©Praxis Publishing_Focus On Science
©Praxis Publishing_Focus On Science
CONTENTS Introduction to Cells 1 1.1 Cells and Microscopes 1 1.2 Animal and Plant Cells 5 1.3 Unicellular and Multicellular Organisms, and Cell Specialisation 8 Objective Questions 10 Concept Map 12 HOTS Daily Application 13 Online Quick Quiz 13 Structures and Functions of the Human Body Systems 14 2.1 Food and Digestive System 14 2.2 Circulatory System 21 2.3 Respiratory System 26 2.4 Excretory System 32 Objective Questions 33 Concept Map 35 HOTS Daily Application 36 Online Quick Quiz 36 Work, Energy and Simple Machines 37 3.1 Work 37 3.2 Power 39 3.3 Sources and Forms of Energy 39 3.4 Simple Machines 46 Objective Questions 54 Concept Map 56 HOTS Daily Application 57 Online Quick Quiz 57 Vibrations, Waves and Light 58 4.1 Vibrations 58 4.2 Waves 61 CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 4.3 Light and Optical Instruments 69 Objective Questions 76 Concept Map 79 HOTS Daily Application 80 Online Quick Quiz 80 Assessment 1 81 Elements, Compounds and Mixtures 89 5.1 Atoms and Molecules 89 5.2 Elements 91 5.3 Compounds 95 5.4 Mixtures 98 Objective Questions 103 Concept Map 105 HOTS Daily Application 106 Online Quick Quiz 106 Acids and Alkalis 107 6.1 Acids and Alkalis 107 6.2 Neutralisation 117 Objective Questions 120 Concept Map 122 HOTS Daily Application 123 Online Quick Quiz 123 Structure of the Earth and Natural Disasters 124 7.1 Structure of Earth 124 7.2 Movement of Tectonic Plates 127 7.3 Earthquakes 130 7.4 Volcanoes 132 Objective Questions 135 Concept Map 137 HOTS Daily Application 138 Online Quick Quiz 138 Assessment 2 139 CHAPTER 5 CHAPTER 6 CHAPTER 7 ii ©Praxis Publishing_Focus On Science
Introduction to Cells CHAPTER 1 1.1 Cells and Microscopes 1. Underline the correct words. (a) A cell is the (basic, complex) unit that makes up all living things. (b) Cells are very (big, small) and we (can, cannot) see them with the naked eye. (c) There are (many, few) cells in our body. (d) Scientists use (Petri dishes, microscopes) to study cells. 2. Tick (✓) the correct statements. (a) Cells divide so that organisms can grow. ✓ (b) All the cells in our body have the same shape and size. (c) Cells provide structural support to organisms. ✓ (d) Cells carry out many processes to sustain life. ✓ 3. The figure shows one of Robert Hooke’s observations with a microscope. (a) What type of microscope did Robert Hooke used? A compound microscope (b) What was he analysing with his microscope? Explain what it is. A thin slice of cork. Cork is the thick layer of dead tissue that is found in the bark of the tree. (c) What did he call those tiny room-like structures? Cells (d) (i) Did he know the functions of the room-liked structures? No (ii) Give a reason for your answer in (d) (i). Those were dead cells. (e) He described his observations in his book. What is the name of his book? Micrographia Extra Info Robert Hooke i Chapter 1 Introduction to Cells 1 ©Praxis Publishing_Focus On Science
4. The figure below shows a microscope used by Anton van Leeuwenhoek in 1664. (a) (i) What is Anton van Leeuwenhoek known as? The Father of Microbiology (ii) Give a reason for your answer in (a)(i). He was one of the first people to observe microorganisms with a microscope of his design. He discovered the existence of microorganisms. (b) What type of microscopes did Leeuwenhoek build? Single-lens microscopes 5. Complete the table below to compare light microscopes and electron microscopes. Light microscopes Aspects Electron microscopes Smaller and lighter Size and weight Bigger and heavier A beam of light Illuminating source A beam of electrons Lower Magnifying power Higher Lower Resolving power Higher Both dead and live specimens Specimen type Only dead specimens No Is the specimen preparation complex? Yes The image is seen directly through the eyepiece How is the image seen? The image is seen on a screen or photographic plate Yes Is the image seen coloured? No, it is black and white Extra Info Anton van Leeuwenhoek i 2 ©Praxis Publishing_Focus On Science
6. Label the parts of the light microscope with the words given. Diaphragm Fine focus knob Stage Objective lens Base Eyepiece Coarse focus knob Mirror (a) Eyepiece (e) Coarse focus knob (b) Objective lens (f) Fine focus knob (c) Stage (g) Diaphragm (d) Mirror (h) Base 7. There are three types of objective lenses. Name them and differentiate them. Low-power, medium-power and high-power objective lens. The low-power objective lens magnifies the image of the specimen to 4 times. The medium-power objective lens magnifies the image of the specimen to 10 times. The high-power objective lens magnifies the image of the specimen to 40 times. Chapter 1 Introduction to Cells 3 ©Praxis Publishing_Focus On Science
8. Match the parts of a light microscope with their functions. Diaphragm Sharpens the focus quality of the image after using the coarse focus knob Coarse focus knob Controls the amount of light that enters the condenser Fine focus knob Moves the stage up or down in initial focusing Mirror Reflects the light into the diaphragm Stage Magnifies the image formed by the objective lens Eyepiece The platform to place the slide 9. Number the steps below to show the correct sequence to use a light microscope. Place the slide on the stage and use the clips to hold it. 4 Look through the eyepiece and turn the coarse focus knob until the image comes into focus. 6 Place the microscope on a flat surface in a bright place. 1 Turn the coarse focus knob for the lens to be as close to the specimen as possible. 5 Adjust the fine focus knob until a sharp image is formed. 7 Select the low-power objective lens and adjust it to be above the hole of the stage. 2 Adjust the diaphragm and mirror so that there is enough light to view the specimen through the microscope. 3 4 ©Praxis Publishing_Focus On Science
1.2 Animal and Plant Cells 1. The figures below show the steps to prepare a slide of a human cheek cell. The slide is observed. S The cover slip is lowered slowly to cover the slide. T The scraping is mixed with a drop of methylene blue solution on the slide. U The inner side of the cheek is scraped with the broad end of a toothpick. V A filter paper is used to draw the excess solution to the opposite side of the cover slip. W (a) Arrange them in the correct sequence. V U T W S (b) Why do you think the broad end of the toothpick is used instead of its sharp end to scrape the inner side of the cheek? To avoid hurting the inner side of the cheek. (c) Why is methylene blue solution used in the preparation of a slide of cells? To colour the cells so that they are clear when observed under the microscope. (d) Why is the cover slip lowered slowly over the slide? To prevent air bubbles from being trapped under the cover slip. (e) Why do we usually observe a slide under the microscope using the low-powered objective lens and then only followed by the high-powered objective lens? It is easier to locate the specimen on the slide as the field of view of the low-powered objective lens is wider. Chapter 1 Introduction to Cells 5 ©Praxis Publishing_Focus On Science
