Teacher’s Guide Focus-on Science Grade 8 26 © Praxis Publishing Singapore Pte. Ltd. 16 There are valves between the atria and the ventricles to stop the blood from flowing backwards through the heart. 17 A flow chart to simplify the blood circulation in the heart: Lungs Pulmonary Arteries Right Ventricle Right Atrium Vena Cava Body Tissues Aorta Left Ventricle Left Atrium Semilunar valve Tricuspid valve Biscupid valve Semilunar valve Pulmonary Veins 18 One complete contraction and relaxation of the heart to pump blood is called a heartbeat. 19 The heart beats normally when the body is at rest, but it beats faster when the body is working harder. Health Issues Related to the Circulatory System 20 Cardiovascular diseases are diseases related to the heart and blood vessels such as atherosclerosis, hypertension, heart attack (myocardial infarction) and stroke. 21 Atherosclerosis is the hardening and narrowing of the arteries due to the build-up of plaque inside the arteries. Plaque which consists of fat, cholesterol, calcium and other substances can partially or completely block blood flow to the heart. 22 High blood pressure, or hypertension, is a condition when the pressure in the blood vessel of a person is higher than normal. It is one of the contributing factors to heart attacks and stroke. 23 Heart attacks occur when the flow of blood to the heart is blocked due to a buildup of plaque in the coronary arteries of the heart. 24 Strokes occur when the blood vessel to the brain is either blocked by a clot or ruptures. 25 Cardiovascular diseases are caused by a variety of factors, such as poor diet, especially a diet high in fat and salt, lack of exercise and smoking tobacco. Extension / Follow-up Activities Making a simple stethoscope The students are divided into groups. They can use a filter funnel and a cardboard tube to build a simple stethoscope. The filter funnel is placed on the chest of a student. One end of the cardboard tube is fixed over the end of the filter funnel. The other student will place his ear at the other end of the cardboard tube and he will be able to hear the sound of the heartbeat (‘lub-dub’). It is the sound of the heart valves closing. The student counts the number of heartbeats per minute of his friend. ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 27 © Praxis Publishing Singapore Pte. Ltd. Textbook Answers Activity 5 p. 43 Discussion: Heart rate increases after exercising. The demand for oxygen and food in the body increases to provide the extra energy required to carry out the activity. The heart beats faster to deliver both oxygen and food to the muscles, that is why our heart rate increases when we exercise. Think About It p. 43 Discussion: Veins do not pulsate; therefore, you can’t feel a pulse in the veins – only in the arteries. All arteries have a pulse, but it is most easily felt at points where the blood vessel approaches the surface of the body. Lesson 2.3 Respiratory System Learning Outcomes • Describe the structures and organs of the respiratory system • Explain how gas exchange takes place in the alveoli of the lungs • Describe the movement of the rib cage and diaphragm during inhalation and exhalation • Know the diseases related to the respiratory system Key Understanding We need to breathe to stay alive. Oxygen transported around our body is obtained from the air we breathe in. When we breathe, air moves into and out of the lungs, the organ in which gas exchange takes place between the atmosphere and the body. The organs and other parts of the body involved in breathing make up the respiratory system. Induction 1 Get students to answer the following questions to gauge their prior knowledge. (a) Why do we breathe? (b) Which gas do we breathe in? (c) Which gas do we breathe out? 2 Allow students to respond to the questions, then look over their responses and provide more information as needed to assist identifying any gaps in understanding. Teaching and Learning Activities Textbook pp. 45-47 1 Start the discussion by introducing the terms inhalation and exhalation. Ask the students what they understand by the terms inhalation and exhalation. Ask them what the function of the respiratory system is. 2 By referring to the diagram on p. 46, describe the structure of the respiratory system. Ask the students why it is advisable to breathe in through the nose rather than through the mouth. When a person breathes in through the nose, air that passes the nasal cavity becomes warm and the dust particles in it get filtered out by tiny hairs called cilia before the air enters the lungs. When a person breathes in through the mouth, cold and dusty air enter the lungs. ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 28 © Praxis Publishing Singapore Pte. Ltd. 3 Explain the pathway of air after entering the nasal cavity. 4 A simulation model of the respiratory system can be viewed by scanning the QR code given on p. 46. 5 Let students carry out Activity 6 to compare the breathing rates of a person at rest and after exercising. Remind the students that breathing in and out again counts as one breath. Students should notice that their breaths per minute increase after exercising. This is because more oxygen is taken into the body, and more carbon dioxide has to be removed from the body. 6 Ask the students what will happen to the breathing rate if the student runs instead of walking, and for a longer time. Tell them that the breathing rate will rise even higher because when they run and for a longer period, the muscles use even more oxygen and food. 7 Talk about adaptations of the alveoli in the lungs for efficient gas exchange by referring to the diagram given on p. 47. 