Story Transcript
Science
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TEXTBOOK
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For Cambridge Lower Secondary
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SMART
Yap Wei Chong
Introduction
Unit 1A: Obtaining food Chapter 1: Nutrition in living things 1.1 Nutrition in plants 1.2 Nutrients in our diet
Chapter 2: The human digestive system
This book is divided into clear and manageable units covering Biology, Chemistry and Physics. The units are further divided into chapters, each dealing with a topic from the syllabus.
Unit 1B: E lements, compounds and mixtures
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2.1 Physical and chemical processes in food digestion 2.2 Organs of the alimentary canal and their functions 2.3 The role of enzymes
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Chapter 3: The particle theory of matter
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3.1 The particle theory of matter and the properties of matter 3.2 Gas pressure 3.3 Diffusion in gases and liquids
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Chapter 4: Elements and the Periodic Table
18 18 19 20
24 26 26 30 31
35
4.1 Atoms 4.2 The Periodic Table 4.3 Elements and their uses
35 37 39
Chapter 5: Compounds and mixtures
42
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Welcome to the Science SMART series. This series has been designed to help you understand and master the knowledge and skills you need to cover for the Cambridge Lower Secondary Science Curriculum Framework for Stage 8.
The chapters have many useful features to help you make sense of the topics and understand all aspects of them. These features are explained on pages iv and v.
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CONTENTS
Unit 1
5.1 Compounds 5.2 Mixtures 5.3 Mixtures–solutions 5.4 Separating mixtures
Unit 1C: L ight Chapter 6: Properties of light 6.1 Properties of light rays 6.2 Pinhole camera 6.3 Shadows 6.4 Luminous objects and non-luminous objects
Chapter 7: Reflection of light 7.1 Laws of reflection 7.2 Regular and irregular reflection 7.3 Application of the laws of reflection
Chapter 8: Refraction of light 8.1 Refraction 8.2 Application of refraction of light
Chapter 9: Dispersion of white light and colours 9.1 Dispersion of white light 9.2 Seeing colours emitted by a light source 9.3 Seeing colours in non-luminous objects
42 45 48 49
54 56 56 57 59 60
62 62 64 66
70 70 73
76 76 77 78
Unit 3
Unit 2A: Respiration and circulation
86
Chapter 10: Transport in flowering plants
88
10.1 Absorption of water and mineral salts 10.2 Transport of water and mineral salts
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Unit 2B: M etals, non-metals and corrosion
20
23
13.1 Differences between metals and non-metals 13.2 How are metals obtained? 13.3 Reactions between metals and dilute acids
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14.1 Rusting of iron 14.2 Ways to reduce rusting
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Unit 2C: Sound
Chapter 15: Transmission of sound
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15.1 How is sound produced? 15.2 How does sound travel to our ears? 15.3 What happens inside our ears? 15.4 The speed of sound
Chapter 16: The oscilloscope
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18.1 Gametes 18.2 The male reproductive system 18.3 The female reproductive system 18.4 Menstrual cycle 18.5 Fertilisation 18.6 Foetal development 18.7 Sexually transmitted diseases
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96 97 98 100 101
105 109 110 111 112
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Unit 3B: C hemical reactions Chapter 19: Chemical reactions of metals
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12.1 What happens to our body when we breathe? 12.2 Airways and our lungs 12.3 Gas exchange in the lungs 12.4 Aerobic and anaerobic respiration 12.5 Smoking
Chapter 18: The human reproductive system
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Chapter 12: The human respiratory system
93 95
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93
16.1 The cathode ray oscilloscope 16.2 Interpreting information from the CRO
118 120 120 126 128
150 152
17.1 Puberty 17.2 Physical and emotional changes 17.3 How does our diet affect growth? 17.4 How can some diseases affect growth? 17.5 How do drugs affect our body?
89
11.1 Structure of the heart 11.2 How does the heart transport blood around the body? 11.3 Double circulation 11.4 Blood 11.5 Blood vessels 11.6 Scientists’ discoveries 11.7 Disorders of the circulatory system
Chapter 14: Corrosion
Chapter 17: Growth and puberty
88
Chapter 11: The human circulatory system
Chapter 13: Metals and non-metals
Unit 3A: Reproduction and growth
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Unit 2
19.1 Reactions of metals with dilute acids 19.2 Reactions of metals with water or steam
Chapter 20: Common compounds 20.1 What is in a compound? 20.2 Oxides 20.3 Carbonates 20.4 Sulfates 20.5 Chlorides 20.6 Hydroxides
152 152 153 154 155
159 159 160 161 163 164 165 169
172 174 174 176
181 181 183 184 186 187 189
132 133 134
Unit 3C: Forces and magnets Chapter 21: Speed
136 138 138 139 141 142
144 144 145
21.1 Speed and average speed 21.2 Distance-time graphs
Chapter 22: Magnetism 22.1 The properties of magnets 22.2 Identifying magnets 22.3 Magnetic induction 22.4 Magnetisation and demagnetisation 22.5 Magnetic fields 22.6 Electromagnets 22.7 Uses of magnets and electromagnets
Glossary
194 196 196 201
205 205 208 208 211 213 216 218
222
iii
Textbook features Lt d
UNIT 1A
Obtaining food Nutrition is important to all living organisms—plants and animals alike. However, the ways in which plants and animals get nutrients are very different.
It is crucial for our body to break down food into smaller pieces and nutrients that can be absorbed. The focus of Chapter 2 will be the human digestive system, also known as the alimentary canal.
An overview and introduction to the unit topic is provided in clear, simple English. This helps you to see where the topic fits into your everyday experience.
Make predictions using scientific knowledge and understanding. (8Ep6)
Take appropriately accurate measurements. (8Eo1)
The organs and functions of the alimentary canal.
Present results as appropriate in tables and graphs. (8Eo4)
The function of enzymes.
Make simple calculations. (8Ec1) Identify trends and patterns in results (correlations). (8Ec2) Discuss explanations for results using scientific knowledge and understanding. Communicate these clearly to others. (8Ec6) Compare results with predictions. (8Ec3) Present conclusions to others in appropriate ways. (8Ec7) Interpret data from secondary sources. (8Ec5)
nutrition peristalsis diet digestion deficiency enzyme alimentary canal photosynthesis
Obtaining food
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UNIT 1A
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Each chapter includes key question(s) to lead pupils into the topic. Chemical processes
CHAPTER 2 In this chapter
After the food has been breakdown into smaller pieces, it moves through a series of organs called the alimentary canal. The chemical break down of food in our body requires chemical substances. It begins in our mouth.
The human digestive system
• Understand the functions of enzymes as biological catalysts in breaking down food to simple chemicals. (8Bh4)
The salivary glands in our mouth produce and release saliva. The saliva contains chemical substances that can help to breakdown food.
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• Recognise the organs of the alimentary canal and know their function. Secondary sources can be used. (8Bh3)
•
What happens to food as it enters our mouth?
•
How do our body break down and absorb the nutrients in food?
The food that we consume is not in the form that our body can absorb and use. It must be broken down into simpler substances. This process where our body breaks down food into simpler substances is called digestion. The group of organs that are involved in digestion are known as the digestive system.
Food is broken down into simpler substances through physical and chemical processes in our body.
Brainstorm
Physical processes Physical processes begin in our mouth and involve our teeth. Food is physically broken down into smaller pieces by our teeth. We have four types of teeth to help us cut, tear, crush and grind our food.
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UNIT 1A
2.2 Organs of the alimentary canal and their functions
Type of teeth
11. Canine
Shape
Function
Incisor
Premolar
Molar
• Chisel-shaped • Chisel-shaped • Wide
• Broad
• Sharp biting surface
• Flat biting surface
• Flat biting surface
• Large flat biting surface
To cut food
To tear food
To crush food
To grind food
Look out for QR codes throughout the book. These are links to additional information on websites and some videos for you to find out more.
Digestion of food continues as the food travels along the alimentary canal.
Which organs make up the alimentary canal? What are their functions? Let us find out!
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Imagine that this is your lunch and you gobble down your food without chewing it into smaller pieces. What do you think would happen?
Salivary glands
2.1 Physical and chemical processes in food digestion
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Which organs are involved in the human digestive systems?
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The relationship between diet and fitness.
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The effects of nutritional deficiencies.
Use a range of equipment correctly. (8Eo2)
Recall
Brainstorm feature provides you with the opportunity to think and reason about a topic.
The need of plants for carbon dioxide, water and light for photosynthesis and that this process makes biomass and oxygen. The constituents of a balanced diet and the functions of various nutrients.
Identify important variables; choose which variables to change, control and measure. (8Ep5)
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Learning objectives from the Cambridge Lower Secondary Curriculum Framework with their unique codes are listed here.
Pupils build on their previous knowledge the characteristics common to all living things to develop their knowledge of:
Discuss and control risks to themselves and others. (8Eo3)
Vocabulary
• • •
Test predictions with reference to evidence gained. (8Ep2)
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• • • • • •
In this unit
Plan investigations to test ideas. (8Ep4)
An overview of outcomes you are expected to achieve at the end of the Unit is found here.
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• • • • •
Discuss the importance of developing empirical questions which can be investigated, collecting evidence, developing explanations and using creative thinking. (8Ep1)
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Scientific enquiry
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Recall related content by attempting questions covered in previous stages or chapters.
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In Chapter 1, we will look more closely at how plants make food through a process called photosynthesis. We will also learn about different types of nutrients in food to understand what is a balanced diet.
Spotlight Learn about how food travels through our digestive system.
Investigate!
Aim: To find out about the position and functions of different organs of the alimentary canal.
GROUP WORK
Instructions: 1 Gather information from the Internet about the organs in the alimentary canal. 2 Present your findings. In your presentation, include the following:
• •
The name and position of the organs in the alimentary canal The functions of each organ
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Obtaining food
Cambridge International recommended vocabulary is highlighted. The meanings are included in the Glossary at the back of the book.
Investigative activities are usually found before a new concept so that you can try to find out the Science for yourself. You are expected to make your own conclusions. These activities are also designed to build your practical skills. Activities that require you to research on the Internet are indicated with this symbol .
12.
Investigate! Super scientist
Aim: To observe what happens when we chew some pieces of bread in our mouth. You will need: Few pieces of bread, iodine solution, dropper, white tile and some tissue papers.
Super scientist introduces you to the lives of scientists and their work.
Instructions: Add a few drops of iodine on a piece of bread. Leave it aside.
2
Chew a few pieces of bread for a few minutes.
3
Note the taste of the bread as you chew.
4
Remove the bread from your mouth.
5
Place it on a piece of tissue paper for observation.
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Questions: 1
Which type of carbohydrate is present in bread? Explain.
2
What did you observe in Step 5?
3
What do you think is added to the bread as you are chewing it?
4
What happen to the taste of the bread change as you chew it?
5
What do you think happen to the starch in bread after you chewed it?
Investigate!
Simple sugars
Enzymes speeds up chemical reactions in our body without being changed themselves. Substances that speed up reaction without undergoing any changes are known as catalysts. Hence, enzymes are biological catalysts.
Starch
Figure 2.1 Amylase helps to break down complex
PAIR WORK
sugars, starch, into simple sugars. Amylase
A healthy diet is made up of food from all groups in the Eatwell Guide in their recommended amounts. Regular amount of exercise of about 150 minutes per week is also essential to maintain a healthy lifestyle.
Effects of nutritional deficiencies
10. We should eat less foods that are rich in sugars and fats as they contain little nutrients. Some fats, such as olive oil, are good for us. They can be taken in moderation.
Instruction: 1 Research using the Internet or books to answer the following questions. Questions: 1 Which nutrients might be lacking in these people?
Milk, cheese and yoghurt are made from milk. They are rich in proteins and calcium. We should choose low fat options.
a) Person A has frequent cramps.
b) Person B has sores or discolouration on his tongue.
p Figure 1.7 The Eatwell Guide shows the portion we should eat for each food group.
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p Figure 1.8 Guideline Daily
The following infographic shows some common signs of nutritional deficiency.
Aims: To investigate more about the Guideline Daily Amount (GDA) and the recommended daily intake of nutrients for snacks that you often eat. Instruction: Use the Internet or other resources to find out more about the topics mentioned above.
Too little calcium Results in weak bones and teeth
Too little iron Causes anaemia in which one lacks healthy red blood cells
Questions: What types of snacks do you often eat?
2
How many servings of the snacks does it take to exceed the recommended daily intake of sugar and fat for an adult female/male?
Too little fibre
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UNIT 1A
Obtaining food
Causes constipation (infrequent bowel movements) and weight gain
Check My Understanding 1 Describe the five main
food groups present in a balanced diet and the importance of each food group. 2 Describe the
consequences when a person does not consume enough iron.
Too little vitamin D Causes rickets which can lead to weakening or softening of bones
Worksheet 1.3
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Spotlight features provide you with extra tidbits of information relevant to the idea being discussed.
Too little vitamin C Causes scurvy whose symptoms include bleeding gums, weakness and sore limbs
Investigate!
Allowance label
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9.
Spotlight
How do your food intake and physical activity affect your body weight?
How can we ensure that we consume enough biotin (also known as vitamin B7) to reduce the effects of hair loss and/or skin problems?
Guideline Daily Amount (GDA) The Guideline Daily Amount (GDA) is a nutritional label that shows the value and the percentage of the daily value per serving of the food indicated. The GDA allows us to make informed choices about the foods we are going to buy and consume.
Investigate!
Aim: To investigate nutritional deficiencies.
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Pulses (beans, lentils and peas), meat, fish and eggs are rich in proteins. We should aim for at least two portions of fish every week. We should eat less red and processed meat and more lean meats.
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We should drink at least 6 to 8 glasses of water a day.
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Eat at least 5 portions of a variety of fruits and vegetables a day. They should make up a third of the foods we eat a day. They are rich in vitamins, minerals and fibre.
GROUP WORK
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When we do not consume sufficient nutrients from a particular food group or when our body is lacking a particular vitamin, we may develop nutritional deficiencies in our body. 6 to 8 a day
Worksheet 2.3
A healthy lifestyle—proper nutrition and exercise
The Eatwell Guide divides the foods we consume into 5 main groups. Starchy foods that are rich in carbohydrates should make up a third of the foods we eat. We should choose whole grains as they are rich in fibre.
You will work in pairs or in groups, as indicated by these icons.
Name an enzyme. Describe its function.
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Workbook activity icons indicate where you should revise what you have learnt by completing a Worksheet.
Check My Understanding
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PAIR WORK
Aim: To find out the effect of the enzyme, amylase on starch solution. You will need: Starch solution, enzyme (amylase) solution, Benedict’s solution, boiling tubes, safety goggles, test tubes, beaker, tripod, wire gauze, lighter, Bunsen burner and heating apparatus. Instructions: 1 Plan an experiment to prove that amylase breaks Plan VAPOURS down starch in bread into simple sugars. 2 Let your teacher check your plans. 3 Carry out your experiment. Record your results in a suitable format. 4 Compare the results of the experiment with your predictions.
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13.
English biochemist, William Prout, was born in 1785. He was the son of a farmer. Prout discovered that the digestive juices of animals contain significant amounts of hydrochloric acid. This led to the discovery that humans also have hydrochloric acid in their digestive juices.
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Check My Understanding are questions inserted at various junctures within a chapter to provide immediate feedback on your understanding and reinforces your knowledge.
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Each chapter ends with a summary of key concepts in the form of a concept map to help you revise what you have learnt. Chapter Summary
Science Connect
Chapter Summary Nutrition in living things
Nutrition in living things
The body is unable to use ts excreted. Thus, patients would be a simple test that f glucose?
Plants
dical tests! A doctor will s diabetes or not.
Human beings
Make their own food
yr
through
op (2)
experiences constipation.
Carbon dioxide + Water With With With a a little some lot of simple simple simple sugars sugars sugars
Chlorophyll Light
causes Benedict’s solution to change colour
Iodine solution to change colour
Oxygen + Glucose With With With a a little some lot of simple simple simple sugars sugars sugars
takes place in
Proteins
Biuret solution to change colour
Veins
needs
1
What do plants need for photosynthesis?
2
What do plants produce during photosynthesis?
3
What test can we conduct to find out whether photosynthesis has taken place in a plant? (1)
Wide
Fats Leaf arrangement
Leaf stalk
can cause
b) i) Name the tests you can conduct to test if your predictions are true.
(1)
ii) What would you observe if your predictions are true?
(1)
4
Spongy layer
Lower epidermis
Paper to become translucent
Fried chicken
a) Predict and name two groups of nutrients that this food contains. (2)
Vitamins, minerals and water
Stoma
A person experiences constipation. a) What do you think can be a possible reason? b) How can he change his diet to avoid having constipation?
Each chapter ends with Revision questions to evaluate your consolidated understanding.
Biuret solution to change colour
needs
Wide
Leaf arrangement
Leaf stalk
Fats
can cause
Upper epidermis
Cuticle
Palisade layer Spongy layer
(1) (2)
cause
Thin
Veins
(2)
d) Besides this food, what food groups should a person have for a meal to have a balanced diet? (3) 5
Palisade layer
Guard cell
(2)
c) Explain why we should not eat too much of fried chicken. (2)
Upper epidermis
Cuticle
Proteins
have adaptations to help plant photosynthesise
Revision
cause
Thin
Transport tissue
such as Glucose
Leaves
have adaptations to help plant photosynthesise
(1) (2)
produce
needs
Oxygen + Glucose
Simple sugars
causes
Photosynthesis
Leaves
es this food, what food groups should on have for a meal to have a balanced (3)
n he change his diet to avoid constipation?
Light
Carbohydrates
Starch
through
Benedict’s solution to change colour
takes place in
n why we should not eat too much d chicken. (2)
o you think can be a e reason?
Chlorophyll
Human beings
Make their own food
such as Glucose
Iodine solution to change colour
(2)
C
at would you observe if your dictions are true?
Simple sugars
causes
produce
needs
me the tests you can conduct est if your predictions are true.