2. Label the animal cell with the words given. Cytoplasm Cell membrane Nucleus Mitochondrion Cell membrane Mitochondrion Nucleus Cytoplasm 3. Label the plant cell with the words given. Chloroplast Cell membrane Nucleus Mitochondrion Cell wall Vacuole Cytoplasm Vacuole Cell wall Mitochondrion Nucleus Cell membrane Cytoplasm Chloroplast 4. Ahmad was analysing a cell using a light microscope. He managed to identify the nucleus, cell wall, cell membrane and the big vacuole. Based on Ahmad’s observation, state the type of cell Ahmad was analysing. Give your reasons. It is a plant cell. A plant cell has a cell wall and a big vacuole that an animal cell does not have. 6 ©Praxis Publishing_Focus On Science
5. Complete the table below on cell structures and their functions. Structure Function Nucleus Controls all the activities in the cell Cytoplasm As a medium where chemical reactions occur Cell membrane Controls the movement of materials in and out of the cell Mitochondrion Produces energy for the cell Vacuole Contains cell sap and maintains the turgidity of the cell Chloroplast Contains green pigment to carry out photosynthesis Cell wall Maintains the shape of the cell and provides support 6. How is an animal cell similar to a plant cell? Give two similarities. Both have cell membrane, cytoplasm, nucleus and mitochondria. Both carry out life processes. 7. How does an animal cell differ from a plant cell? Compare by completing the table below. Aspects Animal cell Plant cell Size Generally smaller Generally bigger Cell wall Does not have a cell wall Has a cell wall Vacuole Usually absent Has one or a few large ones Chloroplast Does not have chloroplasts Has chloroplasts Shape Does not have a fixed shape Has a fixed shape Food storage Glycogen granules Starch granules Position of nucleus Usually at the centre of the cell Usually at one side of the cell Chapter 1 Introduction to Cells 7 ©Praxis Publishing_Focus On Science
1.3 Unicellular and Multicellular Organisms, and Cell Specialisation 1. Categorise the organisms below into unicellular and multicellular organisms. Amoeba Spirogyra Paramecium Yeast Cat Mucor Bird Chlamydomonas Unicellular organisms Multicellular organisms Amoeba Spirogyra Paramecium Cat Yeast Mucor Chlamydomonas Bird 2. Match the specialised human cells to their correct functions. Carries information in the form of nerve impulses to different parts of the body Red blood cell Nerve cell Carries genetic information Sperm cell Transports oxygen throughout the body Epithelial cell Contracts and relaxes to produce movements for many human parts Muscle cell Lines the surfaces of organs Extra Info Unicellular and multicellular cells i 8 ©Praxis Publishing_Focus On Science
3. Tick (✓) the correct statements based on each of the specialised plant cells below. (a) Palisade cells contain a lot of chloroplasts. ✓ They absorb sunlight to make water. They are located mainly on the leaves. ✓ Palisade cell (b) Guard cells Guard cells shaped like a cube. They allow gas exchange to occur in plants. ✓ They help to reduce water loss in plants. ✓ (c) Epidermal cell Epidermal cells protect the plant from the external environment. ✓ They are usually not transparent. They prevent the loss of water from the plant. ✓ (d) Tracheid Tracheids are found in xylem tissues of plants. ✓ They help to transport water and minerals in plants. ✓ They are broad and filled with cytoplasm. (e) Sieve element Sieve elements help in gas exchange and making food. They transport food from the leaves to other parts of the plant. ✓ They are found in phloem tissues of plants. ✓ Chapter 1 Introduction to Cells 9 ©Praxis Publishing_Focus On Science
1. Which of the following was first observed with a microscope that led to the discovery of cells? A Cork C Honeycomb B Fly D Leaf 2. Which of the following people contributed greatly to microbiology? I Robert Hooke II Alexander Graham Bell III Anton van Leeuwenhoek IV Isaac Newton A I and II only C II and IV only B I and III only D III and IV only 3. Why are there no electron microscopes in school labs, only light microscopes? I Electron microscopes are very expensive compared to light microscopes. II The slides for light microscopes are easy to prepare. III Light microscopes give better resolutions than electron microscopes. A I only C I and II only B III only D I, II and III 4. We are always advised to place the light microscope near a window when using it to observe a specimen. Which is the best reason for this? A It is airy so that the specimen can stay alive. B It is nearer to the nature. C The lenses work best near the window. D It is brighter and we can see the specimen clearer. 5. Akim was preparing a slide of onion cells. He added a drop of methylene blue solution on the specimen. Why did Akim do that? A To make some components of the cells more visible B To make the cover slip more visible C To preserve the cells better for longer observation D To magnify the image of the specimens 6. The figures below show the steps in preparing a slide of onion epidermal cells. Which of the following shows the correct sequence? A M, J, L, K C M, K, J, L B M, J, K, L D J, M, L, K 7. Jack is observing some cells using a microscope. How does he conclude that the cells are plant cells? A The cells are green. B The cells are irregular and round in shape. C The cells have chloroplasts. D He sees the nucleus in each cell. Objective Questions A B C D Choose the best answer. 10 ©Praxis Publishing_Focus On Science
8. The figure below shows a plant cell. X What will happen to the cell if structure X is not working? A The cell is unable to carry out photosynthesis. B The cell will not have enough energy for itself. C All the substances will leave the cell. D The cell might lose its turgidity. 9. Which of the following are found in a human red blood cell? I Nucleus III Cell membrane II Cytoplasm IV Cell wall A I and II only C II and III only B I and IV only D III and IV only 10.Which is the function of the mitochondria in a cell? A They control all the activities in the cell. B They help to make food in the cell. C They control the movement of substances in and out of the cell. D They produce energy for the cell. 11. The figure below shows three organisms. Amoeba Chlamydomonas Yeast Which of the following statements is not correct in describing these organisms? A They are made up of one single cell. B They are also known as microorganisms. C They are very tiny. D They are found abundant in dry areas such as deserts. 12. A fly is a multicellular organism. Which of the following supports the statement above? A It is made up of many cells. B It has very huge cells. C Its cells are similar in size and carry out similar functions. D It is big as we can see them with our eyes. 13. Plant cells have a fixed shape but animal cells do not. What is the reason for this? A Plant cells have a cell wall. B Animals cells have small or no vacuoles. C Plant cells have many chloroplasts. D Plant cells are larger than animal cells. 14. Suppose that a disease destroys all the guard cells of a plant. What do you think will happen to the plant? A It will lose a lot of water through its leaves. B It will have more flowers and fruits. C Its roots are unable to absorb water and minerals. D Its leaves will turn brown. 15.Which of the following statements is not true? A Palisade cells in plants have many chloroplasts to carry out photosynthesis. B Plants have root hair cells to absorb water and minerals from the soil. C Animals have epithelial cells to cover their outer surfaces. D Muscle cells allow movements by contracting and relaxing. Chapter 1 Introduction to Cells 11 ©Praxis Publishing_Focus On Science
