SAMPLE CHAPTERS FOCUS ON SCIENCE GRADE 8

CONTENTS About This Book iv Introduction to Cells 1 1.1 Cells and Microscopes 2 1.2 Animal and Plant Cells 5 1.3 Unicellular and Multicellular Organisms, and Cell Specialisation 9 Recall 12 Put on your Thinking Cap 13 Project 14 Structures and Functions of the Human Body Systems 15 2.1 Food and Digestive System 16 2.2 Circulatory System 38 2.3 Respiratory System 45 2.4 Excretory System 50 Recall 53 Put on your Thinking Cap 54 Project 55 Work, Energy and Simple Machines 56 3.1 Work 57 3.2 Power 58 3.3 Sources and Forms of Energy 59 3.4 Simple Machines 73 Recall 86 Put on your Thinking Cap 87 Project 88 Vibrations, Waves and Light 89 4.1 Vibrations 90 4.2 Waves 93 4.3 Light and Optical Instruments 107 Recall 122 Put on your Thinking Cap 123 Project 124 CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 ii

Elements, Compounds and Mixtures 125 5.1 Atoms and Molecules 126 5.2 Elements 130 5.3 Compounds 138 5.4 Mixtures 143 Recall 153 Put on your Thinking Cap 154 Project 155 Acids and Alkalis 156 6.1 Acids and Alkalis 157 6.2 Neutralisation 176 Recall 181 Put on your Thinking Cap 182 Project 183 Structure of the Earth and Natural Disasters 184 7.1 Structure of Earth 185 7.2 Movement of Tectonic Plates 196 7.3 Earthquakes 202 7.4 Volcanoes 205 Recall 208 Put on your Thinking Cap 209 Project 210 CHAPTER 5 CHAPTER 6 CHAPTER 7 iii

ABOUT THIS BOOK Focus-on Science is a pedagogy-driven series developed to provide a clear and effective learning trajectory for Grade 7 to Grade 9 students. The inquiry approach used in the Textbook assists students in acquiring scientific knowledge and science process skills through a variety of activities, experiments and projects. To make learning more engaging, photographs, infographics, diagrams and examples are used to present the content. In addition, animations, videos, simulations and Augmented Reality (AR) models are included to help bring science to life. Chapter Opener A short write-up with trigger questions based on a photo, as in the chapter introduction, to pique students’ interest. Experiment Engages and helps students to develop science process skills, manipulative skills and an inquisitive attitude through well-designed laboratory experiences. Our body is made of cells. Have you ever wondered how many cells are there in our body? Are all the cells of the same shape and size? Are there any other cells besides human cells in our body? Introduction to Cells CHAPTER 1 What will you learn? Understand what cells are Know the history of microscopes Differentiate between a light microscope and an electron microscope Proper handling of a light microscope including the preparation of specimen slides Compare animal and plant cells Compare unicellular and multicellular organisms Give examples of specialised cells and their functions Problem statement How does the length of a pendulum affect the period of the pendulum? Hypothesis As the length of the pendulum increases, the period of the pendulum increases. Manipulated variable Length of pendulum Responding variable Period of pendulum Constant variable Mass of the pendulum bob Materials and apparatus Thread, pendulum bob, retort stand and clamp, stopwatch, and metre ruler Procedure 1 Prepare a pendulum with a 20 cm long thread. B A Retort stand Thread Pendulum bob Diagram (a) Diagram (b) 2 Hang the pendulum on a retort stand clamp. 3 Pull the hanging pendulum to one side and release. 4 Record the time for the pendulum to make 20 complete oscillations. Repeat this step to obtain the second and third reading. 5 Repeat steps 1 to 4 using different lengths of thread (40 cm, 60 cm, 80 cm and 100 cm) for the same pendulum Result Record your result. Length of pendulum (cm) Time taken for 20 oscillations / s Period, T(s) Reading 1 Reading 2 Reading 3 Reading 4 20 40 60 80 100 Discussion What is the relationship between the length of the pendulum and the period of the pendulum? Conclusion Can the hypothesis be accepted? Write down your conclusion. 1 Experiment Investigating the effect of the length of a swinging pendulum on its period 95 Chapter 4 Vibrations, Waves and Light What will you learn? The chapter’s learning outcomes which provide an idea of what students will learn. iv

Science Facts Provides additional information related to the topic taught in order to stimulate students’ interest in learning science. Activity Provides students with a total learning experience through learning by doing, encouraging them to reflect on the experience and think critically. 1.3 Unicellular and Multicellular Organisms, and Cell Specialisation Organisms are living things. Organisms can be divided into two groups, namely unicellular organisms and multicellular organisms. Unicellular and Multicellular Organisms Unicellular organisms are organisms that are made up of a single cell (‘uni’ means one). Most of them are invisible to the naked eye, hence, they are also called microscopic organisms. They can only be observed under the microscope. These organisms usually live in seas, rivers and lakes. They perform all the processes of life, such as respiration, response, digestion, excretion, reproduction and growth. Examples of unicellular organisms Multicellular organisms are organisms that are made up of many cells (‘multi’ means many) of different types. Each type of cell has a different structure and carries out a specific function. Like unicellular organisms, multicellular organisms perform all the processes of life. Humans, plants, animals and some fungi and algae are examples of multicellular organisms. Examples of multicellular organisms Give one similarity between unicellular and multicellular organisms. Think About It Amoeba Euglena Paramecium Chlamydomonas Bacteria viewed under microscope (Escherichia coli) Viruses are not classified as cells and therefore are neither unicellular nor multicellular organisms. They are not considered living things as they do not perform some processes of life such as breathing and growing. They infect all types of organisms, including animals and plants. Science Facts Hydra Millipede Spirogyra Mucor Cat Mushroom 9 Chapter 1 Introduction to Cells Introduction to Cells Activity 2 Observing onion cells Onion epidermis Forceps Onion epidermis Filter paper Iodine solution Mounting pin Cover slip Scalpel Scale of an onion leaf Caution Be careful when using the scalpel and forceps to avoid getting hurt. Aim: To observe onion cells Materials and apparatus: Onion, iodine solution, scalpel, glass slide, cover slip, filter paper, mounting pin, forceps and microscope Procedure: 1 Cut an onion bulb vertically and remove one of the inner scale leaves. Preparation of a slide of onion cells 2 Then, remove the inner epidermal layer from the scale leaf using a pair of forceps. 3 Spread out the epidermal layer on a drop of water in the middle of a slide. 4 Cover the specimen with a cover slip using a mounting pin. 5 Add a drop of iodine solution on one side of the slide. 6 Put a filter paper on the opposite side of the slide to draw the iodine solution over the specimen. 7 Observe the onion cells through the microscope with a low-power objective lens followed by a high-power objective lens. 8 Draw a few onion cells and label them. Observation: Draw what you observe. Discussion: 1 What is the purpose of using iodine solution? 2 What is the shape of the onion cells? Conclusion: Write down your conclusion. 6 How to Use a Light Microscope Although a microscope has several parts, its lenses are the most crucial parts. It is through the microscope’s lenses that the image of a specimen can be magnified and observed in detail. Follow the steps below to handle a microscope properly: 1. Place a microscope on a flat surface with the mirror facing a light source. 2. Select the low-power objective lens and position it above the hole of the stage. 3. Adjust the diaphragm and mirror so that there is sufficient light to view the specimen through the microscope. 4. Place the specimen slide on the stage and hold it with the clips. 5. Turn the coarse focus knob to lower the objective lens close to the specimen without touching it. 6. Look through the eyepiece. Turn the coarse focus knob anticlockwise until the object is in focus. Change to a high-power objective lens if necessary. 7. Adjust the fine focus knob until a sharp image is obtained. Eyepiece: used to look through the specimen and it magnifies the image formed by the objective lens to ten times (10×). Medium-power objective lens: magnifies the image of the specimen to 10 times. Tube: connects the eyepiece to the objective lenses. High-power objective lens: magnifies the image of the specimen to 40 times. Coarse focus knob: used to move the stage up or down in initial focusing. Low-power objective lens: magnifies the image of the specimen to 4 times. Fine focus knob: used to sharpen the focus quality of the image after it has been brought into focus with the coarse focus knob. Stage: the platform to place the slides. Clips: hold the slides in place on the stage. Mirror: reflects light towards the diaphragm. Arm and base: for holding and supporting the microscope. Condenser: focuses light from the mirror onto the specimen. Diaphragm: controls the amount of light that enters the condenser. Resource 4 Think About It Provides questions that encourage students to find the answers to support constructivist learning. Resource Helps students make learning more enjoyable and in a more engaging way via scanning QR codes to access fascinating videos, animations, simulations, AR models, etc. Resource v

