauze, plasters, milk of magnesia, gentian violet lotion, pairs of scissors, blades, etc.

In an event of an accident in the laboratory, the Science Master or the Laboratory Assistant must be told at once. Thereafter, depending on the severity of damage, the victim is hurriedly conveyed to the hospital for full medical attention.

12 Porridge on the fire as a hazard to family

Porridge put on the fire becomes very hot and begins to send little droplets of hot porridge scattering all around the pot containing it. Anybody sitting or standing within a short distance from it may receive a burn if any hot droplets fall on his/her skin. This can therefore cause a hazard.

A ladle used when stirring the porridge may cause a burn, if it is brought into contact with the skin when it is hot. If the person preparing the porridge fails to clean his/her hands of slippery substances and attempts to take the pot containing the food from the fire, he/she may cause a serious disaster. There could be a spillage of very hot material which may cause scalding on coming into contact with the skin of anybody standing around, including hungry children.

Another source of potential hazard is for someone to attempt to remove hot porridge from the fire without using a good and convenient pad to prevent heat from reaching his/her hands. In the same way, there could be a spillage of very hot porridge on the floor also becoming another hazard if not cleaned in time.

The floor could be very slippery and anybody stepping on it could trip and fall to hurt him/herself.


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Unit 6 The Life Cycle of Flowering Plants

Section 3: CyclesAfter studying this section, pupils will be able to:

1. recognise that there are repeated patterns of change in nature and understand how these patterns arise

2. develop an understanding that agricultural production is cyclic in nature

3. appreciate the cyclic nature of the life of plants and its importance in crop production.

4. develop skills in vegetable crop production.


IntroductionThis unit is concerned with the life cycle of the flowering plant. Pupils will learn about the processes of pollination, fertilisation, fruit and seed formation, seed dispersal and germination as important processes in this cycle. The conditions needed for germination will be considered in some detail. Finally, pupils will consider the importance of the life cycle of flowering plants in the context of vegetable crop production.


1 describe the life cycle of flowering plants

2 demonstrate the conditions necessary for germination of a seed

3 explain how knowledge about the life cycle of flowering plants is important in vegetable crop production.


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Syllabus topic

Section in Pupil’s Book

Pupil’s Book Page


Pupil’s Book Page

Life cycle of flowering plants 6.1 115 6.1 117

Conditions needed for germination 6.2 118 6.2 119

Flowering plants and vegetable production

6.3 120

Lesson planningThe syllabus provides a logical order of work on the life cycle of flowering plants and the major processes involved. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Activity 6.1 will take several weeks to complete so pupils should initiate this at the start of the unit. What they are doing will become clear to them as they work through the unit.

2. As a way of introducing pupils to flowering plants, briefly remind them of the major parts of a flowering plant: root, shoot, leaves and flowers. Point out that flowering plants only appear like this for part of their life cycle.

3. Describe the life cycle of a flowering plant by discussing each of the following processes:

• flowering

• pollination

• fertilisation

• fruit and seed formation

• seed dispersal

• seed germination.

4. Pupils should remember some of the above processes from work in primary school. It is important that they see them both as individual processes and as part of a larger cyclic process.

5. Explain to pupils that they are going to focus on the process of germination.


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6. Activity 6.2 is likely to take several days. Pupils should set up Activity 6.2 to investigate the external conditions needed for germination prior to discussing them.

7. Discuss the internal conditions necessary for germination. This should include:

• the viability of seeds

• the need for a food store within the seed

• the role of enzymes in converting the food store into nutrients that can be used for growth.

8. Discuss the external conditions necessary for germination. This should include:

• the presence of oxygen/air

• the presence of sufficient moisture

• the effect of temperature on germination.

9. As an opportunity for developing critical thinking skills, pupils could be asked to design an experiment to find the optimum temperature at which seeds germinate.

10. Point out to pupils that knowing about and understanding the life cycle of flowering plants is important in crop production. Discuss the importance of each of the following in the context of crop growing:

• temperature

• light

• availability of water.


PollinationPollination is the transfer of pollen from the male to the female part of a flower.

In abiotic pollination, pollen is transferred without the assistance of animals. The commonest form of abiotic pollination is by wind. Only about 10% of flowering plants are pollinated in this way.

In biotic pollination, pollen is transferred by animals. Insects are mainly involved but some species are pollinated by animals such as hummingbirds, sunbirds, spider hunters, honeyeaters and fruit bats.

The general characteristics of flowering plants that rely on abiotic pollination are:


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• small flowers

• petals green or dull in colour

• do not produce nectar

• flower faces down for easy shaking

• stamens and stigma hang outside the petals

• stigma has feathered branches to assist in catching pollen

• large number of pollen grains produced

• pollen grains are light and have a smooth surface.

Grasses are a common example of wind-pollinated flowering plants.

The general characteristics of flowering plants that rely on biotic pollination are:

• larger flowers

• petals often have bright colours

• flowers have nectaries that produce nectar

• flower faces upwards

• stamens and style are within the petals

• stigma is unbranched and shaped like a pinhead

• smaller number of pollen grains produced

• pollen grains are heavier and have a spiked surface for sticking to animals.

Roses are a common example of insect-pollinated flowering plants.

Seed dispersalIt is in the interest of a parent plant to disperse seeds as far away as possible to prevent competition for water, nutrients and light. Seed dispersal allows a species to colonise new areas and reduces the likelihood that the species will become extinct in the event of adverse conditions.

There are a number of mechanisms by which seeds are dispersed.

Gravity

When heavy fruits like apples, coconuts and passion fruits are ripe they fall to the ground and may roll away from the parent plant. As the fruit rots, the seeds are released onto the ground. Gravity dispersal may be followed by later dispersal by animals or water.


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Dehiscence

The seed pods of some flowers, such as those in the pea family, dry and shrink in the sun. This sets up a tension force within the pod. Eventually, when the seed pod splits, the two halves curl back suddenly and the seeds are flicked out away from the parent plant.

Wind

There are three mechanisms through which seeds can be dispersed by the wind.

Some seeds are extremely small and may be carried great distances on the wind like specks of dust. Orchid seeds are dispersed in this way. This is a very haphazard process so it is not surprising that plants which disperse their seeds in this way produce very large numbers of seeds.

Some seeds are contained in fruits which are shaped like the blades of a propeller. As the seed falls it spins through the air which increases the time it takes to reach the ground. During the time that the fruit falls it may be carried a significant distance away from the parent plant.

Some seeds are contained in fruits which are shaped like parachutes. The seeds are extremely light and may be carried large distances, even by a light wind, before falling to the ground.

Water

The seeds of some plants that live in or near water, such as water lilies, are carried away by moving water and deposited considerable distances from the parent plant.

Animals

Animals may disperse seeds, either by ingestion or by the seeds becoming attached to them.

When an animal, such as a bird, eats a fleshy fruit the seeds or pips can pass through the animal’s body without being digested. They will eventually pass out with the faeces, well away from the parent plant.

Some seeds are contained in fruits which are covered in spikes or hooks. As an animal brushes past a plant, the fruits attach themselves to the animal’s fur. The fruits will remain attached until such time as they fall off or are removed by the animal, which is likely to be at a considerable distance from the parent plant.


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Resources• Test tubes

• Cotton wool or filter paper

• Palm oil or similar

• Boiled water

• Tomato seedlings

• Pots of fertile loamy soil

• Small seeds such as cress or Crotalaria

Opportunities to encourage critical thinking skillsGermination requires both oxygen and an adequate quantity of water. The rate at which seeds germinate is determined, to some extent, by the temperature.

Pupils could be asked to design an activity to find the optimum temperature at which seeds germinate. In doing so they must ensure that, while carrying out germination at several different temperatures, all other factors are controlled, i.e. kept the same for all germinating seeds. These will include:

• area of growing medium

• quality of growing medium

• amount of light

• amount of water given

• availability of fresh air.

Pupils should be encouraged to evaluate their own methods, discussing any weaknesses which may lead to unreliable results.


1 How much were pupils able to recall about work carried out on the flowering plant in primary school? Are there any parts of this unit which could be given a lighter touch, and others which would benefit from a little more time?


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2 Was there any part of this unit that went down particularly well with pupils? Analyse why this was so successful. Was it just that the content was easy to understand or interesting, or was it taught in such a way as to capture the imagination? Can this be built on for future teaching?

3 Were pupils able to readily relate the content of this unit to their experiences outside school? Could they immediately see a link between the unit content and what happens in the fields and gardens around where they live – or does this need to be emphasised more?

4 Both Activities 6.1 and 6.2 require a long time to complete. Is it going to be necessary to find time in the next unit to complete these and summarise the results? Is there a case for starting these activities during the previous unit to ensure that they can be completed within this unit?


1 B

2 C

3 B

4 D

5 B

6 a It is necessary for seeds to be dispersed because seeds need to be carried away from the parent plant to a place where conditions are right for them to germinate. This prevents overcrowding of the plants and competition for light, water and nutrients.

b Two adaptations for wind dispersal are: the presence of wings on the seed or tufts on fruits and seeds.

7 a Flowering plants go through a life cycle consisting of the following stages: flowering, pollination and fertilisation; fruit and seed formation; seed dispersal; and germination.

b Knowledge of the life cycle in flowering plants can be used in vegetable crop production in the following two ways: 1. Germination and growth; and 2. Pollination and fruit formation. The proper range of temperature, water and light must be available for germination and growth. Therefore, seeds sown must be watered to improve germination. Also, light is important in vegetable crop production because it provides energy for photosynthesis. Light also affects the opening of stomata and helps in the formation of chlorophyll, which is important in photosynthesis. For flowering vegetable crops, such as tomatoes and garden eggs, it is important to ensure that there is adequate water for growth (nutrient uptake and transportation of assimilates) during flowering and fruit formation and that no harmful chemicals are sprayed to destroy pollinators.


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8 There are certain conditions necessary for the germination of seeds. Some of these conditions are internal while others are external. The internal conditions include the following: a seed must be viable and not damaged by heat, chemicals or pests; a seed must have enough stored food reserves to maintain it until it can start photosynthesising; the right enzymes must be available within the seed to break down stored food to release energy for growth of the seedling.

The external conditions necessary for germination include: oxygen which is needed in respiration to release stored energy; water which is needed to soften the seed coat so the plumule and radicle can come out. Water is also needed for chemical reactions to take place. Finally, a suitable temperature (warmth) is needed to ensure that the enzymes will work best for germination to take place.


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Unit 7 Vegetable Crop Production

IntroductionThis unit is concerned with producing crops of vegetables and follows on from work in the previous unit. Pupils will consider methods of vegetable crop production, which crops are commonly grown and what factors affect the yields. They will also learn the importance of weeding, watering and fertilising in crop production and discuss the uses of vegetable crops.


1. describe the principles of crop production

2. explain the term ‘vegetable crop’

3. explain the factors influencing vegetable crop production

4. perform cultural practices in vegetable production

5. outline the uses of vegetable crops.



Pupil’s Book Page


Pupil’s Book Page

Crop production 7.1 123

Vegetable crops 7.2 127

Vegetable crop production 7.3 127

Cultural practices and vegetable production

7.4 129

Uses of vegetable crops 7.5 135 7.1, 7.2 135, 136

Lesson planningThe syllabus provides a logical order of work on the principles of crop production, the factors which affect it and some common local practices. Teaching strategies should be


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determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Activity 7.2 is likely to take several weeks. This should be started at the beginning of the unit and time should be allocated to it as necessary during the course of the unit and afterwards.

2. Ask pupils to imagine that they are to earn their living growing crops. They must suggest some different processes which are a necessary part of this. Make a list of their suggestions on the board.

3. Discuss the importance of selecting appropriate land for crop production.

4. Discuss how the land should be prepared for planting crops.

5. Discuss the different varieties of crops they might grow. Write a list of these on the board.

6. Discuss different ways of propagating crops including planting seed.

7. Ask pupils to explain the importance of the various stages in crop production. These should include:

• controlling weeds competing for nutrients, water and sunlight

• providing growing crops with nutrients – fertilising

• dealing with pests and diseases that damage crops

• harvesting crops

• processing crops

• selling crops.

11. Define what is meant by a vegetable crop. Ask pupils to identify some vegetable crops which are grown locally and some which are not. Make two lists on the board.

12. Discuss factors that will determine the success or otherwise of growing crops. This should include:

• the climate

• the nature and quality of soil

• the availability of water

• the nearness to a market when the time comes to sell the crop.

13. Describe how seedlings are raised in nursery beds.

14. Discuss how seedlings are cared for prior to transplanting.

15. Explain the need for transplanting seedlings as they grow bigger.


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16. Discuss how young plants are cared for up to the point where they are harvested.

17. Pupils should work through Activity 7.1 looking at local practices in vegetable growing.

18. Discuss the importance of vegetable crops in providing food and also, in some cases, providing medicines.

19. Explain to pupils how some vegetable crops are grown for consumption within Ghana while others are grown mostly for export in order to earn foreign currency. Pupils could be asked to identify some export crops and say which countries buy them.

20. Discuss the importance of vegetable growing in providing employment so that people can earn a living.

21. As an opportunity for developing critical thinking skills, pupils could be asked to evaluate the plausibility of introducing a new crop to the area.