Complete the concept map below Concept Map about cells. Robert Hooke discoverers of cells types Animals • Reproductive cells • Muscle cells • Red blood cells • Epithelial cells • Osteocytes • Nerve cells Light microscopes Multicellular organisms Plants • Palisade cells • Guard cells • Root hair cells • Tracheids • Sieve elements types Cell specialisation have Unicellular organisms types Electron microscopes How to use Animal cells Plant cells types Organisms observed with How to prepare slides Microscopes Anton van Leeuwenhoek Cells 12 ©Praxis Publishing_Focus On Science
HOTS Daily Application Kasim and his friend were observing a drop of water from a nearby river using a microscope. They managed to observe the organism shown below. His friend concluded that the organism must be a unicellular organism since it was so tiny. However, Kasim disagreed with his friend. What is your opinion? Give an explanation. There are multicellular organisms that are too tiny that they cannot be seen with the naked eyes. Some animals and fungi are very small but they are multicellular organisms. Online Quick Quiz Chapter 1 Introduction to Cells 13 ©Praxis Publishing_Focus On Science
Structures and Functions of the Human Body Systems CHAPTER 2 2.1 Food and Digestive System 1. Fill in the blanks to complete the table below regarding the nutrients that our body needs. Type of nutrients Food sources Function Carbohydrates Bananas, potatoes, rice • To provide energy for life processes Proteins Meat, milk, eggs • For growth by building new cells • To repair worn-out cells • As a source of energy Fat Cooking oil, cheese, butter • As a thermal insulator • As a source of energy • To protect internal organs Vitamins Vegetables, fruits, eggs • For good health and growth Minerals Eggs, vegetables, meat • For good health and growth Water Plain water, soups, fruits • As a medium for biochemical reactions in cells • As a transport medium for respiratory gases and nutrients • To regulate body temperature 2. Underline to indicate if the statements are true or false. (a) Glucose, lactose and galactose are examples of monosaccharides. True / False (b) Vegetables and fruits are high in dietary fibres which help to prevent constipation. True / False (c) Proteins are made up of amino acids. True / False (d) Our body produces all the needed amino acids. True / False (e) Animal fat contains unsaturated fats which are healthier. True / False (f) Our body needs cholesterol to make cell membranes, hormones and vitamin D. True / False (g) A lack of vitamin B12 can cause beriberi. True / False 14 ©Praxis Publishing_Focus On Science
(h) Vitamins A, D, E and K can dissolve in water. True / False (i) Goitre patients are usually prescribed with salt fortified with phosphorus. True / False (j) Water helps in the breakdown of food substances during digestion. True / False (k) One gram of carbohydrate provides four calories of energy. True / False (l) The main function of proteins is as a source of energy for our body. True / False 3. Answer the following questions based on the nutrition facts label of a can of nuts shown on the right. (a) How much is one serving of nuts? 55 g of nuts (b) How many calories would you have consumed if you finished the whole can of nuts? 1 840 calories (c) If you consumed 220 g of the nuts, what percentage of your daily intake requirement of fats would you have taken in? 40% (d) If you consumed two servings of the nuts, (i) how many grams of carbohydrates would you get? 74 g (ii) what percentage is this of your daily intake of carbohydrates? 26% (e) How many servings of nuts would you need to get your daily requirement of calcium? 5 servings (f) If the recommended amount of sodium for Abu who has hypertension is 1200 mg/day, would it be advisable for him to consume the entire can of nuts at once? Explain. No. The entire can of nuts contains 1280 mg of sodium. This exceeds the recommended daily sodium intake for Abu. Extra Info Reading food label i Chapter 2 Structures and Functions of the Human Body Systems 15 ©Praxis Publishing_Focus On Science
4. The USDA (U.S. Department of Agriculture) created MyPlate, an easy food guide to eating a balanced diet. (a) What is a balanced diet? A diet that fulfils all the nutritional and energy needs of the body (b) What happens if we do not eat a balanced diet? We will either have excess or inadequate intake of a nutrient which could impair our health and well-being. We could get tired or sick easily. (c) Describe the MyPlate guide. Half of the plate is filled with vegetables and fruits. The other half is filled with grains and proteins. Dairy products such as milk and yoghurt are recommended too. (d) Give three examples of food that are rich in proteins. Meat, eggs, nuts 5. Fill in the blanks and complete the table given. (a) The amount of energy in a food can be determined using a calorimeter . (b) One calorie is the total amount of heat needed to raise the temperature of 1 gram of water by 1oC at a pressure of 1 standard atmosphere. (c) Class of food Energy value (kJ/g) (kcal/g) Carbohydrates 17 4 Proteins 17 4 Fat 37 9 6. Joko is an athlete. He takes 560 g of carbohydrates, 150 g of proteins and 118 g of fat a day. (a) Find the total energy Joko gets from his food in kcal. (560 × 4) + (150 × 4) + (118 × 9) = 3902 kcal (b) What happens if Ani, a clerk takes the same amount of food as Joko? Ani who is a clerk does not need that much of energy. The extra energy is stored as a layer of fat in her body. Too much body fat may lead to health problems such as diabetes and heart disease. Vegetables Fruits Protein Grains Dairy Extra Info MyPlate i 16 ©Praxis Publishing_Focus On Science
7. Tick (✓) those who need more energy in their daily life based on each of the following factors. (a) Age (i) Young men ✓ (ii) Old men (e) Health condition (i) Healthy people (ii) Sick people ✓ (c) Gender (i) Women (ii) Men ✓ (b) Occupation (i) Construction workers ✓ (ii) Architects (f) Body size (i) Small-sized people ✓ (ii) Big-sized people (d) Climate (i) People living in cold climate countries ✓ (ii) People living in hot climate countries 8. Tick (✓) the healthy foods and cross out (✗) the unhealthy ones. French fries ✗ Carbonated drinks ✗ Green vegetables ✓ Banana ✓ Watermelon ✓ Sweets ✗ Ice cream ✗ Eggs ✓ Fish ✓ Chapter 2 Structures and Functions of the Human Body Systems 17 ©Praxis Publishing_Focus On Science