THINKING CAP Put on your 1 Explain how energy is transferred and transformed when an arrow is shot using a bow? 2 What can be done to increase the mechanical advantage of an inclined plane without changing its height? Give a reason. 3 A wheel and axle system has a mechanical advantage of 3 and the radius of the axle is 15 cm. What is the radius of the wheel? 4 Why are pulleys used to lift objects during the construction of buildings? 87 Chapter 3 Work, Energy and Simple Machines 1 The building blocks of an organism which can function on their own are called . 2 A typical cell is made up of cell membrane, a nucleus and . 3 The mitochondrion is a structure in the cytoplasm that produces for the cell. 4 is a British scientist who observed a slice of cork and showed that the plant tissue were made up of tiny, room-like structures. 5 made a single-lens microscope that could magnify objects up to 250 times and he discovered bacteria. 6 In an electron microscope, a beam of electrons is used to the image of specimens. 7 The light microscope is called a microscope because it contains two types of lenses to magnify an object, namely the eyepiece and the objective lens. 8 In a light microscope, the controls the amount of light that enters the condenser. 9 In the preparation of the slide for human cheek cells, the staining agent that is used is methylene solution. 10 A plant cell has a shape due to the existence of its cell wall. 11 Unicellular organisms are organisms that are made up of cell only. 12 Multicellular organisms are organisms that are made up of cells of different types. 13 A spider is an example of a organism. 14 Euglena is an example of a organism. 15 Cells that have different shapes and structures to carry out different functions are called cells. 16 cells contract and relax to produce movements. 17 Palisade cells contain lots of chloroplasts to enable them to carry out . 18 Nerve cells, red blood cells, muscle cells and epithelial cells are examples of specialised cells in . 19 The specialised cells in plants are cells, guard cells, root hair cells, xylem cells and phloem cells. RECALL Fill in the missing words. 12 Project Making a Periscope Activity objective: To design and create a periscope Problem statement: A periscope is an optical instrument people use to look at things over walls, corners, or other obstacles from a hidden position. Submarines have periscopes so that those who are inside the submarines can see objects above the surface while still underwater. We can demonstrate how a periscope works by making our own periscope. Concept applied: Reflection of light to enhance the ability to see objects over walls, corners or other obstacles Procedure: 1 Sketch a few designs of your periscope. 2 Prepare a variety of building materials (plane mirrors, shoe box/milk cartons). 3 Choose a design. Build the model that you have sketched. 4 Test your model by holding the periscope up to your eye and looking through it. 5 Think about improvements that you can make to your model such as adjusting the position of the plane mirrors to make the image clearer to the observer. Make the necessary changes to your model and test it again. You can choose another design, if required. Solution: Design of the model of periscope and its features Presentation: Compare your own model of periscope with your friends. Share the information with the class about what you learned about the application of the concept of reflection of light. 124 Put on your Thinking Cap Challenges students with questions that promote higher-order thinking skills. Recall Assists students in recalling concepts learned and serves as a summary of key points. Project Appears at the end of each chapter that helps students develop problem-solving and critical thinking skills, and to connect what students have learned to the real world. vi

Rina is breathing in fresh air at the park. Do you know what happens to the inhaled air? Do you know what are the structures involved in breathing? Structures and Functions of the Human Body Systems CHAPTER 2 What will you learn? Understand nutrients and balanced diet List the classes of food additives, their usage and the side effects that arise from their intake Identify the structures of the human digestive system Describe the processes of food digestion, absorption of digested food and defaecation Identify the structures and organs of the circulatory system and describe their functions Know the health issues related to the circulatory system Identify the structures and organs of the respiratory system Explain breathing mechanisms Identify the structures and organs of the excretory system and explain the excretion process Health effects of smoking, alcohol consumption and drug addiction

2.1 Food and Digestive System Have you heard of the phrase “You are what you eat”? Well it is true! The food we consume daily plays an important role in our well-being. Food is the source of the nutrients we need. Nutrients Our body breaks down the food we eat into basic nutrients. The chart below shows the different types of nutrients that we can obtain from food. Types of Nutrients Carbohydrates Vitamins Fats Minerals Proteins Do you know why some people eat banana after a workout? Think About It 16

Apart from the nutrients shown, water is equally essential for our body. A combination of different nutrients is found in most types of food. However, some types of food contain more of a particular nutrient than others. Carbohydrates Carbohydrates are organic compounds that contain three elements: carbon, hydrogen and oxygen. All carbohydrates are made up of units of sugar molecules, also known as saccharides. There are two types of carbohydrates as shown in the chart below: simple carbohydrates and complex carbohydrates. Carbohydrates Simple Complex Monosaccharides • Glucose • Fructose • Galactose • Maltose • Lactose • Sucrose • Starch • Dietary fibre Disaccharides Polysaccharides Simple carbohydrates are small molecules that consist of one sugar unit (monosaccharides) such as glucose, fructose and galactose or two sugar units (disaccharides) such as sucrose, lactose and maltose. They are found in food such as fruits, table sugar and milk. Complex carbohydrates are much larger molecules that consist of thousands of sugar units bonded together. Complex carbohydrates include dietary fibre and starch. Starch is found in bread, cereal, pasta, potatoes, peas and corn. The body needs to break down starch into sugars that will then be used to provide energy. Dietary fibre is found in fruits, vegetables, nuts, beans, wholemeal bread and cereal. Consuming food rich in dietary fibre can help a person feel full and less likely to overeat because his body cannot break down most of the dietary fibre. A deficiency of dietary fibre can cause constipation, a condition that occurs when undigested food that move along the large intestine becomes hard and dry and the removal of faeces from the rectum becomes painful. Food rich in starch Food rich in dietary fibre What is the difference a person feels when he consumes wholemeal bread compared to white bread? Think About It Chapter 2 Structures and Functions of the Human Body Systems 17

The main function of carbohydrate is to provide energy so that life processes such as growth, reproduction and movement can be carried out. One gram of carbohydrate provides four calories of energy. Both simple and complex carbohydrates, except dietary fibre, are eventually converted by our body into glucose, also known as blood sugar. Glucose can be used immediately, serving as the main source of energy for cells, tissues and organs, or stored in the liver and muscles as glycogen to be used later. Simple carbohydrates provide bursts of energy as they are digested quickly. On the other hand, complex carbohydrates take longer to be digested and thus provide longer-lasting energy when compared to simple carbohydrates. Why do simple sugars found in table sugar or honey taste sweet to our tongue, but complex carbohydrates found in rice do not have a similar taste? Think About It Proteins Proteins are organic compounds. Protein molecules consist of long chains of smaller molecules called amino acids. The amino acids are composed of carbon, hydrogen, oxygen and nitrogen elements. Some amino acids contain sulphur and phosphorus elements as well. Our body needs 20 different types of amino acids to function well. These 20 types of amino acids combine in various ways to make proteins in our body. Out of the 20 types, 11 are non-essential amino acids and the other 9 are essential amino acids. Non-essential amino acids are synthesised by our body whereas essential amino acids are obtained from the food we eat. We can get proteins from many sources, including animals and plants. Proteins obtained from animal sources have all the essential amino acids whereas proteins obtained from plants only have some of the essential amino acids. The proteins we eat are digested into their basic units, which are amino acids. The main function of protein is to build and repair body tissues. Protein also supplies us with energy. One gram of protein provides four calories of energy. There are many other functions of proteins as follows. Meat, fish, cheese, eggs, milk and beans are good sources of proteins. 18

Why do babies and children need plenty of protein in their diet? Who else need plenty of protein in their diet? Give a reason. Think About It In a healthy person, protein contributes only a small amount of energy to the body. In a person whose diet does not contain enough carbohydrates and fats, the body will use amino acids to produce energy. The body cannot store protein, so once their needs are met, the excess protein consumed is usually stored as fat, while the surplus of amino acids will be converted to urea and removed from the body through the urine. Kwashiorkor is a severe protein deficiency disorder that affects mainly children in regions facing famine. Some of the symptoms of kwashiorkor are oedema (fluid retention in the belly), retarded growth and fatigue. Marasmus is a disorder caused by severe deficiency of protein and calories. It affects mainly children in regions of high poverty. Some of the symptoms of marasmus are severe weight loss and muscle wasting. If not treated properly, it can be fatal. Science Facts Bulging eyes Swollen face Thin limbs Thin upper arms Wrinkled skin Prominent ribs Protuding stomach Long and thin legs Curved legs A source of energy to our body Build new cells or replace dead cells Functions of proteins Synthesise enzymes, antibodies and hormones Required for growth Help repair worn-out or damaged cells and tissues Chapter 2 Structures and Functions of the Human Body Systems 19

Fat Fat is an organic compound that consists of carbon, hydrogen and oxygen elements. Fat is made up of glycerol and fatty acids. Fat is an energy source for our body. One gram of fat provides nine calories of energy which is two times the energy supplied by carbohydrates. Fat can come from plant or animal sources. There are three types of fat, namely saturated fat, unsaturated fat and trans fat. Most animal fat are saturated whereas most plant fat are unsaturated. Saturated fat exists in solid form whereas unsaturated fat exists in liquid form at room temperature. Trans fat is usually found in fried food. A small amount of fat is important for good health. Large amounts of fat can be harmful especially animal fat, which are saturated fat, as they can lead to obesity and problems in the circulatory system such as heart diseases. Unsaturated fat is healthier to be consumed compared to saturated fat. Therefore, it is advisable to have a diet low in saturated fat. Trans fat is the unhealthiest one among all the types of fat. Eating too much trans fat can cause weight gain, heart diseases and higher risk for type 2 diabetes. Meat Cheese Vegetable oil Avocado Nuts Animal fats are found in these food Plant fats are found in these food Butter 20