The Growing Connection (TGC)Ghana is a country of over 24 million people. Over 70% of its inhabitants live in rural areas. The majority of poor people who live in rural areas are farmers and food producers.

As part of TGC, Ghanaian students have been growing fresh produce since 2003 when the scheme was piloted at the Cape Coast School for the Deaf, which is some 160 kilometres west of Accra. Since the pilot, nine other schools have joined the scheme including another three from the same Cape Coast area.

Most sites start by growing small amounts of crops in patches of ground or earth boxes. From this, a number have progressed to full-sized school farms growing different types of vegetables and other food crops as well as rearing livestock.

The success of the TGC scheme has had a profound effect on many of the students who have taken part. Students have been able to learn about and practise both traditional and new methods of growing. Crop yields have been such that students have been able to feed themselves, feed other students, give produce away to villagers in need, and sell at local markets. This has allowed students to learn about the economics of farming as well as about production.

Schools in Ghana involved in the TGC scheme have had the opportunity to visit each other and have been able to learn from each other, as well as making many friends.


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Staple foodsA staple food is one which is eaten regularly and in quantities such that it provides the consumer with a high proportion of the energy and nutrients they need on a daily basis. Most people live on a diet consisting of a small number of staple foods together with smaller quantities of other foods.

The nature of staple foods varies from country to country and continent to continent. However, they are typically:

• cheap to buy

• readily available

• able to supply one or more of carbohydrates, proteins and fats.

Some foods may become staples for only part of a year, such as when other foods are in short supply. For the remainder of the year a wider range of foods may be available.

Most staples are derived from the following:

• cereals, such as wheat, maize, barley and rice

• starchy tubers or root vegetables such as yams, taro, cassava and sweet potato

• pulses such as beans

• fruits such as breadfruit and plantain.

In Africa essential staple foods are yams, plantains, green bananas and cassava. These crops are grown all over the continent and eaten either on their own or combined with other crops.

Most staple foods are produced on a small scale in a household-based subsistence economy. A typical household may grow main staples, such as millet and sorghum. One or more cash crops may also be grown for sale or local consumption. In addition, many households may grow other vegetables, such as plantains and onions, together with a variety of spices and herbs. These will be consumed by the family and any surplus sold locally.

A list of common staple foods in Africa includes:

Aubergine/Eggplant Bananas Barley

Beans Cassava (Manioc/Tapioca) Cinnamon

Clove Coconut Coriander/Cilantro

Cumin Curry plant Garlic

Ginger Green banana Groundnut


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Lentils Millet

Nutmeg Okro Onions

Parsley Rice Sorghum

Sweet Potatoes Tamarind Wheat

Yams Spinach

Some of the main starch-rich dishes eaten in Ghana are:

• Banku – cooked fermented corn dough and cassava dough.

• Fonfom – a maize dish eaten in Southern Ghana.

• Fufu – pounded cassava/yam and plantain.

• Gari – made from cassava.

• Kenkey – fermented corn dough, wrapped in corn/plantain leaves and cooked.

• Konkonte – made from cassava powder.

• Omo Tuo – pounded rice.

• Tuo Zaafi – a maize dish eaten in Northern Ghana.

• Waakye – made from rice and beans.

The use of different staple foods in cooking has changed considerably over time due to the influence of Arab traders and then Europeans, in particular the British.

Prior to trade outside Africa, the most important vegetable staples were barley, millet, rice, sorghum and lentils. In Eastern Africa, Arab traders introduced dried fruits and spices, and later fresh oranges, lemons and limes which were incorporated into cooking. Domestic pigs were introduced from Asia and new breeds of sheep, goats and cattle from Europe.

Several important staples were introduced to Africa from other parts of the world as a result of European explorers. For example, beans, cassava, groundnuts, maize, tomatoes and sweet potatoes were all introduced to Africa as a result of the exploration of the American continent. At the same time, spices like pepper, cinnamon, clove, curry and nutmeg were introduced from Asia.

Resources• Garden tools, e.g. cutlass, hoe and hand fork

• Plot of land in the school

• Tomato seeds


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• Organic or inorganic fertiliser

• Watering can for watering

• Container for harvesting such as a dish or basket

Opportunities to encourage critical thinking skillsPupils could be asked to identify a crop which is not widely grown in their area but is grown elsewhere in Ghana or perhaps in neighbouring countries. They could then be asked to evaluate whether this crop could and should be grown in their area.

In carrying out their analysis, pupils would need to take into account a variety of considerations such as:

• Is the soil in their area suitable?

• Is the climate in their area suitable, e.g. is it warm enough, is there sufficient rain?

• Could the crop be easily harvested?

• Is there a demand for the crop, i.e. would local people buy it or could it be exported?

• Would it be financially worthwhile to grow the crop?

• Could any land set aside to grow the crop be better used growing something else?


1 Review the lesson spent introducing vegetable crop production. Did the pupils have a realistic understanding of what is needed to grow vegetable crops or does more time need to be spent discussing different aspects in greater detail?

2 Were you able to provide the class with information about the crops grown locally? If the answer to this question is no, this needs to be researched in advance of teaching the unit in the future.

3 How successful were pupils in answering the revision questions and particularly the short answer questions 15 and 16? Did all of the pupils gain at least half marks on the questions? Was there any particular question answered badly by most or all


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of the pupils? If so this indicates that some remedial work should be carried out on that particular part of the unit before moving on.

4 Activity 7.2 required a long time to complete. Is it going to be necessary to find time in the next unit to complete this and summarise the results? Is there a case for starting this activity during the previous unit to ensure that it can be completed within this unit?


1 C

2 B

3 B

4 B

5 C

6 C

7 D

8 D

9 D

10 D

11 B

12 B

13 D

14 D

15 a The following are four benefits of vegetables to humans:

1. Humans use vegetables for food.

2. Vegetables contain vitamins and minerals and are also good sources of water, roughage, protein and carbohydrates which help us to grow well and be healthy.

3. We can earn money from the sale of vegetables. Some vegetables, such as garden eggs and tomatoes, are grown and sold on the local market. Others such as ‘tinda’ and cluster beans are grown in Ghana and exported to Asia for foreign exchange.

4. Some vegetables, such as garlic, have medicinal value and contribute to our health.

b Several factors are important in vegetable crop production. Three of these factors important in vegetable crop production are: climatic factors, soil factors, and nearness to markets.


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Climatic factors are important because vegetables grow best under ideal climatic conditions that include temperature, rainfall, solar radiation and wind. It is important to select an area for vegetable production that has a good climate with adequate temperature, rainfall, sunshine and wind so the plants can receive good light, warmth and water for photosynthesis.

Soils for the production of vegetables should be sandy loam soils, which are well drained. The site should be on flat to gently sloping land so that run-off will not cause serious erosion problems. The soil should be fertile and therefore rich in humus.

Vegetables grown for sale in markets must be harvested and sold quickly when the crop is mature. Because vegetables are very perishable and can spoil quickly, it is important for vegetable farms and gardens to be near markets where they will be sold. In cases where markets are far away, it is important to make sure that there is reliable transportation to quickly convey the vegetables to the markets when they are mature.

c Vegetables are plants grown for their edible parts, which are usually eaten along with other main staples. Some vegetables may be eaten raw while others are cooked in soups, stews or other food preparations. Some of the important vegetables grown in Ghana are tomato, pepper, garden egg, okro, cabbage, lettuce, onion, cucumber, French beans and melon. Vegetables are an important source of food because they contain vitamins, minerals and other nutrients which help us to grow well and be healthy.

16 a Three cultural practices in vegetable crop production are: weed control, fertiliser application and pest and disease control.

It is important to control weeds because weeds compete with vegetable crop plants for water, nutrients, sunlight and space. The vegetable crops need all of these to be able to grow and yield well. Weeds also sometimes harbour pests and diseases which attack vegetable crops. Weeds can be controlled mechanically through methods such as cutting or slashing, hoeing, mulching or crop rotation. We can also control weeds by using chemicals called herbicides. Chemicals should be used carefully and wisely to avoid poisoning.

Fertilisers can improve soil fertility and give good yields in vegetable production. We can use organic or inorganic fertilisers. Examples of organic fertilisers are compost and animal manure. Inorganic fertilisers may be straight fertilisers which supply only one major nutrient, or compound fertilisers which supply more than one nutrient. Whenever nutrient deficiencies are observed during vegetable crop production, the problem can be solved by applying fertilisers. Fertilisers should be applied properly following the recommended rates and procedures.

It is very important to control pests and diseases because they reduce the yield of vegetable crops; also they reduce the quality of vegetable produce and therefore reduce the profits you can make from selling the produce.


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b It is important to consider growing vegetables near market centres because vegetables are very perishable and can spoil quickly. Growing vegetables near market centres allows them to be harvested and sold quickly while they are still fresh. In cases where markets are far away, it is important to make sure that there is reliable transportation to convey the vegetables to the markets when they are mature.

c Pests and diseases can be controlled by:

1. Removing all diseased vegetable plants and burying or burning them to prevent passing the diseases to healthy vegetable crops.

2. Weeding your vegetable garden always to prevent pests and diseases from being passed from weeds to vegetable crops.

3. Practising crop rotation to make sure that diseases do not complete their life cycles and attack the next crop you grow.

4. Spraying diseases and pests with chemicals to control them when the attack is very bad. It is important to follow the directions given for the application of the chemicals.


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Section 4: SystemsAfter studying this section, pupils will be able to:

1. recognise that a system is a whole, consisting of parts that work together to perform a function

2. show an understanding of the role of the respiratory system of humans

3. appreciate the basic principles underlying various farming systems.

Unit 8 Farming Systems

IntroductionThis unit is concerned with the different ways in which farmers manage their fields in order to maximise crop yields. Pupils will learn about different farming systems and will be asked to draw up a crop rotation programme.


1. differentiate between various farming systems

2. draw up a plan for a crop rotation programme.



Pupil’s Book Page


Pupil’s Book Page

Different farming systems 8.1 144 8.1 147

Crop rotation 8.2 146 8.2 151


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Lesson planningThe syllabus provides a logical order of work on different systems of farming. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Point out to pupils that although all farmers produce crops, they do not all do it in the same way. There are a number of different farming systems that may be employed.

2. Explain the term ‘land rotation’ and discuss some of the advantages and disadvantages of this system of farming.

3. Explain the term ‘crop rotation’ and discuss the advantages of this.

4. Explain the term ‘mixed cropping’ and discuss some of the advantages and disadvantages of this system of farming.

5. Explain the term ‘mixed farming’ and explain the advantages of this both in raising crops and animals.

6. Explain the term ‘organic’ and discuss some of the advantages and disadvantages of this system of farming, both in the short term and in the long term.

7. Describe how a crop rotation plan can be drawn up, and discuss the factors that need to be considered and taken into account when doing so.

8. Discuss the crop rotation plan provided in the Pupil’s Book. It is important that pupils appreciate this is not simply a random arrangement of crops and that there are sound scientific reasons for the decisions made.

9. Pupils should work through Activity 8.1 drawing up a 3-year crop rotation programme.

10. Pupils should work through Activity 8.2 looking at and reviewing different systems of farming.

11. As an opportunity for developing critical thinking skills, pupils could be asked to consider a crop rotation programme to cover 4 years.


Farming in GhanaA little over half of the country is classified as agricultural land and around half of this is under cultivation. This reflects the importance of farming as a means both of providing work and feeding the population.


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Over half of the farms in Ghana are small and cover less than 1.2 hectares and there are relatively few large farms covering over 10 hectares. Farming is therefore still the means by which many individuals provide food for themselves and their families.

The farming systems used in different parts of the country depend to a large extent on such things as the nature of the soil, the climate and the availability of water. It is, however, possible to make some generalisations.

The bush fallow system is favoured where there is sufficient land so that fields may be rested or allowed to lie fallow after one to three years of cultivation. This allows time for the soil fertility to regenerate. Staples and cash crops are often grown together.

In the forest zone, tree crops such as cocoa, oil palm, coffee and rubber are widely cultivated together with food crops such as maize, plantain and cassava.

In the middle area of the country, maize, legumes, cocoyam or yam are grown as sole crops or as part of a mixed crop system with cash crops such as cotton and tobacco.

The majority of rural households keep some livestock but livestock farming also goes on alongside arable farming. Cattle production is more common in the savannah zone of the north of the country, while poultry farming is more concentrated in the south. Goat and sheep production tend to be less centralised and more widespread throughout the country.

Livestock production is important, not just because it provides meat, eggs and dairy products but also because the animal manure provides a means of maintaining the fertility of the soil. Cattle are also used as draught animals to transport goods thus reducing the demand for fuels.

Farming in Northern GhanaSome interesting farming systems are to be found in Northern Ghana. The land consists of dry savannah which accounts for 40% of the country. The soils are generally not very productive and are difficult to cultivate, shallow and easily waterlogged. Soils are often deficient in humus due to the sparse vegetation which grows on them.

The greatest problem, however, is the lack of rain over part of the year. Rainfall is generally low and erratic and typically 1000 mm per year. There is a prolonged dry season from November to April when strong dry winds, the harmattan, exacerbate the situation.

It is clearly not an area in which large crops of vegetables and fruits can be grown on a regular basis. However, it does have considerable potential for extensive grasslands for livestock and arable farming.