9. (a) Name two purposes of using food additives. To make food last longer To improve the food’s appearance so that it is more appealing (b) For each type of food additive, state its function and an example. Colourings Function: To improve the appearance Example: Turmeric Antioxidants Function: To prevent the oxidation of fatty food Example: Butylated hydroxyanisole Preservatives Function: To reduce food spoilage Example: Salt Essences Function: To improve the smell Example: Lemongrass Sweeteners Function: To add sweetness Example: Honey Flavourings Function: To enhance food flavour Example: MSG Food additives 10. What is food digestion? Food digestion is the process of breaking down big and complex food particles into small, simple and soluble molecules that can be absorbed into the bloodstream and transported into every part of the body. 11. Fill in the blanks. There are two types of digestion, namely physical digestion and chemical digestion. Physical digestion involves the grinding of food into tiny pieces by the teeth with the help of the tongue and saliva. The peristaltic movement due to the contraction and relaxation of the muscles along the digestive tract and the churning process by the stomach are parts of physical digestion. Chemical digestion involves breaking down food into simpler molecules with the help of enzymes . It occurs in the mouth , stomach and small intestine. 18 ©Praxis Publishing_Focus On Science
12. (a) The diagram shows the human digestive system. Fill in the blanks. 9 Rectum • Stores faeces 8 Large intestine • Reabsorption of water and minerals occurs 5 Pancreas • Produces pancreatic juice which consists of trypsin, lipase and amylase into the duodenum 4 Stomach • Produces hydrochloric acid to kill bacteria and activate the protease enzyme • Protein protease polypeptides 3 Liver • Produces bile and stores it in the gall bladder before releasing it into the duodenum • Bile emulsifies fat into small droplets and creates an alkaline condition for the pancreatic enzymes to work 1 Mouth • Food is chewed and crushed. • Starch amylase maltose 2 Oesophagus • Peristaltic movement brings the food down to the stomach. 6 Duodenum • Starch amylase maltose • Fat lipase fatty acids + glycerol • Polypeptides trypsin peptides 7 Ileum • Maltose maltase glucose • Sucrose sucrase glucose + fructose • Lactose lactase glucose + galactose • Peptides erepsin amino acids • Fat lipase fatty acids + glycerol • Digestion is complete and absorption of food occurs 10 Anus • Removes faeces through defaecation process Extra Info Human digestive system i Chapter 2 Structures and Functions of the Human Body Systems 19 ©Praxis Publishing_Focus On Science
(b) Complete the flow map below to show the flow of food in the human digestive system. Mouth Stomach Anus Large intestine Oesophagus Rectum Duodenum Ileum 13.Akim is eating a chicken drumstick. (a) State the first part in his digestive system where the food will be digested. Explain. Stomach. Meat contains proteins. Proteins are first digested in the stomach. (b) What enzyme is used to digest the food? Protease (c) Why does his body need to digest the food before using it? The food needs to be broken down into small molecules which can be absorbed into the bloodstream and brought to cells to be used. 14. State the final products of digestion. Class of food Carbohydrates Proteins Fat Final products Glucose Acid amino Fatty acids and glycerol 15. The figure shows the structure of the villi. (a) Where are the villi found in our digestive system? Small intestine (b) What is the main function of villi? They absorb the digested food from the small intestine. (c) Name structures P and Q. State their functions. P: Lacteal. Absorbs fatty acids, glycerol and fat-soluble vitamins Q: Blood vessels. Absorb glucose, amino acids and water-soluble vitamins (d) Relate how the characteristics of villi enhance their roles in the digestive system. Each villus has tiny projections called microvilli to increase the surface area for absorption. It is very thin (one-cell thick) and has a network of blood capillaries that increases the effectiveness of absorption of digested food. P Q 20 ©Praxis Publishing_Focus On Science
16. Daniel is suffering from constipation. Suggest three ways to help him prevent this from reoccurring in the future. Eat more vegetables and fruits. Exercise regularly. Drink 3 litres of water on average every day. 2.2 Circulatory System 1. (a) What is the function of the circulatory system in our body? To carry useful materials such as oxygen and nutrients to other parts of the body and to remove waste materials from them. (b) List the three main components of our circulatory system. Briefly describe the function of each component. Component Function Heart To pump the blood throughout the body Blood To carry useful and waste materials Blood vessels To carry the blood throughout the body (c) Why is our circulatory system considered a closed system? The blood is contained within the blood vessels and is separated from the body’s tissues. 2. (a) Why is our blood red? It is caused by the presence of haemoglobin pigments in the red blood cells in the blood. (b) (i) What is plasma? The liquid component of our blood. (ii) What percentage is the plasma in our blood? About 55%. (iii) What does plasma contain? Water and soluble substances such as hormones, minerals, glucose and amino acids. Chapter 2 Structures and Functions of the Human Body Systems 21 ©Praxis Publishing_Focus On Science
(c) State the three types of blood cells and compare them in the table below. Type of blood cells Red blood cells White blood cells Platelets Relative size Small The largest The smallest Function To carry oxygen and carbon dioxide To protect the body by fighting infections To protect the body by clotting blood at injury sites Shape Biconcave Variable Variable Life span 120 days Variable 2 to 8 days (d) Adi was not feeling well. He went for a blood test and found that his white blood cell count was high. Explain this. The production of white blood cells was increased to fight an infection in his body. 3. The figure below shows the blood flow through three types of blood vessels in our body. X Z Y (a) Name the types of blood vessels shown. X: Artery Y: Capillary Z: Vein (b) Complete the table below to compare the characteristics of the blood vessels. Characteristics X Y Z Wall structure Thick, muscular, elastic One-cell thick Thin, less muscular and less elastic Lumen size Small Very small Large Presence of valve No valves No valves Has valves Blood content Oxygenated blood except for the pulmonary artery Oxygenated blood at the arteriole ends and deoxygenated blood at the venule ends Deoxygenated blood except for the pulmonary vein Blood pressure High Low Very low Direction of blood flow From the heart to all parts of the body From arteries to veins From all parts of the body to the heart 22 ©Praxis Publishing_Focus On Science
4. Underline words that are incorrect. Write the correct words to replace them. (a) The heart is a muscular organ, made up of smooth muscles. cardiac (b) The heart has four chambers, consisting of two atria and two septa. ventricles (c) There are three valves in the heart, namely the quadcuspid, tricuspid and bicuspid valves. semilunar (d) The right side of the heart receives oxygenated blood. left side (e) The aorta brings deoxygenated blood into the heart. vena cava (f) Coronary arteries supply oxygenated blood to the lungs. heart 5. Label the parts of the heart. Aorta Vena cava Semilunar valves Tricuspid valve Pulmonary veins Left atrium Septum Right atrium Pulmonary artery Right ventricle Left ventricle Bicuspid valve (a) Vena cava (f) Aorta (g) Pulmonary artery (h) Pulmonary veins (i) Left atrium (j) Bicuspid valve (k) Left ventricle (l) Septum (b) Semilunar valves (c) Right atrium (d) Tricuspid valve (e) Right ventricle Extra Info Human heart i Chapter 2 Structures and Functions of the Human Body Systems 23 ©Praxis Publishing_Focus On Science
