thebiotutor.com 2F Respiration Time: 29 minutes Total marks available: 29 Total marks achieved: Andy Todd

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1 thebiotutor.com 2F Respiration Time: 29 minutes Total marks available: 29 Total marks achieved:

2 Q1. John wanted to investigate the effect of temperature on the rate of carbon dioxide production by yeast. He set up this apparatus. (a) The oil layer prevents the entry of air into the glucose solution. Explain why this is necessary. (b) John varied the temperature of the water bath between 15 C and 65 C. He measured the rate of carbon dioxide production by counting the number of bubbles per minute. (i) Sketch the shape of the graph that John would obtain on the axes below. (3)

3 (ii) Give the dependent variable in this experiment. (iii) Give the independent variable in this experiment. (c) Give two variables that John would need to keep the same in his experiment. (d) Suggest one way that John could improve the reliability of his experiment. (e) Suggest how John could improve the accuracy of his measurement of the rate of carbon dioxide production. (f ) Yeast is used to produce beer. Write the word equation for the respiration of yeast that occurs during the

4 production of beer. (3) (Total for question = 14 marks)

5 Q2. The diagram shows a human sperm cell. (a) How many chromosomes are there in the nucleus? (b) Respiration takes place in the middle piece of the sperm cell. Explain why respiration is important to a sperm cell. (c) A sample of semen contains 40 million sperm cells. Only sixty percent of these sperm cells are capable of swimming. Calculate how many sperm cells in this semen sample are capable of swimming. Show your working. Answer... (d) Some men are infertile because they do not produce enough sperm cells or the sperm cells they produce are not good swimmers. There is a test that can be used to find out if a man is infertile. Semen is added to a solution in a test tube. The test tube is then sealed. The solution stays purple if oxygen is present and changes to pink if oxygen is absent. The diagram shows how the test works.

6 (i) A man used this test and the solution remained purple. What does this suggest about the man's sperm? Explain your answer. (ii) Suggest two reasons why the results of the test might not be correct (Total for question = 9 marks)

7 Q3. The diagram shows the apparatus used in a seed germination experiment. (a) The two samples of seeds started at the same temperature of 18 C. The diagram shows the temperature reading on each thermometer after 48 hours. (i) Complete the table to show the temperature of flask A and flask B.

8 (ii) Give a biological explanation for the difference in the temperature of flask A compared to flask B. (b) The seeds in both flasks were washed in disinfectant before being put into the flasks. Suggest why this was done. (c) The cotton wool kept the thermometers in place and prevented the seeds from falling out of the flasks. Suggest why cotton wool was used rather than a rubber bung. (d) The seeds used in the experiment were from the same species. Suggest one other variable that needs to be controlled in this experiment. (Total for question = 6 marks) Q1. This question described an experiment to investigate anaerobic respiration in yeast. Only the best candidates were able to explain the function of the oil layer. Many responses suggested keeping out air, gases or other impurities. The best answers described how the oil prevents oxygen from entering the solution and

9 ensures that anaerobic respiration occurs. In (b) most could sketch the shape showing an increase in respiration rate and some levelling off and the best showing a reduction. In (c) the better candidates could identify the dependent and independent variables and name two variables that should be controlled in the experiment. Less able candidates wrote about amount of yeast or glucose rather than the mass, volume or concentration. In part (d) almost all responses suggested how to increase the reliability. In (e) most candidates could suggest that collecting the gas produced in a syringe or inverted measuring cylinder would enable a more accurate determination of volume per unit time. The best responses gained full marks for a word equation showing how glucose is converted to ethanol and carbon dioxide. Some responses included oxygen and water. Q2. This question gave a diagram of a sperm cell and in (a) most students could give the number of chromosomes present in its nucleus. In (b) most could explain the importance of respiration in providing energy for the sperm to swim using its tail. In part (c) almost all could correctly calculate the number of sperm capable of swimming from the data provided. Part (d) described a fertility test that measures the oxygen use by respiring sperm. In (i) the best students realised that if the solution stayed purple no oxygen was being used for respiration by the sperm so they must be dead or not moving. In (ii) the best answers explained that a break in the seal, a lack of temperature control or a small semen sample could make the results incorrect. Other students suggested that one sample may be atypical. Q3. This question provided students with a diagram showing an experiment to investigate germination and energy release in seeds. In part (a) (i) almost all students correctly read the temperatures from the thermometer scales. In part (ii) about half of the responses could explain the results from the two flasks despite the fact that this experiment is referred to in the specification. In part (b) most could explain that washing the seeds in disinfectant prevents the growth of bacteria. However, in part (c) very few students could suggest why cotton wool is used rather than a rubber bung. Only the best students could suggest that it allows oxygen in and carbon dioxide to escape from the flask. In part (d) most response correctly gave a variable that should be controlled. Q1.

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