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In earlier times when the population was low the main farming system was shifting cultivation. This involved growing a mixture of drought-resistant crops like millet and guinea corn with yam, pulses and vegetables. As a result of the increasing demand for land, this form of migratory farming has been modified to a bush fallow system.

The bush fallow system is a form of agroforestry in which out-fields, several kilometres from the compound, are cultivated in rotation. This system includes lowland farms, upland farms and floodland farming, where rice is cultivated in flooded areas. A number of dams and irrigation projects were needed to allow all-year production.

Compound farming also takes place in suitable areas. In-fields surrounding a compound are cultivated on a mixed cropping basis. The fertility of the soil is regenerated by traditional means involving the use of household waste and manure from livestock. The land nearest the compound is a kitchen garden in which vegetables and some staples such as millet and corn are grown. Beyond this will be a larger and less-regularly fertilised area where other staples are grown, and beyond that the land serves for grazing animals.

Resources• Flipchart

• Marker pens

Opportunities to encourage critical thinking skillsCrop rotation programmes are traditionally drawn up to cover a 3-year rotation of crops.

Pupils could be asked to challenge this traditional 3-year rotation period by investigating whether there are any real advantages in moving to a 4-year rotation period. Such a study could involve:

• researching how crops are rotated in other countries

• drawing up some sample 4-year crop rotations

• finding the views of local farmers on a 4-year crop rotation

• evaluating whether there are any real advantages to a 4-year crop rotation.

Diagnostic assessment exercisesThese diagnostic assessment exercises will help to gauge to what extent the specific objectives of this unit have been achieved. You should be honest in your appraisals


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since the outcomes will assist you in improving your teaching in the future. If, on reflection, you feel that certain parts or aspects of the unit have not been well understood, some remedial work should be undertaken before moving on.

1 Review the lesson spent introducing farming systems. Did the pupils understand why farmers may operate in different ways? Was it necessary to go over any farming system more than once?

2 How successful were pupils in drawing up a 3-year crop rotation programme? Did pupils have sufficient knowledge of groups of crops, such as cereals, legumes, deep root crops and cover crops, or should more time be spent discussing these in the future?


1 D

2 B

3 B

4 D

5 D

6 a Crop rotation is a system of farming where a farmer keeps one farmland, but grows different types of crops on different portions or plots of the same land in a definite sequence or order. By rotating the crops the farmer makes sure that the same crops do not grow continuously on the same plot of land. This improves soil fertility and reduces pests and diseases buildup.

A 3-year rotation using maize, yam and cowpea:

Farm or field divided into three plots

Year 1 Year 2 Year 3

Plot 1 Cowpea Maize Yam

Plot 2 Maize Yam Cowpea

Plot 3 Yam Cowpea Maize

b Cowpea was selected for the rotation because it is a legume and will improve the fertility of the soil by fixing nitrogen. Also, when its leaves fall and rot the nutrients in the leaves will be added to the soil.

Maize was added to the rotation because it is a shallow feeder and will not remove nutrients from the same zone as yam.

Yam was added to the rotation because it feeds at a different root zone from maize. When the three are arranged as above, the fertility of the soil will be maintained and yield would improve.


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7 a Organic farming and land rotation

Land rotation is when a farmer stays in one place and keeps two or more farms. The farmer moves from one farm to another farm with more fertile land as the fertility of the old farmland declines. The farmer then allows the old farm to lie idle and fallow for a long time and returns to it when it becomes fertile again. Organic farming, however, is when a farmer uses knowledge of good agricultural practices to obtain good crop yields without harming the natural environment or the people who live and work in it. In organic farming, land is prepared without destroying the organic matter in the soil. Soil fertility is improved through such practices as composting, crop rotation, mulching, manuring and the use of legumes as cover crops. Farmers also grow crops such as legumes in mixture or in rotation with other crops to improve the land. In addition, farmers try to avoid using harmful chemicals which may poison the soil and water. To control pests, diseases and weeds, farmers use a combination of practices such as use of resistant crops, good cultivation practices, using natural pesticides and encouraging useful predators that eat pests. Finally, in organic farming the land preparation is carefully done to avoid erosion.

Advantages of organic farming

1. The farmer saves money because he or she does not have to buy expensive fertilisers.

2. The farmer gets good yields from season to season because the land remains fertile

3. The food produced is healthier because chemical sprays are not used or are used only in small quantities.

4. The environment is protected from damage due to such harmful things like erosion and poisonous chemicals

5. Harmful pests do not become more resistant to chemicals because little or no chemical is used.

6. Good animal husbandry practices are used in organic livestock production and therefore the meat produced is healthy.

7. Sometimes organic produce is sold at higher prices, bringing the farmer more income.

Advantages of land rotation

1. The farmer always has fertile land on which to farm.

2. The old farmlands have enough time to become fertile again.

3. The farmer has fewer disease and pest problems because he moves from farm to farm.

4. The farmer saves money by not building new settlements every time he moves to a new farmland.

b Mixed farming and mixed cropping


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Mixed cropping is a system of farming where different crops are grown together on the same piece of land. Usually the crops grown depend on what the farmer wants to use at home or sell for some income. For example, the farmer may grow maize, tomato, pepper, beans and cocoyams all mixed together on the same piece of land.

Mixed farming, however, is a system of farming where the farmer raises crops and livestock on the same farm. The livestock are prevented from destroying the crops by housing them, or by using a barrier such as a fence or barbed wire. For example, a farmer may be growing crops such as maize and cowpeas and at the same time rearing chickens, goats, sheep and ducks on the same farm.

Advantages of mixed cropping

1. The farmer gets different crops from the same field.

2. If one crop fails the farmer will still have other crops from the same field.

3. The different crops produce a lot of leaves which cover the soil well and prevent erosion and weed growth.

4. The different crops are able to take up nutrients from the soil more efficiently because they have different root systems. If leguminous crops are grown they help to improve the fertility of the soil.

Advantages of mixed farming

1. The farmer can use both crops and meat from the farm.

2. The manure from the livestock can be used to fertilise the crops.

3. What is left of the crops after harvest can be used to feed the livestock.

4. The farmer is less likely to suffer total losses in the event of disease or pest attack. This is because some of the crops or animals are likely to withstand the attack.

5. The farmer has more sources of income. He can sell some of his livestock while he stores his crops till prices are best for the crops.

6. Where cattle are raised, the farmer can use some of the bullocks for ploughing or carting goods.

Land rotation and crop rotation

c Land rotation is farming system in which a farmer cultivates a piece of land for sometime and leaves it to cultivate a new one when the old one has lost its fertility, but returns to the old one when it regains its fertility.

Crop rotation is the system of farming in which different types of crops are grown in different plots on the farm indefinite sequence or cycle.

Advantages of land rotation

1. The farmer always has fertile land on which to farm.

2. The old farmlands have enough time to become fertile again.

3. The farmer has fewer disease and pest problems because he moves from farm to farm.


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4. The farmer saves money by not building new settlements every time he moves to a new farmland.

Advantages of crop rotation

1. The farmer gets different kinds of crops from the same field. In this way he is able to satisfy his food needs for different crops.

2. Because the farmer grows different crops, he has a smaller risk of total crop failure. If one crop does not do well he still has others.

3. Crop rotation improves the soil. The legume plants fix nitrogen while the leaves of different crops cover the soil and prevent erosion.

4. The fallow period helps the soil to become fertile again.

5. Because different crops are grown every season, pests and diseases that attack each crop do not get the chance to build up to very high levels.


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Unit 9 Respiratory System of Humans

IntroductionThis unit is concerned with the human respiratory system. Pupils will learn the meaning of the term ‘respiration’ and discuss the structure and function of the major parts of the respiratory system including the nose, larynx, trachea, bronchi and lungs. The final part of the unit is given over to discussing the differences between aerobic and anaerobic respiration.


1. explain what is meant by the term 'respiration'

2. draw and label the human respiratory system

3. distinguish between the two types of respiration in terms of the use of oxygen.



Pupil’s Book Page

Pupil's Book Activities

Pupil’s Book Page

Respiration 9.1 155

Structure of the human respiratory system

9.2 155 9.1 157

Aerobic and anaerobic respiration 9.3 158

Lesson planningThe syllabus provides a logical order of work on the human respiratory system. If the teacher thinks it appropriate, aerobic and anaerobic respiration could be considered before looking at the structure of the respiratory system. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Describe the process of cell respiration and discuss its importance in providing the cells of the body with the energy needed to drive metabolic processes.


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2. Explain to pupils that the term ‘respiration’ or ‘external respiration’ is sometimes used to describe breathing. Pupils should be encouraged to use the term ‘respiration’ in the context of cell respiration only to avoid confusion.

3. Discuss the role of the respiratory system in absorbing oxygen from the air in order that respiration can take place.

4. Ask pupils if they can name any of the parts of the respiratory system. Make a list on the board and add to it as necessary so that the following are identified:

nose, epiglottis, larynx, trachea, bronchus, bronchiole, alveolus.

5. Point out to pupils that some of these words have unusual plural forms, i.e. bronchus / bronchi; alveolus / alveoli.

6. Pupils should work through Activity 9.1 identifying the different parts of the respiratory system. They should first be shown each part on an illustration and then on a specimen.

7. When the trachea is discussed each pupil should feel for their own in their neck and identify the rings of cartilage around it. Ask pupils why these rings of cartilage are important.

8. Identify the alveoli as the place where gaseous exchange takes place.

9. Describe the structure of alveoli and explain the importance of each feature in gaseous exchange. This should include:

Number of alveoli – very many to ensure large surface area

Thin membrane – gases can pass through easily

Moist – gases can dissolve on surface

Rich supply of blood vessels – oxygen absorbed and carried around the body

10. As an opportunity for developing critical thinking skills, pupils could be asked to compare the human respiratory system with that of an insect.

11. Point out to pupils that so far they have considered only one type of respiration in which oxygen is present. Explain that in certain cases, such as when muscle cells are very active, the supply of oxygen cannot keep up with what is needed for this type of respiration so the cells need another way of obtaining energy in the absence of oxygen.

12. Introduce the term ‘aerobic respiration’ to describe respiration that involves oxygen.

13. Introduce the term ‘anaerobic respiration’ to describe respiration that takes place in the absence of oxygen.

14. Discuss the differences between the two forms of respiration.


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15. Explain to pupils why they become short of breath and need to pant after exercise and why they may get muscle cramp due to the build up of lactic acid in the muscles. Introduce the term ‘oxygen debt’ and explain how lactic acid that has built up in cells may be further metabolised once sufficient oxygen becomes available.


The need for gaseous exchangeRespiration requires oxygen and one of the waste products is carbon dioxide. All living things therefore must absorb oxygen into their body and expel carbon dioxide out of their body. This process is called gaseous exchange because one gas, carbon dioxide, is being exchanged for another, oxygen.

Respiration is the process by which energy is released from sugar and used by cells to drive metabolic processes.

Animals take in oxygen and expel carbon dioxide continuously. Any accumulation of carbon dioxide would lower the pH of the blood, because it forms a weak acid. If not removed, this would damage cells.

Plants take in carbon dioxide during the day in order to carry out photosynthesis. The process produces oxygen so the plant is able to use some of this for respiration. At night, plants must take in oxygen continuously for respiration, and give out carbon dioxide.

Gaseous exchange in humansIn humans and other mammals, gaseous exchange takes place in the lungs. These are two spongy, elastic organs that occupy most of the thoracic cavity (chest). Air enters through the nose and mouth and passes through the nasal cavity, through the larynx and into the trachea. From the trachea it passes along the bronchi, the bronchioles and finally into millions of tiny air sacs or alveoli.

The nose plays an important role in protecting the delicate lining of the lungs because it:

• moistens the air with water vapour

• warms the air from the rich blood supply to the nasal cavity

• has hairs and mucus which trap dust particles and micro-organisms.

Air passes from the nose into the larynx through a small hole which is covered by a flap of tissue called the epiglottis. When a person swallows food or a drink, the


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epiglottis closes over the top of the larynx, preventing food passing into the trachea. If food or drink does enter the trachea the person will choke. This reflex helps to expel material from the trachea. The larynx (voice box) contains the vocal cords. These vibrate as air passes over them, enabling people to make sounds.

Air passes from the larynx into the trachea. There are incomplete rings of cartilage, which strengthen the wall of the trachea and help to prevent it from collapsing during breathing. This is similar in structure to the suction tube on a vacuum cleaner. The inner lining of the nasal cavity and the trachea are covered in tiny hairs called cilia and they produce large quantities of mucus. The mucus traps dust particles in the air which may damage the delicate lining of the lungs. The cilia then move the mucus to the top of the trachea where it is swallowed or coughed up.

The trachea divides into a pair of bronchi (singular: bronchus), each serving one lung. The bronchi then divide into smaller bronchioles. These bronchioles end in small air sacs called alveoli (singular: alveolus).

There are millions of alveoli in each lung, producing a very large surface area for gaseous exchange. The structure of the alveoli is such as to allow an efficient exchange of gases. The alveolus wall is only one cell thick and is surrounded by a dense network of tiny blood vessels called capillaries. The inside wall of the alveolus is always moist. The following points are important in explaining gaseous exchange:

• The air entering the lungs has a high concentration of oxygen.