Examples of food containing saturated, unsaturated and trans fats Saturated fat Unsaturated fat Trans fat Beef Olive oil French fries Poultry Sunflower oil Cookies Butter Sesame oil Cholesterol is a fat-like substance found in the blood and it helps the body make cell membranes, hormones and vitamin D. The cholesterol in the blood comes from the food we eat and the liver. The cholesterol produced by the liver is enough to meet the daily requirement, therefore there is no need to get it from food. Cholesterol is carried in the bloodstream as lipoproteins, which is a combination of protein and fat found in the blood. There are two types of lipoproteins, namely the low-density lipoproteins (LDL) and high-density lipoproteins (HDL). When we consume a high amount of saturated fats, there will be an increase in the low-density lipoproteins (LDL), considered as the ‘bad cholesterol’. High levels of low-density lipoproteins (LDL) contribute to atherosclerosis, which is the fatty build-up in the walls of arteries making the arteries narrower, disrupting blood flow and increasing the risk for heart diseases such as heart attack and stroke. On the other hand, high-density lipoproteins (HDL), considered as the “good cholesterol” carry cholesterol from other parts of the body back to the liver to be removed from the body. A healthy level of HDL may protect a person against heart diseases. Apart from supplying energy to our body, fat plays several other roles as shown in the chart below. Functions of fat As an energy source Excess fat that is stored under the skin acts as a thermal insulator Protect internal organs such as the heart and kidneys Constituent of cell membranes and nerve cells Adds flavour to food and contribute to the sense of fullness Transports fat-soluble vitamins such as vitamin A, D, E and K to be effectively absorbed by the body Fried chicken Chapter 2 Structures and Functions of the Human Body Systems 21

Vitamins In addition to carbohydrates, proteins and fats, we need vitamins in tiny amounts for good health and growth. Vitamins are organic compounds that are absorbed directly from the food into our body with no digestion required. A lack of vitamins in our diet can lead to various deficiencies and diseases. On the other hand, vitamins must not be taken in excess because they can be toxic to the body. There are two categories of vitamins: water-soluble and fat-soluble vitamins. Water-soluble vitamins are vitamins B and C which cannot be stored in the body, thus they must be taken regularly from our diet. Fat-soluble vitamins are vitamins A, D, E and K which can be stored in the body. Green leafy vegetables Dairy products Yeast Vitamin B2 (riboflavin) Vitamin B2 releases energy from food and is required for the health of the nervous system and the heart. A deficiency of this vitamin can cause sore eyes, a swollen tongue, and skin lesions at the corners of the mouth, nose and ears. Liver Unpolished rice Nuts Vitamin B3 (niacin) Vitamin B3 releases energy from food and is required for the health of the nervous system, skin, intestines and heart. A deficiency of this vitamin can cause pellagra, a disease characterised by dermatitis, diarrhoea and dementia. Sources of Vitamin B1 , B2 , B3 and B12 Vitamin B1 releases energy from food and is required for the health of the nervous system. A deficiency of this vitamin can cause beriberi, characterised by weight loss and weakness in the limbs. Vitamin B1 (thiamine) Eggs Nuts Legumes Vitamin B12 (cobalamin) Vitamin B12 is required in the formation of red blood cells and for the health of nervous system. A deficiency of this vitamin causes anaemia, neurological disorders and weight loss. Red meat Eggs Dairy products Water-soluble vitamins 22

Vitamin A Vitamin A is for maintaining healthy skin and good eyesight. A deficiency of this vitamin causes night blindness and scaly skin. Sources of Vitamin A Carrots Green vegetables Dairy products Vitamin D Vitamin D is for the growth and development of teeth and bones. A deficiency of this vitamin causes rickets, a disease in children where their bones become soft and weak. Dairy products Eggs Sunlight Sources of Vitamin D Vitamin E Vitamin E acts as an antioxidant, helps in the formation of red blood cells, maintains the functions of reproductive system and strengthens the immune system. A deficiency of this vitamin causes anaemia and infertility. Sources of Vitamin E Nuts Green vegetables Olive oil Vitamin K Vitamin K helps in the blood clotting process. A deficiency of this vitamin causes prolonged and excessive bleeding. Sources of Vitamin K Egg yolk Milk Cabbage Fat-soluble vitamins Vitamin C Vitamin C helps to fight diseases, heals wounds, is required for the absorption of iron and maintains the health of gums and mouth. A deficiency of this vitamin can reduce the ability of the body to fight infections and may cause scurvy, a disease where the bleeding of the gum occurs. Sources of Vitamin C Citrus fruit Tomatoes Vegetables Chapter 2 Structures and Functions of the Human Body Systems 23

Minerals Minerals are non-organic substances required by our body. We need tiny amounts of minerals for proper growth and to stay healthy. The table below shows a variety of minerals, their sources, functions and symptoms of deficiencies. Mineral Sources Functions Symptoms of deficiency Calcium Milk, cheese, anchovies, green vegetables • Aids in blood-clotting • Strengthens bones and teeth • Delayed blood clotting • Rickets in children • Osteoporosis in elderly people Magnesium Green leafy vegetables, whole grains, meat • Regulates functions of muscles and nerves • Keeps the bones strong • Weak bones • Muscle weakness • Fatigue Sodium Table salt • Regulates body fluid • For the proper functioning of nerves • Muscle cramps • Fatigue Iron Green leafy vegetables, liver, meat, egg • For the formation of haemoglobin in red blood cells • Anaemia Iodine Seafood, seaweed, iodised salt, green vegetables • For the formation of hormones in the thyroid gland • Goitre (swelling of the thyroid gland) Phosphorus Milk, cheese, eggs • For the formation of healthy bones and teeth • For the contraction of muscles • Tooth decay • Weak muscles Potassium Bananas, potatoes, fish, meat, nuts • Regulates body fluid • For the proper functioning of nerves and muscles • Weak muscles • Fatigue Chlorine Table salt • Regulates body fluid • For the proper functioning of nerves • Muscle cramps • Loss of appetite Activity 1 1 Work in groups. 2 Make a poster of both the fat-soluble and water-soluble vitamins, their sources (other than the ones given above), importance and effects of deficiencies, including the factors that can cause vitamins to be destroyed. You may search on the Internet for the information. 3 Each group will then present their findings to the class. Understand vitamins 24

Water Water is essential in many life processes. Water makes up about 60% to 70% of our body mass. When proper water balance is maintained in the body, all the processes in the body can be carried out efficiently. The daily water loss through our sweat, urine, and the air we breathe out needs to be replaced. An average person needs to consume approximately six to eight glasses of water daily. Water can also be obtained from food with high water content. Water loss can affect the physiological processes and physical performance of the body. If the water that is lost is not replaced, dehydration occurs. An extreme water loss can be fatal. Examples of other sources of water apart from consuming water directly We need to consume about 2.5 litres of water daily. The functions of water Medium of transportation for respiratory gases and nutrients Medium for all cellular biochemical reactions Main component of cells and blood plasma Removes excretory waste through sweat and urine Dissolves nutrients and transports them throughout the body Enables the breakdown of food substances during digestion Regulates body temperature Functions of water Chapter 2 Structures and Functions of the Human Body Systems 25

A Balanced Diet A balanced diet fulfils all the nutritional and energy needs of the body. It consists of carbohydrates, fat, proteins, vitamins, minerals and water in the correct quantities and proportion. A balanced diet for a person varies based on his lifestyle, health conditions and specific nutritional requirements. In the latest recommendation by the USDA (United States Department of Agriculture) of the balanced meal known as the MyPlate guide, vegetables and fruit must form about half of the food plate serving since they are the healthiest food. The remaining food plate serving should contain proteins and grains accompanied by a small serving of dairy product with low-fat content. A person can be healthy and energised by eating the right food in the right amount. A balanced diet is required for the healthy growth and development of the body. Each food group plays a role, for example, carbohydrates and fat are sources of energy, proteins repair and build new tissues for growth, vitamins and minerals keep us healthy and dietary fibre prevents constipation. However, if a person overeats, the extra energy is stored as a layer of fat. Too much fat may lead to health problems such as heart diseases and diabetes. On the other hand, if a person eats less than what is required, he may suffer from malnutrition. Malnutrition can weaken the immune system, making the person susceptible to diseases. Therefore, by following the minimum daily energy requirements, health issues related to overeating and malnourishment can be prevented. Protein Grains Vegetables Fruits Dairy Nutrition Facts Label A nutrition facts label on packaged food product lists the types of nutrients found in the product, the serving size, and the calories per serving of the food product. This enables consumers to make the best decision on how much to eat, or how they can better balance their food choices throughout the day. They can choose food that are high in nutrients they need more of, such as protein and low in nutrients they need less of, such as fat. The value of energy on labels shows how much energy the food contains. It does not measure how much energy a person gets from it. This is because certain foods use a lot more energy to digest than others. Number of servings in the whole container (If everything in the container is eaten, you have consumed 6 times the amount of calories and nutrient values shown on the label) Calories per serving (Number of calories or the amount of energy one serving of the product contains) Size of one serving of this product (All of the nutrition information on the label is based on one serving of the product) Percent daily value (The intake of each nutrient per serving that contributes to a total daily 2000 calories diet of an average person - this enables consumers to estimate how much they need daily) MyPlate, the plate guide illustrating recommended proportions of food groups to be consumed in each meal. 26

Activity 2 1 Work in groups. 2 Each group must obtain two nutrition facts labels of the same type of food product but from different brands. 3 Compare the information on both labels. 4 As a consumer, determine which product you should choose by asking yourself these questions: • Which one has more nutritional values? • Which one is healthier to be consumed? 5 Present your findings to the class. Understand food labels Energy Content of Food All of us need energy to move around, grow and build new tissue and repair damaged tissue. Food is the source of energy for our body. In a calorimeter, a food sample is burned inside a closed, insulated container. As heat energy is released from the combustion, the temperature of the surrounding water rises. The equation to calculate the energy value of a food sample by using a calorimeter is as follows: Energy value of food (kJ g–1) = Water mass (g) × 4.2 J g–1 ºC–1 × Increase in water temperature (ºC) Food sample mass (g) × 1000 The amount of energy in a food can be determined by burning a sample of food in a calorimeter and measuring the amount of heat released. The amount of heat produced from the complete combustion of one gram of food is known as the energy value of the food. It is measured in kilojoules per gram (kJ g–1). The energy value can also be measured in calories. 1 kilojoule = 1000 joules 1 calorie (cal) = 4.2 joules 1 calorie or 4.2 joules is defined as the quantity of heat energy needed to raise the temperature of 1 gram of water by 1 degree Celsius at a pressure of 1 standard atmosphere. Food sample Water Ignition wires Thermometer Insulated container 70 60 50 40 30 20 10 80 90 100 Stirrer Chapter 2 Structures and Functions of the Human Body Systems 27