Plants
However, do note that diabetes must still be confirmed by proper medical tests! A doctor will usually carry out a urine test and a blood test to confirm if a person has diabetes or not.
causes
Photosynthesis
Carbon dioxide + Water
Starch
Science Connect invites you to explore the applications of what you have learnt in the real world.
Diabetes is a condition disease that affects how the body uses glucose. The body is unable to use the glucose in the blood. Glucose stays in the blood and eventually gets excreted. Thus, patients with diabetes usually produce urine with high levels of glucose. What would be a simple test that any Science student could do on urine samples to test for high levels of glucose?
Carbohydrates
Transport tissue
Lower epidermis
Guard cell
Paper to become translucent
Vitamins, minerals and water
Stoma
[17]
[17]
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UNIT 1A
Obtaining food
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Scientific method Lt d
In our Plan VAPOURS , we need to have:
V
ariables: Independent variable (to be changed) Dependent variable (to be observed/measured) Controlled variables (to be kept constant)
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rediction that can be tested
What will happen? What would the results be like?
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bservations and/or measurements to take
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Choose and use apparatus and materials correctly
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pparatus and equipment
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The temperature of the water will increase at a faster rate for the burning of sugar than for the burning of bread.
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Observations are qualitative and measurements are quantitative. How can I take measurements accurately? How should I record my observations and measurements?
See page 10 in Unit 1A. (Investigative activity 6) Independent variable: • The type of food Dependent variable: • The temperature increase of the water caused by the burning of the food Controlled variables • The mass of food sample burnt • The mass of water to be heated
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2 Plan an investigation
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What is the energy content of the food I eat?
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Form a question that can be investigated
Example:
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1 Question
nderstanding
heat energy
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Based on what I know and the research I have done, what is the best way to test my prediction? What is the reason for carrying out certain steps?
Record the temperature every 30 s for a total of 3 min.
stored energy
What should I do to keep myself and others safe during this investigation?
• Wear safety goggles and heat
isks and safety precautions
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teps in sequence
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What is the order in which I will carry out the steps?
handling hot apparatus.
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resistant gloves. • Use tongs or gloves when
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Evaporating dish
vi
Flat-bottom flask
Round-bottom flask
Pipette pump
Burette
Pipette
Gas jar
Crucible
3 Present evidence How can I organise my results in a table that is clear and easy to read?
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The results for the burning of sugar has a steeper slope than the result for the burning of bread (from 0 s to T s).
How do I draw an appropriate chart or graph?
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The graph also shows us that the temperature of water peaked earlier for the burning of sugar than the burning of bread.
4 Analyse evidence
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Temperature of the water against time
What can I do about the anomalous results?
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5 Explain
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How can I explain the evidence using scientific knowledge and understanding?
Burning of bread
T Time (s)
As the food sample is burning, the energy stored in it is released as heat energy. This energy is transferred to the water, which caused its temperature to increase. From the graph, we can conclude that the temperature of water increases at a faster rate for the burning of sugar. This shows that sugar releases energy faster than bread.
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Are the trends observed from my results similar to my prediction? What is my conclusion?
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Burning of sugar
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How can I tell if any of my results do not fit this trend/pattern?
Temperature of water (˚C)
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What are the trends and patterns in my results?
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How can I communicate this clearly to others?
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Horseshoe magnet
Test tube holder
Bar magnet
Test tube rack
Microscope slide and cover slip
Microscope
Bell jar
Water trough
Displacement can
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Nutrition is important to all living organisms—plants and animals alike. However, the ways in which plants and animals get nutrients are very different.
te
Obtaining food
Lt d
UNIT 1A
on
In Chapter 1, we will look more closely at how plants make food through a process called photosynthesis. We will also learn about different types of nutrients in food to understand what is a balanced diet.
du
ca
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It is crucial for our body to break down food into smaller pieces and nutrients that can be absorbed. The focus of Chapter 2 will be the human digestive system, also known as the alimentary canal.
Scientific enquiry
E
Discuss the importance of developing empirical questions which can be •
ls to n
investigated, collecting evidence, developing explanations and using creative thinking. (8Ep1)
A
Plan investigations to test ideas. (8Ep4) • Test predictions with reference to evidence gained. (8Ep2) • Make predictions using scientific knowledge and understanding. (8Ep6) • Discuss and control risks to themselves and others. (8Eo3) • Identify important variables; choose which variables to change, •
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control and measure. (8Ep5)
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Use a range of equipment correctly. (8Eo2) • Take appropriately accurate measurements. (8Eo1) • Present results as appropriate in tables and graphs. (8Eo4) • Make simple calculations. (8Ec1) • Identify trends and patterns in results (correlations). (8Ec2) • Discuss explanations for results using scientific knowledge and • understanding. Communicate these clearly to others. (8Ec6)
Vocabulary
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Compare results with predictions. (8Ec3) • Present conclusions to others in appropriate ways. (8Ec7) • Interpret data from secondary sources. (8Ec5) •
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UNIT 1A
Obtaining food
nutrition peristalsis diet digestion deficiency enzyme alimentary canal photosynthesis
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Pupils build on their previous knowledge the characteristics common to all living things to develop their knowledge of:
In this unit
The need of plants for carbon dioxide, water and light for photosynthesis and that this process makes biomass and oxygen. The constituents of a balanced diet and the functions of various nutrients.
The effects of nutritional deficiencies.
23
A
The relationship between diet and fitness. The organs and functions of the alimentary canal.
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C
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yr
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The function of enzymes.
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Nutrition in living things
In this chapter • Explore how plants need carbon dioxide, water and light for photosynthesis in order to make biomass and oxygen. (8Bp1)
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• How do plants get their food?
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CHAPTER 1
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1.1 Nutrition in plants
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• How about us? What kind of nutrients do we need to have in our diet?
• Identify the constituents of a balanced diet and the functions of various nutrients. Secondary sources can be used. (8Bh1)
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Living things need air, food and water to survive. Nutrition is the process of getting food and turning it to living matter. We get food from plants or animals. For plants, they make their own food.
• Understand the effects of nutritional deficiencies. (8Bh2)
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• Understand the relationship between diet and fitness. (8Bh6)
Photosynthesis
Recall Where do plants get their nutrition from?
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Plants make food through the process known as photosynthesis. Photosynthesis is a chemical process in which plants use energy from light to make food from water and carbon dioxide. What else do plants produce during photosynthesis?
1.
Investigate!
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GROUP WORK DEMONSTRATION Aim: To identify and measure the gas produced during photosynthesis. You will need: Lamp, retort stand, 15-cm ruler, scissors, 500-ml beaker, boiling tube, wooden splint, Bunsen burner, lighter, filter funnel, pond water, tubing, syringe and 3 sprigs of pondweed (each of about 7 cm to 10 cm long). Part I: Instruction: 1 Your teacher will submerge some pondweed in pond water and put it into a filter funnel with an inverted boiling tube on top. The gas will be collected in the boiling tube. A glowing splint will be put into the boiling tube. O Question: 1 What happened to the glowing splint? Name the gas that was collected. Part II: Instructions: 1 Your teacher will show you ways of measuring the amount of gas produced by counting bubbles and by measuring the volume of gas produced with a small syringe. 2 Plan an investigation to find out the correlation between Plan VAPOURS the amount of light and the rate of photosynthesis.
Beaker
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Boiling tube
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Pond water
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Filter funnel
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UNIT 1A
Pondweed
Obtaining food
3 4
Let your teacher to check the plan. Carry out the investigation.
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Questions: 1 Predict what you will observe in the experiment. 2 How did your results compare with your prediction? If your prediction does not match the results, explain why.
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Besides food, oxygen gas is also produced during photosynthesis. In investigative activity 1, we also observed that as the light intensity increases, the rate of photosynthesis will increase.
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How can we test for the presence of starch?
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Ethanol
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To find out whether photosynthesis has taken place in a plant, we can test for the presence of starch in a leaf using iodine solution. Let us find out how to do so.
2.
Investigate!
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Plants make food in the form of sugar. Glucose, which is a type of simple sugar, is formed during photosynthesis. Plants can convert glucose into a type of complex sugar known as starch. Plants store food in the form of starch. Plants usually store food in their leaves. Plants can also store food in stems and roots.
Hot water Boiling chip Folded up leaf
PAIR WORK
Brainstorm Why is it necessary to boil the leaf in ethanol before adding iodine?
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Aim: To test for the presence of starch in a leaf using the iodine test. You will need: Forceps, safety goggles, 500-ml beaker, hot water (70–90°C) boiling tube, leaf, ethanol, boiling chips, white tile, dropper and iodine solution. Instructions: 1 Use the forceps to place a leaf into a beaker of hot water (70–90ºC). Keep the leaf in the hot water for about 1 to 2 minutes. 2 Next, place the leaf into a boiling tube and add the boiling chips. Add enough ethanol to cover the leaf. 3 Place the boiling tube in the hot water bath for about 5 minutes for the ethanol to boil. 4 Use the forceps to remove the leaf from the boiling tube and rinse it with tap water. 5 Place the leaf on a white tile. Next, add a few drops of iodine on the leaf. Predict what you will observe.
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Without starch
With starch
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O observe the changes to the leaf and record your observations. Questions: 1 Explain the purpose of wearing safety goggles in this experiment. R 2 How did your results compare with your prediction? If your prediction does not match the results, explain why.
Yellowish brown iodine solution will turn blue-black if starch is present in leaves. If starch is not present, the colour of the iodine solution remains unchanged. As the process, photosynthesis, is not visible to us, the iodine test can tell us whether a plant has photosynthesised.
Figure 1.1 The results of
the starch test on leaves
5
What is needed for photosynthesis?
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What does a plant need to carry out photosynthesis besides carbon dioxide and water? In Primary Science, we learnt that light is needed for plants to make food. In Stage 7, we learnt that chlorophyll, which is found in chloroplasts, helps plants to take in sunlight to make food. Are light and chlorophyll needed for photosynthesis? How do we prove it?
Investigate!
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3.
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GROUP WORK
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Aim: To show that light and chlorophyll (green pigment) is needed for photosynthesis.
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Instructions: 1
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This experiment shows that carbon dioxide is necessary for photosynthesis to occur.
You will need: plant with normal green leaves, plant with variegated leaves (leaf with green and non-green parts), coloured paper, aluminium foil, forceps, safety goggles, 500-ml beaker, hot water (70–90°C) boiling tube, ethanol, boiling chips, petri dish, white tile and iodine solution. Plan investigations to a) show that light is needed for photosynthesis. b) show that only the green parts of a leaf make starch.
Plan VAPOURS
E
Spotlight
2
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Let your teacher check your plans. 3 Carry out your investigations. Record your results in a suitable format.
Question:
What can you conclude from your experiment? Why do you think so?
A
1
Check My Understanding
23
Light and chlorophyll are needed for photosynthesis to take place in plants. The equation below summarises what we have learnt about the process of photosynthesis.
Name 2 substances that are required for photosynthesis.
2
Name the products of photosynthesis.
Photosynthesis
3
Describe the test for starch in a green leaf.
Carbon dioxide + Water
4
Describe the test for oxygen gas produced during photosynthesis.
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1
6
UNIT 1A
Chlorophyll Light
Glucose + Oxygen
Biomass Biomass refers to materials that comes from living organisms. Plants can convert glucose made during photosynthesis to other products. These products can help plants to grow by making new cells and tissues.
Obtaining food
How are the leaves adapted to carry out photosynthesis?
Recall What is the function of chloroplasts found in leaves?
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The leaves of plants are also known as food factories as most of the food is made here. The leaves of plants have many adaptations to get what is needed for photosynthesis and share the products with the rest of other plant parts.
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Wide Allows the leaf to obtain maximum sunlight for photosynthesis
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Veins A network of vein carries water and minerals to the cells in the leaf and food away from the cells in the leaf to the other parts of the plant
on
parts of a leaf are adapted for photosynthesis
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Thin Allows carbon dioxide to be transported quickly to the cells inside a leaf
u Figure 1.2 How the different
Leaf arrangement Usually grown in a regular pattern so that the leaves are not blocking one another from sunlight
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Leaf stalk Holds the leaf away from the stem so that it can receive the maximum amount of sunlight
q Figure 1.3 The diagram shows the inside of a leaf.
Check My Understanding Describe how the structure of a leaf is 1 adapted for photosynthesis. 2 adapted to prevent water loss.
Upper epidermis
23 20
Palisade layer Contains palisade cells that have many chloroplasts to absorb sunlight for photosynthesis
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Protects the cells in the leaf from the external environment and prevents loss of water
A
Cuticle
Guard cells Lower epidermis
Transport tissues Helps carry water and minerals to the cells in the leaf. They also carry food from the leaf to other parts of the plant Stoma (plural: stomata) is a tiny hole that allows gases to enter and leave the leaf
Spongy layer Has air spaces between the cells to allow carbon dioxide and oxygen to diffuse through the cells
Worksheet 1.1
7
1.2 Nutrients in our diet
Investigate!
Aim: To investigate the different kinds of nutrients in food. Instructions:
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1
GROUP WORK
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You will need: Food labels from 4 different foods.
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4.
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Unlike plants, human beings are unable to make their own food. We need certain substances from the food we eat to live, grow and reproduce. These substances are called nutrients. What kinds of nutrients are in our food?
Bring food labels from four different food packages. 2 Study the food labels. The food label lists the nutrient content of the food. Record the amount of the following in each food: a) Carbohydrates b) Proteins c) Fats
2
Which food has the highest energy content (has the highest calories)? Do you think this is the healthiest food?
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What is a calorie?
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1
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Spotlight
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Questions:
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The three main nutrients in our diet are carbohydrates, proteins and fats. Our bodies also need certain vitamins, minerals and water.
Carbohydrates
A
Bananas
8
UNIT 1A
Sugar
Flour
Rice
Noodles
p Figure 1.4 Foods that are high in carbohydrates
Cellulose is another type of carbohydrate that can be found mainly in plants. Cellulose cannot be digested by the body. It will be passed out as fibre from the body.
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How do we test for the presence of starch?
Carbohydrates provide our body with energy. Starch and sugar are the main carbohydrates found in food. Starch can be found in rice, bread, noodles and cereals. Glucose is an example of sugar with simple structures. We call it a simple sugar. Glucose can be found in ripe fruits.
23
Recall
Obtaining food
How can we test for the presence of carbohydrates? To find out whether carbohydrates are present in foods, we can test for starch and simple sugars. Let us find out how to do so.
Investigate!
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5.
PAIR WORK
Aim: To test for the presence of carbohydrates.
Part I:
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Iodine test on starch, glucose and water 1 Add a few drops of iodine on each of the sample.
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Glucose Water solution
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Benedict’s test on starch, glucose and water 2 Add 2 ml of Benedict’s solution to each boiling tube.
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Cornstarch solution
P on
Instructions:
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You will need: Safety goggles, cornstarch solution (cornstarch dissolved in water), Solution X, glucose solution, water, iodine solution, white tile, droppers, Benedict’s solution, boiling tubes, test tubes, beakers and heating apparatus.
3
Glucose solution
Water
23
Cornstarch solution
A
Benedict’s solution
Heat O
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Heat the mixtures in a boiling water bath for about 3 to 5 minutes. Questions: 1 What did you observe for the iodine test? 2 What did you observe for Benedict’s test? Part II: Which type(s) of carbohydrate is/are present in Solution X?
Instructions:
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1
O O
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Perform the iodine test on Solution X. 2 Perform the Benedict’s test on Solution X.
Questions:
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1
What did you observe for the iodine test? 2 What did you observe for the Benedict’s test? 3 What can you conclude about the type(s) of carbohydrate present in Solution X?
9
The presence of starch and simple sugars is indicated by colour changes in the solution as shown in the table below. Test
Test Sample
Observation(s)
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Without starch Iodine Test
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With starch
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Without simple sugars
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Benedict’s Test With simple sugars
Carbohydrates as a source of energy
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Carbohydrates are a good source of energy. It gives us energy for our daily activities. The energy content of a food can be measured by burning the food and measuring the increase in temperature of the water as a result of the energy released from the food. One of the units of measurement of energy content in foods is in calories (cal) or kilocalories (kcal).
23
A
What might be the result of overeating foods with high energy content? Why do you think this will happen?
With a lot of simple sugars
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Brainstorm
With some simple sugars
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With a little simple sugars
6.
Investigate!
20
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Thermometer
Bread
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Water
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Crucible
10
DEMONSTRATION
GROUP WORK
Aim: To investigate the energy content of carbohydrates.
UNIT 1A
You will need: Bread, white sugar, water, boiling tube, wire gauze, tripod stand, retort stand, thermometer, mass balance, timer, safety goggles, Bunsen burner, lighter and tablespoon. Instructions: 1
Prepare the set-up shown on the left. Put on your safety goggles. Burn a fixed mass (e.g. 10 g) of bread.
2
Record the temperature of the water at every 30 s interval for 3 minutes (180 s) in a table.
3
Repeat Steps 1 and 2 using the same fixed mass of white sugar as the bread.
5
Plot a graph of the temperature of water against time for each of the food product.
Obtaining food
Questions: Explain the purpose of wearing safety goggles for this experiment. 2 Identify the variable that was changed and the variable that was measured. 3 What can you conclude from your results?
Check My Understanding
R
V
1
Describe the function of carbohydrates in our diet.
2
The iodine test and Benedict’s test were performed separately on a food sample. The diagrams below show what was observed.
Proteins
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Proteins are needed for growth and repair of damaged tissues in our body. We can get proteins from both animals and plants. Meat, fish and eggs are rich in proteins. Nuts and beans also have a high amount of proteins.
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Eggs
Fish
Tofu
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Peanuts
Beans
Benedict’s test:
hat can you conclude W about this food?
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How can we test for the presence of proteins?
E
p Figure 1.5 Foods that are rich in proteins
Iodine test:
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Uncooked meat
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1
7.
Investigate!
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A
We can find out whether proteins are present in foods using the biuret test. Let us find out how to do so.