8 Give the students a situation in which a boy was eating and suddenly he starts choking because a piece of food accidentally got stuck in his windpipe. Get volunteers to act out the situation and show what they must do to help the boy. They can get information from the Internet on what to do to help the boy. Textbook pp. 47−48 9 Start the discussion by asking the students to place their hands on their ribs and breathe in, followed by breathing out. Ask them what they feel. At first, they can feel the ribs moving upwards and outwards, followed by the ribs moving back to their original position. Tell them that these movements occur because the ribs are attached to muscles. However, there are other parts that move during breathing, which is the diaphragm. 10 Stress that the lungs are well protected in a rib cage. 11 Let them carry out Activity 7 to understand better the breathing mechanism. 12 Get the students to read through the ‘Science Facts’ about the harmful effects of smoking, not only to a smoker but also people in the vicinity of the smoker. Textbook p. 49 13 Discuss the diseases of the respiratory system. 14 Introduce diseases such as asthma, bronchitis and emphysema. 15 Divide the students into groups and ask them to use the Internet to get more information such as the symptoms and the cause of these diseases and any other diseases of the respiratory system. Tell them to draw a poster as creatively as possible and present their findings in the class. 16 Discuss the importance of taking good care of the respiratory system. Ask the students to come up with some basic rules to protect their respiratory system. Assessment and Evaluation 1 Observe how students participate in class discussions and activities. 2 Evaluate the accuracy and completeness of the students’ responses during the presentation. 3 Have students complete Exercises 1−10 Workbook pp. 26−31 . Students can get extra info on effects of smoking via the QR code given. 4 Provide feedback to students on their performance, highlighting areas they achieved and where they need to improve. ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 29 © Praxis Publishing Singapore Pte. Ltd. Closure To summarise the important ideas and concepts taught in the lesson, consider using the key points provided through strategies such as a class discussion, a summary statement, a quiz, a visual organiser or a reflective writing assignment. Allow students to ask any additional questions for clarification or clear up any doubts. Structure of the Respiratory System 1 When we breathe in, air enters the nasal cavity in the nose before travelling down the trachea (windpipe). 2 The trachea branches into two bronchi, with each entering the right and left lungs respectively. Each bronchus splits into smaller tubes called bronchioles. 3 The bronchioles end in microscopic air sacs known as alveoli. 4 A lung contains millions of alveoli. 5 In the lungs, oxygen from the air we breathe in passes through the walls of the air sacs into the blood capillaries while carbon dioxide passes from the blood capillaries into the air sacs. Finally, carbon dioxide joins the air we breathe out. 6 Alveoli are adapted to make gas exchange in the lungs occur efficiently: the alveoli wall is only one cell thick, the alveoli is surrounded with a network of blood capillaries and the inner surface of the alveoli is moist. Mechanism of Breathing In and Out 7 During inhalation, the rib cage moves upwards and outwards, and the diaphragm contracts and flattens. This causes the air pressure inside the lungs to decrease and eventually the air enters the lungs. 8 During exhalation, the rib cage moves downwards and inwards, and the diaphragm relaxes and arches upwards. This causes the air pressure inside the lungs to increase and eventually air is pushed out. Diseases of the Respiratory System 9 Some of the respiratory diseases are asthma, bronchitis and emphysema. 10 Asthma is a disorder in which the air passages become narrow and swollen and are blocked by excess production of mucus. 11 Bronchitis is an inflammation of the bronchi when they get irritated, followed by production of thick mucus that blocks the tube causing symptoms such as cough and shortness of breath. 12 Emphysema is a condition that results from the damage of the walls of the alveoli in the lungs, therefore with lesser alveoli, less oxygen reaches the bloodstream. Extension / Follow-up Activities Testing the gas we breathe out Prepare a beaker containing freshly prepared lime water (solution of calcium hydroxide). Ask a student to breathe out through a drinking straw into the beaker. Ask the other students what they see. Explain to them that the air they breathe out contains carbon dioxide gas, that is why the lime water turns milky (cloudy). ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 30 © Praxis Publishing Singapore Pte. Ltd. Textbook Answers Activity 7 p. 48 Discussion: 1 Glass jar represents rib cage; thin rubber sheet represents diaphragm; Y-shaped glass tube represents bronchus, and balloons represent lungs. 