• Some of the oxygen from the air dissolves in the moisture on the inside wall of the alveolus.

• The oxygen diffuses through the gaseous exchange surface of the alveolus into the blood because of the steep diffusion gradient – high concentration of oxygen in the lung and low concentration of oxygen in the blood.

• Oxygen diffuses into a red blood cell and combines with haemoglobin to form oxyhaemoglobin in which form it is transported around the body.

• Carbon dioxide is present in the blood as hydrogencarbonate ions, HCO3–. These

ions decompose in the lungs to produce carbon dioxide.

• The carbon dioxide diffuses out of the blood through the gaseous exchange surface of the alveolus into the lungs because of the steep diffusion gradient – high concentration of carbon dioxide in the blood and low concentration of carbon dioxide in the lungs.

• The air that leaves the lungs has a lower concentration of oxygen, but a higher concentration of carbon dioxide than air entering the lungs.


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RespirationThe energy in the food that people eat is released during respiration. This process takes place all the time inside all living cells.

Respiration can be likened to the combustion of a fuel like wood:

fuel + oxygen = carbon dioxide + water + energy

In a similar way in the cells of the body:

food + oxygen = carbon dioxide + water + energy

Respiration is a similar reaction to combustion but in the cells of the body it takes place more slowly and in stages. Some energy is released as heat but most of it is used to make a chemical called ATP. The ATP is then used to provide immediate energy to the cell whenever it needs it. ATP is sometimes called the ‘energy currency’ of a cell. It is like money that the cell can spend when it needs to. Every cell must make its own ATP, which is why it has to respire all the time.

Aerobic respirationAerobic respiration is important for both plants and animals. It is the main way in which cells make ATP.

The word equation for aerobic respiration is:

glucose + oxygen carbon dioxide + water + energy

Some of the energy is released in the form of heat, which helps to maintain a constant body temperature, but most is used to make ATP.

During aerobic respiration:

• glucose and oxygen are used up

• carbon dioxide and water are produced

• energy is released.

There are a number of factors that determine the rate at which respiration takes place. For example:

• Muscle cells respire quickly when they are working hard. If a person is running the cells in leg muscles must respire very quickly to produce ATP.

• Sperm cells respire quickly when they are swimming towards an egg.

• Cells in the digestive system respire quickly when a person is digesting food. They need energy to produce and secrete digestive enzymes.

• Cells in the brain respire quickly when a person is thinking hard.


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When cells are respiring faster than usual, a person needs to breathe faster than usual. This increases the rate at which air is taken into the lungs and the rate at which oxygen is absorbed into the blood. Even breathing faster is sometimes not enough to provide the body with the oxygen needed for aerobic respiration, so another form of respiration is also necessary.

Anaerobic respirationIf insufficient oxygen is available, both plants and animals can continue to respire for some time without oxygen by a process called anaerobic respiration. This process is much less efficient than aerobic respiration, releasing much less energy and producing much less ATP from the same mass of glucose.

The word equation for anaerobic respiration in humans is:

glucose lactic acid + energy

During anaerobic respiration, glucose is converted to lactic acid. Lactic acid is toxic for cells, and eventually stops muscles from working. It is for this reason that cells can only respire anaerobically for short periods of time.

The lactic acid is transported by the blood to the liver where it is decomposed. This requires oxygen. Therefore, after a period of exercise, a person’s body experiences an oxygen debt corresponding to the amount of extra oxygen needed to break down the accumulated lactic acid.

Yeast is a single-celled fungus. It can respire anaerobically, breaking down glucose without using oxygen. However, the product is not lactic acid but ethanol and carbon dioxide:

glucose ethanol + carbon dioxide + energy

This reaction is the basis of fermentation and is used in making alcoholic drinks, and in bread-making where bubbles of carbon dioxide cause the bread to rise and become less dense.

Resources• Chart or model of the respiratory system of a mammal

• Sharp blade

• Hand lens

• Mirror

• Piece of rubber tubing


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• Forceps

• Trachea, bronchus and lungs from a slaughtered cow or goat

Opportunities to encourage critical thinking skillsPupils could be asked to find out about the respiratory system of a typical insect and then to compare this with the human respiratory system.

In making a comparison, pupils could comment on how the human respiratory system is more efficient.


1 Review the introductory lesson on respiration. Did the pupils understand the difference between external respiration and cell respiration? Was it necessary to go over any aspects of respiration more than once?

2 How easy was it for pupils to identify the different parts of the respiratory system on the specimen from the information given on the wall chart? Were these teaching aids satisfactory, or is there a need to improve on them for future lessons on this unit?

3 Were pupils put off or confused by the large number of new scientific terms introduced in this unit: epiglottis, larynx, trachea, bronchus, bronchi, bronchiole, alveolus, aerobic, anaerobic? Is it necessary to devise some way of dealing with them?

4 Was there any part of this unit that appeared particularly interesting to pupils? Analyse why this was so successful. Was it just that the content was easy to understand or interesting, or was it taught in such a way as to capture the imagination? Can this be built on for future teaching?


1 B

2 D

3 B


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4 B

5 C

6

a a nasal cavity, b nostril/nose, c larynx, d trachea, e rib bones, f left bronchus, g air sac (alveolus), h pleural membrane, i diaphragm, j bronchiole, k oesophagus, l epiglottis, m pharynx

b i moves downward and becomes flattened.

c g (air sac).

7 (a)

Aerobic respiration Anaerobic respiration

Involves the use of oxygen It does not involve the use of oxygen

Large amount of energy released Less energy released

Water is produced as a by-product No water produced as a by-product

No lactic acid formed Lactic acid is formed

b i Inhalation is the process by which air gets into the body. It is also known as breathing in.

ii Gaseous exchange is the process whereby air (oxygen) taken into the lungs gets into the bloodstream and carbon dioxide from the bloodstream also moves out into the lungs.

iii It is the type respiration in cells which involves the participation of oxygen to release a large amount of energy, with carbon dioxide and water produced as by-products.


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Section 5: EnergyAfter studying this section, pupils will be able to:

1. recognise that energy has a source can be transformed into various forms

2. be aware of renewable and non-renewable sources of energy

3. understand the transformation pathways of various sources of energy

4. understand the mechanics of the use of LEDs, diodes, resistors and capaci-tors

5. be aware of some of the characteristics and uses of light energy.

Unit 10 Sources of Energy

IntroductionThis unit is concerned with large-scale sources of energy. Pupils will learn about renewable and non-renewable energy sources, looking at examples of each. They will consider the production of energy from a renewable energy source, such as a biogas generator, solar heater or windmill, in some detail.


1. explain the term ‘energy’

2. describe renewable and non-renewable sources of energy

3. demonstrate the production of energy from a renewable source.



Pupil’s Book Page


Pupil’s Book Page

Energy 10.1 164

Renewable and non-renewable sources of energy

10.2 164

Examples of renewable energy sources

10.3 168 10.1, 10.2 169Continued on page 118


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Lesson planningThe syllabus provides a logical order of work on sources of energy. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Activity 10.2 involves designing and making a biogas unit. Pupils should start work on this at the beginning of the unit as it will take a couple of weeks for the fermentation to become established.

2. Ask pupils to try and define energy. After discussion they will realise that it is far easier to describe what energy does than what it is.

3. Explain that energy is measured in joules. Larger amounts of energy are given in kilojoules, megajoules and even gigajoules.

4. Explain to pupils that there are many sources of energy and that they can be conveniently placed in two groups: renewable sources and non-renewable sources.

5. Explain that renewable sources of energy are those which are renewed by natural processes at a rate which is similar to the rate at which they are used – therefore they will always be available and will not run out.

6. Give a brief account of, and discuss some examples of, renewable sources of energy including:

• Solar

• Wind

• Biomass

• Geothermal

• Hydroelectric.

7. Explain that non-renewable sources of energy are those which are used up far more quickly than they are being replaced by natural processes. Therefore at some time in the future, supplies of each non-renewable source of energy will finish.

8. Explain the term ‘fossil fuel’ in relation to non-renewable sources of energy.

9. Give a brief account of and discuss some non-renewable sources of energy including:

• Coal.

• Crude oil.

• Natural gas.


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10. Pupils should work in groups on Activity 10.1 making a solar heater.

11. Pupils should complete work on Activity 10.2 by testing their biogas.

12. As an opportunity for developing critical thinking skills, pupils could be asked to evaluate the relative advantages and disadvantages of a renewable energy source and a non-renewable energy source.


Historical perspective on energyOver the millions of years that it has taken the human race to develop, many sources of energy have been used. The earliest humans were hunter-gatherers living in caves. They obtained the energy they needed by digesting food. The food was rapidly replaced by nature so their activities had very little effect on the environment.

The discovery of how to make fire was an important milestone in human development. Wood became an important fuel and the heat energy released by burning it kept people warm, allowed them to cook food, and also to make simple pottery by baking clay.

Unfortunately the discovery of fire also increased the damage caused by humans to the environment. The trees which were chopped down could not be rapidly replaced and the smoke polluted the air. In the early days of human development this didn’t matter very much because there weren’t many people, but as the world population grew, so did the demand for wood and the smoke released into the atmosphere. In many countries of the world today wood is still the most important fuel for heating and cooking.

Our ancestors also learnt that some animals could be used to provide energy. Long before the invention of tractors, cattle and horses were used to provide the energy needed to work the land, and to transport goods from place to place. In many countries animals are still important sources of energy.

Over 5 000 years ago people were using wind to power boats. Winds are caused by the differential heating of the atmosphere resulting in differences in pressure. All the great voyages of discovery were made in sailing boats powered by wind energy. It is only within the last 150 years that other methods of powering ships have developed, and even today many people still enjoy sailing boats as a hobby.

Wind also provided energy for windmills. Windmills are known to have existed over 1 500 years ago. They were used to grind corn and to pump water. In some places wind is still used to pump water out of wells.


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In recent years wind turbines have been developed which use wind energy to generate electricity. Wind farms have an important future as a renewable energy source.

Mills can also be powered by flowing water. As far back as Roman times, water mills were used to grind corn. For a period at the start of the Industrial Revolution in Europe, many factories were powered by water wheels.

Hydroelectric power stations use energy from flowing water to generate electricity. These are another important renewable energy source.

The steam engine gradually took over from flowing water providing power for factories in the nineteenth century. The energy needed to convert water to steam was provided by burning fossil fuels like coal. Steam engines were used to power commercial shipping and steam locomotives. There were also some early motor cars powered by steam.

During the latter part of the nineteenth century, scientists realised the value of petroleum as a source of different fuels to provide energy. These fuels are still extremely important in sustaining our modern way of life.

Energy sources for the futureFossil fuels are non-renewable sources of energy and reserves will one day be exhausted. Coal is likely to remain available longer than natural gas and crude oil but it is thought that even coal reserves will be exhausted within two hundred years. There are a number of renewable energy sources that will eventually become more important in satisfying people’s energy demands.

Ethanol – in many countries cars run on a mixture of ethanol and petrol. The ethanol is made by fermenting carbohydrates like sugar cane, which are a renewable energy source since they can be continually grown.

Biogas – which is largely a mixture of methane and carbon dioxide, is made by the fermentation of animal dung. Once the gas is extracted what is left is a valuable fertiliser to spread on fields to increase crop yields.

Geothermal energy – is the result of heat released when nuclear reactions take place deep in the Earth. Heat energy is obtained by forcing cold water through the rocks so that it is heated.

Hydroelectricity – uses the kinetic energy of moving water to drive turbo-generators which generate electricity.


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Nuclear fusion – is the process by which energy is made inside the Sun. Nuclei of small atoms are combined to form larger atoms with the loss of some mass, which is converted into energy.

Solar energy – is used directly to make electricity in photovoltaic cells and indirectly as active solar heating in which the Sun’s energy is used to heat water.

Tidal energy – uses the gravitational potential energy of water trapped at high tide to drive turbo-generators, make electricity when the water is released at low tide.

Waste – materials which are disposed of by incineration are increasingly being used in power stations. The heat produced during burning can be used to generate steam which, in turn, drives generators to make electricity.

Waves – move up and down in a regular fashion and this movement can be used to generate electricity.

Wind turbines – use kinetic energy from the wind to generate electricity.

Resources• Materials to construct a solar heater

• A plastic container with a cover

• Plastic tubing

• Nozzle to fit onto the plastic container

• Cow dung or poultry droppings or vegetable peelings

Opportunities to encourage critical thinking skillsPupils could be asked to analyse and evaluate the advantages and disadvantages of a traditional coal-fired power station and a wind farm composed of 100 wind turbines.

Their analysis could take into account such factors as:

• cost of construction

• cost of energy source

• amount of electricity produced by one wind turbine compared with a power station

• continuity of electricity produced

• amount of pollution produced

• visual effect on the landscape

• cost of decommissioning.


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1 Was Activity 10.2 successful in that it produced biogas which could be shown to be flammable? If not, this activity needs to be reviewed and any new procedure tested well in advance of teaching this unit in future.

2 By the end of the unit did pupils appear to have a balanced and realistic view of the relative advantages and disadvantages of renewable energy sources? Did they appreciate that they have many desirable features but at present cannot satisfy the world’s energy demands?