23
Aim: To test for proteins using the biuret test.
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Instructions:
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Part I: Biuret test
20
You will need: Coconut milk, egg white, fruit juice, Solution Y, test tubes, droppers, safety goggles, sodium hydroxide solution and copper(II) sulfate solution.
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Prior to the experiment, discuss with your teacher regarding safety precautions. 1 Look at the list of materials needed. Identify a risk and suggest a safety R precaution. Take this safety precaution during the experiment. 2 Add 2 ml of sodium hydroxide solution to 2 ml of the sample to be tested in a test tube. Shake the solution thoroughly. 3 Add copper(II) sulfate solution, drop by drop into the solution. Shake the mixture after each drop. 4 Allow the mixture to stand for about 5 minutes. O 5 Record your observations.
Questions: 1 2
Which of the samples provided contain protein? What did you observe for the samples with proteins?
11
Part II: What is in Solution Y? Instruction:
Check My Understanding
1
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a) Name the test that can be used to test for the presence of protein.
The presence of proteins is indicated by colour changes in the solution as shown in the table below.
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2
b) W hat would you observe if the food contains protein?
Test
P
Describe the function of proteins in our diet.
Test Sample
Observation
on
1
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Repeat Steps 2 to 4 of Part I with Solution Y. Questions: 1 What did you observe? 2 What can you conclude about solution Y?
Worksheet 1.2
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With proteins
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Biuret Test
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Without proteins
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The biuret solution is a blue solution made of sodium hydroxide and copper(II) sulfate. Proteins give a violet colour with biuret solution.
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Fats
A
Fats provide about twice as much energy as compared to the same mass of carbohydrates. They are usually found in foods like butter, cheese and oily fish. Fats are mainly stored under our skin to keep us warm. It functions as a store of energy. Obesity and other health problems (such as the heart or arteries failing to function) may develop when excessive intake of fats is part of one’s diet.
high in fat
How can we test for the presence of fats?
23
p Figure 1.6 Foods that are
20
We can test for the presence of fats in foods using the paper test. Let us find out how to do so.
8.
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Filter paper
Butter
12
Cooking oil
UNIT 1A
Water
Investigate!
PAIR WORK Aim: To test for fat using the paper test. You will need: Butter, cooking oil, water, Substance Z, droppers, cotton bud and filter papers. Part I: Paper test Instructions: 1 Apply a little butter, cooking oil and water on different strips of filter paper. O 2 Hold each strip of filer paper up against the light. Question: 1 What did you observe?
Obtaining food
Part II: Does Substance Z contain fats? Instructions: 1 Get pupils to rub Substance Z on a piece of filter paper. Questions: 1 What did you observe? 2 What can you conclude about Substance Z?
Test Sample
Observation
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Test
te Opaque
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Without fats
P
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Fats form a translucent patch (some light can pass through) on paper. If water or a substance without fat was placed on paper, the paper will remain opaque (light cannot pass through) after it has dried.
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O
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Paper Test
Translucent
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With fats
Vitamins, minerals and water
A
Besides the carbohydrates, proteins and fats, we need many types of vitamins. We also need some minerals and water. Here is a table showing why these nutrients are important to us. Vitamin A
Vitamin B1
Necessary for our body to break down glucose into energy
Calcium
t
20
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Necessary for good eyesight
Makes up our bones and teeth
Keeps body tissues in good shape and helps us to heal
Vitamin D Helps us to absorb calcium from foods
Prevents us from falling ill easily
Iron Transports oxygen in our blood.
Fibre
Vitamin K Helps our blood to clot so that we do not bleed too much when we have a wound
Water
Regulates our body Promotes the movement temperature of material through Dissolves nutrients in the digestive system the blood to deliver them to cells Increases stool Dissolves waste substances bulk and remove them from our body
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Makes up our bones and teeth
Phosphorus
Vitamin C
C
A balanced diet Eatwell guide The National Health Service in the United Kingdom has come up with the Eatwell Guide to give people recommendations on their daily nutritional needs. It is a visual aid to help us have a balanced diet.
13
The Eatwell Guide divides the foods we consume into 5 main groups.
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We should drink at least 6 to 8 glasses of water a day.
We should eat less foods that are rich in sugars and fats as they contain little nutrients. Some fats, such as olive oil, are good for us. They can be taken in moderation.
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6 to 8 a day
Eat at least 5 portions of a variety of fruits and vegetables a day. They should make up a third of the foods we eat a day. They are rich in vitamins, minerals and fibre.
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Starchy foods that are rich in carbohydrates should make up a third of the foods we eat. We should choose whole grains as they are rich in fibre.
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Pulses (beans, lentils and peas), meat, fish and eggs are rich in proteins. We should aim for at least two portions of fish every week. We should eat less red and processed meat and more lean meats.
Milk, cheese and yoghurt are made from milk. They are rich in proteins and calcium. We should choose low fat options.
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p Figure 1.7 The Eatwell Guide shows the portion we should eat for each food group.
Guideline Daily Amount (GDA)
Allowance label
9.
Investigate!
20
p Figure 1.8 Guideline Daily
23
A
The Guideline Daily Amount (GDA) is a nutritional label that shows the value and the percentage of the daily value per serving of the food indicated. The GDA allows us to make informed choices about the foods we are going to buy and consume.
Instruction: 1
14
UNIT 1A
Use the Internet or other resources to find out more about the topics mentioned above.
Questions: 1
What types of snacks do you often eat? 2 How many servings of the snacks does it take to exceed the recommended daily intake of sugar and fat for an adult female/male?
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Aims: To investigate more about the Guideline Daily Amount (GDA) and the recommended daily intake of nutrients for snacks that you often eat.
Obtaining food
A healthy lifestyle—proper nutrition and exercise A healthy diet is made up of food from all groups in the Eatwell Guide in their recommended amounts. Regular amount of exercise of about 150 minutes per week is also essential to maintain a healthy lifestyle.
Lt d
Effects of nutritional deficiencies
P
Investigate!
on
10.
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When we do not consume sufficient nutrients from a particular food group or when our body is lacking a particular vitamin, we may develop nutritional deficiencies in our body.
ti
Aim: To investigate nutritional deficiencies.
b) Person B has sores or discolouration on his tongue.
Spotlight How do your food intake and physical activity affect your body weight?
How can we ensure that we consume enough biotin (also known as vitamin B7) to reduce the effects of hair loss and/or skin problems?
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2
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Instruction: 1 Research using the Internet or books to answer the following questions. Questions: 1 Which nutrients might be lacking in these people? a) Person A has frequent cramps.
The following infographic shows some common signs of nutritional deficiency.
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23
A
Too little vitamin C Causes scurvy whose symptoms include bleeding gums, weakness and sore limbs
Too little calcium Results in weak bones and teeth
Too little iron Causes anaemia in which one lacks healthy red blood cells
Too little fibre Causes constipation (infrequent bowel movements) and weight gain
Too little vitamin D Causes rickets which can lead to weakening or softening of bones
Check My Understanding 1 Describe the five main
food groups present in a balanced diet and the importance of each food group.
2 Describe the
consequences when a person does not consume enough iron.
Worksheet 1.3
15
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Diabetes is a condition disease that affects how the body uses glucose. The body is unable to use the glucose in the blood. Glucose stays in the blood and eventually gets excreted. Thus, patients with diabetes usually produce urine with high levels of glucose. What would be a simple test that any Science student could do on urine samples to test for high levels of glucose?
Lt d
Science Connect
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on
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However, do note that diabetes must still be confirmed by proper medical tests! A doctor will usually carry out a urine test and a blood test to confirm if a person has diabetes or not.
Revision
What do plants need for photosynthesis?
2
do plants produce during What photosynthesis? (1)
What test can we conduct to find out whether photosynthesis has taken place in a plant? (1)
c) Explain why we should not eat too much of fried chicken. (2)
d) Besides this food, what food groups should a person have for a meal to have a balanced diet? (3)
A
23
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4
(1)
20
3
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b) i) Name the tests you can conduct to test if your predictions are true. (2)
1
ii) What would you observe if your predictions are true?
5 A person experiences constipation. Fried chicken
a) Predict and name two groups of nutrients that this food contains. (2)
a) What do you think can be a possible reason?
(1)
b) How can he change his diet to avoid having constipation?
(2)
UNIT 1A
(2)
Obtaining food
[17]
Chapter Summary
Human beings
Carbohydrates
te
Plants
Simple sugars
causes
Photosynthesis
produce
needs
Light
Oxygen + Glucose
ls to n
Leaves
have adaptations to help plant photosynthesise
Glucose
causes
With With With a a little some lot of simple simple simple sugars sugars sugars
E
takes place in
ca
Chlorophyll
such as
Benedict’s solution to change colour
Iodine solution to change colour
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Carbon dioxide + Water
ti
through
on
P
Starch
Make their own food
Lt d
Nutrition in living things
Proteins
cause
A
Thin
Veins
Biuret solution to change colour
23
needs
20
Wide
Leaf arrangement
can cause
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Leaf stalk
Fats
Upper epidermis
Cuticle
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Palisade layer Spongy layer
Transport tissue
Lower epidermis
Guard cell
Paper to become translucent
Vitamins, minerals and water
Stoma
17
CHAPTER 2 In this chapter
• What happens to food as it enters our mouth?
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• Understand the functions of enzymes as biological catalysts in breaking down food to simple chemicals. (8Bh4)
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The human digestive system
• Recognise the organs of the alimentary canal and know their function. Secondary sources can be used. (8Bh3)
on
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• How do our body break down and absorb the nutrients in food?
2.1 Physical and chemical processes in food digestion
E
Which organs are involved in the human digestive systems?
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Recall
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ti
The food that we consume is not in the form that our body can absorb and use. It must be broken down into simpler substances. This process where our body breaks down food into simpler substances is called digestion. The group of organs that are involved in digestion are known as the digestive system.
A
Physical processes begin in our mouth and involve our teeth. Food is physically broken down into smaller pieces by our teeth. We have four types of teeth to help us cut, tear, crush and grind our food.
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Imagine that this is your lunch and you gobble down your food without chewing it into smaller pieces. What do you think would happen?
Physical processes
23
Brainstorm
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Food is broken down into simpler substances through physical and chemical processes in our body.
18
UNIT 1A
Type of teeth Canine Shape
Function
Obtaining food
Incisor
Premolar
Molar
• Chisel-shaped • Chisel-shaped • Wide
• Broad
• Sharp biting surface
• Flat biting surface
• Flat biting surface
• Large flat biting surface
To cut food
To tear food
To crush food
To grind food
Chemical processes
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After the food has been breakdown into smaller pieces, it moves through a series of organs called the alimentary canal. The chemical break down of food in our body requires chemical substances. It begins in our mouth.
on
P
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The salivary glands in our mouth produce and release saliva. The saliva contains chemical substances that can help to breakdown food.
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E
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Salivary glands
Digestion of food continues as the food travels along the alimentary canal.
23
A
2.2 Organs of the alimentary canal and their functions
20
Which organs make up the alimentary canal? What are their functions? Let us find out!
Learn about how food travels through our digestive system.
t
Investigate!
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11.
Spotlight
GROUP WORK
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Aim: To find out about the position and functions of different organs of the alimentary canal.
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Instructions: 1 Gather information from the Internet about the organs in the alimentary canal. 2 Present your findings. In your presentation, include the following: The name and position of the organs in the alimentary canal
• •
The functions of each organ
19
The alimentary canal is a continuous tube of differing widths that runs from our mouth to our anus.
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Function(s) of each organs Salivary glands: Release saliva which contains the chemicals substances, to break down complex sugar into simpler forms of sugar.
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Teeth: Break up large pieces of food into smaller pieces by the cutting and grinding of the teeth.
P
Tongue: Pushes food around the mouth, mixes it with saliva and rolls it into a ball-shaped structure. Food is then pushed down into the oesophagus.
on
Gullet/oesophagus: Pushes food down the stomach through a process known as peristalsis.
ti
The movement of peristalsis is the alternate contraction and relaxation of muscles in the oesophagus which pushes food along it.
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Stomach: Churns the food. It also contains hydrochloric acid, to kill bacteria in the food, and enzymes which help in the digestion of proteins.
20
23
Large intestine: Absorbs water and mineral salts into the bloodstream, leaving behind waste known as faeces.
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Sketch a diagram to show the organs in the alimentary canal. Describe the functions of the different organs.
Worksheets 2.1 & 2.2
20 UNIT 1A
Small intestine: Digests and absorbs most of the nutrients in food, such as carbohydrates, proteins and fats.
Rectum: Faeces are stored in the rectum and passed out through the anus.
Anus: Faeces are passed out through the anus.
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Check My Understanding
Liver: Produces bile. Bile is stored temporarily in the gall bladder until is released into the small intestine to help in the breakdown of fats.
A
Pancreas: The pancreas secretes a digestive juice, which contains enzymes, into the small intestine to break down carbohydrates, proteins and fats.
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E
These enzymes work best in acidic conditions.
2.3 The role of enzymes Enzymes are substances produced by our body to speed up chemical reactions. Chemical digestion of food occurs with the help of enzymes. The salivary glands in our mouth release the enzyme, amylase. This enzyme helps to break down food in our mouth.
Obtaining food
12.
Investigate!
Super scientist
Aim: To observe what happens when we chew some pieces of bread in our mouth.
Lt d
You will need: Few pieces of bread, iodine solution, dropper, white tile and some tissue papers. Instructions:
on
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English biochemist, William Prout, was born in 1785. He was the son of a farmer. Prout discovered that the digestive juices of animals contain significant amounts of hydrochloric acid. This led to the discovery that humans also have hydrochloric acid in their digestive juices.
13.
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E
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O Add a few drops of iodine on a piece of bread. Leave it aside. 2 Chew a few pieces of bread for a few minutes. 3 Note the taste of the bread as you chew. 4 Remove the bread from your mouth. 5 Place it on a piece of tissue paper for observation. Questions: 1 Which type of carbohydrate is present in bread? Explain. 2 What did you observe in Step 5? 3 What do you think is added to the bread as you are chewing it? 4 What happen to the taste of the bread change as you chew it? 5 What do you think happen to the starch in bread after you chewed it?
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1
Investigate!
PAIR WORK
Check My Understanding Name an enzyme. Describe its function.
Worksheet 2.3
yr
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20
23
A
Aim: To find out the effect of the enzyme, amylase on starch solution. You will need: Starch solution, enzyme (amylase) solution, Benedict’s solution, boiling tubes, safety goggles, test tubes, beaker, tripod, wire gauze, lighter, Bunsen burner and heating apparatus. Instructions: 1 Plan an experiment to prove that amylase breaks Plan VAPOURS down starch in bread into simple sugars. 2 Let your teacher check your plans. 3 Carry out your experiment. Record your results in a suitable format. 4 Compare the results of the experiment with your predictions.
Simple sugars
Enzymes speeds up chemical reactions in our body without being changed themselves. Substances that speed up reaction without undergoing any changes are known as catalysts. Hence, enzymes are biological catalysts.
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Starch
Figure 2.1 Amylase helps to break down complex
sugars, starch, into simple sugars. Amylase
21
Science Connect
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Gastric pain can result when the stomach produces an excessive amount of acid. Do you know that some lifestyle changes can reduce the risk of experiencing gastric pain? 1 Increase your frequency of meals but reduce the amount
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you eat at each meal.
P
2 Have regular meal times.
on
3 Eating less spicy food and fried food.
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4 Better manage one’s stress level through regular exercise.
A. Digestion breaks down food particles physically to be absorbed by the body.
Fill in the blanks with the most suitable word. A list of helping words are provided below.
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B. The anus absorbs nutrients from food before releasing the rest as solid waste.
C. Digestion starts in the stomach.
D. Our body only absorbs carbohydrates.
A
23
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2
The purpose of the large intestine is to . (1) A. absorb water and mineral salts into the bloodstream
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3
Which of the following statements is correct? (1)
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1
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Revision
B. break down water and mineral salts before they are absorbed into the bloodstream
C. digest fats
D. break down carbohydrates, proteins and fats
22 UNIT 1A
Obtaining food
Each word can be used once, more than once, or none at all.
(4)
water vitamins small intestine anus stomach peristalsis
a) The is a muscular bag which secretes a digestive juice that is acidic.
b) The carries out chemical digestion of carbohydrates, proteins and fats.
c) The in the alimentary canal does not carry out any digestive processes.
d) The process occurs in the oesophagus. 4 a) What is an enzyme? (1) b) Why enzymes are known as a biological catalyst? (1) 5 Which organ produces bile? Describe the role of bile in the digestive system. (2)
[10]
Chapter Summary
Lt d
Human digestive system
P
Organs
Teeth
on
Cut food into smaller pieces
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has
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Tongue
E
The oesophagus
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transports food by peristalsis to
Churns the food and has hydrochloric acid and enzymes
A
Mixes food with the saliva, rolls food into ball-like structures and pushes food into the oesophagus
The mouth
Saliva
ca
Contains the enzyme, amylase, to break down starch into glucose
ti
such as
20
23
Digests and absorbs most nutrients into the bloodstream
The stomach
The small intestine
The large intestine
Stores faeces
The rectum
Passes out the faeces
The anus
C
op
yr
ig h
t
Absorbs water and mineral salts into the bloodstream
23
UNIT 1B
P
te
Lt d
Elements, compounds and mixtures du
ca
ti
on
Things around us are made of millions of very small particles that we cannot see. We call these particles ‘matter’. In Stage 7, you learnt how to classify matter into solids, liquids and gases. We can also classify matter as elements, compounds and mixtures. What are elements, compounds and mixtures? How can we distinguish between them? In this unit, we will find answers to these questions.