Example 1 A chicken burger contains 40 g of carbohydrate, 23 g of fat and 28 g of protein. Calculate the total energy, in kcal. Solution: Amount of energy from 40 g carbohydrate = 40 g × 4 kcal/g = 160 kcal Amount of energy from 23 g fat = 23 g × 9 kcal/g = 207 kcal Amount of energy from 28 g protein = 28 g × 4 kcal/g = 112 kcal Total amount of energy from the chicken burger = (160 + 207 + 112) kcal = 479 kcal Our body uses energy from food to perform daily activities such as walking, breathing and working. We need different amounts of energy from the food we consume, at various stages of our lives. The average amount of calories a person needs is about 2000 calories per day to maintain his current weight. However, the daily energy requirement or calory intake varies with individuals based on several factors such as work, size or body weight, condition or state of health, climate, age, gender and physical activity of a person. Factors that affect our daily energy requirement A person who does heavy work needs more energy than a person who has a sedentary job. For example, labourers, fishermen and construction workers need more energy compared to clerks and graphic designers. The quantity of energy in 1 g of each nutrient differs. Although the energy value of carbohydrates is not the highest, our body uses carbohydrates as a source of energy first and only when carbohydrates are used up will fat be used. The table shows the energy value of the three main classes of food. Food class Energy value (kJ /g) (kcal / g) Fat 37 9 Protein 17 4 Carbohydrate 17 4 A small-sized individual has a larger surface area per unit volume than a big-sized individual. The rate of heat loss in small-sized individuals is higher, thus they need more energy than big-sized individuals. Pregnant women require a lot of energy for the growing foetus and lactating women also need extra energy to produce milk for their baby. A person who is sick requires a lot of energy to recover from his illness. Work Size or body weight Condition or state of health 28

Consuming Healthy Meals Food contains the nutrients our body needs to build new cells and tissue as well as to repair damaged cells and tissue. Food provides us the substances needed to maintain good health and prevent diseases. Food provides us the energy to do work and carry out life processes. Although we love having a tasty meal, we must also consider its nutritional value. By neglecting the nutritional value of the food we consume daily, we are risking our overall health in the long run. Healthy meals consist of fruit and vegetables, whole grains, lean protein and nuts. These food are rich in nutrients and have a beneficial effect on our health. On the other hand, unhealthy meals such as fast food and snacks, have less nutritional value and are high in fat, salt and sugar. We should avoid or take unhealthy food in small amounts. People living in cold climate countries require more energy to maintain their body temperature compared to those living in hot climate countries. Climate Children and teenagers require more energy compared to adults. This is due to their higher metabolic rate as they are more active and are undergoing rapid growth. Age A male adult requires more energy than a female adult of the same age and body size. This is because the metabolic rate is higher in a male than a female. Gender Physical Athletes need extra calories for both their physical activities and their growth. activity Fruit salad Nasi pecel Gado-gado Healthy meals Fast food Instant noodle Sweet food Unhealthy meals For each food shown on the left, give a reason why it is considered healthy or unhealthy. Think About It Chapter 2 Structures and Functions of the Human Body Systems 29

Food Additives Food additives, which can be natural or synthetic, are substances added to food during food processing, packing or storing for specific purposes. Examples of food containing food additives are cakes, biscuits, ice cream, sweets, fizzy drinks, sausages and jelly. Here are the reasons why food additives are used. There are two main groups of additives: natural food additives and synthetic food additives. Synthetic food additives are synthetised in laboratories or industries from chemical substances. They are much cheaper to be produced on a large scale. They can withstand the heat involved in food processing. Purposes of using food additives Enable food to last longer by preventing growth of harmful microbes Maintain or improve quality of food texture Restore nutrients or colours of food that have been destroyed Change the appearance of food to make it more appealing Cater to the diet needs of specific consumers Some examples of natural food additives Turmeric Pandan leaves Palm sugar Table salt Garlic Lime leaves Synthetic food colourings are commonly used in the making of cakes, desserts and pastries commercially to make it look attractive to consumers. Natural food additives are substances that exist naturally in plants, animals or minerals and extracted to be used in another food product without any chemical reactions involved. There are not many choices of natural food additives and some are expensive. Therefore, a lot of food additives are synthetically manufactured. 30

Food additives are classified according to their usage: preservatives, colourings, sweeteners, flavourings, essence and antioxidants. Food additives Functions Examples of natural and synthetic food additives and food containing the additives Preservatives • Reduce food spoilage • Prevent growth of microorganisms to prolong the storage and shelf life of food Natural: • Salt (vegetables and seafood) • Sugar (fruit) Synthetic: • Vinegar (pickled food) • Boric acid (noodle) • Benzoic acid (ketchup) • Sodium nitrite (processed meat) • Propanoic acid (bread and cheese) Colourings • Add colours to food to make it more attractive Natural: • Pandan leaf, turmeric, carrot, caramel (kueh, drinks, candies, turmeric rice, ice cream) Synthetic: • Sunset yellow (reddish-yellow colouring in beverages, cereals and snack food) • Tartrazine (lemon yellow colouring in soft drinks, pastries and cotton candy) • Brilliant blue (blue colouring in icing and ice cream) • Erythrosine (red colouring in dried fruits, sauces and juices) Sweeteners • Add sweetness • Replace sugar (synthetic sweeteners) Natural: • Cane sugar, honey, palm sugar (beverages and biscuits) Synthetic: • Aspartame (beverages and jams) • Sorbitol (used in food for diabetic patients) • Saccharin (fruit juices, jellies and jams) Flavourings • Improve the taste of food • Enhance the flavour of food Natural: • Sugar, vanilla, salt (cakes and ice cream) Synthetic: • Monosodium glutamate/MSG (Instant noodle and processed meat) Essence • Make the food smell nice • Give fruity odours (synthetic essence) Natural: • Lime leaves (tom yam and laksa) • Vanilla (cakes and biscuits) • Pandan leaves (jellies and coconut milk rice) Synthetic: • Methyl butanoate (apple odour) • Ethyl butanoate (pineapple odour) • Amyl acetate (banana odour) Antioxidants • Inhibit the oxidation of fatty food • Prevent fruit and vegetables from turning brown Natural: • Tocopherol (margarine and mayonnaise) Synthetic: • Butylated hydroxyanisole (butter, cereals and snack food) Chapter 2 Structures and Functions of the Human Body Systems 31

Common side effects due to intake of food additives Monosodium glutamate (MSG) may cause dizziness and difficulty in breathing. Saccharin may cause allergic reactions such as itchiness. Synthetic colourings may cause hyperactivity. Nitrite salts can cause cancer, allergies, rapid breathing, seizures and hyperactivity. Benzoic acid may cause allergy and hyperactivity in children. Excessive consumption of food additives found in processed foods, for a prolong period of time can be detrimental to our health. These food additives also have lesser nutritional value. The chart below shows the common side effects that arise due to the intake of several food additives. Activity 3 Ingredients: Chicken Meat, Modified Tapioca Starch, Soya Protein, Spices, Salt and Sugar. Contains Food Conditioner, MSG as a Flavour Enhancer and Permitted Colouring. Ingredients: Water, Sugar, Seaweed Extract, Citric Acid, Permitted Flavour (Apple, Orange, Strawberry, Pineapple) Potassium Citrate, Potassium Sorbate, Sucralose and Colouring. 1 Work in groups. 2 Get three food labels of any type of packaged food similar to the examples shown above. 3 Study the information on the ingredients in the food products as shown above. 4 Identify all the synthetic food additives and find out their functions. 5 Paste them on a manila card and highlight all the synthetic food additives with their functions stated. 6 Present your findings to the class. Understand food additives Table salt (sodium chloride) is one of the most widely used natural food additives since ancient times. It is also used as preservatives in salted fish, meat and vegetables to make them last longer. How does salt preserve food? Think About It 32

The Digestive System Do you know how the nutrients from the food we consume are absorbed by our cells? This is made possible by our digestive system through the process of food digestion. Food digestion is the breakdown of food that are large, complex and insoluble into smaller, simple and soluble molecules that can be absorbed into the bloodstream and transported to different parts of the body. There are two types of digestion: physical digestion and chemical digestion. Both the processes involve the breakdown of food and occur in the digestive tract, also known as the alimentary canal. Food digestion starts in the mouth with the aid of the teeth, saliva and tongue. The Parts of the Digestive System Food digestion takes place in the alimentary canal that extends from the mouth to the anus. The alimentary canal is long and muscular. It consists of the mouth, oesophagus, stomach, small intestine (duodenum, jejunum and ileum), large intestine (appendix, caecum, colon, rectum) and anus. The total length of the alimentary canal is around 9 metres, and it is open at both ends, at one end is the mouth and at the other is the anus. The small intestine makes up two thirds of the total length of the alimentary canal. There are also other organs in the digestive system which are the liver, gallbladder and pancreas. Each part of the digestive system has its own specialised function. Types of Digestion Physical Digestion Breakdown of large pieces of food into smaller pieces by the grinding action of teeth with the aid of tongue and saliva (chewing) Wave-like contraction and relaxation (peristalsis) by the muscles in the walls of the oesophagus and the whole length of the digestive tract, pushes the food down the tract Squeezing and mixing of food by the muscles of the stomach lining (churning) Contraction and relaxation of segments of muscles in the small intestine (segmentation) • Occurs in the mouth, stomach and small intestine • Breakdown of complex food molecules into simple molecules with the aid of the enzymes • Does not involve peristalsis Chemical Digestion 1 2 3 4 Involves • Occurs in the mouth, oesophagus, stomach and small intestine • Does not involve any enzymes • Involves peristalsis Chapter 2 Structures and Functions of the Human Body Systems 33