3 How successful were pupils in answering the revision questions and particularly the short answer questions 6–8? Did all of the pupils gain at least half marks on the questions? Was there any particular question answered badly by most or all of the pupils? If so, this indicates that some remedial work should be carried out on that particular part of the unit before moving on.

Answers to exercises and practices in the Pupil’s Book

1 A

2 C

3 A

4 A

5 D

6 a A renewable source of energy is an energy source that can be replenished within a shorter period of time. The time must be less than 30 years. Renewable energy sources include solar energy.

b Non-renewal sources of energy are the energy sources that take more than 30 years to replenish, e.g. crude oil.

7 Living things oxidise food nutrients in the cell and release energy to enable organs and systems in the body to function.

8 a Biogas is fuel obtained from biomass. It is renewable because we are always generating organic waste, which is used in producing the gas. Thus its supply is unlimited.

b Biofuel is fuel obtained from organic materials such as wood, seeds animal droppings etc. The fuel is renewable because the supply of organic materials is unlimited.


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Unit 11 Conversion and Conservation of Energy

IntroductionThis unit is concerned with the conversion of energy from one form into others. Pupils will look at different forms of energy including potential energy and kinetic energy. They will consider a variety of energy transformations in commonly used equipment. In the final part of the unit pupils will discuss how energy is conserved during energy conversions.


1. list the various forms of energy

2. explain potential and kinetic energy

3. demonstrate how various forms of energy are transformed

4. give reasons for conserving energy.



Pupil’s Book Page


Pupil’s Book Page

Forms of energy 11.1 173

Potential energy and kinetic energy

11.2 175 11.1 176

Energy transformations 11.3 177 11.2, 11.3, 11.4, 11.5

178, 179, 180, 181

Energy conservation 11.4 181 11.6 182

Lesson planningThe syllabus provides a logical order of work on the conversion and the conservation of energy. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:


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1. Briefly discuss Activity 11.6 at the start of the unit so that pupils can start to gather information from home.

2. Point out to pupils that energy exists in a number of different contexts or forms such as heat or light. Ask pupils to name some other forms of energy. Make a list to include:

• heat

• light

• potential energy

• kinetic energy

• electricity

• magnetic energy.

3. Explain to pupils that there is only one entity called energy but it has different effects in different contexts. For this reason it is much easier to refer to different forms of energy, even though it is not strictly accurate.

4. Explain to pupils that potential energy is energy which is stored in some way. For example, an object held above the ground has ‘gravitational potential energy’. If it is released, the potential energy changes to kinetic energy and the object is pulled to the ground due to the force of gravity. Similarly, chemicals may be considered to have ‘chemical potential energy’. If the chemical is treated in some way, such as a firework being ignited, the chemical energy changes into heat and sometimes light and sound energies.

5. Describe kinetic energy as the energy associated with an object which is moving.

6. Discuss heat, light and sound as forms of energy and ask pupils to give examples of them.

7. Discuss electricity as a form of energy. Emphasise how convenient it is to be able to channel energy along a thin wire and use a range of appliances to convert electricity to other forms of energy.

8. Give pupils the equation for calculating gravitational potential energy, PE = mgh, and work through some sample calculations.

9. Pupils should work through Activity 11.1 to find the chemical potential energy in an oily seed. Explain to pupils that the energy released is measured indirectly by finding out by how much it will raise the temperature of a known mass of water. Explain the significance of the specific heat capacity of water in this calculation.

10. Give pupils the equation for calculating kinetic energy, KE = ½ mv2, and work through some sample calculations.


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11. As an opportunity for developing critical thinking skills, pupils could be asked to consider the motion of a simple pendulum in terms of the transfer between gravitational potential energy and kinetic energy.

12. Work through Activity 11.2 with students demonstrating the exothermic reaction between calcium oxide and water. Explain that, once again, the energy released raises the temperature of water.

13. Pupils should work through Activity 11.3 investigating the energy changes in a simple electric circuit.

14. Demonstrate and discuss Activity 11.4 considering the energy changes that take place in an electric iron.

15. Demonstrate and discuss the energy changes that take place in a public address system. This Activity 11.5.

16. Explain to pupils that energy can neither be created nor destroyed but simply changed from one form into others. When we talk about converting energy, we are talking about using the available energy to do as much useful work as possible and losing as little energy as possible doing work which has no use. For example, when we heat a room we want as much energy as possible to stay in the room to raise the temperature and as little energy as possible lost through windows, gaps in doors, etc. to the outside.

17. Discuss some of the advantages of conserving energy.

18. Pupils should work through Activity 11.6 using data already obtained from home.

Additional information for the teacherEnergy cannot be used up or destroyed but simply converted from one form into others. For example, when a fuel is burnt the chemical energy it contains is not lost, but converted into heat energy and light energy. Energy conversions can be shown as simple energy flow charts.

When a candle burns the chemical energy it contains is converted to light and heat.

chemical energy light energy + heat energy

The electrical energy passing into a television is converted to light (the picture), sound and there is also some heat produced.

electrical energy light energy + sound energy + heat energy

Animals obtain energy either by eating green plants or by eating animals that feed on the plants. The green plants absorb energy from sunlight.


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solar energy chemical energy

The food that animals eat helps to maintain their body processes. In some groups of animals this includes maintaining their body temperature. It also gives them the energy they need to move around.

chemical energy heat energy + kinetic energy

In a motor car the chemical energy in the fuel is converted to heat, sound and kinetic energy.

chemical energy thermal energy + sound energy + kinetic energy

It should be noted that in almost all energy conversions some heat energy is produced. This is usually lost to the air.

Resources• Test tube

• Test tube holder

• Thermometer

• Electronic balance

• Mounted needle

• Measuring cylinder

• Beaker

• Oily seed (e.g. palm kernel, groundnut, jatropha, shea butter)

• Quicklime (calcium oxide)

• 3V dry cells x 2

• Insulated connecting wires

• Switch

• Flashlight bulb

• Bulb holder

• Source of mains electricity

• Electric iron

• Cloth

• Microphone connected to a loudspeaker

• Source of electricity (a.c. or d.c.)


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• Amplifier

Opportunities to encourage critical thinking skillsPupils could be asked to make a simple pendulum composed of a mass tied to a string which is suspended on a stand and clamp.

They could then be asked to observe the motion of the pendulum and comment on such things as:

• when the potential energy of the mass is minimum and when it is maximum

• when the kinetic energy of the mass is minimum and when it is maximum.

They could use the formulae given to calculate:

• the difference in gravitational potential energy between the maximum and the minimum values

• the maximum velocity of the mass as it swings.

Pupils could be asked to comment on any assumptions they make about the transfer between potential energy and kinetic energy, and whether these assumptions are valid or not.


1 Did pupils gather suitable and sufficient data to complete Activity 11.6 or do they need more prompting and guidance in future?

2 This unit involves a number of practical activities. Were pupils able to follow instructions easily or was it necessary to provide a large amount of support? Can the instructions given for some of the practical work be modified so as to make them easier for pupils to follow?

3 Were pupils able to carry out calculations on gravitational potential energy and kinetic energy in the Pupil Book? If it was necessary to work through additional examples, this should be borne in mind when modifying lesson plans for the future.


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4 Identify two aspects of teaching and learning in this unit that appeared to go well. Decide how you can build on these to improve your delivery of the content for this unit.


1 B

2 C

3 A

4 B

5 C

6 a Chemical energy converted into electrical energy which is converted further into heat and light energy.

b Biomass (plant and animal matter) contain stored energy from the sun in the form of chemical bonds. Anaerobic bacteria decomposes (chemical breakdown) the materials in a process called fermentation releasing biogas (methane and carbon dioxide gases). In the process some of the chemical energy in converted into heat energy. Thus

Biomas BiogasFermentation

(chemical energy) (chemical energy) (chemical + heat energy)

7 a The friction that occurs in the filament of the bulb generates heat in addition to the glowing of rare gases in the bulb.

b Wasted heat in a coal pot can be channelled through the conductor to dry seeds or warm water and other liquids.

8 The kerosene wets the wick and heat from the match stick head converts the chemical energy into thermal energy and light energy.

9 a A horse converts food into chemical energy in its cells.

b The chemical energy is converted into elastic energy in the muscles of the horse, which is converted into kinetic energy as the horse runs.

10 Electrical energy is wasted in the home through:

i. Electrical appliances such as a radio, TV, light bulb being left on.

ii. Use of freezers, fridges and irons without a thermostat.

iii. Use of second hand gadgets that draw excess electrical energy.

11 The construction of houses can help conserve energy when enough windows and doors are made to allow sunlight and wind to freely flow into the rooms. This will cut down the cost of using air conditioners, fans and light from bulbs during the day.

12 High population leads to high energy use and increases the cost of energy supply.

13 Ghana has abundant crude oil resources, tidal waves, geothermal reserves and rivers that can be harnessed to produce hydroelectric power. However, experts have to be


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imported before any of the energy resources can be utilised. Ghana needs human capital for processing our energy resources.

14 a Gravitational potential energy is the energy possessed by a body by virtue of its height from the surface of the Earth. Chemical potential energy is the latent chemical energy possessed by a substance which can be released through a chemical reaction.

Kinetic energy is the energy released by a body in motion. For example, a big boulder rolling down a mountain releases energy which can uproot trees along its track.

b. Kinetic energy from:

bulls is used for ploughing

camels is used to transport luggage from place to place

horses is used for races (game) to entertain and gain tariffs

horses to draw carts and transport dignitaries.


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Unit 12 Light Energy

IntroductionThis unit is concerned with some of the properties of light. Pupils will consider the rectilinear propagation of light and learn how this accounts for the properties of the pinhole camera, the formation of shadows and the formation of eclipses. They will also be introduced to the reflection and refraction of light and discuss some of the applications of these properties.


1. demonstrate that light travels in a straight line

2. describe the operation of the pinhole camera

3. describe the formation of shadows

4. demonstrate the formation of an eclipse

5. demonstrate the reflection of light

6. demonstrate the refraction of light.



Pupil’s Book Page


Pupil’s Book Page

Rectilinear propagation of light

12.1 186 12.1 186

Pinhole camera 12.2 188 12.2 189

Shadows 12.3 190 12.3 191

Eclipses 12.4 192 12.4 193

Reflection 12.5 194 12.5, 12.6, 12.7

195, 196, 197

Refraction 12.6 199 12.8, 12.9, 12.10

199, 201, 203


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Lesson planningThe syllabus provides a logical order of work on light. If the teacher thinks it is appropriate, refraction could be considered before reflection. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Explain to pupils that the rectilinear propagation of light is simple, and another way of saying that light travels in straight lines.

2. Pupils should work through Activity 12.1 so satisfy themselves that light travels in straight lines.

3. Explain the terminology of ‘ray’ and ‘beam’ used to describe light and explain that a beam consists of several rays of light.

4. Describe and discuss the pinhole camera.

5. Pupils should work through Activity 12.2 constructing a pinhole camera and investigating the image formed from it.

6. As an opportunity for developing critical thinking skills, pupils could be asked to investigate the relationship between the distance of the object from the pinhole and the height of the image.

7. Introduce the terms ‘transparent’, ‘translucent’ and 'opaque’ to describe the ability of a material to allow light to pass through it. Ask pupils to identify examples of materials which have these properties.

8. Explain how a shadow is formed by an object made of an opaque material. Point out that this is evidence that light travels in straight lines; if light rays were able to bend around objects there would be no shadows.

9. Demonstrate the difference between point light sources and extended light sources. Explain how an object illuminated by an extended light source casts a region of complete shadow, called the umbra, and a region of partial shadow, called the penumbra.

10. Pupils should work through Activity 12.3 investigating shadows.

11. Describe an eclipse as the result of the shadows cast by the Earth and the Moon.

12. Describe how solar eclipses occur when the Moon passes between the Sun and the Earth and discuss what is seen from the Earth.

13. Describe how lunar eclipses occur when the Earth passes between the Sun and the Moon and discuss what is seen from the Earth.

14. Pupils should work through Activity 12.4 investigating eclipses.


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15. Explain the term ‘reflection’ and discuss how this may be regular or irregular depending on the nature of the reflecting surface.

16. Pupils should work through Activity 12.5 investigating reflection.

17. State and discuss the two laws of reflection of light.

18. Pupils should work through Activity 12.6 confirming the laws of reflection of light for themselves.

19. Discuss the nature of the image formed during reflection in terms of real images and virtual images.

20. Pupils should work through Activity 12.7 investigating the nature of the image formed by a plane mirror.

21. Ask pupils to identify some common uses of plane mirrors. Discuss these applications.

22. Explain the term ‘refraction’ in terms of optical density and describe how a beam of light may appear to bend as it passes from one medium into another.

23. Pupils should work through Activity 12.8 investigating refraction when light travels between air and water.

24. State and discuss the laws of refraction.

25. Pupils should work through Activity 12.9 investigating the laws of refraction.

26. Pupils should work through Activity 12.10 investigating real and apparent depth and use their knowledge of refraction to explain this phenomenon.

Additional information for the teacherVisible light is that part of the electromagnetic spectrum which can be detected by the human eye. The wavelength of visible light is around 380–740 nanometres (1 x 10-9 m). The infrared region of the electromagnetic spectrum is found at a longer wavelength than 740 nm and the ultraviolet region at a shorter wavelength than 380 nm.