6. (a) (i) How big is our heart? The size of a clenched fist (ii) Where is our heart located? In our chest between the two lungs (b) (i) Why are there valves in our heart? To make sure the blood flows in one direction (ii) What happens if the valves are not functioning? The blood will flow back (c) Why is the wall of the left ventricle thicker than the wall of the right ventricle? This is because the blood in the left ventricle is to be pumped to the whole body, thus it requires a greater pressure to do so. The blood in the right ventricle is to be pumped to the lungs, thus it requires a lower pressure. Thicker walls can withstand greater pressure. (d) (i) What is the function of the septum? To separate the right chambers from the left chambers (ii) Why is this function important? To prevent the oxygenated blood in the left chambers from mixing with the deoxygenated blood in the right chambers (e) Name the largest artery and the largest vein in our body. Largest artery: Aorta Largest vein: Inferior vena cava 7. (a) Complete the flow map to show the flow of deoxygenated blood in the heart starting from the blood in the vena cava. Vena cava Right atrium Right ventricle Pulmonary artery Lungs (b) Complete the flow map to show the flow of oxygenated blood in the heart starting from the blood in the lungs. Lungs Pulmonary vein Left atrium Left ventricle Aorta 24 ©Praxis Publishing_Focus On Science
8. Fill in the blanks to describe our double circulatory system. Our human circulatory system is a double circulatory system. It has two separate circulations and the blood enters the heart twice. The circulatory system consists of the pulmonary circulation and the systemic circulation. In the pulmonary circulation, the deoxygenated blood is pumped from the heart into the lungs through the pulmonary artery. In the lungs, gas exchange occurs and the blood is oxygenated. Then, the oxygenated blood enters the heart through the pulmonary vein. In the systemic circulation, the heart pumps the blood into the aorta to be distributed to all parts of the body except the lungs . In the cells and tissues, gas exchange occurs and the blood is deoxygenated. The deoxygenated blood returns to the heart through the vena cava . 9. State two advantages of having a double circulatory system. It ensures the blood is fully oxygenated before being pumped to other parts of the body. The blood can be pumped to other parts of the body at a higher pressure. 10. Match each of the cardiovascular diseases to the correct description. It is the build-up of fat, cholesterol and other substances on the artery walls, causing the arteries to narrow and block the blood flow. Stroke It occurs when the blood vessels supplying blood to the brain are blocked or has burst. Hypertension It happens when the blood flow to the heart is reduced or blocked usually due to build-up of fat and cholesterol in the coronary arteries. Heart attack It happens when the pressure exerted by the flowing blood against the artery walls is higher than normal. Atherosclerosis Other parts of the body Lungs Chapter 2 Structures and Functions of the Human Body Systems 25 ©Praxis Publishing_Focus On Science
11. (a) What are cardiovascular diseases? Diseases related to the heart and blood vessels (b) How can atherosclerosis lead to other cardiovascular diseases such as heart attacks and strokes? When the blood supply to the heart is blocked, a heart attack occurs. When the blood supply to the brain is blocked, a stroke occurs. (c) (i) Which cardiovascular disease is known as ‘the silent killer’? Give your reason. Hypertension. Most people who have it do not have any symptoms and may not be aware of it. Hypertension can seriously hurt important organs such as the heart, brain, kidneys and eyes. (ii) How do we know if we have this disease? By measuring our blood pressure with a sphygmomanometer (d) Give three warning signs of stroke. Weakness or numbness of the face, arm or leg Trouble speaking or understanding Dizziness (e) List four ways to take care of our circulatory system. Have a healthy and balanced diet, limiting the intake of sugary, oil and salty foods Exercise regularly Maintain an ideal body weight Do not smoke or consume alcohol 2.3 Respiratory System 1. (a) State the main function of our respiratory system. Enables gas exchange between the blood in our body and the external environment (b) What do these terms mean? Exhalation: The process of letting air out from the lungs Inhalation: The process of taking air into the lungs 26 ©Praxis Publishing_Focus On Science
(c) What is the process of inhalation and exhalation by the lungs known as? Breathing or external respiration (d) Label the parts of our respiratory system below. Nostril Nasal cavity Trachea Bronchiole Intercostal muscle Lung Bronchus Alveolus Rib Diaphragm Blood capillaries Nostril Nasal cavity Trachea Intercostal muscle Lung Bronchiole Blood capillaries Alveolus Bronchus Rib Diaphragm (e) Complete the flow map below to show the pathway of inhaled air in our respiratory system. Nostrils Bronchus Nasal cavity Alveolus Bronchiole Trachea 2. Joko ran around the field twice just now. He is now breathing rapidly. Explain why this happens. Joko needs more oxygen to do the activity. His lungs are filled with air and emptied at a higher rate to cope with this demand. Chapter 2 Structures and Functions of the Human Body Systems 27 ©Praxis Publishing_Focus On Science
3. The figure below shows the gas exchange between an alveolus and a blood capillary. (a) Fill in the blanks to label the figure. Alveolus Oxygenated blood Blood capillary Red blood cell Deoxygenated blood X Y (ii) Deoxygenated blood (i) Blood capillary (iii) Alveolus (iv) Oxygenated blood (v) Red blood cell (b) What are gases X and Y? X: Carbon dioxide Y: Oxygen (c) Explain the movement of gas Y. The concentration of oxygen (Y) is higher in the alveolus than in the blood capillary. So, the oxygen dissolves in the moist inner surface of the alveolus and diffuses across its wall into the red blood cells in the blood capillary. 4. Match the adaptations of the alveolar structures with their importance. Large number of alveoli Provides a short diffusion distance Moist inner surface of alveolus Increases the surface area for gas exchange One-cell thick wall Increases the capacity of gas exchange Extensive blood supply Oxygen can dissolve easily in the moisture before diffusing across the wall 28 ©Praxis Publishing_Focus On Science