The epiglottis plays an important role in both the digestive system and the respiratory system. What do you think happens if there is no epiglottis? Think About It Human digestive system Peristalsis, the wave-like pattern produced by the contraction and relaxation of muscles along the alimentary canal. Digestion in the Mouth The digestive process begins in the mouth. The chewing action of teeth cuts the food into smaller pieces to increase the surface area of the food for the digestive enzymes to act on. The presence of food stimulates the salivary glands in the mouth to secrete saliva. Saliva contains the digestive enzyme, salivary amylase, which breaks down starch into maltose. Starch + Water Maltose Salivary amylase The tongue then rolls the partially digested food into a small ball called bolus with the help of the saliva and pushes it into the oesophagus. The oesophagus is a long, narrow tube with strong muscles in its walls. The bolus is then pushed through the oesophagus into the stomach by peristalsis. Peristalsis is the rhythmic contraction and relaxation of muscles which pushes food along the alimentary canal. Oesophagus Salivary gland Stomach Pancreas Small intestine Rectum Anus Mouth Tongue Epiglottis Liver Gall bladder Large intestine Appendix Pharynx Resource Contracted muscle Relaxed muscle Bolus of food 34

Digestion in the Stomach The stomach is a sac-like muscular organ at the end of the oesophagus. The glands in the stomach wall secrete a liquid called gastric juice. Gastric juice consists of hydrochloric acid, mucus, and the digestive enzyme, pepsin. • Hydrochloric acid kills bacteria in the food that enters the stomach, creating an acidic environment for the enzyme, pepsin, and stopping the action of the salivary amylase. • Mucus protects the stomach wall from the hydrochloric acid and digestive enzymes. • Pepsin breaks down protein into polypeptides. Activity 4 Analyse the action of enzyme Aim: To study the action of the enzyme in saliva on starch. Materials and apparatus: 1% starch suspension, iodine solution, Benedict’s solution, Bunsen burner, glass rod, wire gauze, 250 ml beaker, boiling tubes, boiling tube holder, stopwatch, dropper, tripod stand, retort stand with clamp, thermometer Procedure: 1 Add 10 ml of starch suspension into two boiling tubes, J and K. 2 Rinse your mouth and collect some saliva. 3 Add 4 ml of saliva into boiling tube K. Stir with a glass rod. 4 Test the solutions in both the boiling tubes for simple sugar and starch immediately. Test for simple sugar: Take 2 ml of solution from each boiling tube and place them into different boiling tubes. Add a few drops of blue Benedict’s solution to each boiling tube and heat the tubes in a boiling water bath for a few minutes. Record the colour of the contents. If the solution contains sugar, it will change from blue to a red brick colour. Test for starch: Take 2 ml of solution from each boiling tube and place them into different boiling tubes. Add a few drops of iodine solution and record the colour of the contents. If the solution contains starch, iodine solution changes colour from yellow to blue-black. 5 Then, put both boiling tubes in a water bath at 37ºC and leave them for 10 minutes. Test the solutions in both the boiling tubes for simple sugar and starch. Observation: Record your observations. Boiling tube Beginning of activity End of activity Starch Sugar Starch Sugar J K Discussion: 1 The water bath must be maintained at 37ºC. Give a reason why. 2 What happens to the starch in boiling tube K at the end of the activity? Explain. Protein + Water Polypeptides Pepsin Chapter 2 Structures and Functions of the Human Body Systems 35

The stomach stores food for about three to four hours, enabling the food to mix with the gastric juice. From the stomach, the partly digested, semi-liquid mass called chyme moves into the small intestine when the sphincter muscle relaxes. Sphincter muscles are found at the connection between stomach and small intestine. Sphincter muscles control the flow of food out of the stomach and allow only small amount of food into the duodenum (first part of the small intestine) at one time. Digestion in the Small Intestine The small intestine consists of the duodenum, jejunum and ileum. Duodenum receives • chyme from the stomach • bile produced by the liver • pancreatic juice secreted by the pancreas. The liver produces a greenish liquid called bile and stores it in the gall bladder. Bile flows into the duodenum through the bile duct. Bile emulsifies fat into small droplets and creates an alkaline condition for the pancreatic enzymes to work. The pancreas secretes pancreatic juice into the duodenum through the pancreatic duct. The pancreatic juice contains digestive enzymes such as trypsin, lipase and pancreatic amylase. Unlike pepsin, these enzymes require an alkaline environment to function. • Trypsin further breaks down polypeptides into peptides. Polypeptides + Water Peptides Trypsin • Lipase breaks down fat molecules into fatty acids and glycerol. Fat + Water Fatty acids and glycerol Lipase • Pancreatic amylase breaks down starch into maltose. Starch + Water Maltose Pancreatic amylase Stomach Sphincter muscles Pancreas Liver Gall bladder Bile duct Duodenum Jejunum Ileum Resource 36

Digestion ends in the small intestine with fatty acids, glycerol, amino acids and glucose as the final products. Absorption of Digested Food in the Small Intestine The jejunum and ileum are adapted to enable simple molecules produced from the digested food to diffuse through its wall. The final breakdown of food occurs in the ileum. The glands on the ileum wall secretes intestinal juice which consists of the enzymes maltase, sucrase, lactase, erepsin and lipase. • Maltase breaks down maltose into glucose. Maltose + Water Glucose Maltase • Sucrase breaks down sucrose into glucose and fructose Sucrose + Water Glucose + Fructose Sucrase • Lactase breaks down lactose into glucose and galactose. Lactose + Water Glucose + Galactose Lactase • Erepsin breaks down peptides into amino acids. Peptides + Water Amino acids Erepsin • Lipase breaks down fat into fatty acids and glycerol. Fat + Water Fatty acids + Glycerol Lipase Digestion of carbohydrate Digestion of proteins Digestion of fat When nutrients enter the blood, they are carried away to the liver and then throughout the body. Nutrients travel through the bloodstream to feed all the cells in the body. There are some substances that cannot be absorbed by the villi. Thus, they are left in the small intestine. • The small intestine is long, enabling greater absorption of nutrients. • Their internal layer is highly folded and covered with many finger-like projections called villi. Villi play a major role in the absorption of digested food. • The villi wall is one-cell thick, which helps speed up nutrient absorption. • Each villus has many specialised epithelial cells with tiny projections called microvilli to increase the surface area for nutrient absorption. • The villi have a network of blood capillaries that ensures glucose, amino acids and water-soluble vitamins are absorbed easily. • Each villus contains a structure called lacteal to absorb fatty acids, glycerol and fat-soluble vitamins. Lumen of small intestine Folds of small intestine Microvilli Small intestine Villus Epithelial cells with microvilli Chapter 2 Structures and Functions of the Human Body Systems 37

Defaecation The digested food and most of the water we drink are absorbed into the body in the small intestine. The remaining food that cannot be digested, dead cells, fibre and water enter the large intestine. In the large intestine, some of the water is reabsorbed. The remaining semi-solid waste is called faeces. It moves slowly with the help of the peristaltic action. It takes between 12 to 24 hours to reach the rectum. When the faeces accumulates in the rectum, it puts pressure to the rectum and triggers the urge to expel the faeces out of the body. The rectum muscles will contract to pass the faeces out of the body from the anus. This process is called defaecation. The absorption of water from the large intestine into the blood The circulatory system The waste from a meal you consume should be expelled from your body within about 24 hours if your gut is working well. In people who suffer from constipation, the waste will remain in the large intestine for quite some time and almost all of the water will be removed. This causes the faeces to become dry and hard. The best way to relieve constipation is to add more fibre to the diet. 2.2 Circulatory System Our body has a system to transport materials to and from the cells. Nutrients and oxygen need to be transported to cells whereas carbon dioxide and waste need to be removed from the cells. The circulatory system transports useful materials to where they are needed, and waste materials to where they are to be removed. The main components of the circulatory system are the heart, blood vessels and blood. • Blood is the circulating fluid, and it transports both useful materials and waste materials. • The heart is the pumping device which pushes the blood around the body via muscular contractions. • The blood vessels which consist of arteries, veins and capillaries transport materials to the tissues and back to the heart. • Some of the blood vessels have valves to prevent backflow ensuring the blood flows in one direction only. The circulatory system is a closed system since the blood flows in blood vessels that are connected to one another. Heart Blood in the blood vessels Large intestine Small intestine Rectum Anus 38