Light, in common with all other forms of electromagnetic radiation, travels through a vacuum at a speed of 299 792 458 ms-1. This value is commonly taken to be 300 000 000 or 3 x 108 ms-1 for ease of calculation.

Electromagnetic radiation is emitted and absorbed in tiny packets of energy called photons. It exhibits properties consistent with both waves and particles, and for this reason is said to have wave-particle duality.

Since the time of the Ancient Greeks, learned people have speculated about the nature of light.


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In the fifth century BC Empedocles postulated that everything was composed of four elements: fire, air, earth and water. He believed that the Goddess Aphrodite made the human eye out of the four elements and then lit a fire in the eye which shone out making it possible to see. In order to explain why it was not possible to see at night, Empedocles postulated some sort of interaction between the rays from the eye and sunlight.

In 300BC Euclid studied the properties of light and postulated that light travelled in straight lines. He also described the laws of reflection and studied them.

In ancient India the Vaisheshika school postulated the existence of basic ‘atoms’ of earth, water, fire and air. They believed that light rays were a stream of high velocity atoms. These particles could have different properties depending on their speed and arrangement.

In the early seventeenth century Descartes stated that light was a mechanical property of a luminous body. In 1637 he published a theory of refraction which incorrectly assumed that light travelled more quickly through a denser medium. This conclusion was made on the basis of the behaviour of sound. Descartes’ theory of light is regarded as the start of the modern understanding of light.

In the seventeenth century Gassendi proposed a particle theory of light which was published after his death in the 1660s. Isaac Newton studied Gassendi’s work and favoured the particle theory of light over the wave theory.

Around the same time Hooke published a wave theory of light and Huygens proposed a wave theory independently several years later. The wave theory accounted for many of the observed properties of light including different colours being caused by different wavelengths.

The wave theory was favoured over the particle theory by the majority of scientists at this time although it couldn’t account for all of the properties of light. It was only in the twentieth century that the particle theory was to re-emerge.

In 1900 Planck suggested that light, as a wave, could only gain or lose specific amounts of energy which he called quanta. In 1905 Einstein took this further suggesting that quanta have a real existence as light particles called photons.

Modern quantum theory pictures light as having some properties best explained by considering light as a wave, and other properties best explained by considering light as a particle.


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Resources• Materials to make a pinhole camera

• Light source (e.g. candle)

• Flashlight

• Sharp nail

• Plane mirror

• Shiny silver-coated objects

• Objects that have dull surfaces, e.g. wood or paper

• Mathematical instruments

• Flat Styrofoam or soft plain board

• Optical pins or similar

• Measuring tape

• Transparent containers (beakers or plain drinking glasses or a bottled water container cut into two) x 2

• Stick or pencil

• Coin

• Squares of cardboard x 3

• String

• Ruler

• Globe

• Tennis ball

• Candle

• Pair of compasses

• Rectangular glass block

Opportunities to encourage critical thinking skillsPupils could be asked to modify Activity 12.2 by using a small candle as the object.

The object could be placed at different measured distances from the pinhole, and each time the height of the image in the pinhole camera could be measured.


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Pupils should tabulate their results and then use them to draw a graph. They should comment on the shape of the graph, i.e. the pattern formed, and use the graph to make predictions about:

• the size of the image when the object is at a specified distance from the pinhole

• the distance the object must be placed to produce an image of a specified height.


1 Were pupils able to state the difference between a real image and an imaginary image after it was explained to them? Was it necessary to spend additional time discussing this?

2 Were pupils able to apply what they had learnt about the formation of shadows to account for the formation of eclipses? It is important that pupils appreciate that even massive bodies such as the Earth and the Moon follow the same laws of physics as small bodies on the Earth.

3 This unit involves a number of practical activities which require a certain level of manual dexterity. Were pupils able to obtain satisfactory results or was it necessary to demonstrate practical techniques in advance of the activities?



1 D

2 B

3 A

4 C

5 A

6 D

7 A


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8

mirror

9

opaque object

blackshadow(umbra)

screen

point source

10 a Parallel rays are rays of light that travel without meeting each other.

b Convergent rays are rays that are moving towards each other and will eventually meet.

c Divergent rays spread out and move away from each other.

11light-tight box

inverted image

object

h0u v

h1


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Unit 13 Basic Electronics

IntroductionThis unit is concerned with simple electric circuits. Pupils will be introduced to electronic components including the light emitting diode (LED), diode (P-N junction), resistor and capacitor and observe their effects in electric circuits. They will also consider how a capacitor can be charged and allowed to discharge in a circuit.


1. explain the term ‘electronics’

2. demonstrate the behaviour of discrete components in a d.c. electronic

circuit

3. demonstrate the charging and discharging action of a capacitor.



Pupil’s Book Page


Pupil’s Book Page

Electronics 13.1 210

Components in a circuit 13.2 210 13.1, 13.2, 13.3

211, 214, 216

Charging and discharging a capacitor

13.3 216 13.4 217

Lesson planningThe syllabus provides a logical order of work on electronics. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Introduce the term ‘electronics’ and briefly describe electronic circuits in terms of combinations of different components.

2. Introduce the diode as a P-N junction device. Describe how it allows current to flow in one direction but not in the opposite direction. Point out the importance


139


of placing a diode in the correct orientation in a circuit. Give the symbol for a diode.

3. Introduce the LED as an example of a diode that is widely used in electronic circuits. Give the symbol for an LED. Warn pupils that they should not connect LEDs directly to cells or batteries as the currents involved will instantly destroy the device. A resistor must be used to reduce the current.

4. Pupils should work through Activity 13.1 investigating the properties of an LED.

5. Describe and discuss the terms ‘forward biased’ and ‘reverse biased’ in terms of the properties of an LED.

6. Briefly describe and discuss some uses of diodes.

7. Introduce resistors as electronic components that resist the flow of current. Give the symbols for a fixed and a variable resistor.

8. Explain that the unit of resistance is the ohm; the symbol is Ω.

9. Explain how resistors are colour coded to show their resistance, and demonstrate how the value of a resistor can be deduced by interpreting this coding.

10. Pupils should work through Activity 13.2 investigating the effect of a resistor in a circuit.

11. Introduce capacitors as electronic devices that store small amounts of electric charge.

12. Describe and discuss the structure of a capacitor as two conducting plates separated by an insulator called a dielectric.

13. Pupils should work through Activity 13.3 investigating the effect of a capacitor in a circuit.

14. Explain how a capacitor may be charged and then discharged in an electronic circuit and describe the effects of this.

15. Pupils should work through Activity 13.4 investigating charging and discharging a capacitor.

16. As an opportunity for developing critical thinking skills, pupils could be asked to investigate how to control the rate at which a capacitor charges or discharges using resistors.


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Evolution of the electric cellNear the end of the eighteenth century the Italian scientist Galvani was dissecting a dead frog when he accidently touched an iron dissecting pin with brass forceps. He was amazed to see the frog’s leg twitch violently.

Some static electricity had built up on Galvani as he worked. His iron dissecting pin and brass forceps had provided a metallic pathway which allowed electric charge to flow. The flow of electric charge became known as an electric current.

Voltaic pileA few years later another Italian scientist, Alessandro Volta, showed that placing any moist material between two different metals had the same effect. In 1800, Volta described a pile he had made consisting of alternative copper discs and zinc discs. Each disc was separated from its neighbours by cloth soaked in brine (salt solution). This was the first electrical cell. This gave rise to a lot of interest and a number of other cells were soon developed.

Daniell cellThe Daniell cell was invented in 1836 by John Frederic Daniell, and was a considerable improvement on the Voltaic pile. It consisted of a zinc rod, suspended in zinc sulphate solution held in the porous pot.

This pot was itself surrounded by copper sulphate solution in which a copper rod was suspended. The porous pot prevented the solutions mixing but allowed electricity to flow.

Leclanché cellA better cell was patented by Georges Leclanché in 1866. The early version is sometimes described as a wet Leclanché cell. It consisted of a porous pot filled with a mixture of manganese(IV) oxide and a little carbon ground up and packed around a carbon rod. The pot and a zinc rod were immersed in an electrolyte of ammonium chloride solution.

The wet cell proved cumbersome to use and was eventually modified into the familiar dry Leclanché cell which is still widely used today.


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Current and potential difference

Current

An electric current is the movement or flow of charge through a conductor, such as a metal wire. The charge is carried by tiny particles called electrons. The unit of electric current is the ampere, which is often abbreviated to amp. The symbol for this unit is A.

The electric current in a circuit is measured using an ammeter. The range of values on an ammeter can be altered by adding a device called a shunt across the terminals.

An ammeter is placed in series with other components in a circuit. It is important that the ‘+’ terminal of the ammeter is connected to that part of the circuit connected to the ‘+’ terminal of the cell or battery.

The currents measured in circuits in the laboratory are often less than one ampere. In order to avoid using fractions of an ampere, two prefixes are used to create smaller units of electric current.

• A milliampere, mA, is 1 th1000 of an ampere so 1000 mA = 1 A.

• A microampere, μA, is 1 th1000000 of an ampere so 1 000 000 μA = 1 A.

Although less commonly used, the same prefixes can be used to create smaller units of potential difference.

Potential difference

Electrons will only pass from one point to another in a circuit if there is a difference in potential energy between them. If a bulb is connected into a circuit of wire, without a cell it will not light up. All of the points in the circuit have the same potential energy so there will be no movement of electrons or transfer of charge.

When a cell is introduced to the circuit, the ‘+’ terminal of the cell has a different potential energy to the ‘-’ terminal. The result is that electrons pass around the circuit through the wires and components and charge is transferred by them. In a sense, the cell or battery acts as a pump which drives electrons around the circuit, allowing them to carry charge to the various components. The unit of potential difference is the volt. For this reason potential difference is sometimes referred to as voltage. The symbol for this unit is V.

The potential difference across a component or a part of a circuit is measured using a voltmeter. The range of values on a voltmeter can be altered by adding a device called a multiplier across the terminals.

In order to measure the potential difference across a component or part of an electric circuit, the voltmeter must be connected in parallel. It is important that the ‘+’ of the


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voltmeter is connected to the end of the component or that part of a circuit connected to the ‘+’ terminal of the cell or battery.

Nowadays, a multimeter is often used to measure current or potential difference in electric circuits. By rotating a central dial, the user can select to use the device as either an ammeter or a voltmeter, and also select an appropriate range of values. A multimeter gives a digital readout.

Resources• 3 V battery

• Switch

• Connecting wires

• Light emitting diode (LED)

• Diode (P-N junction)

• 330 Ω resistor

• 3300 Ω resistor

• Capacitor

• 10 kΩ resistor

• 9 V battery

• 100 µF capacitor

Opportunities to encourage critical thinking skillsPupils could modify Activity 13.4 by using resistors of different values and timing how long it takes to charge and discharge the capacitor.

They could analyse their results and determine the relationship between resistance and time for a given capacitor.


1 The practical activities for this unit require some electronic components. Was it possible to obtain these components easily or do they need to be sourced more effectively in advance of future lessons?


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2 Were any LEDs burnt out in Activity 13.1? Was it necessary to re-emphasise that these should not be connected directly to a battery?

3 Were pupils happy to accept the action of different electronic components in a circuit without becoming worried about what goes on inside them? Did pupils need prompting not to get distracted in this way?

4 How successful were pupils in answering the revision questions and particularly the short answer questions 6–9? Did all of the pupils gain at least half marks on the questions? Was there any particular question answered badly by most or all of the pupils? Is there a need for remedial work before moving on?

Answers to exercises and practices in the Pupil’s Book

1 D 3 C 5 B

2 A 4 A

6 a When a diode is placed in an electronic circuit and it allows current to freely flow it is said to be forward biased.

b A reverse biased diode does not permit the free flow of electric charge.

7

Forward biased diode in a circuit

+–

6V

Battery Switch

Connectingwire Diode

a. Forward biasing


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+–

6V

Reverse biased diode in a circuit

b. Reverse biasing

8 A diode is an electronic device which allows current to flow in one direction only.

9

Battery

Capacitor

Positive platereceives charge

Negative platereleases chargeinto the battery

+–

9V


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Section 6: Interactions of MatterAfter studying this section, pupils will be able to:

1. appreciate that interactions between and within matter help humans to better understand the environment and their role in it

2. show understanding of ecosystems

3. trace the interdependency of organisms in an ecosystem

4. develop skills of managing waste in the environment

5. show understanding of both physical and chemical processes in everyday life

6. appreciate that air can be polluted as a result of human activities.

Unit 14 Ecosystems

IntroductionThis unit is concerned with looking at some different ecosystems. Pupils will learn the meaning of terminology including ecosystem, habitat, adaptation and environment. They will consider how energy from the Sun drives all of the processes in any ecosystem, and discuss examples of activities that disrupt the ecosystem.


1. explain the term ‘ecosystem’

2. explain the term ‘habitat’

3. describe how organisms adapt to their environment

4. describe how the energy derived from the Sun is used by organisms in an ecosystem

5. describe the activities that disrupt the balance in the ecosystem.