Scientific enquiry
E
Discuss explanations for results using scientific knowledge and • understanding. Communicate these clearly to others. (8Ec6)
24 UNIT 1B
Vocabulary
C
op
yr
ig h
t
20
23
A
ls to n
Compare results with predictions. (8Ec3) • Plan investigations to test ideas. (8Ep4) • • Use a range of equipment correctly. (8Eo2) Discuss and control risks to themselves and others. (8Eo3) •
particles diffusion element atom chemical symbol Periodic Table
Elements, compounds and mixtures
compounds
Lt d te P on ti ca du E ls to n
In this unit
A
Pupils build on their previous knowledge of the particle theory of matter and how this can explain the properties of solids, liquids and gases, to develop their knowledge of: The changes of state, gas pressure and diffusion.
23
The chemical symbols for the first twenty elements of the Periodic Table. Elements, compounds and mixtures.
C
op
yr
ig h
t
20
25
The particle theory of matter
In this chapter
te
• Can particles move from one place to another?
P
3.1 The particle theory of matter and the properties of matter
on
• Show how the particle theory of matter can be used to explain the properties of solids, liquids and gases, including changes of state, gas pressure and diffusion. (8Cs1)
Lt d
CHAPTER 3
Gas
ls to n
E
What is the particle theory of matter?
ca
ti
The particle theory of matter states that all matter is made up of small particles that are in constant random motion. The differences in the states of matter can be explained in terms of the particle theory of matter.
du
Recall
ion
ora
tio
n
sat
ion
23
Solid Freezing
20
Solids usually have more particles per unit volume than liquids, causing them to be denser than liquids. This is why most solids will sink in water. However, ice is an exception. Watch this video to find out why ice floats on water.
en
vap
A
Spotlight
g/E
nd
b
Su
ilin
Co
t
a lim
Bo
Liquid
F igure 3.1 The order and arrangement of particles and the
processes they go through to change from one state to another
In Stage 7, we explored the properties of solids, liquids and gases. Do you still remember their properties?
C
op
yr
ig h
t
Melting
26 UNIT 1B
Elements, compounds and mixtures
Gas
Arrangement of the particles
Regular
Random
Random
Distance between the particles
Very close to one another
Close to one another
Far apart from one another
Movement of the particles
Only vibrate in fixed positions
Able to slide over one another
Move at high speeds in all directions
Forces of attraction between the particles
Very strong
Strong
Weak
P on ti
Aim: To investigate the compressibility of solids, liquids and gases.
GROUP WORK
du
You will need: Syringe filled with sand, syringe filled with water and syringe filled with air. Instructions:
Plan an experiment to investigate the compressibility of solids, liquids and gases.
2
Predict what you will observe for each state of matter in the experiment.
Plan VAPOURS
ls to n
E
1
3
Let your teacher to check the plan. 4 Carry out the experiment. Record your observations.
P
3
Compare your results with your predictions. If your prediction does not match your results, explain why.
4
A
Based on the results, comment on the compressibility of each state of matter.
state undergo boiling to change to the liquid state. Freezing and melting take place at the same temperature. Particles in the solid and liquid states have a fixed volume.
20
2
2 Particles in the solid
23
1
State whether the following statements are true or false. 1 Particles in the liquid and gaseous states take the shape of the container.
O
Questions:
h c K
Check My Understanding
Investigate!
ca
1.
Lt d
Liquid
te
Solid
Worksheet 3.1
yr
ig h
t
As you can see from investigative activity 1, solids and liquids are not compressible. They have a fixed volume. This is because the particles in solids and liquids are already very closely packed. Thus, they cannot take up a smaller space. However, gases are compressible. They do not have a fixed volume. This is because the particles in gases are far apart from one another, with a lot of space between them. Thus, the gas particles can be ‘squashed’ together.
C
op
As you have learnt in earlier stages, solids have a fixed shape and cannot flow because the particles are held together by very strong attractive forces. Liquids can flow and take the shape of their containers because the attractive forces between liquid particles are not as strong as the attractive forces between solid particles. Liquid particles can slide over one another. Gases take the shape of their containers and flow freely because the attractive forces between the particles are weak. Gas particles can move freely at high speed.
27
Now, let us take a look in detail at what happens to the particles as they undergo changes in states as a result of heating.
Lt d
Melting and boiling Boiling
Temperature (°C)
te
Mixture of liquid and gas
Boiling point
Mixture of solid and liquid
Liquid
• Some particles gain sufficient energy and move more vigorously.
Solid
P
ca
du
• The particles overcome the attractive forces between one another and break free.
• The liquid has become a gas.
Time (min)
E
• These particles break free of their fixed positions.
• All solid particles have gained sufficient energy. • The particles are able to overcome the very strong attractive forces holding them together. • The particles can move and slide past one another. • The solid has become a liquid.
F igure 3.2 The heating curve
20
23
A
• The particles gain energy and vibrate faster.
• Some solid particles gained sufficient energy to overcome the strong attractive forces between them.
ls to n
• Heat energy is transferred to the solid particles.
• The particles move far apart from one another at high speeds and become randomly arranged.
ti
Melting point
Gas • All liquid particles have gained sufficient energy to overcome the attractive forces.
on
Melting
• Heat energy is transferred to the liquid particles.
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op
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Evaporation
28 UNIT 1B
Heat energy is transferred to the liquid particles. The liquid particles gain energy and move faster. The particles soon have sufficient energy to overcome the forces of attraction holding them together. Particles escape the surface and are able to move far apart from one another at high speed. The liquid has become a gas.
Sublimation Heat energy is transferred to the solid particles. The solid particles gain energy quickly and overcome the forces of attraction holding them in fixed positions. The particles move far apart from one another at high speeds and are randomly arranged. The solid has become a gas and bypassed the liquid state completely.
Elements, compounds and mixtures
Now, let us take a look in detail at what happens to the particles as they undergo changes in states as a result of cooling.
Lt d
Freezing
te
Temperature (°C)
ti
• All the liquid particles have lost sufficient energy. • The particles are now in a regular arrangement.
Time (min)
• They can only vibrate about in fixed positions.
ls to n
• The • Some liquid particles particles lose sufficient energy lose energy for the particles to and move come close together. more • The forces of slowly. attraction between the particles get stronger.
Solid
ca
Freezing Mixture of solid and liquid
du
• Heat is removed from the liquid particles.
E
Freezing point
on
P
Liquid
• There are very strong forces of attraction between the particles.
23
A
• The liquid has become a solid.
ig h
t
20
Figure 3.3 The cooling curve
yr
Condensation
C
op
Heat is removed from the gas particles. The particles lose energy and move more slowly. Gradually, they come close enough for forces of attraction to form. The particles can now only slide past one another. The gas has become a liquid.
Worksheet 3.2
29
3.2 Gas pressure
How does gas particles in an enclosed cylinder behave under different conditions?
Do you remember in investigative activity 1, when you depressed the syringe filled with air? How did it feel?
Lt d
Spotlight
te
p F igure 3.4 Gas particles moving in a syringe
on
P
Gas particles are constantly colliding with one another and with other objects. When a gas particle hits a surface, it exerts a small force on that surface. The total resultant effect of these forces exerted by all the gas particles is known as gas pressure. When we depressed the syringe, the gas particles occupy a smaller space.
ti
The particles in the gaseous state are always in constant, random motion. Let us find out how gas particles behave when they are in an enclosed container.
Investigate!
du
2.
GROUP WORK Aim: To observe the effects of gas particles moving inside an enclosed container. You will need: Balloon, air pump, flexible measuring tape, large bowl of iced water and large bowl of hot water. Instructions: P 1 Predict what you will observe if you pump air into a balloon. 2 Stretch a balloon a few times. Pump air into the balloon. Measure the O size of the inflated balloon. 3 Then, tie up the end of the balloon. Place the balloon in a large bowl of hot water. Measure the size of the balloon. O 4 Place the balloon in a large bowl of iced water. Measure the size of the O balloon. Questions: 1 What did you observe when air is pumped into the balloon? 2 What did you observe when the balloon is placed in a large bowl of hot water? 3 What did you observe when the balloon is placed in a large bowl of iced water?
op
yr
ig h
t
20
23
A
ls to n
E
Describe the movement of particles in solids, liquids and gases.
ca
Recall
C
In investigative activity 2, when air is pumped into the balloon, there are more air particles colliding with the inner walls of the balloon than the outer walls of the balloon.
p F igure 3.5 Before air is
pumped into the balloon
30 UNIT 1B
p Figure 3.6 After air is
pumped into the balloon
Elements, compounds and mixtures
The frequency of the collision of the gas inside the balloon is higher than the outside of the balloon. Thus, the gas pressure inside the balloon is higher. The walls of the balloon are pushed outwards and the balloon increases in size.
Check My Understanding
2
The ___________ the temperature, the lower the gas pressure.
on
In investigative activity 2, the inflated balloon increased in size when it is placed in hot water. This is because the gas pressure inside the balloon has become higher. The higher gas pressure inside the balloon causes the walls of the balloon to be pushed further outwards.
Lt d
Use the particle theory of matter to explain the concept of gas pressure.
te
Gas particles have more energy at high temperatures. They move faster and hit surfaces more frequently at higher speeds. The frequency of collision of the gas particles against the surfaces is higher at high temperatures. Hence, gas pressure is higher at high temperatures.
1
P
Higher temperature, higher pressure
ti
Lower temperature, lower pressure
Observe the diffusion of bromine gas in a glass container.
du
ca
Gas particles have less energy at lower temperature. They move slower and hit surfaces less frequently at lower speed. The frequency of collision of the gas particles against the surfaces is lower at low temperature. Hence, gas pressure is lower at low temperature.
Spotlight
ls to n
E
In investigative activity 2, the inflated balloon decreases in size when it is placed in cold water. This is because gas pressure inside the balloon has become lower. The lower gas pressure inside the balloon causes the walls of the balloon to be pushed inwards.
23
Diffusion in gases
A
3.3 Diffusion in gases and liquids
Why would the pressure inside a gas cylinder increase as temperature increases? What hazards will this cause?
t
Investigate!
ig h
3.
20
As we have learnt earlier, gases are constantly moving in all directions at high speeds. Let us explore how gas particles move from one place to another.
Brainstorm
DEMONSTRATION
Aim: To demonstrate diffusion of gas particles in the air. Instructions:
Predict whether the pupils at the back of the classroom will be able to P smell the perfume.
2
Your teacher will spray the perfume at the front of the classroom. Raise your hand when you smell the perfume.
op
yr
1
C
3
Questions: 1
Who raised his/her hand first? Who raised his/her hand last? How far are O they sitting from the teacher who sprayed the perfume?
2
What happens to the perfume particles as they enter the air?
31
Worksheet 3.3
Lt d
As we have observed in investigative activity 3, pupils sitting at the front of the classroom will smell the perfume first, while pupils sitting at the back will smell the perfume last. This is because the perfume particles reach the pupils sitting closest to the perfume first. The particles then continue to move to fill the classroom and reaches the pupils sitting at the back of the classroom.
Diffusion in liquid
4.
P
te
Now, let us carry out the following experiment to find out how particles in a liquid move from one place to another.
Investigate!
on
d
PAIR WORK
ls to n
E
du
ca
ti
Aim: To observe how liquid particles move from one place to another. You will need: Potassium manganate (VII) crystal, glass beaker, straw, forceps, water and stopwatch. Instructions: 1 Fill the beaker with water. 2 Place a straw in the beaker.
A
Use a pair of forceps to put one crystal of potassium manganate (VII) into 3 the beaker through the straw. The crystal will dissolve in the water.
4
ig h
Check My Understanding
t
20
23
Leave the beaker to stand. Observe the liquid in the beaker at every 10-s interval until no 5 further change has occurred.
yr
1 What is diffusion?
Which states of matter 2
C
op
can undergo diffusion?
O
Question: 1 Describe the appearance of the liquid in the beaker in Step 5. 2 What do you think has happened to the dissolved potassium manganate (VII) crystal?
Likewise, in investigative activity 4, we observed that the dissolved potassium manganate (VII) particles, move from the crystal to other parts of the water in the beaker. The investigations show that liquid and gas particles move from a region that has more particles to a region that has fewer particles. This phenomenon is known as diffusion, which is the movement of particles from a region of higher concentration (more particles per unit volume) to a region of lower concentration (lesser number of particles per unit volume).
32 UNIT 1B
Elements, compounds and mixtures
Particles in the liquid and gaseous state flow 1
B. solid particles are closer to one another than liquid and gaseous particles.
C. liquid and gaseous particles have weaker attractive forces than in a solid.
D. liquid and gaseous particles have stronger attractive forces than in a solid.
Lt d te
A. The liquid perfume takes the shape of the container it is in.
ls to n
Explain how diffusion occurs. (2) Which of the following best explains why the scent from a strong perfume can be detected as it spreads across a class? (1)
B. The gaseous perfume particles move from a region of higher concentration to a region of lower concentration.
a) explain why gaseous particles can take the shape of the container. (2)
C. The liquid perfume particles undergo freezing to form solid particles.
b) explain why a liquid is difficult to compress. (2)
D. The liquid perfume particles undergo boiling to form gaseous particles.
[13]
20
23
A
2 Using the particle theory of matter,
c) explain what gives rise to gas pressure. (2)
ig h
t
5
(3)
du
A. solid particles move more slowly than liquid and gaseous particles.
condenses to form water droplets? 4
E
ca
3 What happens to the particles as water vapour
more easily than particles in a solid because __________________________ (1)
P
ti
Revision
Worksheet 3.4
on
The diagrams show how particles move during diffusion. The blue particles and orange particles are moving in constant random motion. The blue particles will move from a region of higher concentration into the spaces between the orange particles. The same goes for the orange particles. Eventually, both type of particles will spread out evenly in the space provided.
yr
Science Connect
C
op
When we cut an onion, it releases a chemical called propanethial S-oxide that turns from liquid state to gaseous state easily. These gas particles diffuse from a higher concentration to a lower concentration. When the gas particles reach our eyes, they irritate our eyes, causing us to tear.
33
Solid
The particle theory of matter
Liquid
Gas
on
P
te
explains
Lt d
Chapter Summary
Gas pressure
ti
Diffusion of gases and liquids
E
du
ca
Physical properties of matter
Volume
Shape
Solids and liquids cannot be compressed, but gases can be compressed.
Solids and liquids have fixed volumes, but not gases.
Solids have fixed shapes, but not liquids and gases.
A
Gas particles colliding with the inner walls of a container
C 34 UNIT 1B
The movement of particles from a higher concentration to a lower concentration
23
20 t ig h
is caused by
op
yr
ls to n
Compressibility
is
Elements, compounds and mixtures
affected by
Temperature
CHAPTER 4
In this chapter • Understand that elements are made of atoms. (8Cp3)
Elements and the Periodic Table
Lt d
• Give chemical symbols for the first twenty elements in the Periodic Table. (8Cp2)
te
• What are the simplest particles?
P
• What are elements?
ca
ti
The concept of an element was discovered mainly in the 17th century during the onset of the industrial revolution where materials became extensively used. Before we explore more about elements, we need to learn about atoms.
on
• What is the Periodic Table?
du
4.1 Atoms
E
Size of an atom
Spotlight How small is an atom?
ls to n
An atom is so small (with a radius of around 0.0000000001 m) that we cannot even see them with a light microscope. We can only view atoms through an electron microscope.
A
Size of an atom
ig h
Protein
t
20
23
Atoms form the building blocks of all elements and materials around us. Atoms cannot be broken down into any simpler substances.
Chloroplast
Human cheek cell Rose
Frog egg
yr
Virus Ant
C
op
Atom
Electron microscope Human
Light microscope
Blue whale
Human eye
p Figure 4.1 Comparison of the size of an atom to other things
35
What is in an atom?
ti
on
P
te
Lt d
Within an atom, there are three subatomic particles known as protons, neutrons and electrons. The protons and neutrons are found within the nucleus. The nucleus is the centre of an atom. The electrons can be found moving around the nucleus. Electron
Proton
ca
Neutron
du
p Figure 4.2 The structure of an atom
Atoms are the building blocks of substances Recall
t
ig h
Check My Understanding
Fill in the missing blanks. 1 An element is made up of the _________ kind of atoms. 2 An element is a substance which cannot be broken down into _________ substances.
A Na
Na
Na
Na
Na
Na
Mg Mg Mg
Na
Na
Na
Na
Mg Mg Mg
Mg Mg Mg He
He
Atoms of magnesium
He
Atoms of helium
Elements can also exist as a group of atoms chemically combined. A group of atoms chemically combined is known as a molecule. Non-metallic elements such as hydrogen, oxygen, nitrogen, chlorine and fluorine exist as diatomic molecules.
op
yr
Na
Atoms of sodium
O O
Fl
Fl
C
Fl
O O
O O
Fl
p Figure 4.3 Molecules of oxygen and fluorine
36 UNIT 1B
He
He
Na
20
• How do particles move in the different states of matter?
Elements can exist as individual atoms. Metallic elements exist as atoms. Non-metallic elements such as helium, neon and argon are also made up of atoms. The diagram below shows the particle arrangement of some of these common elements.
23
• How are particles arranged in the different states of matter?
ls to n
E
Matters are made up of atoms. Matters that are made up of the same kind of atoms is called an element. An element is a substance that cannot be broken down into simpler substances. Elements exist in different states at room temperature and pressure.
Elements, compounds and mixtures
Fl
Fl
4.2 The Periodic Table
Elements around the world can be found in the Periodic Table. There are currently 118 elements in the Periodic Table.
Am
95
te
An example of an element found naturally is hydrogen, which is in the gaseous state under room conditions. A synthetic element would be Americium which was first produced in 1944 during World War II.
Lt d
Americium
on
In the Periodic Table, every element has a unique chemical symbol. Some elements are named after their Latin names, while some are named after famous scientists. Chemical symbols are used to represent elements. The chemical symbols usually take the first letter or first two letters of the element’s name. Since the same chemical symbols are used worldwide, this allows scientists to communicate effectively and accurate with one another. In this chapter, we will focus on the first 20 elements in the Periodic Table.
P
A unique symbol for each element
is often used in smoke detectors.
du
ca
ti
p Figure 4.4 Americium
E
He
Spotlight
Chemical symbol
ls to n
What are the elements in a complete Periodic Table?