Blood Blood is a body fluid in the circulatory system. Blood transports oxygen, water, and nutrients to the cells where they are needed. It transports waste materials such as carbon dioxide away from the cells to prevent build-up and problems arising from it. The chemical messengers or hormones produced in the body also circulate through the blood. They control and regulate growth, reproduction and many other processes in the body. The human blood consists of 55% plasma and 45% blood cells. In one drop of blood, there are millions of blood cells, namely red blood cells, white blood cells and platelets suspended in a pale yellowish liquid called the plasma. The plasma is made up of 90% water and 10% soluble substances such as hormones, mineral salts, glucose, acid amino and waste materials. The plasma leaks out through the capillary walls to fill the space between the cells close to the capillaries. This enables substances to be transported between the blood and the cells. Red blood cells • Red blood cells, also known as erythrocytes, carry oxygen around the body. • The cells are biconcave (both sides of the surfaces curve inwards), which provides a larger surface area to help in the transportation of oxygen. • They contain oxygen-carrying pigment called haemoglobin. Platelets • Platelets help clot blood at an injured site. • Platelets do not transport substances. White blood cells • White blood cells are bigger than red blood cells. • White blood cells come in different sizes and shapes. • They help defend the body from infections. They attack and destroy germs that cause diseases. Blood cells seen under the microscope Plasma (55%) Red blood cells (41%) White blood cells and platelets (4%) Chapter 2 Chapter 2 Structures and Functions of the Human Body Systems Structures and Functions of the Human Body Systems 39

Blood Vessels There are three types of blood vessels: arteries, veins and capillaries. Venule Valve Arteriole Arteries • Arteries are blood vessels that carry blood away from the heart to the rest of the body. • Arteries have thicker and strong walls compared to veins due to the higher blood pressure of blood flow. Capillaries • Capillaries are a network of tiny blood vessels that connects arteries to veins. • They have very thin walls to enable substances to get in or out of the capillaries easily. Veins • Veins are blood vessels that carry blood back to the heart. • They have thinner walls compared to arteries due to the lower blood pressure in the veins. • They have valves to prevent any backflow of the blood so that blood flows in one direction only. Why do arteries not have valves? Think About It Artery Vein Capillary As you can see in the diagram below, capillaries close to the cells allow substances to move in and out of the cells easily. Blood Body cells Blood out Venule Carbon dioxide and other waste products move into the blood Oxygen and nutrients move into the body cells Blood in Arteriole Capillary Exchange of materials in capillaries Blood flows slowly in the capillaries. Oxygen and nutrients in the blood move through the capillary walls into the body cells that need them. At the same time, carbon dioxide and other waste products that are not needed by the cells move out from the cells into the blood through the capillary walls. Substances usually move from the place where their concentration is higher to places where their concentration is lower. 40

The differences between the artery, vein and capillary are given in the table below. Artery Vein Capillary Diagram Smaller lumen Thick layer of muscles and elastic fibres Larger lumen Thin layer of muscles and elastic fibres Very small lumen One layer of cells Wall Thick, muscular and elastic wall Thin, less muscular and less elastic wall Very thin walls, one cell thick Valve Absent (except in the pulmonary artery) Present Absent Lumen Small Large Very small Colour Red Bluish-red Bluish-red Blood content Oxygenated blood (except in the pulmonary artery) Deoxygenated blood (except in the pulmonary vein) Oxygenated blood at the arteriole ends and deoxygenated blood at the venule ends Heart The heart is the size of a clenched fist and lies in the chest between the two lungs, towards the left side. The heart is a muscular organ with its walls made of cardiac muscles. The heart receives its own blood supply. Coronary arteries provide nutrients and oxygen to the heart muscles while the coronary veins remove wastes from the heart muscles. The heart has four chambers. The two upper chambers are called auricles or atria (singular: atrium) and the two lower chambers are called ventricles. The right and left atria receive blood returning to the heart. The left and right ventricles pump blood out of the heart. The septum divides the right and left sides of the heart. The left ventricle has a much thicker muscular wall than the right ventricle. This is because the right ventricle pumps blood to the lungs situated next to the heart whereas the left ventricle must pump blood from the heart to the whole body. The walls of the atria are thinner than the walls of the ventricles. Coronary arteries Chapter 2 Structures and Functions of the Human Body Systems 41

When the atria contract, blood is pushed into the ventricles. There are three valves in the heart: tricuspid, bicuspid and semilunar valves. The tricuspid valve connects the right atrium to the right ventricle. The bicuspid (or mitral valve) connects the left atrium to the left ventricle. Semilunar valves are located at the entrances of the aorta and the pulmonary artery to prevent the backflow of blood into the ventricles. All the valves prevent backflow of blood to ensure the blood flows the right way around the heart. The right-hand side of the heart receives blood low in oxygen and rich in carbon dioxide from around the body and pumps it into the lungs. This blood is called the deoxygenated blood. The left-hand side of the heart receives blood rich in oxygen from the lungs and pumps it around the body. This blood is called the oxygenated blood. Stethoscope is a device used by doctors to listen to the sound of the heartbeat. Before the invention of stethoscope, doctors had to place their ear directly onto a patient’s chest to listen to their heartbeat. Science Facts 1 Deoxygenated blood from the body (head and lower body) enters the right atrium through the superior and inferior venae cavae whereas oxygenated blood from the lungs enter the left atrium through the pulmonary veins. 2 Both the right and left atria contract and pump blood into the ventricles. Both the tricuspid and biscuspid valves close to prevent backflow of blood into the atria. 3 Both the right and left ventricles contract forcing the semilunar valves to open. 4 The left ventricle will pump oxygenated blood into the aorta and the rest of the body. The right ventricle will pump deoxygenated blood into the pulmonary artery and the lungs. The flow of blood in the heart Key: Deoxygenated blood Oxygenated blood Septum Bicuspid valve Pulmonary veins From lungs Pulmonary artery To lungs Aorta To head and body 2 From head and body Superior vena cava Semilunar valves Tricuspid valve Inferior vena cava From trunk and legs 1 1 1 4 4 3 2 2 3 Right atrium Right ventricle Left ventricle Left atrium Resource 42

The human circulatory system is known as a double circulatory system. This is because it has two separate circuits and blood passes through the heart twice. In one complete circulation, the heart pumps the blood twice - once to the lungs, known as the pulmonary circulation and once to the body, known as the systemic circulation. Pulmonary circulation • Deoxygenated blood in the right ventricle is pumped into the lungs through the pulmonary artery. This blood has a greater concentration of carbon dioxide than oxygen. • In the lungs, gas exchange occurs. Carbon dioxide molecules diffuse out into the lungs, while oxygen molecules diffuse from the lungs into the blood. The blood is now oxygenated. A Systemic circulation • Oxygenated blood from the lungs returns to the left atrium through the pulmonary vein. • The left ventricle will pump this blood into the aorta to be distributed to all parts of the body (except the lungs). In the tissues and organs, gas exchange occurs. The blood is now deoxygenated. • The deoxygenated blood then returns to the right atrium through the veins. B A double circulatory system makes sure that the cells of the body receive blood which is rich in oxygen. This system makes sure that our blood becomes fully oxygenated in the lungs before it is transported to the rest of the body. Every time our heart pumps or beats, a ‘lup-dup’ sound is heard. It is the sound of the heart valves closing. The heartbeat is called the pulse. The heart rate or pulse rate is the number of heartbeats per minute. A healthy adult normally has a resting heart rate of about 60 to 100 beats per minute. Activity 5 Determining the heart rate per minute at rest and after exercising Procedure: 1 By referring to the diagram on the right, use your index and third fingers of one hand to press lightly on the opposite wrist, just below the base of the thumb. 2 You will be able to feel the pulse in your radial artery between your wrist bone and the tendon on the thumb side of your wrist. 3 Count the number of beats in 15 seconds. Right atrium B A Pulmonary vein Left atrium Left ventricle Aorta Pulmonary artery Right ventricle Venae cavae Chapter 2 Structures and Functions of the Human Body Systems 43

4 Multiply the value by four and that is your heart rate per minute. 5 Now, run around the school field once and repeat steps 1− 4. 6 Sit still for 10 minutes, then repeat steps 1− 4. Observation: Record the heart rate per minute before exercising, immediately after exercising and after resting for a while. Discussion: Does the heart rate decrease or increase after exercising? Give a reason. Conclusion: Write down your conclusion. Blood pressure is the pressure exerted by the blood when it flows inside the blood vessels. When a doctor checks your blood pressure, it is the blood pressure in arteries that is measured. A healthy adult will have a blood pressure reading of around 120/80 mm Hg. Science Facts Health Issues Related to the Circulatory System We need to ensure that our circulatory system is healthy because it plays a major role in bringing nutrients and oxygen to all the cells in our body. Blood needs to flow freely through our arteries. 40 60 80 100 120 0 5 Time (min) Healthy Heart 10 Heart rate (bpm) 40 60 80 100 120 0 5 Time (min) Unhealthy Heart 10 Heart rate (bpm) An example of graphs showing the heart rate (beats per minute) of a healthy individual compared to that of an unhealthy individual. Cardiovascular diseases are diseases related to the heart and blood vessels such as atherosclerosis, hypertension, heart attack (myocardial infarction) and stroke. Your pulse is taken from an artery that passes close to your skin. You cannot take your pulse by pressing your fingers against a vein. Give a reason. Think About It Atherosclerosis is the build-up of plaque inside the arteries. Plaque is formed from cholesterol, dead tissues and other substances. Factors that contribute to plaque build-up include a high-fat diet, high cholesterol, smoking, obesity and diabetes. As plaque builds up, it narrows the arteries and disrupts blood flow. Atherosclerosis becomes a threat to health when the plaque build-up prevents blood circulation in the heart or the brain. Atherosclerosis Blood flow is restricted Plaque formed in the artery 44