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Unit 14 Ecosystems



Pupil’s Book Page


Pupil’s Book Page

Ecosystem 14.1 221 14.1 221

Habitat 14.2 221 14.2 221

Adaptation 14.3 222 14.3 225

Energy transfer in an ecosystem 14.4 226

Threats to ecosystems 14.5 228 14.4, 14.5, 14.6

229, 230, 233

Lesson planningThe syllabus provides a logical order of work on ecosystems. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Explain and discuss the terms ‘environment’ and ‘ecosystem’. Carry out the brainstorming Activity 14.1.

2. Explain and discuss the term ‘habitat’. Carry out the brainstorming Activity 14.2.

3. Explain and discuss the term ‘adaptation’.

4. Discuss some examples of how organisms are adapted to their habitats. These should include:

• tilapia

• weaver bird

• cactus.

5. Discuss fresh water and sea water as having similarities because they are both aqueous environments, but differences because of the nature of fresh water and sea water. Pupils should appreciate that organisms which are adapted to live in one could not live in the other. Pupils should carry out Activity 14.3 where they identify adaptations of organisms from different habitats.

6. Explain that the energy which drives an ecosystem is provided by the Sun and is transferred through an ecosystem by food chains and food webs.


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Unit 14 Ecosystems

7. Pupils should appreciate that a food web is a combination of different food chains involving common organisms.

8. With reference to food chains and food webs discuss the difference between producers and consumers.

9. Explain how consumers can be further classified as primary, secondary and tertiary consumers.

10. Discuss the role of decomposers in an ecosystem and stress their importance in recycling nutrients.

11. As an opportunity for developing critical thinking skills, pupils could be asked to use their observational skills to identify a food chain or a food web in a local ecosystem.

12. Explain how ecosystems may be disturbed by both natural and human activity.

13. Pupils should work through Activity 14.4 identifying some natural activities that disrupt ecosystems.

14. Discuss some possible effects of natural activities on ecosystems.

15. Pupils should work through Activity 14.5 identifying some human activities that disrupt ecosystems.

16. Discuss some possible effects of human activities on ecosystems.

17. Explain how an ecosystem exists as a series of natural balances which are inter-related and inter-dependent.

18. Pupils should work through Activity 14.6 thinking about how the growth of the human population on Earth places strains on natural balances and how the effects of a growing population on ecosystems can be kept to a minimum.


EcologyEcology is the study of how organisms interact with each other and how they interact with the physical and chemical factors of their environment.

An ecosystem is a unit of the natural world. Each ecosystem consists of both biotic (living) factors and abiotic (non-living) factors. These different factors interact to provide a stable self-sustaining system.


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Unit 14 Ecosystems

A habitat is the place where an organism lives. For example, a habitat might be a pond, a rock pool, a forest or a desert. Within an ecosystem there may be a number of different habitats which are linked together.

An ecological niche is the role that an organism has in a habitat. Organisms may occupy the same habitat but have different niches. For example, both caterpillars and aphids are found living on plants, but the caterpillars eat leaves while the aphids feed on sap.

The population of a species is the number of that species living in a habitat at a particular time. Populations change over time. A community is the collective term for all the populations of organisms living together in a habitat. Species within a community may interact with each other in a number of ways.

Biotic factors in ecosystemsBiotic factors are the living factors of an ecosystem. Organisms are affected by other organisms within an ecosystem. Biotic factors determine how organisms inter-relate. The following are some important biotic factors.

Competition

Members of the same species compete with each other for everything that they need. This is often food but it may be other things like light and water. If different species have the same needs then they will compete for them.

Predation

When one species kills and eats another it is called predation. The organisms that do the eating are called predators while the organisms which are eaten are prey.

Parasitism

If an organism feeds off the living body of another organism, and does it harm, it is called a parasite and the organism it feeds off is the host. Both animals and plants may have parasites.

Symbiosis

Sometimes two different organisms live together in a way that is good for both of them. It is said that these two organisms have a symbiotic relationship. Such relationships exist in both the animal and plant worlds. Symbiosis is sometimes called mutualism.

Abiotic factors in ecosystemsAbiotic factors are the non-living factors of an ecosystem. Conditions may vary from habitat to habitat within an ecosystem.


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Unit 14 Ecosystems

Light

Light is essential for photosynthesis and therefore for the growth of green plants.

Light is also important to animals. Some insects move about only at night to avoid being eaten by birds. Some animals feed at night and, as a consequence, the animals that feed on them also hunt at night.

Sunlight is essential for humans to manufacture vitamin D in cells below the skin. A lack of vitamin D results in a disease called rickets.

Temperature

Organisms are only able to live within a particular range of temperatures. Within this range, some organisms can survive at low temperatures, such as inside the Arctic Circle, while others are able to cope with the extreme temperatures experienced in a desert.

Availability of water

All living organisms need water to survive. Aquatic organisms like fish are adapted to live in water, either fresh water or in the sea.

The amount of water available in terrestrial habitats will depend on such things as the amount of rainfall, and may vary substantially over a year.

Humidity

Humidity is a measure of how much water vapour there is in the air.

Humidity is important because it affects the rate of water loss from plant leaves during transpiration and from an animal’s body by evaporation.

Wind

Wind has both good and bad effects on plants and animals.

Wind is beneficial because it:

• produces currents in the world’s oceans that bring with them nutrients from the deep oceans

• helps air to dissolve in water bodies

• transports the pollen of some plants

• disperses the seeds of some plants.


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Unit 14 Ecosystems

Wind is damaging because:

• wind causes soil to dry out very quickly

• strong winds can damage plants and uproot trees

• near water, wind produces waves that cause erosion and make it difficult for plants and animals to survive

• wind causes soil erosion by blowing away loose topsoil.

Salinity

Salinity is a measure of the mass of salts dissolved in water. The sea has a high salinity while the water in rivers and lakes contains very little salt so has a low salinity.

Some organisms are adapted to live in the sea, and cannot live in fresh water where the salt content is very low. Other organisms are adapted to live in fresh water and would die if they were put in the sea.

A very few animals and plants are able to survive in both fresh water and salty water.

pH

pH is a measure of acidity and alkalinity. Most water and soil is slightly acidic or slightly alkaline, but some environments are more acidic and some are more alkaline.

pH affects the distribution and growth of organisms. For example, the number of earthworms and bacteria that cause decay in soil are normally reduced in acidic soils. This means that the rate of decay is slowed down which reduces the fertility of the soil.

Resources• Access to the Internet or reference books

• Reference books for identification of aquatic organisms

• Fishing net

• Collecting jars

• Hand lens

Opportunities to encourage critical thinking skillsPupils could be asked to make observations of a local ecosystem over a period of several days with a view to identifying what different organisms eat and which organisms are eaten by other organisms.


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Unit 14 Ecosystems

They should analyse their observations and use them to draw up a food chain or food web for the ecosystem.

For example, at different times they may observe:

• a bee feeding on nectar from flowers

• a spider feeding on a bee

• a lizard feeding on a spider.

These observations would be consistent with the following food chain:

flower bee spider lizard


1 Did pupils become confused by some of the new terminology used in this unit such as ecosystem, habitat, food chain, food web, producer and consumer? Was it necessary to spend extra time explaining these? Would some wall charts assist understanding?

2 How easy was it to find a suitable location for pupils to conduct Activity 14.3? Did the chosen site provide suitable examples of adaptation? Is there a need to look for alternative sites for use in the future?

3 How knowledgeable were pupils about the effects of natural and human activities on ecosystems prior to this unit? Do pupils need more or less background information by way of an introduction to this topic?

4 Identify two aspects of teaching and learning in this unit that appeared to go well. Decide how you can build on these to improve your delivery of the content for this unit.


1 C

2 C

3 B

4 B

5 B


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Unit 14 Ecosystems

6 a i A habitat is a natural home or a place where an organism can successfully live.

ii An ecosystem is a definable area made up of a community of organisms interacting with each other and their non-living surroundings to produce a stable system.

iii A food chain is a feeding relationship among organisms where energy in food is linearly transferred from green plants (producers) through A series of consumers with each stage providing food for the next one.

iv A food web is a complete feeding relationship with many food chains linked.

b i Adaptation describes the special features an organism has that enable it to live successfully in its habitat.

ii Adaptation of a fish to life in water:

• streamlined body shape for easy movement in water

• lateral line detects vibrations in water so as to escape from danger

• gills for exchange of dissolved gases in water

• fins for movement

• swim bladder for altering depth during movement (provides buoyancy)

• caudal fin provides thrust to propel fish forward

• scales protect the fish and provide a smooth surface for easy movement.

7 a In an ecosystem, food is the source of energy for living organisms. Food is only produced by plants (primary producers) using energy from the Sun. The energy derived from the Sun is therefore locked up in the food molecules made by plants. When plants are fed on by herbivores, the energy in the food is transferred to them. The energy in the herbivore is subsequently passed on to other organisms in food chains and food webs. It can therefore be concluded that without the Sun’s energy, plants cannot make food which serves as source of energy for living organisms. The Sun is therefore regarded as the source of all energy in an ecosystem.

b Ways in which the balance of nature may be disrupted:

• bush burning

• excessive hunting

• oil spillage

• environmental pollution

• illegal mining

• uncontrolled logging (deforestation)

• industrialisation

• road construction.

Natural disasters include:

• flooding

• earthquakes and tremor

• volcanic eruptions

• hurricanes, tsunamis and tornado


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Unit 14 Ecosystems

• erosion.c. Ways of maintaining a balance in nature:

• educate people on the dangers of destroying habitats and destabilising the ecosystem

• afforestation - tree planting, establishment of forest reserves to protect endangered species

• wildlife conservation by establishment of natural parks and game reserves

• recycling of materials that do not decompose

• proper disposal methods to avoid environmental pollution

• ban on use of harmful chemicals for fishing.

8a i Herbivore – an animal that feeds mainly on plants or products of plants. It is described as a primary consumer in a food chain or food web, e.g. sheep.

ii Carnivore – an animal that feeds on the other animals or on flesh. It is a secondary consumer, e.g. lion.

iii Omnivore – an animal that feed on both plant and animal material, e.g. humans.

9 a 3 different food chains:

grass grasshopper toad snake

green leaf caterpillar lizard bird

grass grasshopper bird man lion

grass goat man lion

grass grasscutter man lion

b

Lion

ManSnake

Toad

Grasshopper Grasshopper

Bird

Grasscutter

Grass


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Unit 15 Air Pollution

IntroductionThis unit is concerned with air pollution. Pupils will learn about some sources of air pollution, the names of the pollutants and the possible harmful effects associated with them.


1. state the names and sources of common air pollutants

2. list the possible harmful effects of air pollutants.



Pupil’s Book Page


Pupil’s Book Page

Sources of common air pollutants

15.1 237

Harmful effects of air pollutants 15.2 238 15.1, 15.2 238, 240

Lesson planningThe syllabus provides a logical order of work on air pollution. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Explain the term ‘pollutant’ as applied to air. This can be defined as a gas or particles which are not normally present in air or not normally present in such large concentrations.

2. Give examples of air pollutants including:

• carbon monoxide

• sulphur dioxide

• nitrogen dioxide

• chlorofluorocarbons (CFCs)


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• particulates.

Discuss the sources of these air pollutants.

3. Explain how carbon dioxide might be considered a pollutant even though it is always present in air. The reason it may be considered a pollutant is because certain processes, such as the combustion of fossil fuels, greatly increase the concentration of carbon dioxide in air.

4. Pupils should work through Activity 15.1 discussing the possible harmful effects of air pollutants. This discussion should include:

• carbon monoxide

• sulphur dioxide

• nitrogen dioxide

• carbon dioxide

• chlorofluorocarbons (CFCs)

• smoke/particulates.

5. As an opportunity for developing critical thinking skills, pupils could be asked to research into how the levels of some pollutant gases have changed over the years by accessing the data available on the Mauna Loa Observatory website.

6. Pupils should work through Activity 15.2 discussing ways to reduce air pollution.


The evolution of the Earth’s atmosphereThe composition of the atmosphere has undergone many changes since the Earth was formed. These changes have had a considerable impact on different aspects of the Earth’s chemistry. We can conveniently divide the evolution of the atmosphere into three stages.

First atmosphere

Immediately after the Earth was formed and started to cool it is likely that gases were forced to the surface and out of the ground. Initially these gases were probably moving so fast that they escaped the Earth’s gravity and passed into space but eventually a stable atmosphere developed around the Earth.

Assuming that the composition of these gases was similar to those which pass out of volcanoes today, the atmosphere would have consisted of about 80% water vapour,


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10% carbon dioxide, 5% hydrogen sulphide and smaller proportions of other gases including nitrogen, hydrogen, carbon monoxide, methane and the noble gases.

As the Earth cooled, much of the water vapour condensed to liquid water and the ensuing rainfall led to the formation of the oceans. Gradually other gases dissolved in the oceans. A large proportion of the carbon dioxide dissolved and this was the first step to forming carbonate rocks.

Second atmosphere

It is thought that around 3500 million years ago, nitrogen was a major component of a second type of atmosphere. However, the atmosphere still did not contain any oxygen.

Fossils of algae which were capable of photosynthesis have been found and dated to 2700 million years ago. Around the same time there is evidence that an oxygen-containing atmosphere was developing.