5. Fill in the blanks to describe the mechanism of inhalation and exhalation. (a) Inhalation The external intercostal muscles contract and the rib cage moves upwards and outwards . The diaphragm contracts and becomes flattened . The volume of the thoracic cavity increases , lowering the air pressure in the lungs. The air from outside enters the lungs. (b) Exhalation The internal intercostal muscles contract and the rib cage moves downwards and inwards . The diaphragm relaxes and arches upwards . The volume of the thoracic cavity decreases , increasing the air pressure in the lungs. The air in the lungs is forced out . 6. Rudy prepares a model of the human respiratory system as shown below. Name the parts of the respiratory system that are represented by each part of the model. Trachea Lungs Diaphragm Thoracic cavity Rubber sheet Glass jar Balloons Y-shaped glass tube Chapter 2 Structures and Functions of the Human Body Systems 29 ©Praxis Publishing_Focus On Science
7. Roy sets up the apparatus as shown below to study the effects of smoking on the lungs. Rubber stopper Rubber tube Cigarette Thermometer U-shaped tube Moist cotton To filter pump Glass tube Conical flask Hydrogen carbonate indicator Roy turns on the filter pump and after some time, he observes some changes. He records his observations as shown below. • The reading of the thermometer rises from 27°C to 29°C. • The white cotton turns yellowish. • The hydrogen carbonate indicator turns from red to yellow. (a) Why does the filter pump need to be turned on? To force the cigarette smoke to move through the apparatus set-up (b) The white cotton represents a part of our respiratory system. What is the part called? Lungs (c) Why does the white cotton turn yellowish? The cigarette smoke contains tar. The tar sticks to the cotton. (d) Why does the hydrogen carbonate indicator change colour to yellow? Cigarette smoke is acidic. (e) Why does the thermometer record a higher reading? Cigarette smoke contains heat. (f) Based on Roy’s observations, suggest three ways on how cigarette smoke affects our lungs. The heat from smoke dries the alveoli, making it difficult for oxygen to dissolve. The acidic smoke irritates the respiratory tract. The tar covers the surface of the alveolus and reduces the rate of gas exchange. Extra Info Effects of smoking i 30 ©Praxis Publishing_Focus On Science
(g) What conclusion can you make from the activity? Smoking cigarette is harmful to our respiratory system. 8. Match the harmful substances found in cigarette smoke to their effects on our body. Carbon monoxide A poisonous gas that prevents red blood cells from carrying much oxygen Have the potential to cause the growth of abnormal cells Sticks to and kills cells on the respiratory tract, increases production of phlegm and may cause lung cancer An addictive drug, making smokers reluctant to quit smoking Cause discomfort to the eyes and air passage, coughing, sneezing and sore throat Carcinogens Tar Nicotine Irritants 9. Fill in the blanks to describe some respiratory diseases. (a) Asthma is caused by the narrowing of airways with excessive mucus being produced. The patient finds it difficult to breathe, experiences wheezing and feels tightness in the chest. (b) Bronchitis is caused by the inflammation of the lining of the bronchi due to infection by bacteria, viruses or chemicals. A patient with chronic bronchitis experiences persistent coughing with a lot of sputum. (c) Emphysema involves damage to the alveoli . Thus, the area for gas exchange reduces significantly. The patient experiences shortness of breath even while resting and his lips and fingernails may turn blue with exertion. (d) Lung cancer is the uncontrolled growth of cells leading to the formation of tumours in the lungs. Smoking increases the risk of lung cancer. 10. State two ways to take good care of our respiratory system. Do not smoke. Go out and get fresh air. Chapter 2 Structures and Functions of the Human Body Systems 31 ©Praxis Publishing_Focus On Science
2.4 Excretory System 1. Tick (✓) the correct statements. (a) Excretion refers to the chemical reactions that occur in an organism to sustain life. (b) An example of metabolic reactions is cellular respiration whereby glucose is broken down to produce energy, water and carbon dioxide. ✓ (c) Metabolic products which are the product of metabolic reactions are not needed by the body. ✓ (d) Metabolic waste is kept in the body for future use. (e) Excretion is the removal of metabolic waste from the body of an organism. ✓ (f) The excretory system is a group of tissues that work together to remove metabolic waste from the organism. (g) The lungs, skin, kidneys and liver are excretory organs. ✓ (h) The metabolic products excreted by our skin are water and carbon dioxide. 2. State two importance of the excretory system in humans. To dispose of toxic wastes such as urea and carbon dioxide To dispose of excess substances such as salt and water 3. (a) Where are our kidneys located? At either side of our backbone, in the abdomen above the waist (b) What is the main function of our kidneys? To filter out waste products and excess water from the blood and excrete them as urine (c) What does urine consist of? Water, salt minerals, urea (d) State the function of each part of our urinary system mentioned below. (i) Urinary bladder: To store urine temporarily (ii) Urethra: To drain the urine from the urinary bladder to the exterior (iii) Ureter: To drain the urine from the kidneys to the urinary bladder (e) State two ways to ensure that our kidneys are always healthy. Drink 3 litres of water on average per day Avoid salty food 32 ©Praxis Publishing_Focus On Science
1. Which group of food consists of high protein content? A Noodles, rice and honey B Kale, bananas and mangoes C Meat, fish and beans D Butter, cheese and peanuts 2. Three hundred years ago, many sailors used to die at sea due to a disease known as scurvy. They felt tired and weak. They had painful and swollen joints, bleeding gums and skin that bruised easily. Which of the following statements is true about the above-mentioned disease? A The sailors lack of carbohydrates that provide energy. B The sailors had too much salt as they did not have much fresh water. C This disease can be cured by adding lime juice to their diet. D This disease is due to the deficiency of fats in their diet. 3. The figure below shows the relative energy values in 10 g of foods W, X and Y each. W Energy value Foods X Y What is represented by foods W, X and Y? Food W X Y A Margarine Apple Rice B Apple Margarine Rice C Rice Apple Margarine D Margarine Rice Apple 4. Which is true about physical digestion? A It happens only in the mouth. B It breaks down food with the help of enzymes. C It involves only the peristalsis in the digestive tract. D The teeth help to break down the food into smaller pieces. 5. The figure below shows our digestive system. P What happens if organ P fails to function? A The protein in the food cannot be broken down in the stomach. B The fat in the food becomes hard to be digested. C The faeces will become very hard. D The ileum will not secrete intestinal juice. Objective Questions A B C D Choose the best answer. Chapter 2 Structures and Functions of the Human Body Systems 33 ©Praxis Publishing_Focus On Science