High blood pressure, or hypertension, is a condition when the blood pressure of a person is higher than normal. The higher the blood pressure levels of a person, the higher the risk for other health problems, such as heart disease, heart attack, and stroke and can be fatal if left untreated. Hypertension can often be controlled with some lifestyle changes or medication. Hypertension When the coronary arteries of the heart become narrower, the blood flow through them is restricted. This means that insufficient food and oxygen reach the muscles of the heart, causing angina (severe chest pain). A completely clogged blood vessel in the heart can cause a heart attack (myocardial infarction). Heart attack A stroke occurs when a blood vessel in the brain ruptures or when there is a blockage in the blood supply to the brain. Oxygen does not reach the brain cells and the brain cells die. The functions controlled by that part of the brain will be affected. Some of the symptoms of a stroke are slurred speech and numbness in the face, arm and leg, especially on one side of the body. Risk factors for stroke include old age, high blood pressure, diabetes, high cholesterol and smoking. The best way to lower the risk of stroke is to have blood pressure in the normal range. Stroke 2.3 Respiratory System Our respiratory system enables gas exchange between the blood in our body and the environment. Breathing is the external respiration process where air moves into and out of the lungs, the organ in which gas exchange takes place between the atmosphere and the body. Breathing involves inhalation and exhalation. When we inhale, we take in air or more specifically oxygen which is used by the body cells. When we exhale, we let the air out to get rid of the carbon dioxide in it. Chapter 2 Structures and Functions of the Human Body Systems 45

Structure of the Respiratory System When we breathe in, air enters the respiratory system through the nasal cavity in the nose. The inside of your nose is warm, wet and hairy. As it passes the nasal cavity, air is warmed and moistened whereas the dust gets trapped in the hair. After the air leaves the nasal cavity, it goes down the trachea, also known as the windpipe. The wall of the trachea contains C-shaped rings of cartilage which support and prevent the trachea from collapsing during inhalation. The trachea is also lined with cilia (tiny hairs) which remove dust, dirt and bacteria from the air. In the chest, the trachea branches into two bronchi (singular: bronchus) with each entering the right and left lungs respectively. The lungs are in a space called the thoracic cavity. The lungs are protected inside the ribcage that consists of the ribs and intercostal muscles. Thoracic cavity is separated from the abdominal cavity by a muscular sheet known as the diaphragm. Each bronchus splits into smaller tubes called bronchioles. The bronchioles end in tiny air sacs called alveoli (singular: alveolus). The alveolus is the site of gas exchange where oxygen comes into the blood and carbon dioxide is removed from the blood. When you breathe out, the air leaves the body through the nose and also through the mouth when you speak. Activity 6 Counting our breaths 1 Count how many breaths you take in a minute by using a stopwatch. Repeat this three times. Breathing in and out again counts as one breath. 2 Find the average number of breaths you take in one minute. 3 Repeat steps 1 to 2 but this time walk around the classroom for a few minutes before counting your breaths. 4 Make a comparison and explain the difference between the breathing rate of when you are at rest and after exercising. Resource Bronchiole Intercostal muscles Larynx Nasal cavity Nostril Pharynx Epiglottis Trachea Right lung Diaphragm Left lung Alveolus Bronchus 46

The amount of oxygen a person requires varies with his activity. When a person breathes more deeply, a bigger volume of air goes into the lungs. When a person takes shallow breaths more quickly, the lungs will be filled and emptied more often. Adaptation of the Alveoli for Efficient Gas Exchange There are millions of alveoli in the lungs that make it look like a sponge. The alveoli are adapted to make gas exchange in the lungs occur easily and efficiently. The adaptations are as shown in the chart below. Inhaled air Alveolus wall Alveolus Exhaled air Deoxygenated blood Capillary Red blood cell Oxygenated blood Oxygen Carbon dioxide A network of blood capillaries surrounds the alveolus to speed up the gas exchange to and from the alveolus. The inner surface of the alveolus which is moist enables oxygen to dissolve in the moisture before being transported through its wall. The alveolus wall is one-cell thick allowing the air and the blood to be close enough to one another for efficient gas exchange. There are millions of alveoli which gives a greater surface area for gas exchange. Mechanism of Breathing In and Out The breathing mechanism consists of inhalation and exhalation. The taking in of air is called inhalation. The letting out of air is called exhalation. There are two sets of muscles that aid in breathing: the external and internal intercostal muscles between the ribs and the diaphragm under the lungs. 1 External intercostal muscles contract and pull the rib cage upwards and outwards 2 Diaphragm muscles contract and flatten 3 Volume of thoracic cavity increases causing air pressure in the lungs to decrease 4 The higher air pressure outside forces air to enter the lungs Rib cage Air enters Thoracic cavity Diaphragm 1 4 3 2 Inhalation Chapter 2 Structures and Functions of the Human Body Systems 47

1 Internal intercostal muscles contract and rib cage moves downwards and inwards 2 Diaphragm muscles relaxes and arches upwards 3 Volume of thoracic cavity decreases causing air pressure in the lungs to increase 4 The higher air pressure inside the lungs pushes air out Diaphragm Rib cage Air exits Thoracic cavity 1 4 3 2 Exhalation Activity 7 Understand the breathing mechanism Aim: Investigate the relationship between the air pressure in the thoracic cavity and the process of inhalation and exhalation Materials and apparatus: Thin rubber sheet, balloons, glass jar, Y-shaped glass tube and cork Procedure: 1 Set up a model of the chest as shown in the diagram. 2 Pull down the rubber sheet and observe if there are any changes to the size of the balloons. 3 Push up the rubber sheet and observe if there are any changes to the size of the balloons. Observation: Record your observations. Discussion: 1 What do the glass jar, thin rubber sheet, Y-shaped glass tube, and balloons represent in the human respiratory system? 2 When the thin rubber sheet is pulled down, what breathing process is shown? 3 When the thin rubber sheet is pushed up, what breathing process is shown? Conclusion: Write down the conclusion. Balloon Glass jar Thin rubber sheet Y-shaped glass tube Cork Smoking is harmful to the respiratory system of smoker as well as people who are in the vicinity of the smoker. This is because they breathe in either the smoke emitted from the burning cigarette or the air exhaled by the smokers. These people are known as passive smokers. Science Facts 48

Diseases of the Respiratory System Cigarette smoke, air pollutants such as exhaust fumes from vehicles, gases from factories and haze contain harmful substances that cause various diseases of the respiratory system. Asthma is a chronic disorder in which the air passages of the lungs periodically become too narrow due to mucus being produced excessively, arising from the sensitivity of the patient towards air pollutants. The patient may suffer wheezing, chest tightness, coughing, and breathing difficulties. Asthma Bronchitis Bronchitis is the inflammation of the bronchi that may be caused by tar and irritants in cigarette smoke. A patient with chronic bronchitis will have persistent coughing, shortness of breath and chest tightness daily for months or years. Bronchitis Inflamed bronchus and excess mucus production Alveolar membranes break down Normal Bronchitis Normal Emphysema Emphysema is a condition due to the damage of alveoli in the lungs caused by harmful substances such as irritants in cigarette smoke. Thus, the surface area for gas exchange is reduced. A person with emphysema is constantly short of breath and feels tired even from just doing light work. Smoking is the leading cause of this disease. There is no cure for this disease, but the symptoms of this disease can be controlled. Emphysema Lung cancer is a disease in which there is uncontrolled growth of cells in the lungs mainly due to cigarette smoke. Cigarette smoke contains chemical substances such as tar that is carcinogenic. Some of the symptoms of lung cancer include persistent coughing, blood in the phlegm, and pain when breathing. Lung cancer It is important that we take good care of our respiratory system for it to function properly. Some of the good habits that we can practice to protect our respiratory system are as follows. • Stay away from smoking • Ensure there is a supply of fresh air in the place you are in • Keep floors and carpets dust free • Avoid open burning • Turn off the engine of the vehicle you are in while waiting Chapter 2 Structures and Functions of the Human Body Systems 49

2.4 Excretory System The metabolic reactions in our body produce some waste products that our body must remove. If waste products accumulate in the body, the toxicity may affect our health or damage the organs in our body, which can be fatal. Therefore, waste products must be disposed of. The disposal of metabolic waste products from the body is called excretion. This is carried out by the excretory organs: skin, lungs, kidneys and liver. Skin Skin, the largest organ in the body, is made up of three layers: epidermis, dermis and subcutaneous layer. Apart from acting as an excretory organ, it is also a heat insulator, a sensory organ and a barrier that protects the body from harmful microbes. Blood vessels Hair Sweat pore Sweat duct Sweat gland Adipose tissue Dermis Epidermis Subcutaneous layer Structure of human skin The dermis layer is where the sweat glands are found. There are many sweat glands throughout the body especially under the armpits, palms of the hands and soles of the feet. A sweat gland is made up of a coiled tube connected to a sweat duct that opens on the surface of the epidermis as a sweat pore. Excess water from blood capillaries is absorbed by sweat glands and released from the skin as sweat. The sweat is made up of 99% water and 1% waste products from the blood such as sodium chloride and urea. Lungs Carbon dioxide and water are produced during cell respiration as waste products. Carbon dioxide and water diffuses out of the blood capillaries into the alveoli. Carbon dioxide and water are expelled from the lungs via exhalation. 50

