Cambridge IGCSE Combined and Co-ordinated Sciences Chapter B8 Notes on activities for teachers/ technicians Activity B8.01 Investigating heat production by germinating peas Apparatus and materials required Session 1: • pea or bean seeds • two beakers of water • Bunsen burner, tripod and gauze Session 2: • boiled peas or beans • • • • • • soaked peas or beans from Session 1 mild disinfectant solution two vacuum flasks two cotton wool plugs for flasks two thermometers clamp stands to support flasks Safety and welfare Eye protection must be worn when boiling the seeds. Otherwise, there are no particular safety issues associated with this activity. Answers to questions A1 Students will probably find that the flask with the live peas had the higher temperature, because they were generating heat as they respired. A2 So that you know any heat produced has come from the peas, and not from any other living organisms. A3 They need some air space to allow them to get oxygen. A4 This allows the carbon dioxide released by the respiring peas to move out of the flask. A buildup of carbon dioxide could prevent them getting oxygen for respiration. A5 The energy released inside the peas is used for making new cells as the peas germinate. 1 © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences Chapter B8 Activity B8.02 Investigating the production of carbon dioxide by anaerobic respiration in yeast Apparatus and materials required • four boiling tubes, fitted with bungs and glass tubing, as shown in the diagram in Activity B8.02 of the coursebook • boiled, cooled water • sucrose or glucose • fresh or dried yeast • boiled yeast suspension • glass rod • pipette • limewater or hydrogencarbonate indicator solution • two beakers to support boiling tubes • wax pencil or other way of marking tubes • liquid paraffin Safety and welfare Ensure that all ends of glass tubing are rounded and smooth. Care must be taken when handling boiling water. Notes Use fast-action yeast if available, as other types of yeast can sometimes be reluctant to become active. Answers to questions A1 to remove all oxygen from it, so the yeast has to respire anaerobically A2 to avoid killing the yeast or denaturing its enzymes A3 to prevent oxygen moving from the air into the solution A4 The indicator should show the presence of carbon dioxide, produced by the yeast during anaerobic respiration. A5 alcohol A6 Students should consider: • which variable they will change − in this case, the type of sugar • what they will measure − for example, the rate at which the indicator changes colour, or the number of bubbles produced in a set period of time • what they will keep constant − for example, temperature, concentration of sugar solution, amount of yeast • how they will record their results − for example, by drawing an outline results table • how they will interpret their results. 2 © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences Chapter B8 Activity B8.03 Comparing the energy content of two kinds of food Apparatus and materials required • Students are to plan their own investigation, so will ask for their own apparatus. However, they are likely to need the following: two foods that are likely to have different energy contents − for example, a peanut and a cashew nut, plain popcorn and popcorn soaked in oil, plain bread and bread soak in oil • means of setting light to the food • mounted needle (to hold the food) • boiling tube held in a clamp on a retort stand • small measuring cylinder or syringe • thermometer Safety and welfare An increasing number of students in many countries are allergic to peanuts. It may therefore be best to avoid using peanuts in this practical, as for some children even the tiniest crumb or even smell of one may cause a severe and dangerous reaction. Notes This is a classic experiment, for good reason. It is often a surprise to students that foods can be used as fuel in this way. There are many sources of error, particularly in the large amount of heat that is lost from the burning food without being transferred to the water which enables students to find plenty to say about the reliability of their results. Activity B8.04 Examining lungs Apparatus and materials required For demonstration: • set of sheep’s lungs • large board and dissecting instruments • long glass tube • access to hot, soapy water and paper towels Safety and welfare Although lungs are no more likely than other meat to cause infection, they should be treated with caution. If possible, students should wear old shirts or lab coats. They could also wear surgical gloves if you think this is a good idea. In any case, hands and all apparatus must be washed very thoroughly in hot, soapy water at the end of the practical session. The lungs must be disposed of appropriately. You may not want to allow students to blow down a tube into the lungs, but you might be prepared to do this yourself. Take great care that the tube is absolutely clean before touching it with your mouth, and that you do not breathe in. 3 © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences Chapter B8 Answers to questions A1 red or pink, because they contain many blood vessels A2 soft and spongy, because they contain thousands of air-filled, thin-walled alveoli A3 so that they can slide easily against the lining of the thorax as they inflate and deflate A4 The oesophagus is behind the trachea, and leads to the stomach. A5 The trachea feels bumpy, because it is supported with C-shaped rings of cartilage to stop it closing when the air inside it is at low pressure. A6 This is the larynx (voice box), which contains cords under tension that vibrate as air passes over them. A7 The lungs will inflate. Activity B8.05 Comparing the carbon dioxide content of inspired air and expired air Apparatus and materials required • apparatus as shown in the diagram in the coursebook Safety and welfare The rubber tubing and glass tubing must be sterilised before use. Do not allow more than one student to use the same piece of rubber tubing. Ensure that they breathe in and out gently, and do not suck. Answers to questions A1 in tube B, as this is the one that the long tube from the mouthpiece goes into A2 in tube A, as this is the one where the long tube connects with the air outside A3 This liquid should stay the same for a long time, though it may change colour after breathing has taken place for some minutes. A4 This liquid should change (limewater to cloudy, hydrogencarbonate indicator to yellow) much sooner. A5 There is more carbon dioxide in expired air than in inspired air. Activity B8.06 Investigating the effect of exercise on rate and depth of breathing Apparatus and materials required • a stopwatch or other timer Safety and welfare There are no safety issues associated with this activity. Notes Students could use the instructions for Activity B7.02 for guidance. Take care, however – it is very common for students to confuse heart rate with breathing rate. There is no simple way in which students can measure the depth of breathing before and after exercise. If you are lucky enough to have a spirometer, you could make use of this. 4 © Cambridge University Press 2017