2 Inhalation 3 Exhalation Conclusion: Breathing process involves inhalation and exhalation. Lesson 2.4 Excretory System Learning Outcomes • Explain the excretion process • Identify the organs of the excretory system and their excretory products • Know the health effects of smoking, alcohol consumption and drug addiction Key Understanding Our body produces waste products as a result of the metabolic reactions that take place in our cells. The waste products such as urine, sweat and carbon dioxide must be removed from our body because they become toxic when accumulated in the body. Skin, lungs, kidneys and liver are the excretory organs. Induction Start off by asking students why they throw away leftover food or rubbish or things they do not need anymore. Ask them what happens if they do not discard the leftover food or the daily rubbish. Then explain to them that if they do not throw away the rubbish, their house will be smelly and will be invaded by disease-carrying pests such as flies and rats. Therefore, the same concept applies to waste products in our body. If the waste products are not excreted, they will become toxic and make us sick, or damage our organs and may even lead to death. Teaching and Learning Activities Textbook pp. 50–51 1 Hold a discussion and get students to give examples of bodily waste products that they know. 2 Ask them if sweating is healthy and the reasons for their answer. Water released through the sweat pores in the skin evaporates and the body is cooled down as a consequence. Excess heat will be released, especially during workout when the muscles heat up more; sweating cools down the body. 3 Ask them if passing urine is healthy and the reason for their answer. Passing urine flushes out waste products. 4 Introduce all the excretory organs in the body, which are the skin, lungs, kidneys and liver by explaining their structures, functions and how waste products are excreted through them. 5 Ask them if they know which parts of the body have the most sweat glands based on their own experience. Although sweat glands can be found all over the body, the highest concentration of the sweat glands are in the palms of the hands, soles of the feet and under the armpits. ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 31 © Praxis Publishing Singapore Pte. Ltd. 6 Ask the students what the excretory products from the lungs are. The waste products from the lungs are water and carbon dioxide which are excreted together in the exhaled air. One way to detect the presence of water in the exhaled air is to get a volunteer to breathe out onto a cold mirror. Ask the other students to observe the surface of the mirror. The mirror fogs up when you breathe on it. This is because since there is water vapour in the breath, when it touches the mirror’s cool surface, the vapour condenses to form a liquid which is seen as tiny water droplets on the mirror. 7 Ask the students what colour should urine be. Emphasise to them that if their urine is colourless or light yellow, they are consuming enough water but if their urine is darker yellow, they are not drinking enough water. 8 Ask the students if defaecation is an excretion process. Explain to them that defaecation is the removal of undigested food from the digestive tract via the anus. The faeces is not formed due to metabolic reaction, therefore defaecation is not an excretion process. 9 Get them to try out the question in ‘Think About It’ on p. 51. Encourage them to do some research to get more information from the internet. Textbook p. 52 10 Start the discussion on smoking by asking the students what cigarette smoke does to the body. Divide the students into groups and get each group to make a poster as creatively as possible showing the harmful substances in cigarette smoke and the detrimental effects of smoking to the body. They can use secondary sources to get more information such as from magazines, newspapers and the Internet. They will then present their findings to the class. 11 Ask the students the difference between medicines and drugs. Medicines are substances prescribed by the doctor and taken by the patient to make them feel better or to cure their diseases. All medicines are drugs but not all drugs are medicines. Drugs are substances taken without doctor’s prescription and when taken excessively, can eventually cause addiction. 12 Ask the students to name medicines they or their family members have taken before. Ask them if they obtained the medicine from a doctor, a pharmacist or recommended by their parent? Ask them would it be safe for another family member to take their medicine, for instance, their younger sister. Ask them if other household substances could be harmful or addictive if consumed excessively in the long run? 13 Discuss with the students some of the precautions one should be wary of when taking medicines. Get the students’ input. For example, the dosage of the medicine, the interval, the place to keep the medicines at home, parents’ administration of medication to their children and the disposal of unused medicines. 14 Discuss with the students the short-term and long-term effects of consuming alcohol. Assessment and Evaluation 1 Assess students’ understanding of all the processes of excretion by observing their participation in class discussions, whether they provide examples, scenarios, share their thoughts, or work in pairs or small groups. 2 Access students’ understanding of the health effects of smoking, alcohol consumption and drug addiction through their participation in class discussions and activities. 3 Have students complete Exercises 1−3 Workbook pp. 32 . Provide feedback to students on their performance, highlighting areas they achieved and where they need to improve. ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 32 © Praxis Publishing Singapore Pte. Ltd. Closure • To summarise the important ideas and concepts taught in the lesson, consider using the key points provided through strategies such as a class discussion, a summary statement, a quiz, a visual organiser or a reflective writing assignment. You may also ask students to summarise them in their own words. Allow students to ask any additional questions for clarification or clear up any doubts. Skin 1 Sweat is a waste product released from the skin. 2 Sweat contains water, urea and salts. 3 Sweat is produced in the sweat glands which absorb excess water from blood capillaries. 4 Sweat leaves the skin through the pores on the surface of the skin. 5 When sweat evaporates, it cools off the body. Lungs 6 The waste products from the lungs are water and carbon dioxide, produced during cell respiration. 7 When we breathe out, the water and carbon dioxide produced are removed from the body. Kidneys 8 The waste product excreted by the kidneys is the urine. 9 Urine is a yellowish liquid which consists of water, urea and mineral salts. Liver 10 The liver detoxifies blood by getting rid of toxic substances from the food we consume. 11 Liver breaks down toxic substances and converts them into harmless materials before transported to the kidneys to be excreted through the urine. Health effects of smoking, alcohol consumption and drug addiction 12 Smoking cigarette, alcohol consumption and drug addiction may have short-term and long-term effects on the human body. 13 The harmful substances in cigarette smoke can cause addiction, cancer and increase the risk of heart diseases. 14 Some of the short-term effects from drinking alcohol are becoming drunk, lose concentration, difficulty to walk and slow reaction time. 15 Some of the long-term effects from drinking alcohol are higher risk of cancers associated with the digestive system and liver diseases such as cirrhosis, fibrosis and liver cancer. 16 Drugs which are taken without a doctor’s supervision lead to addiction. 17 There are several categories of drugs that causes addiction when taken excessively and misused such as stimulants that increase alertness, depressants that reduce anxiety, and hallucinogens that cause hallucination. • Ask students to reflect on what they have learned in this chapter by completing the sections ‘Recall’ Textbook p. 53 and ‘Concept Map’ Workbook p. 35 . • Let students complete the ‘Objective Questions’ Workbook pp. 33 – 34 and ‘Online Quick Quiz’ Workbook p. 36 to check their mastery of this chapter. ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 33 © Praxis Publishing Singapore Pte. Ltd. • To reinforce students’ critical thinking skills, have them answer the questions in ‘Put on Your Thinking Cap’ Textbook p. 54 and ‘HOTS Daily Application’ Workbook p. 36 that require them to analyse, evaluate or create based on the knowledge they have acquired. • Give students a preview of what will be covered in the upcoming chapter to help them get ready. Before proceeding to the next chapter, evaluate students’ performance in the midterm assessment Workbook pp. 81 – 88 . Textbook Answers Think About It p.51 Drink lots of water, exercise regularly and observe a healthy diet Recall p. 53 1 oxygen 2 complex 3 Monosaccharides 4 amino acids 5 saturated 6 atherosclerosis 7 C 8 haemoglobin 9 Water 10 energy value 11 preservatives 12 enzymes 13 Hydrochloric acid 14 lipase 15 bile 16 ileum 17 heart 18 Veins 19 Coronary 20 alveoli 21 contraction 22 Emphysema 23 urinary bladder Put On Your Thinking Cap p. 54 1 A teen boy has a higher metabolic rate than a teen girl. 2 When you cook vegetables too long, some of the nutrients in them such as water-soluble vitamins (vitamin C especially) gets reduced or destroyed. The longer you cook, more nutrients get destroyed. ©Praxis Publishing_Focus On Science
Teacher’s Guide Focus-on Science Grade 8 34 © Praxis Publishing Singapore Pte. Ltd. 3 This is because of the temporary lowering of his blood pressure. He can sit down and put his head between the knees so that it is lower than the heart or he can lie down with his legs elevated. Project: Risk Factors that Impact Heart Health Textbook p. 55 1 Introduction (a) Introduce the concept of hearth health. (b) Explain to students that they will carry out their research in groups of four. (c) Give a brief overview of the steps involved in the research. (gathering information on the Internet and books, analysing information collected, and presenting the findings creatively). 2 Planning and execution (a) Instruct students to elect a leader in their group who can delegate subtasks to the group members before planning what are the information required and where to search for the information. (b) Provide guidance and support as needed during the planning process. (c) Encourage students to follow their plan carefully. (d) Remind students to gather their information from reliable sources to obtain accurate information. 3 Solution and presentation (a) Instruct students to gather information based on the aspects stated in their textbook but they are encouraged to add more aspects. (b) Allow students to share their findings with the class through a presentation as creatively as possible. They can discuss the similarities and differences in their findings with their peers. 4 Assessment Assess students based on their plan, execution and presentation with the following criteria. (a) The clarity and completeness of the plan (b) The accuracy and completeness of the information gathered (c) The quality of the analysis and conclusions drawn (d) The effectiveness of the presentation and results. ©Praxis Publishing_Focus On Science