Kidneys We have two kidneys situated at either side of our backbone, in the abdomen, and just above the waist. Each kidney is connected to a renal artery, a renal vein and a ureter. Renal arteries transport blood that contains waste products to the kidneys whereas renal veins carry filtered blood from the kidneys. The main function of the kidneys is to filter waste products and excess water from the blood and excrete them from the body as urine. Urine is a yellowish liquid that contains water, mineral salts and urea. The urine from the kidney are channelled to the urinary bladder by the ureter. The urinary bladder stores urine. When the bladder is full, we will feel the urge to urinate. The muscles at the urinary bladder contract to expel the urine through the urethra to the exterior. Livers The liver detoxifies blood by getting rid of toxic substances from the food we consume. These toxic substances are broken down and converted into harmless materials by the liver and then transported to the kidneys to be eliminated through our urine. Excess amino acids that cannot be stored in our body will also be converted into urea to be excreted through our urine. Our excretory system plays a major role in the disposal of toxic or poisonous wastes from our body. How do we keep our excretory system healthy? Think About It Left lobe of liver Falciform ligament Aorta Hepatic vein Right lobe of liver Gall bladder We should take good care of our kidneys as they help to filter the blood. They remove toxic waste materials from our body and regulate the balance of fluid and mineral salts in our body. Humans can still lead a healthy life with only one healthy kidney. However, if both kidneys fail, the patient may die if he does not go for dialysis regularly. Left renal artery Aorta Left renal vein Left kidney Right renal vein Ureter Urethra Right renal artery Right kidney The urinary system Urinary bladder Vena cava Chapter 2 Structures and Functions of the Human Body Systems 51

Health Effects of Smoking, Alcohol Consumption and Drug Addiction Smoking, alcohol consumption and drug addiction may have short-term and long-term effects on the human body. Smoking Drug addiction Alcohol consumption Smoking has many negative effects on the body. This is due to the harmful substances in the cigarette smoke that the smokers breathe in. Some of the harmful substances and their effects are: • Nicotine causes addiction, damages brain tissues, hardens artery walls and causes blood to clot easily, thus increasing the risk of heart diseases. • Carbon monoxide gas prevents the red blood cells from transporting oxygen to the body cells. • Tar particles stick to and kill cells in the air passages and increase the production of phlegm in the lungs. • Carcinogens cause the growth of abnormal cells in the body which are cancerous. Other problems or conditions that can be caused by smoking: • Shortness of breath, wheezing, chest pain and tightness • Higher risk of stomach cancer and ulcers • Higher risk of stroke, heart attack and other heart diseases • Higher risk of respiratory illnesses such as asthma, emphysema and bronchitis According to World Health Organisation (WHO), alcohol consumption is responsible for various illnesses and disabilities of millions of people globally each year, and deaths as well. Short-term effects from drinking alcohol which is reversible once the alcohol has been processed and excreted from the body: • Slowing down of the reflexes and may affect balance • Difficulty in thinking and concentrating • Slurred speech • Blurred vision • Slower breathing and heart rate • May result in abdominal pain, indigestion and bloating Drunk driving increases the risk of accident that may cause serious injuries, or even death. Long-term effects on heavy drinkers (alcoholics): • Difficult for the body to digest food and absorb vital nutrients • Higher risk of cancers associated with the digestive system • Higher risk of cardiovascular diseases • Higher risk of liver diseases such as cirrhosis, fibrosis and liver cancer Drugs are chemical substances that are used to treat diseases but when taken without a doctor’s supervision, they can lead to addiction. There are several categories of drugs such as stimulants that increase alertness, depressants that reduce anxiety, and hallucinogens that cause hallucination. Over time, drug misuse affects the health of drug addicts. Stimulants such as methamphetamines can lead to heart disease or heart failure. Drugs injected through needles can cause bacterial infections in blood vessels or collapsed veins from repeated use. Certain drugs cause damage to the stomach, liver and kidney. 52

1 Carbohydrates are organic compounds that contain the elements carbon, hydrogen and . 2 Dietary fibre is an example of a carbohydrate. 3 such as glucose, fructose and galactose are examples of simple carbohydrates. 4 The molecules that make up protein are called . 5 Most animal fat are fats. 6 High levels of low-density lipoproteins contribute to which is the fatty build-up in the walls of arteries making the arteries narrower. 7 The deficiency of vitamin may cause scurvy, a disease where the bleeding of the gum occurs. 8 Iron is required in the formation of in red blood cells. 9 makes up about 60% to 70% of our body mass. 10 The amount of heat produced from the complete combustion of one gram of food is known as the of the food. 11 Boric acid is a food additive that is used in noodles as a . 12 Chemical digestion involves the breakdown of complex molecules into simple molecules with the aid of . 13 kills bacteria in the food that enters the stomach. 14 The pancreatic juice contains digestive enzymes such as trypsin, and pancreatic amylase. 15 In the duodenum emulsifies fats into small droplets. 16 The final breakdown of food occurs in the last section of the small intestine called the . 17 The main components of the circulatory system are the , blood vessels and blood. 18 are blood vessels that have valves and carry blood back to the heart. 19 arteries provide nutrients and oxygen to the cardiac muscles. 20 In the lungs, bronchioles end in tiny air sacs called . 21 During inhalation, the rib cage is pulled upwards and outwards due to the of external intercostal muscles. 22 is a condition due to the damage of alveoli in the lungs that can be caused by irritants in cigarette smoke. 23 The urine from the kidney is channelled to the by the ureter. RECALL Fill in the missing words. Chapter 2 Structures and Functions of the Human Body Systems 53

THINKING CAP Put on your 1 In your opinion, why does a 15-year-old boy need more energy than a 15-year-old girl of the same body size? 2 Why is it not advisable to cook vegetables too long? 3 Zaki felt dizzy after donating blood. Why is that so? How can he overcome it? 54

Project Risk Factors that Impact Heart Health Activity objective: To identify the risk factors that impact the heart health and raise awareness about cardiovascular diseases. Problem statement: One of the main causes of death in Indonesia is cardiovascular diseases. Cardiovascular diseases are all types of diseases that affect the heart or blood vessels. How to raise awareness among the population about cardiovascular diseases and ways to maintain a healthy heart? Concept applied: Healthy heart Procedure: 1 Divide the class into groups of four to carry out this task. 2 Appoint a leader in each of the groups to delegate the subtasks to the group members. 3 Have a discussion on how to present the information gathered. Solution: The information gathered must at least include the following aspects and you are encouraged to add more. (a) What are the main types of cardiovascular diseases? (b) What are the symptoms of each disease? (c) What are the risk factors for cardiovascular diseases? (d) How does smoking or consuming alcohol affect the heart health? (e) How to create awareness among the community on how to maintain a healthy heart so that cardiovascular diseases can be prevented? Presentation: Write a comprehensive report and present it to the class as creatively as possible. Chapter 2 Structures and Functions of the Human Body Systems 55

Work, Energy and Simple Machines CHAPTER 3 What will you learn? Define work and power Calculate work and power using equations and proper units Explain different forms of energy Describe the relationship between mechanical energy with potential energy and kinetic energy Differentiate between the types of simple machines used in daily life Describe how different types of simple machines work and their benefits in daily life Understand the concept of mechanical advantage of simple machines and how to calculate it Identify the simple machines in the human body A delivery man is holding a tray of fresh food while waiting for his customer. No work is being done by the man at that moment. Do you know why? What do you think must happen for work to be done?

3.1 Work Who do you think is doing work – a boy who is playing video games or a boy who is playing football? Work is said to be done when a force is used to move an object through a distance in the direction of the force. The force must be exerted in the same direction as the moving object. Work is defined as the force exerted on an object multiplied by the distance the object moves in the direction of the force. Work done, W (in joules) = Force, F (in newton) × Distance, d (in metres) Example 1 A car is pushed with a force of 600 N. The car moves 100 m horizontally. What is the work done? Solution: Work done, W = force × distance = 600 × 100 = 60 000 J The SI unit of work is joule (J), named in honour of James Prescott Joule, a nineteenth century English physicist. One joule of work is done when 1 N of force is exerted on an object to move it 1 m in the direction of the force. There is no work done when there is no force or no displacement. Example 2 A man exerted a force of 8000 N on a stationary car but the car did not move. How much work was done? Solution: No work was done. Example 3 A boy who weighs 550 N climbs up a flight of stairs. How much work does the boy have to do to climb the stairs? Solution: The boy exerts an upward force to overcome his own weight or the pull of gravity. Work done, W = force x distance = 550 × 3 = 1650 J 3 m 7 m A boy playing video games on his smartphone A boy playing football Chapter 3 Work, Energy and Simple Machines 57

3.2 Power When three athletes run the same distance, they are doing the same amount of work but the amount of time taken by each of them to cover the distance is different. The athlete who took the shortest time has the highest power rating than the other athletes. What is power? Power is defined as the rate at which work is done, or how quickly work is done. It can be calculated by dividing work done by time. What happens to the power produced if more work is done in the same amount of time? Think About It The SI unit of power is watt, named in honour of James Watt, a nineteenth century British scientist who developed the steam engine. Watt can be defined as the power needed to do one joule of work in one second. Power, P (in watt) = Work, W (in joules) Time, t (in seconds) Example 5 Calculate the time taken for a crane that uses 750 W to lift a load of 2000 N to a height of 6 m. Solution: Power, P = Work done Time taken 750 = 2000 × 6 Time taken Time taken = 2000 × 6 750 = 16 s Example 4 A weightlifter lifts 500 N through a distance of 2 m in 4 s. How much power did he use? Solution: We need to calculate the work done before determining the power used. Work done, W = force x distance = 500 × 2 = 1000 J Power, P = Work done Time taken = 1000 4 = 250 watts Example 6 A boy who weighs 50 kg takes 40 s to go up a long flight of stairs with a vertical height of 8 m. Calculate the power of the boy. [Take gravitational field strength, g = 9.8 m s−2] Solution: The force exerted is equal to the weight of the boy (mg). Weight of boy, F = mg = (50.0 kg) (9.8 m s−2) = 490 N Work done, W = Fd = 490 × 8 = 3920 J Power, P = W t = 3920 40 = 98 watts 58