Helium
Chemical name
A
p Figure 4.5 The first letter is always in the
upper case, while the second letter (if any) is always in the lower case.
Oxygen
Fluorine
F
Ne
11
13
14
15
16
17
18
Mg
yr 19
op
K
Si
Silicon
P
Phosphorus
S
Sulfur
Cl
Chlorine
Neon
Ar Argon
20
Ca
Calcium
C
Potassium
Al
Aluminium
O
10
Nitrogen
Magnesium
N
9
Carbon
12
C
8
Boron
Sodium
B
7
Beryllium
Na
Be
6
Helium
Lithium
t
Li
5
He
ig h
4
20
H
Hydrogen 3
2
23
1
37
Super scientist
Spotlight
Dmitri Ivanovich Mendeleev (1834–1907) was a Russian chemist who was an important person in the discovery of the modern Periodic Table. He classified elements that were known at that time and came up with an early version of the Periodic Table. He even predicted the existence of undiscovered elements which were subsequently placed in the Periodic Table, making him a renowned scientist of his time!
on
P
te
Lt d
Visit these websites to find out why the symbols of potassium and sodium do not take the first letter or first two letters of the elements.
ca
ti
Brainstorm
du
How would you go about remembering the first 20 elements and their symbols?
Check My Understanding
ls to n
E
Now that we know the symbols and names of the first twenty elements, let us carry out investigative activity 5 to find out more about each element and how some elements got their names.
5.
Fill in the blanks with the correct symbol of the element.
Aims: •
A
d
Investigate!
Element
Symbol
•
To find out the different uses of the first twenty elements.
Oxygen
_______
•
To find out how certain elements got their names.
Calcium
_______
23 1
Look up the first 20 elements in the Periodic Table at this website.
2
Gather information about the uses and properties of the first 20 elements by clicking on each element.
yr
ig h
t
Helium _______
To describe the physical properties of the first twenty elements.
Instructions:
20
Sodium _______
GROUP WORK
C
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Worksheet 4.1
38 UNIT 1B
3
Record your findings in a suitable format. 4 Do an online search of these three elements: einsteinium, rutherfordium, americium. 5 Find out how these elements got their names. Record your findings in a suitable format. 6 Present your findings.
Elements, compounds and mixtures
4.3 Elements and their uses
H 1
He 2
Li 3
Be 4
Hydrogen is used as a source of energy in the form of hydrogen fuel cell for fuel cell vehicles.
Helium is used to fill airships.
Lithium is used to make batteries.
Beryllium is often combined with other metals such as copper to make things such as springs.
C 6
N 7
O 8
F 9
Helium
Lithium
Beryllium
B 5
Boron
on
ti
Oxygen
ca
Nitrogen
Boron is used to make Pyrex (borosilicate glass), a material that does not break easily and can withstand sudden changes in temperature.
Fluorine
Ne 10
Neon
E
du
Carbon
P
te
Hydrogen
Lt d
Many of the things around us contain elements in their pure form or elements that have been combined with other substances. The diagram below summarises the uses of the first twenty elements in the Periodic Table.
Oxygen is needed for burning to occur.
Fluorine is used to make toothpaste as it prevents the formation of cavities.
Neon is used to make advertising signs.
Na 11
Al 13
Si 14
P 15
Aluminium is used to make foils.
Silicone is used to make a waterproof sealant around windows.
Phosphorus is used to coat the striking surface on the side of a matchbox.
Cl 17
Ar 18
K 19
Ca 20
Chlorine is used to disinfect the water in swimming pools.
Argon is used in light bulbs as they allow the filaments to last longer.
Potassium compounds are used to make soap and detergent.
Calcium is present in limestone. We use limestone as a building material.
ls to n
Carbon is used to make Nitrogen is used to make pencil lead. plant fertilisers.
Mg 12
Magnesium
Aluminium
Silicon
Phosphorus
23
A
Sodium
t
20
Sodium is present in salt. Magnesium is often We use salt to flavour used in fireworks and our foods and to de-ice sparklers since it burns roads in winter. easily and with a bright light.
ig h
S 16
yr
Sulfur
Argon
Potassium
Calcium
C
op
Sulfur is used to treat rubber to make it more durable.
Chlorine
Worksheet 4.2
39
Lt d
Science Connect
P
te
Mercury looks pretty in its shiny, fast-moving silvery liquid form, but do not touch it! It can be extremely poisonous to humans. It is the only metal that is liquid at room temperature. It will evaporate into the air at room temperature.
ls to n
E
du
ca
ti
on
Mercury is a very toxic element and can be absorbed by humans through the air, skin, or by eating food with mercury. Too much mercury can kill a person. Despite its toxic qualities, mercury can still be useful to us. This element is used to make thermometers and barometers.
Revision 1
(1)
4
The symbol for the element fluorine is ________________. (1)
a) within the nucleus of an atom?
(2)
A. F
b) moving around the nucleus?
(1)
B. Fl
Elements are arranged in the _________________________. (1)
C. f
5
D. FL
3
20
23
A
What is an element made of? 2 Which subatomic particles are found
A. Periodic Table
B. Period Table
C. physical properties table
a) Hydrogen
(1)
D. group table
b) Fluorine
(1)
c) Sulfur
(1)
C 40 UNIT 1B
How are the following elements important to us in our daily life?
op
yr
ig h
t
Elements, compounds and mixtures
[9]
Lt d
Chapter Summary
te
Elements
are arranged in the
Properties
Periodic Table
such as
can be represented by
ca
ti
on
P
have
ls to n
1
He
6
10
Oxygen
Fluorine
F
Ne
11
12
13
14
15
16
17
18
20
Nitrogen
ig h 19
yr
K
Si
Silicon
P
Phosphorus
S
Sulfur
Cl
Chlorine
Neon
Ar Argon
20
Ca
Calcium
C
op
Potassium
Al
Aluminium
O
9
Carbon
Mg
N
8
Boron
Magnesium
C
7
Beryllium
Sodium
B
Helium
Lithium
Na
Be
5
23
4
t
Li
2
A
H
Hydrogen 3
Chemical symbols
E
Cannot be broken down into simpler substances
Atoms
du
being made up of
41
Compounds and mixtures
In this chapter • Distinguish between elements, compounds and mixtures. (8Cp6)
P
te
• What happens when different elements come together?
Lt d
CHAPTER 5
ti
on
In Chapter 4, we learnt about how an element is made up of atoms of the same kind and the first twenty elements in the Periodic Table. In this chapter, let us explore how elements can come together to form compounds and how mixtures are formed.
ca
Elements
E
du
An element is made up of atoms of the same kind. An element cannot be broken down into simpler substances. Elements can exist in different states at room temperature and pressure.
ls to n
Recall What are the chemical symbols of sulfur, magnesium and oxygen?
Magnesium
Sulfur
20
23
A
Iron
Figure 5.1 Iron, sulfur and magnesium are elements that exist in the solid state at
C
op
yr
ig h
t
room temperature and pressure.
42 UNIT 1B
Oxygen is an element that exists in the gaseous state at room temperature and pressure. We cannot see it, but it is in the air all around us.
5.1
Compounds
A compound is made up of two or more different types of elements that are chemically combined. Compounds are formed by chemical reactions. Burning is an example of a chemical reaction. So, what do we get when we burn the element, magnesium? What do we get when we burn the elements, iron and sulfur, together?
Elements, compounds and mixtures
6.
.
Investigate!
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GROUP WORK
DEMONSTRATION
Bunsen burner
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Use a pair of forceps to put a magnesium ribbon into the crucible, with the lid partially covering the crucible.
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3
Tripod stand
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Aim: To investigate what are formed when elements are burnt. You will need: Safety goggles, mass balance, magnesium ribbon, iron filings, sulfur powder, Bunsen burner, wire gauze, tripod stand, lighter, spatula, two crucibles and forceps. Part I: Instructions: 1 Read through the rest of the instructions and describe two safety precautions that are needed. Take the necessary safety precautions. R 2 Set up an experiment as shown Crucible on the right.
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O Light the Bunsen burner and observe. Note: Do not look directly at the magnesium when it is burning as the light given off is very bright. 5 Turn off the Bunsen burner once the glow has dimmed. Questions: 1 Describe the appearance of the magnesium ribbon before the experiment. 2 Describe the substance left behind in the crucible after the magnesium ribbon has finished burning. 3 Does the substance left behind look similar to or different from the magnesium ribbon?
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Part II:
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Instructions: 1 Set up the experiment as shown in the diagram in Part I. Note: It is advisable to conduct the following steps in a fume hood as a foul-smelling gas may be produced. This gas can be harmful to those with asthma. 2 Collect 56 g of iron filings and 32 g of sulfur powder. Mix the iron filings and sulfur powder in the crucible. O 3 Turn on the Bunsen burner and light it. Observe what happens. 4 Weigh the product formed on a mass balance and record its mass. O 5 Keep the substance formed for investigative activity 7. Questions: 1 Describe the appearance of the iron filings and sulfur powder before the experiment. 2 Describe the appearance of the substance left behind in the crucible after heating the iron filings and sulfur powder. 3 Does the substance left behind look similar to or different from the iron filings and sulfur powder? 4 Comment on the mass of the product formed.
43
In investigative activity 6, we observed that new substances are formed after we burn or heat different elements together. During burning or heating, the atoms of different elements form new strong attractive forces with one another. These attractive forces are called chemical bonds.
Spotlight How does magnesium ribbon burn in the air.
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When we burn magnesium, it combines with oxygen in the air to form the compound, magnesium oxide. Magnesium oxide has a different physical appearance from magnesium and oxygen. Silver solid
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Magnesium
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Elements
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Magnesium oxide
Colourless gas White solid
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Compounds
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Oxygen
Check My Understanding
The attractive forces formed between the atoms in a compound are called chemical __________.
A
Elements
Iron
Grey solid
Sulfur
Yellow solid
Iron sulfide
Dark grey/black solid
Some chemical reactions give off __________ energy and __________ energy.
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A compound looks __________ from the elements that it is made up of.
Compounds
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A compound is made up of two or more different types of __________ that are chemically combined.
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1
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Fill in the blanks.
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When we burn iron and sulfur, iron combines with sulfur to form iron sulfide. Similarly, for iron sulfide, it has a different physical appearance from iron and sulfur.
44 UNIT 1B
During some chemical reactions, heat and light energy may be given off, just as we have observed in investigative activity 6.
Elements, compounds and mixtures
In the following word equation, iron and sulfur are the reactants. They are written on the left of the equation. Iron sulfide is the product. It is written on the right of the equation.
In investigative activity 6 we learnt that magnesium reacts with oxygen to form a compound. That compound is magnesium oxide.
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Remember how we have used a word equation in Stage 8 Unit 1A Chapter 1 to represent the process of photosynthesis? We can use a word equation to represent a chemical reaction. From the word equation, we can tell what substances are needed for a reaction to occur (reactants) and what substances are formed during the reaction (products).
Check My Understanding
1
Write a word equation to represent the chemical reaction.
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Iron + Sulfur Iron sulfide
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Writing word equations
2
Draw particle diagrams for the chemical reaction. The diagram for the product, magnesium oxide is shown below.
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Particle diagrams
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We can also use particle diagrams to represent chemical reactions.
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Iron atom Sulfur atom
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p Figure 5.2 Arrangement of atoms in iron, sulfur and iron sulfide
Magnesium atom Oxygen atom
Mixtures
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5.2
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A
The total number of iron atoms and sulfur atoms is equal to the number of atoms that make up iron sulfide. This is in accordance with the law of conservation of mass which states that no atoms are created or destroyed in a chemical reaction. Thus, the total mass of the reactants will be equal to the total mass of the products of a chemical reaction.
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What do we get when we mix the elements, iron filings and sulfur powder, together?
7.
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Investigate!
Aim: To find out the properties of the elements, iron and sulfur, the mixture of iron and sulfur and the compound, iron sulfide.
Worksheet 5.1
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You will need: Iron filings, sulfur powder, iron sulfide from the previous investigative activity 1, spatula, bar magnet, paper and three petri dishes.
45
Bar magnet
Part I: Instructions: Wrap a piece of paper over the bar magnet as shown in the diagram. O Hold a bar magnet close to the iron filings.
2
Replace the piece of paper on the bar magnet and hold the bar magnet O close to the sulfur powder.
Sulfur powder
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Iron filings
1
3
Mix the iron filings and sulfur powder with a spatula. 4 Repeat Step 2 for the mixture of iron filings and sulfur powder.
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Questions:
O
What did you observe when the bar magnet is held close to the iron filings? What can you conclude about iron filings?
2
What did you observe when the bar magnet is held close to the sulfur powder? What can you conclude about iron filings?
3
When the iron filings and sulfur powder are mixed, did you observe any forms of energy being released?
4
What did you observe when the bar magnet is held close to the mixture of iron filings and sulfur powder? What can you conclude about the mixture of iron filings and sulfur powder?
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Instruction: 1
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Part II:
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Repeat Step 2 in Part I with the iron sulfide sample. Question: 2 What do you observe when the bar magnet is held over the iron sulfide sample? What can you conclude about the properties of iron sulfide O sample?
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A mixture is made up of two or more elements or compounds that are not chemically combined. No new substances are formed in a mixture. In investigative activity 7, we mixed iron filings and sulfur powder. The physical properties of the iron and sulfur remain unchanged when we mix them. The iron filings in the mixture are still attracted to the bar magnet. The sulfur powder in the mixture is still not attracted to the bar magnet.
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Brainstorm
When a mixture is made, no chemical reaction is involved and no new bonds are made. The atoms of different elements or compounds do not form new chemical bonds with one another.
Particle diagrams
• Iron filings stirred with magnesium oxide
We can represent the formation of the iron and sulfur mixture using particle diagrams:
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Do we get a mixture or a compound in the following?
• Iron filings stirred with sulfur powder
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Iron atom Sulfur atom
p Figure 5.3 Arrangement of atoms in iron, sulfur and a mixture of iron and sulfur
46 UNIT 1B
Elements, compounds and mixtures
Differences between mixtures and compounds
Check My Understanding
In investigative activity 7, we found out that iron remains a magnetic material while it is in a mixture with sulfur. However, in the compound, iron sulfide, the iron has formed chemical bonds with the sulfur. Iron sulfide is no longer a magnetic material.
a) A mixture cannot be made up of two or more compounds.
b) When a mixture is made, chemical bonds are formed.
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Different types of mixtures
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Unlike a mixture, a compound has different physical properties from the elements that make it up.
Steel is a mixture of iron and carbon.
Solid–liquid
An example is a mixture of sand and water. Sand particles do not dissolve in the water. This type of mixture is known as a suspension.
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An example is a mixture of sugar and water. Sugar dissolves in water. This type of mixture is known as a solution. An example is a mixture of oil and water.
Use particle diagrams to represent the following in the gaseous state.
a) An element
b) A compound
c) A mixture of two elements
d) A mixture of two compounds
e) A mixture of an element and a compound
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Liquid–liquid
c) A mixture has similar properties to the elements or compounds that it is made up of.
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Solid–solid
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Examples
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There are different types of mixtures. Types of mixture
State whether the following statements are true or false.
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Vinegar is a mixture of ethanoic acid and water.
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Liquid–gas
Gas–gas
Worksheet 5.2
A soda drink is a mixture of carbon dioxide gas and a sweetened liquid.
Air is a mixture of gases.
Oxygen 20.9% Nitrogen 78% Argon 0.90% Other gases 0.17% Carbon dioxide 0.03%
47
5.3 Mixtures–solutions
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The most common type of mixture is the solution. A solution is formed when a substance known as the solute dissolves in a solvent. An example of this type of mixture is the sugar solution. A sugar solution can be formed when we dissolve a solid sugar cube in water.
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Sugar cube
Mix
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Sugar solution
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Water
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p Figure 5.4 Sugar is the solute. Water is the solvent.
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The diagram below shows what happens at the particle level when we dissolve a sugar cube in water.
Water particles Sugar particles
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p Figure 5.5 The sugar cube breaks up. Tiny sugar particles fill the gaps in between the water particles evenly.
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In a solution, tiny solute particles spread out evenly in the solvent. The solute particles are too tiny to reflect light or block any light. Hence, all solutions allow light to pass through. A concentrated solution has more solute particles dissolved in a solvent. A dilute solution has fewer solute particles dissolved in a solvent.
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Worksheet 5.3
Brainstorm
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How does the temperature of a solvent affect the solubility of a solute in the solvent?
48 UNIT 1B
p Figure 5.6 Concentrated sugar solution
p F igure 5.7 Dilute sugar solution
A saturated solution will have the maximum amount of solute dissolved in the solvent. Some substances are more soluble in a solvent. It is easier to dissolve them. Solubility describes how soluble a substance is in a solvent.
Elements, compounds and mixtures
5.4
Separating mixtures Recall
Let us learn how each type of mixtures can be separated using the following physical methods.
Lt d
How do we separate a mixture of rice and flour?
Separate solid–solid mixtures
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Use of magnets
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We can use a bar magnet to separate iron filings from a mixture of iron filings and sulfur powder.
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If one of the solids in the mixture is magnetic, we can use magnets to separate the solids.
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Separate solid–liquid mixtures
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Some mixtures contain solids in a liquid and the solids do not dissolve in the liquid. An example is a sand and water mixture. These mixtures can be separated by the methods below.
Decanting
Figure 5.8 A magnet being
used to separate iron filings from a mixture of iron filings and sulfur powder
Spotlight Watch how you can separate a mixture by decanting.
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Large solid particles that do not dissolve in water tend to settle to the bottom of the mixture. The liquid is decanted by pouring it out of the container.
Liquid and
p Figure 5.9 Decanting
insoluble solid
Filter paper
Filtration
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To separate insoluble solids from a liquid mixture, we can perform filtration. The diagram on the right shows the set-up for filtration. The filter paper is like a sieve. The liquid can pass through the filter paper, but not the solid. The solid collected on the filter paper is known as the residue. The liquid collected in the conical flask is the filtrate.