Third atmosphere

Geological activity, such as the formation of sedimentary rocks and their subsequent uplifting, was responsible for the transfer of carbon dioxide from the atmosphere into land-based storage in the form carbonate rocks like limestone.

It is thought that free oxygen was first present in the atmosphere about 1700 million years ago. This eventually rose to a steady concentration of about 15% around 500 million years ago, as a result of the development of green plants which produce oxygen as a by-product of photosynthesis. This provided an atmosphere in which oxygen-breathing life forms could evolve.

There is evidence that over the past 500 million years there has been considerable fluctuation in the oxygen content of the atmosphere. Although we regard the current value of around 21% oxygen as constant, on a geological timescale, this is probably not the case.

The symbols ka, Ma and Ga are sometimes used in textbooks to symbolise 1000 years (kilo annum), 1 000 000 years (mega annum) and 1 000 000 000 years (giga annum) respectively. These are not S. I. units as such but provide geologists with a convenient shorthand when writing very large numbers of years.

Global warmingThe average surface temperature of the Earth has increased by about 0.8 ºC over the last hundred years. Much of this increase has occurred in the last thirty years which suggests that the trend in rising temperature is increasing.


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This apparently small rise in average surface temperature has caused major changes to the climate in different parts of the world.

At the North Pole the average winter temperature is around - 34 ºC while in the summer the average is around 0 ºC. Scientists who have studied the North Pole for some time have become aware that these average temperatures are on the increase. As more ice turns to water, the North Pole is slowly getting smaller and the ice is getting thinner.

In some parts of the world the summers are getting much hotter and drier. The level of water in reservoirs is lower than it has been in the past because of increased evaporation and lack of rain. Water is being used up more quickly than it can be replaced by nature. In areas of the world where there are large forests the vegetation is much drier than in the past due to higher temperatures and lack of rain. Dry vegetation catches fire very easily and forest fires have destroyed huge areas of forest.

The greenhouse effectScientists agree that the Earth is in a period of global warming but there is some dispute over the cause of the increasing temperatures. Most scientists believe that it is caused by increasing concentrations of greenhouse gases in the atmosphere as a result of human activities.

Greenhouse gases are gases which can absorb and emit heat radiation. The main greenhouse gases in the atmosphere are water vapour, carbon dioxide, methane and ozone.

Heat from the Sun passes through the atmosphere and warms the surface of the Earth. The Earth, in turn, emits heat radiation back out into the atmosphere. The


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heat radiation is absorbed by the layer of greenhouse gases in the atmosphere and then re-radiated in all directions. The result is that some of the heat passes out of the atmosphere into space but a great deal of heat is directed back down towards the Earth’s surface.

This is commonly called the greenhouse effect because the glass roof and sides of a greenhouse have a similar effect to the greenhouse gases in the atmosphere. Heat becomes trapped in the greenhouse causing the temperature to rise.

The greenhouse effect should more correctly be called the ‘enhanced greenhouse effect’. The greenhouse effect is not new but has always existed as long as the Earth has had an atmosphere. If it wasn’t for the greenhouse effect, the Earth would never have become warm enough to support life as we know it.

The problem on the Earth now is that the concentrations of the greenhouse gases have increased significantly over the past two hundred years. Now, too much heat is being trapped on the Earth by the greenhouse gases and not enough is escaping into space.

390

380

370

360

350

340

330

320

1960 1970 1980 1990 2000 2010

Car

bon

diox

ide

conc

entra

tion

in p

arts

per

mill

ion

by v

olum

e

Global warming coincides with a slow but steady rise in the concentration of carbon dioxide in the atmosphere. This provides evidence of the link between global warming and the effect of increasing concentrations of greenhouse gases.

The table on the opposite page shows the greenhouse index of some gases in the upper atmosphere compared to carbon dioxide. On this scale carbon dioxide = 1.0.


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Gas Greenhouse index% abundance in upper atmosphere

Index multiplied by abundance

Carbon dioxide 1 0.04 0.04

CFCs 23 000 0.000 000 04 0.000 92

Methane 30 0.000 17 0.005 1

Nitrous oxide 160 0.000 03 0.004 8

Oxygen 0 21.0 0

Ozone 2000 0.000 004 0.008

Water vapour 0.1 1.0 0.1

The contribution of a gas to the greenhouse effect depends on its index and its abundance in the upper atmosphere.

ResourcesNone

Opportunities to encourage critical thinking skillsThe Mauna Loa Observatory in Hawaii, USA, has been monitoring the levels of different gases in the atmosphere since the 1950s.

Pupils can access the observatory website using:

http://www.esrl.noaa.gov/gmd/obop/mlo/

and look at the data provided on how the concentrations of different pollutant gases has changed over the past half century.

They could look for any overall trends in changes in pollutant levels and use their findings to prepare a brief report for the class.



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1 The activities in this unit are all in the form of discussions. Were pupils disappointed not to be doing any practical work in this unit? Is it possible to devise one or two practical-based activities for the next time this unit is taught?

2 Was it appropriate to provide pupils with additional information about global issues such as the depletion of the ozone layer and global warming? Did they find these issues interesting and appreciate their importance?

3 How successful were pupils in answering the revision questions and particularly the short answer questions 6-10? Did all of the pupils gain at least half marks on the questions? Was any particular question answered badly by most or all of the pupils? If so, this indicates that some remedial work should be carried out on that particular part of the unit before moving on.


1 C

2 D

3 A

4 C

5 B

6 a Gases – CO, CO2, NO2, SO2, CFCs

Dust

Smoke

Harmful radiations – x-rays, nuclear reactors (any 3 of these)

b Gases:

Carbon monoxide (CO) – reduces the ability of haemoglobin to carry oxygen; this could lead to suffocation and death.

Carbon dioxide (CO2) – increases in the warming of the Earth’s atmosphere causing the ‘greenhouse effect’.

Nitrogen dioxide (NO2) and sulphur dioxide (SO2) – produces ‘acid rain’ when it dissolves in water vapour. Acid rain corrodes metals, damages walls of buildings, increases acidity of water bodies, causes respiratory diseases in humans and also causes damage to plants.

Chlorofluorocarbons (CFCs) – depletes the ozone layer; increases the amount of harmful radiations, such as ultraviolet light, reaching the Earth’s surface and causing diseases such as skin cancer, cataracts and sunburn.

Dust – reduces visibility, causes respiratory diseases.

Smoke – reduces amount of sunlight reaching plants thereby causing a reduction in rate of photosynthesis. Smoke also reduces visibility.


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Radiations – may cause bone marrow cancer or leukaemia; may cause mutation of genes and chromosomes.

7 a Most of the carbon monoxide comes from exhaust fumes of motor vehicles.

b Use of special carburettors, efficient burning of fossil fuels in factories and homes, and less tobacco smoking can reduce the amounts of CO released into the atmosphere.

8 a SO2 and NO2.

b Acid rain corrodes metals, causes respiratory diseases in humans, and increases the acidity of freshwater bodies resulting in the death of organisms.

9 A high concentration of carbon dioxide in the air causes the ‘greenhouse effect’, whereby the Earth’s temperature increases. A greenhouse gas such as carbon dioxide traps heat in a layer around the Earth. This results in global warming.

10 Ways in which air pollution can be reduced.

• use of sulphur-free fuel to control sulphur dioxide pollution

• fitting filters and absorbers in factory chimneys

• efficient burning of fossil fuels reduces CO pollution

• planting of more trees reduces CO2 pollution

• use of lead-free petrol reduces the release of lead compounds

• radioactive waste should always be properly disposed of

• phasing out the use of CFCs.


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Unit 16 Physical and Chemical Change

IntroductionThis unit is concerned with physical and chemical changes. Pupils will discuss common examples of physical changes and common examples of chemical changes. They will also learn about certain characteristics of each which will help them to differentiate between the two.


1. explain the process of physical change

2. explain the process of chemical change.


Syllabus topicSection in Pupil‘s Book

Pupil’s Book Page


Pupil’s Book Page

Physical changes 16.1 243 16.1, 16.2 244

Chemical changes

16.2 245 16.3 246

Lesson planningThe syllabus provides a logical order of work on physical and chemical change. Teaching strategies should be determined by the nature and content of the topic. Lessons should be planned to cover the following sequence of topics:

1. Explain to pupils that materials may undergo two types of changes: physical changes and chemical changes. Each type of change has certain characteristics by which it can be identified.

2. Explain that physical changes are very easy to reverse. Discuss some examples of physical change including melting/solidifying, boiling/condensing and dissolving.


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3. Pupils should work through Activity 16.1 to demonstrate that a physical change, freezing/melting, is readily reversible.

4. Pupils should work through Activity 16.2 looking at more examples of physical changes.

5. Explain that chemical changes are very difficult or most often impossible to reverse. In a chemical change one or more substances is used up and changed into one or more new substances.

6. Identify some examples of chemical change including cooking, burning, digestion, rusting and fermentation.

7. Pupils should work through Activity 16.3 investigating the effect of heat on an egg as an example of a chemical change.

8. Discuss other examples of chemical changes including rusting and burning.

9. As an opportunity for developing critical thinking skills, pupils could be asked to investigate the effect of heat on hydrated copper sulphate.

Additional information for the teacherPupils will be familiar with a number of physical changes and chemical changes from their everyday life experiences but they will not recognise them as such prior to working through this unit.

In order to differentiate between physical change and chemical change, pupils should be made familiar with the characteristics of each.

Physical change:

• Physical changes do not involve new substances being formed but substances may change state.

• Physical changes are generally easy to reverse.

Chemical change:

• Chemical changes involve changing one or more substances into different substances.

• Chemical changes are generally difficult or impossible to reverse.

The giving out or taking in of heat energy is not a good criterion for identifying chemical change as it also occurs when a substance changes state, which is a physical change.


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Resources• Heat source

• Tripod and gauze

• Beaker

• Boiling tube

• Bench mat

• An egg

• Saucepan

• Tongs

• Elastic band

• Deflated bicycle tyre or football

• Pump

• New iron nail

• Access to a freezer

• Ice

• Small piece of wood or paper

• Match

Opportunities to encourage critical thinking skillsWhen gently heated, blue hydrated copper sulphate is converted to grey anhydrous copper sulphate according to the following equation:

CuSO4.5H2O CuSO4 + 5H2O

If this is carried out in a test tube and only gentle heat is used, pupils will see that the colour of the copper sulphate crystals changes and that droplets of a colourless liquid appear at the top of the test tube where it is cooler.

Pupils could be asked to carry out this experiment and to follow it up with another simple experiment in which droplets of water are added to the grey powder once it has cooled.

From their observations, pupils should argue whether they are observing chemical changes or physical changes.


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1 Are there any additional simple activities that could be added to this unit in order to make it more interesting and enjoyable for pupils?

2 Were pupils able to relate the content of this unit to examples of physical and chemical changes in everyday life? Is it necessary to discuss these in more detail so that pupils may easily make the link between what they learn in the classroom and their everyday experiences and observations?



1 A 2 A 3 C 4 C 5 D 6 C 7 D 8 B 9 B 10 A

11 a Rusting of iron

Rusting of iron is regarded as a chemical change because the individual constituents which reacted to produce the brown rust cannot be obtained once the change has occurred; the reaction is irreversible.

Normally, when a clean, shiny iron nail is left in a damp place, it soon becomes covered with a reddish-brown substance – rust. Rust is an entirely new substance which has been formed.

During rusting, oxygen and water from the air combine with the iron to form hydrated iron oxide which is rust. The iron increases in weight when it rusts.

oxygen + water + iron hydrated iron oxide.

This shows that the process of rusting is a chemical change because the action is irreversible.

b Respiration

During respiration, living organisms respire, that is, they take in oxygen and give out carbon dioxide and water vapour. The oxygen is used to oxidise food in order to provide energy.


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The products of respiration are carbon dioxide, water vapour and energy. These are entirely new products which cannot be broken down to obtain the original oxygen. For this reason, this is a chemical change. The reaction is not reversible.

c Fermentation of food

Fermentation is a chemical change. When kneaded dough is allowed to ferment, yeast or baking powder produces carbon dioxide gas which increases the amount of trapped gas and therefore doubles the size of the dough.

Usually micro-organisms like bacteria and yeast are used during the fermentation process to produce many useful substances. In the production of yoghurt for example, bacteria are allowed to ferment milk. During the process, the lactic acid which is produced acts on milk protein to produce the characteristic yoghurt texture. In all these processes, new materials which are different from the original reactants are produced. The reaction is not reversible.

d Burning of wood into ashes

Wood burns in air and combines with oxygen to form ash, which is a completely new substance. In this regard, the process of burning or combustion is a chemical reaction, which takes place between an active gas (oxygen) in the air and the wood. The ash, which is formed after the reaction, is an entirely new substance. The original wood and oxygen cannot be obtained from the ash. Therefore, burning of wood is a chemical reaction and is not reversible.

12

Physical changes Chemical changesEvaporation Digestion of foodMelting ice Sodium reacting with waterDissolving salt in water Burning of grassCondensation Heating of water

13 Differences between physical and chemical changes:

Physical changes Chemical changesNo new substances are formed New substances are formed No change in mass occurs Changes in massEasily reversible Not easily reversible (irreversible)Heat production is minimal (not usually accompanied by great heat change)

Accompanied by production of great heat change


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