6. The figure below shows the components in our blood. R P Q Which is correctly represented by cells P, Q and R? P Q R A White blood cell Red blood cell Platelet B Platelet White blood cell Red blood cell C White blood cell Platelet Red blood cell D Red blood cell Platelet White blood cell 7. The figure below shows a type of blood vessel. Valve Which is true about this type of blood vessel? A It carries deoxygenated blood except in the pulmonary vein. B It has a wall as thin as one cell. C It has a small lumen. D It allows blood to flow in both directions. 8. Which of the diseases is most probably caused by atherosclerosis? A Heart attack B Hypertension C Emphysema D Kidney failure 9. The figure below shows a model of our respiratory system. Rubber sheet Glass jar Balloon Y-shaped glass tube What happens when the rubber sheet is pushed upwards? Air pressure in the jar Size of the balloons A Increases Become smaller B Decreases Become smaller C Increases Become bigger D Decreases Become bigger 10.What happens if the excretory system malfunctions? A We will not get the nutrients we need to grow and develop. B The nutrients from the food we eat will not reach the cells in our body. C Our cells will not get oxygen to generate energy from the food we eat. D The accumulated metabolic waste will become toxic in our body. 34 ©Praxis Publishing_Focus On Science
Complete the concept map below Concept Map about human body systems. Digestive system Excretory system Respiratory system Human Body Systems Physical digestion Structures Food additives Carbohydrates Proteins Fat Vitamins Minerals Water Kidneys Nasal cavity Trachea Mechanisms Health issues Inhalation Smoking Bronchus Exhalation Diseases Bronchioles Alveoli Gas exchange Lungs Skin Liver Chemical digestion Processes Food Balanced diet Health issues Structures Structures Blood flow Veins Arteries Capillaries Plasma Red blood cells White blood cells Platelets Heart types components components types Circulatory system Blood Blood vessels Chapter 2 Structures and Functions of the Human Body Systems 35 ©Praxis Publishing_Focus On Science
HOTS Daily Application Wati always suffers from abdominal discomfort because her stomach excretes too much hydrochloride acid. Her doctor gives her antacids to neutralise the acid in her stomach. Predict what would happen if Wati consumes too many antacids for a prolonged period of time. Explain your prediction. Wati might experience malnutrition if she takes too many antacids for too long. Overconsumption of antacids will affect her digestion of food. The pH in her stomach would be changed, preventing the digestion and absorption of food by her digestive system. Online Quick Quiz 36 ©Praxis Publishing_Focus On Science
Work, Energy and Simple Machines CHAPTER 3 3.1 Work 1. Analyse each of the situations shown below. Then, answer the questions. (a) Yusri kicks the ball. (i) What happens to the ball? The ball moves. (ii) Is the direction of the movement of the ball the same as the direction of the force exerted on it? Yes (iii) Is work done on the ball? Explain. Yes. There is a force exerted on the ball and the ball moves in the same direction as that of the force. (b) Hadi is pushing a wall. (i) Did the wall move? No. (ii) Is work done on the wall? Explain. No. Although a force is exerted on the wall, the wall does not move. (c) Toni drops a coin on the floor. (i) What is the force exerted on the coin? Gravitational force (ii) What is the direction of this force? Downwards (iii) Is work done on the coin? Explain. Yes. There is a force exerted on the coin and the coin moves in the same direction as that of the force. Extra Info Work i Chapter 3 Work, Energy and Simple Machines 37 ©Praxis Publishing_Focus On Science
2. (a) State the definition of work. Work is defined as the force exerted on an object multiplied by the distance moved by the object in the direction of the force. (b) State the SI unit for work. Joule (J) (c) Is work done when the direction of the object’s motion is perpendicular to the exerted force? No (d) Is work done when the force is exerted on an object but the object does not move? No 3. Calculate the work done in these activities. (a) A force of 3 N pulls a 5 N wooden block horizontally. It moves a distance of 160 cm. 160 cm 3 N 5 N Work = Force (N) × distance (m) = 3 × 1.6 = 4.8 J (b) Surya has a mass of 50 kg. She climbs a flight of stairs as shown. [1 kg = 10 N] Work = Force (N) × distance (m) = (50 × 10) × 3 = 1500 J 38 ©Praxis Publishing_Focus On Science
3.2 Power 1. (a) State the definition of power. Power is the rate at which work is done. (b) State the SI unit for power. Watt (W) 2. A machine lifts 250 kg of bricks vertically up to a height of 60 m above the ground. [1 kg = 10 N] (a) Calculate the work done by the machine. Work = Force (N) × distance (m) = (250 × 10) × 60 = 150 000 J (b) If the power of the machine is 1200 W, what is the time needed to lift the bricks? Power = Work Time Time = Work Power = 150 000 1200 = 125 s 3.3 Sources and Forms of Energy 1. Fill in the blanks. work energy cook processes move Energy is the ability to do work. All living things need energy to perform life processes such as growing, reproduction and movement. Non-living things need energy to do work . For example, cars need energy to move and rice cookers need energy to cook rice. 2. There are two types of energy sources. Name them and give three examples each. Non-renewable energy sources. Examples: coal, petroleum and natural gas. Renewable energy sources. Examples: the Sun, wind and moving water. Extra Info Power i Chapter 3 Work, Energy and Simple Machines 39 ©Praxis Publishing_Focus On Science
3. Give one similarity and one difference between fossil fuels and nuclear energy. Similarity: Both are non-renewable energy sources. Difference: Nuclear energy is clean. Fossil fuels pollute the environment. 4. Tick (✓) the correct statements. Cross (✗) the incorrect statements. (a) Renewable energy sources can be replaced when they are used up. ✓ (b) Wind is moving air. ✓ (c) More energy is generated by a windmill when the wind is blowing slower. ✗ (d) Solar panels are used to convert the energy from the Sun into mechanical energy. ✗ (e) Solar energy is dependent on the weather. ✓ (f) In a hydroelectric power station, water is used to turn the turbines to generate electricity. ✓ (g) Biomass is a renewable energy source that comes from rocks and sand. ✗ (h) Fermentation of corn and sugarcane produces ethanol that can be used to power cars. ✓ (i) Waves are the horizontal movements of surface ocean water. ✗ (j) Geothermal energy is the heat energy found deep in the Earth. ✓ 5. The figure shows a power station. Fill in the blanks to describe how it works using the words below. hydroelectric huge moving dam spins electricity The figure shows a hydroelectric power station. It makes use of moving water from rivers. A dam is built across a river to store a huge amount of water in a reservoir at great heights. Water flows through the small opening at the bottom of the dam and spins the turbines in generators to produce electricity . 40 ©Praxis Publishing_Focus On Science