Residue
Filtrate
p Figure 5.10 Filtration
49
Let us try to separate a mixture of sand and salt using the filtration method.
Investigate!
d Aim: To separate clean and dry samples of sand and salt from a mixture of sand and salt.
GROUP WORK
DEMONSTRATION
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You will need: Safety goggles, sand sample, salt sample, mixture of sand and salt, beakers, filter funnel, filter paper, conical flask, spatula, glass rod, evaporating dish, Bunsen burner, lighter, wire gauze and tripod stand.
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Part I:
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Instructions:
Observe the respective samples of sand and salt. Observe the sand and O salt mixture.
2
Plan an experiment to separate a clean and dry sample of the sand from the mixture.
Plan VAPOURS
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To help you in your planning, you may wish to carry out some tests on the sand and salt samples separately. 3 Let your teacher check your plan. Carry out the experiment. 4 Keep the resulting solution for Part II of this activity. Part II:
Instruction: 1
Salt solution
Your teacher will show you how to separate a clean and dry sample of the salt from the remaining solution using the set-up on the right.
Question:
Worksheet 5.4
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State whether the following statements are true or false. 1 A mixture can be separated into the respective substances that it is made up of through physical methods. 2 During filtration, the solid that cannot dissolve in the liquid will pass through the filter paper and into the container. 3 Evaporation removes excess water from a solution. 4 A magnet can be used to separate a mixture of two elements that are both magnetic.
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Check My Understanding
Wire gauze Tripod stand Bunsen burner
What do you observe forming in the evaporating dish after some time?
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Evaporating dish
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1
Evaporating dish
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250-cm3 beaker
Tripod stand
A solution contains a solid or solids dissolved in a solvent. Some examples include the sugar solution and salt solution. To obtain the solute from the solvent, we can do the following.
Evaporation and crystallisation
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Bunsen burner
p F igure 5.11 Evaporation by using a water bath
50 UNIT 1B
Separate a solute from a solution
The solution can be heated to remove excess water. For a solute that does not break down upon heating, we can heat the solution directly over a flame till all water is removed. An example is a salt solution. This is demonstrated in investigative activity 8. For a solute that breaks down at high heat, we can heat the solution over a water bath. The solution is then left to cool, thus allowing the solute to crystallise. An example is a sugar solution.
Elements, compounds and mixtures
Separating solvent from a solution
Check My Understanding
A mixture can be a solution with a solute dissolved in a solvent. An example is a salt solution.
1
a) What will be collected as the distillate?
b) At what temperature will you see the distillate in the beaker?
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Simple distillation
Lt d
A mixture can also be a solution with two liquids dissolving in each other. An example is an alcohol solution.
Simple distillation is used to separate a salt solution into its components.
Thermometer
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To separate such mixtures, the following set-up is required.
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Cooling water out Condenser
Solution or mixture of liquids
c) What will be left behind in the round bottom flask?
Boiling chips
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Cooling water in
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Distillate
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When the solvent in the solution or one of the liquids in the mixture reaches its boiling point, it turns into vapour. The hot vapour flows through the condenser. Cool water from the tap flows through the condenser and removes the heat from the hot vapour. The hot vapour then condenses to form liquid and is collected in the beaker. The liquid collected in the beaker is known as the distillate.
A
Separating the various solutes dissolved in a solvent
2
A dye contains chemicals E, F and G. Paper chromatography is carried out on this dye. The solubility of each chemical is shown below. Draw the chromatogram. Increasing solubility G
E
F
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Some mixtures contain different types of solutes dissolved in a solvent, such as dyes and inks. Dyes or inks contain several coloured components.
Spotlight
Paper chromatography
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We can separate this type of mixture using paper chromatography. The set-up is shown on the right. The colour components in the black ink will separate as the ink dissolves in the water. Components which are more soluble in a solvent will travel faster and further away from the baseline on the chromatography paper. After the components have separated, the paper with the results is known as the chromatogram.
Glass rod
Clip
Watch this video to see how paper chromatography is carried out.
Paper Beaker
Baseline Water
Worksheets 5.5 & 5.6
51
Revision
B. Magnesium oxide
C. Iron filings
D. Hydrogen gas 2
a) Which diagram shows the particle arrangement of a compound?
b) Which diagrams show the particle arrangement of an element?
Look at the following word equation: Aluminium + Iodine Aluminium iodide
c) Which diagram shows the particle arrangement of a mixture? 4
A. Magnesium oxide
B. Iron filings and sand mixture
b) Name the elements in this reaction.
(1)
C. Salt dissolved in water
c) Is the product formed a mixture or a compound? Explain. (2)
D. Sand in water
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What physical methods can we use to obtain a clean and dry sample of sugar from a mixture of sand and sugar? Outline the steps to be taken in order. (4)
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Look at the particle diagrams below.
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Science Connect
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B.
[14]
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(1)
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(2)
Which of the following can be separated using filtration? (1)
a) Identify the reactants and the products. (1)
(1)
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(1)
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Which of the following is a mixture? A. Chalk and iron sulfide
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1
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We often use the element, silver, to make jewellery because of its shiny appearance. However, silver is prone to corrosion. This means that silver can react with sulfur in the air to form a compound called silver sulfide (a black solid).
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To prevent silver from corroding easily, silver is often mixed with copper to make a mixture called sterling silver. We say that sterling silver is a type of alloy (a mixture of two or more elements, where at least one element is a metal). Sterling silver retains the property of silver (shiny appearance) while having added hardness and strength, as compared to just silver alone. This is why sterling silver is such a popular material to make durable jewellery!
52 UNIT 1B
Elements, compounds and mixtures
Chapter Summary
chemically combine to form
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Elements
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mix to form
mix to form
Mixtures
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Compounds
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have
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have
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Different properties from the elements that they are made up of
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Similar properties to the elements or compounds that they are made up of
can be separated into their respective components by
Physical methods
Simple distillation Filtration
Thermometer
Cooling water out Condenser
Liquid and insoluble
Filter paper
solid
Solution or mixture of liquids Boiling chips
Cooling water in
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Bar magnet
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Use of magnets
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A
such as
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Iron filings
Distillate
Residue
Evaporation and crystalisation
Sulfur powder
Decanting Filtrate
Paper chromatography
Evaporating dish 250 cm3 beaker
Tripod stand Bunsen burner
Glass rod
Clip
Paper Beaker
Baseline Water
53
UNIT 1C
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Light on
Chapter 7 discusses how light changes its direction after striking a surface.
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The study of light helps us to better understand the world around us. In Chapter 6, we explore how light travels and enable us to see everyday objects. We also learn about the formation of shadows.
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In Chapter 8, we study about the bending of light, which is used to explain the formation of rainbows and why objects in the water look closer to us than they really are. We will also learn about the colours of white light.
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Lastly, we will learn about the addition, subtraction, reflection and absorption of colours of light in Chapter 9.
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Scientific enquiry
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23
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Plan investigations to test ideas. (8Ep4) • Make predictions using scientific knowledge and understanding. (8Ep6) • Take appropriately accurate measurements. (8Eo1) • Use a range of equipment correctly. (8Eo2) • Present results as appropriate in tables and graphs. (8Eo4) • Identify trends and patterns in results (correlations). (8Ec2) • Compare results with predictions. (8Ec3) • Discuss explanations for results using scientific knowledge and •
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Vocabulary
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understanding. Communicate these clearly to others. (8Ec6)
54 UNIT 1C
Light
shadow reflection refraction dispersion absorption prism
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Pupils build on their previous knowledge of different types of energy and energy transfers to develop their knowledge of:
In this unit
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How light travels and the formation of shadows. How non-luminous objects are seen.
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Reflection at a plane surface using the law of reflection. Refraction at the boundary between air and glass or air and water. Colour addition and subtraction, and the absorption and reflection of coloured light.
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The dispersion of white light.
55
CHAPTER 6
There are many sources of light around us. Some common examples include light bulbs, candles or even light produced from our mobile devices. How does light travel?
Recall
Investigate!
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1.
How is light important to us?
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6.1 Properties of light rays
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• Describe how non-luminous objects are seen. (8Pl2)
• How does light enable us to see?
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• Use light travelling in a straight line to explain the formation of shadows and other phenomena. (8Pl1)
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Properties of light
In this chapter
Aim: To investigate how light travels.
PAIR WORK
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You will need: Lamp without the shade and rubber hose. Instructions: 1
Light travels in straight lines.
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Turn on the lamp. 2 Position the rubber hose such that it forms a straight line between the lamp and your eye. O 3 Look through the straight rubber hose. 4 Now position the rubber hose such that it forms a curved path between the lamp and your eye. O 5 Look through the curved rubber hose. Questions: 1 What do you observe when you look through the straight rubber hose? 2 What do you observe when you look through the curved rubber hose? 3 Explain your observations in Questions 1 and 2.
Do you notice how light rays from the laser lighting travels in a straight line?
56 UNIT 1C
Light
What about the Sun’s rays that shine through a thick forest? How do they travel?
We can represent light by drawing straight lines. These lines are called light rays. We use arrows to show the direction of the light.
Check My Understanding
We can represent the path of light rays by drawing a __________ diagram.
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Divergent beam
2
Light rays meet at a point.
Light rays tend to move outwards from a source.
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Light rays travel from a very far away source.
Worksheet 6.1
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Convergent beam
Light travels in __________ lines.
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Light rays usually travel in a bundle, which is called a beam of light. Here are some examples of beams: Parallel beam
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p Figure 6.1 This ray diagram shows how light from a torch enters a person’s eyes.
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Fill in the banks
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6.2 Pinhole camera
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A pinhole camera is a simple camera that works based on the concept that light travels in a straight line. It lets light into a dark box through a pinhole. An image of the object can be seen on the screen. Let us make a pinhole camera and see how images are formed on the screen!
Pinhole camera Image Screen
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Object
Investigate! GROUP WORK
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2.
Aim: To investigate the properties of the image formed in a pinhole camera.
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You will need: Shoe box, pen knife, ruler, pencil, black paper, black duct tape, pin and wax paper.
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Part I:
Instructions: 1
Cut a square hole (about 6 cm by 6 cm ) on one end of a shoebox using a penknife.
2
Paste a piece of wax paper over to cover the square. This is the screen of your camera.
57
Cover the box with black paper and any gaps or holes with black duct tape.
4
Pierce a small hole in the other end of the shoebox with a pin to create a pinhole.
5
Point your pinhole camera at an object. Look at the image formed on the screen.
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Use the pin to enlarge the pinhole. Repeat Step 5. Questions: 1 Draw the image that you observed in Step 5. 2 Describe the image observed. 3 After the pinhole has been enlarged, describe what happens to the a) brightness of the image. c) sharpness of the image. b) size of the image.
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Part II:
Plan an investigation to find out what will happen to the image when there are more pinholes in a pinhole camera.
Plan VAPOURS
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Instructions:
2
Let your teacher check your plan. 3 Carry out the investigation.
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State which of the following statements are true or false. 1 A pinhole camera works based on the fact that light travels in a straight line. 2 The image formed in a pinhole camera is the same size as the object. 3 The image formed in a pinhole camera is inverted. 4 A smaller pinhole gives rise to a less sharp image than a larger pinhole.
3
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Check My Understanding
Questions: 1
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What happens to the image during your investigation? 2 What is the relationship between the number of pinholes and the sharpness of the image? As you have observed during investigative activity 2, the image formed on the screen is smaller than the object itself. The image is of the object is also inverted.
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Pinhole camera
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Light rays from a light source bounce off the object and enter through the pinhole. The light rays coming off the object only travel in a straight line. Light Image Object bouncing off the top of the object goes through the pinhole and hits the bottom of the screen. The opposite happens for light bouncing off the bottom of the p F igure 6.2 Image formed in a object. The light coming off the bottom of the object goes through the pinhole pinhole camera and hits the top of the screen.
Pinhole camera
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Worksheet 6.2
What happens to the image when the pinhole is enlarged? The image becomes brighter. It is also fuzzy and less sharp.
Image
Object
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p Figure 6.3 Image formed when the pinhole is enlarged
When the pinhole camera is enlarged, more light rays will be able to enter the pinhole camera through the pinhole. This means that more light rays bouncing off from one point of the object will hit the screen at more than one point. Hence, the image appears fuzzy and less sharp.
58 UNIT 1C
Light
6.3 Shadows
Recall What are some examples of opaque objects and translucent objects?
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Shadows are formed when the path of light is blocked by an opaque object. Sometimes, faint shadows can also be formed when translucent objects block light.
3.
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Let us find how the distance between a light source and an object can affect the size and sharpness of a shadow.
Investigate!
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GROUP WORK
Aim: To investigate how the distance between a light source and an object affects the size and sharpness of its shadow. You will need: Torch, ball on stick and smooth wall. Set up the experiment as shown on the right.
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1
A
Instructions:
2
1
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b) What is the relationship between the distance of the light source from the object and the size of the shadow?
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What is the relationship between the distance of the light source from the object and the size of the shadow
Torch
a) What happens to the sharpness of the shadow at i) Step 2? ii) Step 3?
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2
Ball
2
Why is there a shadow on the ground?
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a) What happens to the size of the shadow formed on the wall at i) Step 2? ii) Step 3?
1
Screen
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Questions:
20
Move the torch near the ball. 3 Move the torch further away from the ball.
Check My Understanding
b) What is the relationship between the distance of the light source from the object and the sharpness of the shadow?
As you have observed from investigative activity 3, the closer the light source is to an object, the bigger and less sharp the shadow of the object will be. Conversely, the further the light source is from an object, the smaller and sharper the shadow of the object will be.
Worksheet 6.3
59
Brainstorm
Luminous objects, such as the Sun or a lamp, give out light. We can see a luminous object when the light enters our eyes directly.
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Can we see luminous objects in the dark? Explain why or why not.
6.4 Luminous objects and non-luminous objects
Lamp (luminous)
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State whether the statements are true or false. 1 A star is a non luminous object. 2 A luminous object is a light source. 3 We can only see a non-luminous object if there is a luminous object nearby. 4 We can see a non luminous object in the dark.
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Reflected light from the lamp
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Clock (non-luminous)
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p F igure 6.4 How we are able to see luminous and non-luminous objects
Non-luminous objects, such as the Moon or a painting, do not give out light. We are only able to see a non-luminous object if light from a light source or luminous object bounces off the non-luminous object and enters our eye.
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Worksheet 6.4
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Science Connect
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A sundial is one of the oldest instruments that can be used to tell time. As the position of the Sun above the sky changes throughout the day, the shadow formed on the sundial changes. In the olden days, people look at the position of the shadow on the sundial to tell the time of the day.
60 UNIT 1C
on
Light from the lamp
ca
Check My Understanding
te
The diagram below shows how we can see a luminous object (the lamp) and a non-luminous object (the clock).
Light
Revision 1
3
The diagram below shows the scene behind a shadow puppet show.
Lt d
How does light travel? (1) 2 A pupil uses a pinhole camera to observe a building. Pinhole camera
Building
(3)
c) i) What will happen to the image if the pupil increases the size of the pinhole in the pinhole camera? (2)
ii) Explain your answer for c) (i).
a) Why is a shadow of the duck puppet cast on the screen? (1)
b) What should the performer do if he wants to cast a bigger shadow of the duck puppet? (1) 4
(2)
Why are we able to see a non-luminous object, such as a textbook, in a well-lit classroom?
du
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b) Describe the image formed on the screen. Explain.
on
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a) Draw light rays on the diagram above to show the path of light entering the pinhole camera. (2)
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Screen
[14]
A
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E
(2)
Chapter Summary
Light
Parallel beam
Convergent beam
20
Properties
23
has
C
op
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Travels in a straight line
Application
Pinhole camera
Inverted image
Divergent beam
Can be blocked by an opaque object
is given off by
is not given off by
Luminous objects
Non-luminous objects
Light enters our eyes directly
Light bounces off the object and enters our eyes
to form
Shadows
Allows us to see
61
CHAPTER 7 • Describe reflection at a plane surface and use the law of reflection. (8Pl3)
• Why are we able to see an image of ourselves when we look into the mirror?
te
• Pepper ghost is an illusion technique used by many magician. How does it work?
Lt d
Reflection of light
In this chapter
on
P
7.1 Laws of reflection
ti
As you have learnt in Chapter 6, we can see non-luminous objects because light bounces off the non-luminous object and enters into our eyes. This is reflection.
Investigate!
du
4.
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How does light get reflected? Let us find out in this activity.
Mirror
20
A
P1
P2
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O i = 40˚ Normal
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B
62 UNIT 1C
23
A
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Aim: To study the law of reflection on a plane mirror. PAIR WORK DEMONSTRATION You will need: Small mirror, cork board, pencil, paper, ruler, protractor and pins. Instructions: 1 Place a piece of paper on a cork board. Draw a straight line AOB across the piece of paper. This line is the plane which is the represents the flat surface. 2 O is the midpoint for line AOB. Draw a dotted line perpendicular to the plane at point O. This new line is the normal. 3 Draw a line at 40º to the normal. This is i. 4 Put two pins, P1 and P2, on the line drawn in Step 3, with the pins being as far apart from each other as possible. 5 Place the mirror on the plane. 6 Bend down and look into the mirror at your eye level. You will see the 2 pins in the mirror. Fix two pins on the paper such that they are in line with the pins you see in the mirror. 7 Remove all the pins and the mirror. 8 Use a pencil to draw a line to connect the two holes left behind by the pins in Step 6. This represents the path of the reflected light. 9 Measure the angle made by the path of the reflected light against the O normal. This is r. Record this result in a table. 10 Repeat Steps 1 to 9 with i of differing values. Record the results in O a table. Questions: 1 Study the values of i and r. What is the relationship between these two angles? 2 Did the path of light go beyond the plane?
