1 The diagram represents two of the stages of aerobic respiration that take place in a mitochondrion.

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1 1 The diagram represents two of the stages of aerobic respiration that take place in a mitochondrion. a Name substance X. b Which stage of aerobic respiration takes place inside a mitochondrion and is not represented on the diagram? c Oxygen is needed for the production of ATP on the cristae of the mitochondrion. Explain why. (3 marks) AQA Biology, 2006, Unit 5 (Question 3) This resource sheet may have been changed from the original 1

2 2 A student used the apparatus shown below to measure the rate of aerobic respiration of a woodlouse at different temperatures. a Initially the student removed the syringe and opened the three-way tap so that air could enter the boiling tube. The water bath was kept at 30 C. The student left the apparatus for 5 minutes before closing the tap. Explain why. b The student closed the tap. After 30 minutes the drop of coloured liquid had moved towards the boiling tube. Explain why the drop of coloured liquid moved towards the boiling tube. (3 marks) c The student repeated the experiment three more times at 30 C after leaving the tap open for 10 minutes between repeats. He then repeated the experiment four times with the water bath at 20 C. This resource sheet may have been changed from the original 2

3 i The syringe is used to reset the apparatus. Describe how. ii The same woodlouse was used each time. Explain why. d The student did not set up a control experiment. i Suggest a suitable control experiment for this investigation. ii Explain why a control experiment is needed. The table below shows the mean results of his investigation at each temperature. Distance moved by bead of liquid in 30 minutes / mm Temperature/ C e The cross sectional area of the tubing is 1 mm 2. Calculate the rate of respiration at each temperature in mm 3 O 2 min 1. f Suggest and explain one reason for the difference in rate of respiration at the two temperatures. This resource sheet may have been changed from the original 3

4 3 a The main stages in anaerobic respiration in yeast are shown in the diagram. i Name process X. ii Give one piece of evidence from the diagram which suggests that the conversion of pyruvate to ethanol involves reduction. iii Converting pyruvate to ethanol is important in allowing the continued production of ATP in anaerobic respiration. Explain why. b A scientist investigated the use of a new source of carbohydrate in the production of ethanol for biofuel. She wanted to find the optimum time to leave a mixture of yeast and this carbohydrate to produce ethanol. The scientist set up an airtight container containing yeast and this carbohydrate. She then measured the oxygen, carbon dioxide and ethanol concentrations over 8 hours. This resource sheet may have been changed from the original 4

5 The results of her investigation are shown in the graph below. i The scientist used a container that was airtight. Give two reasons with explanations why the container had to be airtight. (4 marks) ii Explain the relationship between the concentration of oxygen and the concentration of carbon dioxide between 0 and 3 hours. This resource sheet may have been changed from the original 5

6 iii The scientist concluded that yeast starts to respire anaerobically when the oxygen concentration falls below a certain concentration. What is the oxygen concentration when the yeast starts to respire anaerobically? Explain your answer. iv The scientist recommended that when the ethanol is produced commercially as a biofuel the reaction should be stopped at 6 hours. Suggest why. 4 In aerobic respiration, acetylcoenzyme A is broken down as shown in Figure 1. a i Figure 1 Name: Substance W Stage X ii How many carbon atoms are there in one molecule of acid Z? This resource sheet may have been changed from the original 6

7 iii Write the word oxygen on Figure 1 to show where oxygen is used. b Different fatty acids contain different numbers of carbon atoms. The first stages in the aerobic respiration of palmitic acid and of stearic acid are given in equations 1 and 2. Figure 1 i The greater the number of carbon atoms in a fatty acid, the greater the yield of ATP when the fatty acid molecule is respired aerobically. Use Figure 1 and equations 1 and 2 to explain why. (3 marks) ii Dinitrophenol (DNP) is a metabolic poison. It specifically prevents oxidative phosphorylation at stage Y in Figure 1. However, it does not prevent the oxidation of reduced NAD and reduced FAD. Palmitic acid was respired aerobically in the presence of DNP. This resulted in a net yield of only 6 ATP per molecule of palmitic acid. Use information from Figure 1 and from Equation 1 to suggest why. c ATP is better than either glucose or fatty acids as an immediate source of energy for cell metabolism. Explain why. AQA Biology, 2007, Unit 5 (Question 7) This resource sheet may have been changed from the original 7