6. Fill in the chart to list the forms of energy as described. Stored energy and is released during a chemical reaction (a) Chemical energy Allows us to see things (d) Light energy Stored energy due to its position or condition (f) Potential energy Stored energy due to its vertical position from the ground (h) Gravitational potential energy The sum of kinetic energy and potential energy (j) Mechanical energy Stored energy due to its stretching or compressing condition (i) Elastic potential energy Energy of motion (g) Kinetic energy Produced by vibrations (e) Sound energy Causes things to get hot (b) Thermal energy The most widely used form of energy at homes (c) Electrical energy Forms of energy 7. We eat food to get energy. (a) What form of energy is stored in food? Chemical energy (b) How do we get energy from food? Our body breaks down the food into smaller molecules and chemical reactions occur to release the energy. Chapter 3 Work, Energy and Simple Machines 41 ©Praxis Publishing_Focus On Science
8. When a drum is hit, it gives out a sound. (a) Is sound a form of energy? Yes (b) How is the sound produced by the drum? The drum skin vibrates when it is hit. Our ear detects the vibrations as sound. (c) Can we hear sound in space? Explain. No. In space, there is no medium for the vibrations to travel into our ears. 9. (a) An object with a mass of 0.5 kg is held at a height of 1 m from the floor. [1 kg = 10 N] (i) What form of energy does the ball possess? Explain. Gravitational potential energy. It is due to its height from the ground. (ii) Calculate the energy possessed by the ball. Gravitational potential energy = mgh = 0.5 × 10 × 1 = 5 J (b) The ball is then raised to a height of 1.5 m from the floor. (i) Has its energy increased or decreased due to its new position? Explain. Increased. Its height from the ground has increased. (ii) Find its increased or decreased energy. Increased gravitational potential energy = mg(h2 – h1 ) = 0.5 × 10 × (1.5 – 1) = 2.5 J (c) State all three factors that affect this form of energy. Mass of the object Height of the object from the surface of the Earth Gravitational strength 1.5 m 1 m 42 ©Praxis Publishing_Focus On Science
10.A motorcycle with a mass of 250 kg is moving at a constant velocity of 32 m s–1. A small car with a mass of 640 kg is moving at a constant velocity. The kinetic energy of the small car is four times as much as the kinetic energy the motorcycle possesses. (a) How much kinetic energy does the motorcycle possess? Kinetic energy of motorcycle = 1 2 mv2 = 1 2 × 250 × 322 = 128 000 J (b) What is the velocity of the small car? Kinetic energy of car = 4 × kinetic energy of motorcycle 1 2 mv2 = 4 × 128 000 1 2 × 640 × v2 = 512 000 v2 = 1600 v = 40 m s–1 The velocity of the car is 40 m s–1. 11.An object has a mass of 2 kg. It is dropped from a height of 5 m above the ground. Assume no energy is lost during the fall. [1 kg = 10 N] (a) What is its gravitational potential energy at the height of 5 m? Gravitational potential energy = mgh = 2 × 10 × 5 = 100 J (b) When it has free-fallen for 2 m, what is its mechanical energy? Explain. At the height of 5 m, its kinetic energy is 0 J, its gravitational potential energy is 100 J and its mechanical energy is 100 J. During the fall, there is no loss of energy. Thus, its mechanical energy after falling for 2 m is still 100 J. (c) What is its velocity just before it hits the ground? Just before hitting the ground, its gravitational potential energy is 0 J and its kinetic energy is 100 J. 1 2 mv2 = 100 1 2 × 2 × v2 = 100 v2 = 100 v = 10 m s-1 Chapter 3 Work, Energy and Simple Machines 43 ©Praxis Publishing_Focus On Science
12.A ball weighs 1 kg. It rolls down from the top of the staircase-like platform to the floor as shown. Assume there is no loss of energy during the movement of the ball. [1 kg = 10 N] (a) Find the kinetic energy, gravitational potential energy and mechanical energy of the ball at P. At P, the ball was not moving. Thus, its kinetic energy is 0 J. Gravitational potential energy = mgh = 1 × 10 × 8 = 80 J Mechanical energy = kinetic energy + gravitational potential energy = 0 + 80 = 80 J (b) Find the kinetic energy, gravitational potential energy and mechanical energy of the ball at Q. At Q, its mechanical energy is 80 J as no energy is lost. Gravitational potential energy = mgh = 1 × 10 × 4 = 40 J Kinetic energy = mechanical energy – gravitational potential energy = 80 – 40 = 40 J (c) Find its velocity at R. Kinetic energy = 40 J 1 2 mv2 = 40 1 2 × 1 × v2 = 40 v2 = 80 v = 8.9 m s–1 (d) Find the kinetic energy, gravitational potential energy and mechanical energy of the ball at S. At S, its mechanical energy is 80 J as no energy is lost. Gravitational potential energy = 0 J (height = 0 m) Kinetic energy = mechanical energy – gravitational potential energy = 80 – 0 = 80 J 8 m P S Q R 4 m 44 ©Praxis Publishing_Focus On Science
13. State the law of conservation of energy. Energy cannot be created or destroyed but can only change from one form into another. 14. State the changes in the forms of energy in each of the situations below. (a) Electric bread toaster Electrical energy thermal energy (b) Drawing an arrow on a bow Chemical energy elastic potential energy (c) Hydroelectric power station Gravitational potential energy electrical energy (d) Kerosene lamp Chemical energy light energy + thermal energy (e) Battery-powered torch Chemical energy electrical energy light energy + thermal energy Chapter 3 Work, Energy and Simple Machines 45 ©Praxis Publishing_Focus On Science
3.4 Simple Machines 1. Match the descriptions to the correct terms. (a) (b) (c) (d) (e) (f) A device that makes our work easier Mechanical advantage The force applied to the machine Input force The distance the load moves Output force A measure of the performance of a machine Machine The distance the input force moves Input distance The force the machine applies on an object Output distance 2. Name the types of simple machines based on the descriptions. (a) Made up of one or more wheels with grooves and a rope Pulley (b) Has a bar pivoting on a fixed point known as a fulcrum Lever (c) An inclined plane wrapped around a cylinder Screw (d) Made up of one or two inclined planes that move Wedge (e) Consists of a wheel and an axle that rotate together Wheel and axle (f) A flat, sloping surface that is used to move a load from a lower area to a higher area Inclined plane 3. (a) Give the two formulas of mechanical advantage. Mechanical advantage = Output force Input force Mechanical advantage = Input distance Output distance (b) What does the ideal mechanical advantage represent? It represents the change in input force that would be achieved by the machine if there were no friction to overcome. 46 ©Praxis Publishing_Focus On Science
4. Levers are a type of simple machine. (a) Briefly describe a lever. A lever is a bar that is pivoted on a fixed point called the fulcrum. (b) Each lever has three important parts, namely the fulcrum, load and effort. In each of the example of levers below, name the parts. (i) Paper cutter Load Fulcrum Effort (ii) Scissors Load Effort Fulcrum (iii) Fishing rod Load Effort Fulcrum Chapter 3 Work, Energy and Simple Machines 47 ©Praxis Publishing_Focus On Science