Light
In investigative activity 4, light from the pins travels towards the mirror. This ray of light is known as the incident ray. It hits the mirror and gets reflected off the surface of the mirror. This ray of light is known as the reflected ray. The reflected ray enters our eyes, allowing us to see the image of the pins in the mirror.
te
Reflected ray
r
P
i
Incident ray
Lt d
Normal
on
Plane mirror
ca
The incident ray, reflected ray and the normal to the reflecting surface are all on the same plane.
ti
From investigative activity 4, we observe the first law of reflection:
du
The angle of incidence i is the angle between the normal and the incident ray. The angle of reflection r is the angle between the normal and the reflected ray.
E
In investigative activity 4, we realise that as we vary the angle of incidence, the angle of reflection changes accordingly. Hence, this is the second law of reflection:
ls to n
The angle of incidence is equal to the angle of reflection. Angle of incidence i = Angle of reflection r
1
State whether the following statements are true or false. a) During reflection off a smooth surface, the angle of incidence is equivalent to the angle of reflection.
23
A
Check My Understanding
b) The normal is a real line that is perpendicular to the mirror.
c) The incident ray, reflected ray and the normal all lie on the same plane.
The diagram below shows light rays reflected off a surface. t
ig h
2
t
20
Light ray a
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p
r
q
Light ray b
s
z
Write the corresponding letter from the diagram which matches
a) the incident ray.
d) the reflected ray.
b) the angle of incidence.
e) the surface of the plane mirror.
c) the angle of reflection.
f) the normal.
63
7.2 Regular and irregular reflection The type of surface can affect the reflection of light.
Lt d
te
When light rays hit a smooth or shiny surface, light rays are reflected in the same direction. All reflected rays are in parallel.
P
What can you deduce about the angle of incidence and angle of reflection in a regular reflection of all the reflected rays? What about irregular reflection?
Regular reflection
on
Brainstorm
ti
p F igure 7.1 Light rays are reflected in the same direction.
ca
Irregular reflection
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When light rays hit a dull or rough surface, light rays get reflected in all directions.
E
Spotlight
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A mirror is coated with many types of metals. Watch this video to find out more.
A
p F igure 7.2 Light rays are scattered in all directions.
23
Images formed by a plane mirror
5.
Investigate!
Aim: To find the characteristics of the image formed by a plane mirror. You will need: Plane mirror, pins, graph paper and cork board.
yr
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20
A plane mirror has a flat, smooth and shiny surface. Regular reflection occurs at a plane mirror. Let us find out more about the images formed by a plane mirror.
op
Mirror
C
Graph paper X
Y Cork board
64 UNIT 1C
Light
ls to n
E
du
Lt d te P on
ca
ti
Part I: Instructions: 1 Set-up the apparatus as shown above. 2 Insert pins at Points X and Y. O 3 Observe the images of the pins in the mirror. Part II: Instructions: 1 Write your name on a piece of paper. 2 Place the piece of paper in Step 1 in front of the mirror. 3 Observe the images of the letters in the mirror. O Consider the following questions: • Did the size of the letter change? • Are the images upright or upside down? • Are the images flipped sideways? • If you place another piece of paper between the mirror and the paper with letters on it, do you see the images on the paper? Questions: 1 Using the grid on the graph paper, a) what is the distance of the image of the pins from the glass block? b) what is the distance of Pins X and Y from the glass block? c) what can we conclude about the distance of the image from the mirror and the distance of the pins from the mirror? 2 Refer to your observations in Step 6, what are the characteristics of the image formed by a plane mirror?
Mirror
Image
C
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20
23
Object
A
An image formed by a plane mirror has the following characteristics.
d1
d2
• The image is upright. • The image has the same size as the object. • The image is inverted laterally. The left side of the object will appear on the right side in the image. The right side of the object will appear on the left side in the image. The letter ‘N’ in the word ‘NOTES’ is on the lady’s right. However, it appears on the image’s left.
• The image formed by a plane mirror is virtual. The image formed by the plane mirror cannot be captured on a screen. In investigative activity 5, when we placed a piece of paper (with a name written) in front of the mirror, we do not see the image. Real images can be captured or projected onto a screen. • The distance of the image from the mirror is the same as the distance of the object from mirror. In the diagram on the left, the value of d1 is equal to the value of d2.
Check My Understanding State whether the following statements are true or false. 1 An image in the mirror is laterally inverted as compared to the actual object. 2 The distance between the image and the mirror is the same as the distance between the actual object and the mirror. 3 The image formed is virtual. 4 The image formed is smaller than the actual object.
Worksheets 7.1 & 7.2
65
7.3 Application of the laws of reflection Let us find out how the laws of reflection of light are applied in our daily life.
6.
Lt d
Periscope Investigate!
te
Aim: To construct a simple periscope.
DEMONSTRATION
GROUP WORK
Instructions: 5
Cut off the excess cardboard on the opposite end.
ti
On one piece of cardboard, draw lines at each end at a 45° angle.
Glue a mirror to each end with the reflective sides facing the centre.
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E
2
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1
on
P
You will need: Plastic mirrors, rectangular cardboard pieces, pencil, protractor, ruler and glue gun.
6
Repeat Steps 4 and 5 to cover the final side of the periscope.
7
Trim the excess cardboard on the ends with the mirrors.
8
Cut the excess cardboard pieces to the right size and glue them under the mirrors for better support.
9
Try out the periscope by using it to look over a wall.
Mirror
Mirror
Glue another piece of cardboard on the other side.
23
A
3
Glue the 3rd piece of cardboard, leaving a gap at the end so that the mirror can be seen.
Questions: 1
Applying the laws of reflection, draw three light rays in the diagram below to show how a pupil can see the tree through the periscope.
2
Describe two situations where periscopes would come in useful.
C
op
yr
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20
4
66 UNIT 1C
Light
How does a periscope work?
Super scientist
Light rays
Plane mirror
te
45o
Lt d
The rays of light are reflected twice in the periscope (once at each mirror). The mirrors are positioned such that the reflected light ray leaving the first mirror will hit the second mirror as an incident ray. This incident ray will then be reflected by the second mirror into our eyes. This is how a periscope allows us to see things that are out of our direct field of vision.
John Henry Pepper (1821–1900) is a wellknown British scientist who amazed the world with his scientific experiments. One of his most popular demonstrations was called the ‘Pepper’s ghost’.
P
Object to be seen on a tree
on
Periscope
ca
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High wall (Obstacle)
du
45o
E
Plane mirror
Observer
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p Figure 7.3 How a periscope works
Pepper's ghost illusion technique
The audience is able to see a ‘ghost’ appearing on the stage as a result of reflection along a glass surface.
A
This is an illusion technique used in theatres or amusement parks to create virtual images.
Lit stage Image
C
op
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20
23
A thin glass of transparent film is placed at an angle in front of the stage. Usually, there is another room that is out of the audience's view and the ‘ghost’ will be positioned in this room. When lights in this room are switched on, the ghost's image will be seen on the stage. The image will appear as translucent or ‘ghostly’.
Transparent film/glass
Check My Understanding Describe how a periscope works.
Room
Audience
p Figure 7.4 Light rays from the ghost are reflected in the Pepper's ghost effect.
Light rays from the stage will pass through the transparent glass and reach the audience's eyes. This is why the audience will be able to see the stage. When the light in the other room is turned on, most light rays will pass through the glass. However, some of the light rays from the ghost is reflected off by the glass. The reflected rays reach the audience's eyes. The audience sees the virtual image of the ghost.
Worksheet 7.3
67
Science Connect
Mirror
Image
Eye chart
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Eye chart
Lt d
A plane mirror is often used in an eye test room. The plane mirror makes the images of the letters in the eye chart appear further away.
ti
on
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Patient
3m
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3m
6m
p F igure 7.5 Actual distance required for an eye test
p Figure 7.6 A smaller room is required to conduct the eye
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test when a plane mirror is used.
Revision 1
5
23
A
What are the laws of reflection? (2) 2 Draw diagrams to show how light rays are reflected at
a) the water surface in a
a) Draw the normal in the diagram below. (1) b) i) Draw and label on the diagram the angle of incidence i. (1)
(1)
(1)
c) Draw and label the reflected ray.
(3)
3
Describe five properties of an image formed by a plane mirror. (1)
d) Draw the image of the ball.
(2)
4
Draw the image of the letter below when it is being reflected in the plane mirror. (2)
b) a rocky wall.
yr
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swimming pool.
20
ii) Measure the angle of incidence i. (1)
Incident ray
C
op
Mirror
[15] Plane mirror
68 UNIT 1C
Light
Chapter Summary
Lt d
Reflection of light occurs when
te
Light rays bounce off a surface
P
Smooth surface
on
follow
Regular reflection
ca
2nd
Angle of incidence is equal to the angle of reflection i= r
Rough surface
Irregular reflection
i
r
Reflected ray
20
Incident ray
23
A
Normal
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The normal, incident ray and reflected rays all lie on the same plane.
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1st
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Laws of reflection
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Plane mirror
69
CHAPTER 8
Refraction of light
In this chapter
Lt d
• Investigate refraction at the boundary between air and glass or air and water. (8Pl4)
te
• Have you ever wondered why a straw appears to bend in a glass of water?
P
As light rays travel across two transparent mediums, such as air and water, light rays bend. This bending effect of light is known as refraction.
ti
on
8.1 Refraction Investigate!
p F igure 8.1 Straw in
a glass of water
du
7.
ca
Let us find out how light rays bend as they travel across air and glass.
DEMONSTRATION
PAIR WORK
E
Aim: To observe the bending of light rays as they pass through a glass block.
ls to n
You will need: Glass block, pencil, paper pins, ruler, protractor, cork board and blank paper. Instructions:
Recall
1
Glass block
i
Incident ray
i = 40˚
20
23
A
What are the incident ray and the angle of incidence?
Place a glass block on a piece of paper and trace its outline. Draw the normal. Normal
op
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2
Draw a straight line at 40˚ to the normal. This represents the path of the incident ray. This is the angle of incidence i.
3
Take two pins and place them along this straight line. 4 View the two pins through the glass block on the other side of the glass block. 5 Add the third and fourth pins such that they are in line with images of the first two pins that you see through the glass block.
C
Normal Glass block
i
Incident ray r Emergent ray
70 UNIT 1C
Light
Remove the pins. Draw a straight line connecting the holes left by the third and fourth pins and the side of the glass block. This line represents the ray of light exiting the glass block.
7
Remove the glass block. Draw a line to connect the incident ray and the emergent ray. This line represents the refracted ray. O
te
Extend the normal line. Measure the angle of refraction r. 9 Repeat Steps 1 to 8 with different values of angle of incidence and measure the angle of refraction r. 10 Now, repeat Step 1. Place the two pins on the normal. Repeat Steps 4 to 7.
What happens when light passes through mediums of different densities?
O
P
8
Spotlight
Lt d
6
How do the angle of incidence and the angle of refraction compare with each other?
2
How do the light rays travel with regards to the normal when they a) enter the glass block?
b) leave the glass block? What happens when the incident rays are at the normal?
du
3
ca
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1
on
Questions:
Normal
A
Incident ray
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When a light ray enters the glass block from the air, it bends towards the normal. This is because glass is denser than air. A light ray travels slower across the glass block than through air. The angle of refraction is the angle between the normal and the refracted ray.
20
23
i
i is the angle of incidence r is the angle of refraction
ig h
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r
Refracted ray
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Normal
C
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When light ray exits the glass block and enters the air again, it bends away from the normal. This is because air is less dense than glass. Light ray travels faster across the air. Refraction does not occur if light rays pass through the normal. The light ray will simply travel straight through the glass block.
Check My Understanding Describe how light rays behave as they travel from a denser material to a less dense material.
71
Let us find out how light rays bend as they travel across water and air.
8.
Investigate!
Aim: To find out how light rays travel from water to air.
Lt d
PAIR WORK
You will need: Small coin, empty opaque cup and water. Instructions:
3
Coin
te
Place a coin into an opaque cup. Position your eye such that you see the coin disappearing behind the rim of the cup.
P
2
Maintain your position in Step 2. Get your classmate to fill the cup with water.
on
1
Questions:
Spotlight
1
du
ca
ti
What did you observe at Step 3? 2 Which do you think is a denser medium—air or water? 3 What do you think happens to the light ray from the coin as it travels across the water in the cup and enters the air? No light rays from the coin in the empty cup enter our eyes. Hence, we are able to see the coin.
A
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What will we observe when we move a pencil across a cup of water?
O
Coin
When water is added to the cup, a light ray from the coin has to travel across the water. Light ray then leaves the water and enters the air. Light ray bends away from the normal as it enters the air. This is because water is denser than air. Thus, light travels faster in the air. When the light enters our eyes, our brain is unable to sense the bending of light. Instead, it constructs images based on where the light rays appear to have come from. Therefore, to us, the coin reappears at a higher position than it actually is.
C
op
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20
What does it mean when one material is denser than another?
23
Recall
Worksheet 8.1
Virtual image of coin Coin
72 UNIT 1C
Light
8.2 Application of refraction of light Brainstorm
An object in water appears to be bent.
Lt d
A fisherman catches fish by spearing them while they are in the water. When he sees a fish in the water, should he aim for the fish where it appears to be, above the position where he sees the fish or below the position where he sees the fish? Explain.
E
du
ca
ti
on
P
te
The refraction of light also explains why the straw in a cup of water appears to bend. Light from the top of the straw enters our eyes as usual. However, light from the part of the straw that is in the water bends away from the normal as it enters the air and into our eyes. Since the brain is unable to sense the bending of light caused by refraction, the straw appears to be bent in the water.
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An object in water appears nearer to the water surface.
yr
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20
23
A
Have you ever looked over a fish tank and saw that the fish seemed nearer to you? This is because light rays bend away from the normal as it leaves the water and enters the air and into our eyes.
Image Fish
State whether the following statements are true or false. 1 A pencil in a cup of water will appear to be broken to someone looking through the cup from the side. 2 An object in the water seems to be closer to the water surface than it really is. 3 Light rays bend towards the normal as they travel from water into air. 4 Our brain can sense the bending of light.
C
op
As our brain is unable to sense the bending of light, the image of the fish appears nearer to the water surface.
Check My Understanding
Worksheet 8.2
73
Revision 2 Which arrow correctly shows the ray of
Draw the light rays for each of the diagrams below as the light ray enters or leaves each medium.
Lt d
light that emerges from the glass block? (1)
(1)
Glass
b) Air
(2)
A. reflection
B. dispersion
C. refraction
D. suspension
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Glass
E
Air
(2)
20
23
A
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Science Connect
yr
Have you seen a kingfisher fishing?
C
op
Instead of diving into the water at an angle, it dives straight through the water surface to fish for its food.
74
This method allows the kingfisher to work around the reflection and refraction of light and judge the depth of the prey accurately.
UNIT 1C
Light
A
An object in water seems to be nearer to the observer as a result of ___________.
c)
B
P
3
C
on
Air
D
ti
Water
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Air
a)
ca
1
(1) [7]
Chapter Summary
Lt d
Refraction of light
Object appears to bend.
du
ls to n A
Less denser mediums
23 Glass
such as
Air Incident ray
Normal
i
Light travels faster.
t
20
Water
Fish
in
Denser mediums such as
Image
E
Light travels at different speeds in different mediums. in
Objects in water appears nearer to the water surface.
ca
Light travels across two transparent mediums.
on
occurs when
P
Applications
ti
Bending effect of light
te
is the
ig h
Light travels slower. Angle of refraction
r
Refracted ray
Normal
C
op
yr
Light rays bend towards the normal.
Light rays bend away from the normal.
75
CHAPTER 9 • Explain the dispersion of white light. (8Pl5)
te
• Have you seen a rainbow in the sky? How is it formed?
P
9.1 Dispersion of white light
on
• Explain colour addition and subtraction, and the absorption and reflection of coloured light. (8Pl6)
Lt d
Dispersion of white light and colours
In this chapter
White light or visible light is made up of a mixture of colours.
E
GROUP WORK
You will need: Light ray box, glass prism/diffraction grating and blank white screen or white paper. Instruction: 1
Shine light through the glass prism/diffraction grating. Questions: 1 Draw and colour what you observed. 2 From your results, conclude which colour from the dispersion bends
O
A
The colours seen in a rainbow are formed from the primary colours of lights.
Aim: To investigate what happens when white light is passed through a glass prism.
ls to n
Spotlight
Investigate!
du
9.
ca
ti
Let us observe the colours of white light in the investigation below.
a) the most?
23
b) the least?
yr
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20
When a beam of white light passes through a prism, the white light splits into seven colours—red, orange, yellow, green, blue, indigo and violet. This is the spectrum of white light and the colours always appear in the same order as the colours of a rainbow. The splitting of white light into its constituent colours is known as dispersion.
op
The different colours of white light travel at slightly different speeds.
C
p Figure 9.1 Dispersion of white
light in a prism
76
UNIT 1C
What causes the dispersion of white light as it passes through the prism?
Light
In investigative activity 9, the white light travels across air and enters a glass prism. Glass is denser than air. Hence, the different colours of white light are refracted towards the normal when they enter the glass prism. As the colours of white light travel at different speeds, they are refracted at different angles in the prism. Violet light bends the most, while red light bends the least.
How is a rainbow formed in the sky? A rainbow is formed when sunlight gets refracted in raindrops. The colours of sunlight get dispersed and a spectrum of colours is produced in the sky. This forms the rainbow that we see. Each raindrop acts like a prism in investigative activity 9.
Is it true or false? 1 White light can be split into its respective colours by passing it through a prism. 2 Light of different colours travel at the same speed. 3 Green light bends the most.
How do we see colours emitted by light sources or luminous objects?
du
Addition of colours of light Investigate!
E
10.
A
ls to n
Aim: To investigate the effect of adding different-coloured lights. DEMONSTRATION Instruction: 1 Your teacher will demonstrate what happens when red, green and blue lights are mixed. O Questions: 1 Draw and colour what you observed.
Check My Understanding Based on the Venn diagram below, what colour of light will we get when we mix green light and blue light?
Label your diagram in Question 1 with the names of the colours.
20
23
2
Worksheet 9.1
ca
ti
White light is made up of three primary colours—red, green and blue. The primary colours can be added together to give secondary colours. Let us do the following activity to find out how secondary colours are formed.
on
P
te
9.2 Seeing colours emitted by a light source
Check My Understanding
Lt d
When the colours of white light leave the prism and enter the air, they bend away from the normal at different angles and produce a spectrum of colours.
t
Red
ig h
Yellow
Magenta
White Cyan
Figure 9.2 Venn diagram of
additive colour space
Blue
C
op
yr
Green
Additive colours
Secondary coloured lights are formed when we add primary coloured lights. The adding of colours of light is known as the addition of colours. If we add red and green lights together, we will get yellow light. If we add red and blue lights together, we will get magenta light. When we add green and blue lights together, we will get cyan light. If we add all primary coloured lights together, we will get white light. The addition of colours of light explains how we see colours from light sources.
p Figure 9.3 Amber-coloured
light in traffic lights are produced by mixing red and green lights.
Worksheet 9.2
77
9.3 Seeing colours in non-luminous objects Non-luminous objects do not give off light. How do we see the colours of nonluminous objects?
Subtraction of colours of lights
A non-luminous object gives a colour because it is reflecting off certain light rays, unlike in luminous objects where we see the colour of the light emitted. To understand how we see colours of a non-luminous object, we need to learn about the subtraction of colours of light using light filters. We are looking at which light rays have been subtracted or reflected off the surface of the object. A light filter is usually made of transparent material. It absorbs some colours and allows other colours to pass through. The absorption of colours is also known as the subtraction of colours.
Investigate!
du
11.
ca
ti
What happens when we stack different colour filters together?
on
P
te
Investigate the addition and subtraction of colours through this simulation.
Lt d
Spotlight
C
op
yr
ig h
t
20
23
A
ls to n
E
Aim: To observe the effect of subtraction of colours of light using GROUP WORK light filters. You will need: Red, blue, green, magenta, yellow and cyan light filters, torchlight with white light and projector screen/white wall/white piece of paper. Instructions: O 1 Attach each filter onto the torch and shine it on the screen. 2 Choose two filters of different colours and predict what you will P observe when they are used together. O 3 Attach both filters chosen in Step 2. Compare your observation(s) in Step 3 with your prediction made 4 in Step 2. Questions: 1 a) When you attach a red-light filter to the torchlight, what do you observe? b) What colour of light do you think the red-light filter allows to pass through it? c) What primary colours of light did not manage to pass through the red filter? Explain. 2 a) When you attach a magenta light filter to the torchlight, what do you observe? b) What colours of light do you think the magenta filter allows to pass through it? c) What primary colour of light did not manage to pass through the magenta filter? Explain. 3 a) What happens to the brightness of light after it has passed through a filter? Explain your observation.
78 UNIT 1C
Light
R White
Yellow
R
G
White
B
R
R
G
G
Check My Understanding
B
When we shine white light on a red-light filter, it only allows red light to pass through. It absorbs all other primary colours of white light—green and blue lights.
White
R
R
G
White
B
G
B
B
P
ca
B
G
ti
R
Cyan
on
Magenta
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Similarly, when we pass white light through a yellow light filter, only red and green lights are able to pass through. The blue light is absorbed. We will see yellow light on the screen since red and green lights add to give yellow.
State whether the following statements are true or false. 1 White light is produced when a beam of red, blue and green light is shone at the same spot. 2 A red filter only filters out red light. It lets all other colours of light pass through. 3 Secondary colours are produced when two primary colours are mixed. 4 A magenta light filter will allow green light to pass through it.
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Red
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When we shine white light through a magenta filter. It allows only red and blue lights to pass through. Green light is absorbed by the magenta light filter. We see magenta light on the screen. This is because of the addition of red and blue light.
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As for the cyan light filter, it only allows green and blue lights to pass through. The red light is absorbed. We see cyan light on the screen as the green and blue lights are added.
What happens when we place two light filters over each other? Magenta
A
G
R
B
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B
R
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R White
Yellow
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When we place a yellow light filter over the magenta light filter, we see red light. This is because only the red light can pass through both filters. The green light is absorbed by the magenta filter. The blue light that passes through the magenta filter is absorbed by the yellow light filter.
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White
Yellow
Cyan
R
R
G
G
G
B
If we place a cyan light filter over a yellow light filter, we can only see green light. Green light can pass through both light filters. The blue light is absorbed by the yellow filter, while the red light is absorbed by the cyan filter.
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Cyan
Magenta
R G
G
B
B
B
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White
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Similarly, if we place a magenta filter over a cyan filter, only blue light can pass through both filters. The red light is absorbed by the cyan light filter, while the green light is absorbed by the magenta light filter.
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It is worth noting that the light that we see on the screen is dimmer than the white light. This is because some light has been absorbed by the filters.
Recall
How do we see colours of non-luminous objects?
How do we see nonluminous objects?
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Non-luminous objects are similar to the light filters in investigative activity 11. They absorb coloured lights. The colours of lights not absorbed by the object will be reflected off.
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The colour of the non-luminous objects that we see is the colour of lights that are reflected into our eyes.
Red light
Green light
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A
White light
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When white light hits a red object, such as an apple, only red light is reflected off the apple. All the other colours of white lights are absorbed by the apple.
We see a black apple.
If we shine a green light on the apple, the apple will appear black to us. This is because the apple only reflects red light, but not the green light. The green light is absorbed by the apple. Since no coloured light is reflected off the apple, the apple will appear black.
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Let us observe what happens if we shine coloured light onto non-luminous objects.
C 80 UNIT 1C
We see a red apple.
Light
12. Investigate!
Aim: To observe coloured objects under different-coloured lights.
GROUP WORK
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You will need: Coloured cards (white, red, blue, green, magenta and yellow), white light, yellow filter, magenta filter and whiteboard. Instructions:
P on
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Shine a white light on each of the coloured cards. O 2 Attach a magenta filter to the torch and repeat Step 1. O 3 Attach a yellow filter to the torch and repeat Step 1. Questions: 1 Draw diagrams to explain how we see the red, blue and green cards under white light. 2 What are the primary colours that make up a) yellow light? b) magenta light? 3 Draw diagrams to show which primary coloured lights pass through the a) yellow light filter. b) magenta light filter.
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The diagram below explains what happens when we shine magenta light onto the various coloured cards.
R G
Wh ite
Ma gen ta
B
G
R
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B I am blue!
The red light is absorbed by the blue card. The blue light is reflected into our eyes. We see the blue card as blue.
Wh ite
Ma gen ta
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The blue light is absorbed by the red card. The red light is reflected into our eyes. We see the red card as red.
B
R
A
I am red!
R
Ma gen ta
B
B
Wh ite
R
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Wh ite
R G
Ma gen ta
B
R
B
R B
I am green!
The red and blue lights are absorbed by the green card. No coloured light is reflected off the card. We see the green card as black.
I am yellow!
The blue light is absorbed by the yellow card. The red light is reflected into our eyes. We see the yellow card as red.
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When we attach a yellow filter to the torch, only red and green lights can pass through the light filter. The blue light is absorbed by the filter.
R
Wh ite
Yel low
G
R G
B
Yel low
B
R
R
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Wh ite
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Wh ite
Yel low
B
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R
The red and green lights are absorbed by the blue card. No coloured light is reflected off the card. We see the blue card as black.
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The green light is absorbed by the red card. The red light is reflected into our eyes. We see the red card as red.
R
R
G
Yel low
B
R G
E
G
I am blue!
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I am red!
Wh ite
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The diagram below explains what happens when we shine yellow light onto the various coloured cards.
I am yellow!
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I am green!
A
The red light is absorbed by the green card. The green light is reflected into our eyes. We see the green card as green.
The blue light is absorbed by the yellow card. The red and green lights are reflected into our eyes. The addition of the red and green lights form the secondary colour, yellow. We see the yellow card as yellow.
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Check My Understanding
a) Which coloured(s) light is/are reflected?
b)
Which coloured(s) light is/are absorbed?
2 White light is shone on a cyan toy.
a)
Which primary colour(s) is/are reflected?
b)
Which primary colour(s) is/are absorbed?
3 A pupil wanted to explore how the colour of a green leaf would change
C
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under different coloured lights.
Worksheet 9.3
82 UNIT 1C
1 White light is shone on a blue toy.
Light
a) First, he shone white light onto the leaf. What would be the colour of the leaf that he saw?
b)
c) Draw coloured diagrams to explain your answers for a) and b).
ext, he shone blue light onto the leaf. What colour would the leaf N appear to be?
Science Connect
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Traditionally, we may know that mixing of colour pigments, such as red and blue, gives us muddy purple. We can see in the diagram below. However, printers and paint manufacturers have discovered that cyan, magenta and yellow (colours that you have learnt in the addition of light) can give a wider variety of hues of colours.
Yellow
Cyan
Green
Black
Yellow
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Green
Black Blue
Red
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Violet Orange
P
Blue
Magenta
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Red
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In this chapter, we learnt that the colour of lights can be added to produce different coloured lights. We have also discovered that the colour of an object we see is due to certain light rays reflecting off its surface. Subtractive colours
Additive colours
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Green
Magenta
E
Red
Yellow
Blue
The colour of pigment, paints and inks
A
The colour of lights
Cyan
We see that the Venn diagram of each colour space shown above is the inverse of the other.
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Non-luminous paints act like light filters. They absorb certain coloured lights. When we mix paints (or colour pigments) on paper, the paints act like light filters absorbing coloured lights.
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We use the subtraction of coloured lights to help us explain the paint colours obtained when we mix paints.
Yellow (absorbs Blue)
Green (RGB – R – B = Green)
Cyan (absorbs Red)
Magenta (absorbs Green)
Blue (RGB – R – G = Blue)
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Cyan (absorbs Red)
When we mix magenta paint with cyan paint, the cyan paint absorbs red light like a light filter. The magenta paint absorbs green light like another light filter. The blue light is the only light that is not absorbed in the cyan-magenta paint mixture. Blue light will be reflected by this cyan-magenta paint mixture. Hence, we see the resultant mixture as blue.
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Revision 5 A stage artist wants to create some lighting
(4)
Y Z White light
a) yellow light?
b) magenta light? c) cyan light?
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a) Which primary colour light is absorbed by the light filter? (1)
b) Which primary colour lights can pass through the light filter? (1)
c) Describe the colour of the light shone onto the screen. (1)
A.
Violet
Red
Green
B.
Violet
Green
C.
Red
Green
D.
Red
Violet
7 Sam has a green toy car.
Red
Violet
Green
A
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3 What are the colours in the spectrum of
white light?
(1)
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4 What are the primary colours of
white light?
84 UNIT 1C
Light
d) He adds another light filter over the torch. He wants to change light on the screen to green. Which filter should he use? Explain your answer. (2)
E
Z
(1)
passes white light through the cyan filter and beams the light onto a screen.
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(1)
6 The stage artist has a cyan light filter. He
X
(1)
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X
Glass prism
effect on the stage. Which primary colours of lights should he add or mix to obtain
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Different colours of white light travel at _____________ speeds. As the lights enter the prism, they are _____________ from the normal at __________ angles. When the lights leave the prism, they bend _____________ from the normal at different angles to produce a spectrum of colours. 2 Which of the following shows the correct spectrum of white light? (1)
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1 Fill in the blanks below:
(3)
a) Explain how our eyes see the green toy car under white light.
(2)
b) What colour will Sam’s car appear to be under
i) red light?
(1)
ii) blue light?
(1)
iii) green light? 8 Sam wants to paint his car red. He has magenta, cyan and yellow paints. What should Sam do?
(1)
(2) [24]
Chapter Summary
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White light
can undergo
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has
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Dispersion
Secondary colours
on
Primary colours
occurs when
Colours of white light enter a prism
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Red
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Green
Cyan Magenta
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Blue
Yellow
Added
Absorbed
Reflected
by
explains
explains
Non-luminous objects
23
Different speeds
A
at
can be
20
are refracted at
How we see colours of non-luminous objects
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Different angles
How we see colours emitted by a light source
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leave the prism
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Bend away from the normal at different angles form
Spectrum of white light
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Glossary D
absorption: a light filter preventing the light of certain colour(s) from passing through it aerobic: to describe a type of respiration that involves or requires oxygen to occur alimentary canal: the tube in the body through which food travels from the mouth to the anus as the food gets digested amplitude: the height of the crest of a wave or the depth of a trough from the resting position angle of incidence: the angle between the normal and the incident ray angle of reflection: the angle between the normal and the reflected ray angle of refraction: the angle between the normal and the refracted ray atoms: the smallest units of an element attraction: the pulling of unlike poles of magnets towards each other
deficiencies: lack of certain nutrients that our body needs to grow or stay alive density: the mass of matter per unit volume deoxygenated blood: blood that contains very little amount of oxygen diatomic: describing molecules that are each made up of two chemically combined atoms diet: food or substances that we consume regularly diffusion: the process in which particles or substances move from a region of higher concentration to a region of lower concentration digestion: the process in which the body breaks down food into simpler substances dispersion: the splitting of white light into its constituent colours–red, orange, green, blue, indigo and violet distillate: the liquid substance that is separated from a solution or a mixture of liquids ductility: the ability of a metal to be able to be drawn into wires
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carbohydrates: nutrients that provide our body with energy carbonates: compounds formed from reactions of carbonic acid catalysts: substances that speed up chemical reactions without undergoing changes themselves chemical bonds: attractive forces formed between atoms chemical symbols: symbols that are used to represent elements chlorides: chemical compounds formed in hydrochloric acid reactions circulation: the movement of blood around the body in blood vessels colliding: objects bumping against one another combustion: the chemical process of burning compass: an instrument with a magnetised needle that always points to the Earth’s North pole compounds: substances that are each made up of two or more elements chemically combined compressions: areas where air particles are close to one another correlation: a relationship between two variables in an experiment corrosion: the chemical process of a metal wearing down
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breathe: Take air into the lungs and expel it from the lungs
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222 Glossary
echo: a reflection of sound waves when they hit a hard and flat surface electrolysis: the process of breaking down a compound into elements through the use of electricity electromagnet: a temporary magnet in which its magnetism is induced by electricity element: matter that is made up of the same kind of atoms and cannot be broken down into simpler substances embryo: a ball of cells formed by the division of a fertilised egg cell engulf: surround and destroy enzymes: substances that speed up the chemical digestion of food in the body expiration: the process of letting air out of the lungs
F fats: nutrients that provide our body with twice as much energy as carbohydrates do fertilisation: the process that occurs when the nucleus of a sperm combines with the nucleus of an egg filtrate: the liquid substance separated and collected in a conical flask during filtration foetus: a human embryo that has developed in the uterus frequency: the number of times a repeated event takes place within a certain period of time
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magnet: an object that can attract magnetic materials magnetic field patterns: the lines that show the magnetic force(s) exerted by one or more magnets magnetic poles: the North pole and the South pole of a magnet malleability: the ability of a metal to be shaped when sufficient force is applied to it menstrual: of the discharge of blood mixture: two or more elements or compounds that are not chemically combined molecule: a group of chemically combined atoms
N
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nutrition: the act or process of eating and using the nutrients in food for living and growing
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particles: the smallest units of matter penis: a part of the male reproductive system that is outside the body Periodic Table: a table that displays all the known elements in the world peristalsis: a process of muscular contractions and relaxations that occur along the gullet or oesophagus photosynthesis: a process in which plants make food (glucose) from light, carbon dioxide and water pitch: how high or low a sound is plane mirror: a flat and smooth surface that reflects light primary colours: red, green and blue prism: a transparent object with flat and smooth surfaces proteins: nutrients that our body needs to grow and repair damaged tissues puberty: a stage in human growth where the growth occurs quickly
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law of conservation of mass: a law which states that no atoms are created or destroyed in a chemical reaction longitudinal: to describe waves that travel parallel to the directions of the vibrations
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hallucination: perceiving something that does not exist through one or more of the five senses hormones: chemical substances produced by the human body hydroxides: compounds containing a group of charged atoms that are made up of oxygen and hydrogen implantation: the attachment of an embryo to the uterus lining inspiration: the process of taking in air into the lungs
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H
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gas pressure: an effect of the total resultant force exerted by gas particles as they hit a surface gradient: the steepness of a slope in a graph
oxidation: a chemical process in which oxygen is combined with another element or compound to form a different compound oxides: the products of chemical reactions between metals or non-metals with oxygen oxygenated blood: blood that contains a lot of oxygen
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R
rarefactions: areas where air particles are further apart from one another reflection: the bouncing of light off one or more nonluminous objects and into our eyes refraction: the bending of light as it travels at different speeds across two transparent mediums of different densities repulsion: the pushing of like poles of magnets away from each other residue: the solid substance separated and collected on a filter paper during filtration respiration: the process in which energy stored in food is released rusting: the chemical process of the metal, iron, being worn down puberty: a stage in human growth where the growth occurs quickly
ovary: a part of the female reproductive system where the egg is released and female hormones are produced oviduct: a muscular tube in the female reproductive system that connects the ovary to the uterus
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salts: chemical compounds formed in reactions of dilute acids shadows: dark areas that are formed when the paths of light are blocked by opaque objects solute: a substance that dissolves in a solvent to form a solution solvent: a substance that is able to dissolve one or more substances to form a solution speed: the distance moved by an object or person per unit time sperm duct: a muscular tube that carries sperms from the testes to the urethra stunted growth: impaired growth or development sulfates: chemical compounds formed in reactions of sulfuric acid
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testis: a part of the male reproductive system where sperms and the male hormone are produced
U
A
uterus: a pear-shaped organ in the female reproductive system that has thick muscular walls
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vagina: a muscular tube that joins the cervix to the outside of the body valve: a part in a heart or most veins that ensures that blood only flows in one direction vibration: the back and forth movements of particles in a medium
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word equation: an equation that describes a chemical process or reaction
224 Glossary
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Notes
225
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Notes
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