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1 Centre Number Surname Candidate Signature Candidate Number Other Names Notice to Candidate. The work you submit for assessment must be your own. If you copy from someone else or allow another candidate to copy from you, or if you cheat in any other way, you may be disqualified. Candidate Declaration. I have read and understood the Notice to Candidate and can confirm that I have produced the attached work without assistance other than that which is acceptable under the scheme of assessment. Date General Certificate of Education Advanced Level Examination June 2012 For Teacher s Use Section PSA Stage 2 Skills Section A Section B TOTAL (max 50) Mark Biology BIO6T/Q12/test Unit 6T A2 Investigative Skills Assignment Written Test For submission by 15 May 2012 For this paper you must have: l the task sheet, your results and your calculations l a ruler with millimetre measurements l a calculator. Instructions: l Use black ink or black ball-point pen. l Fill in the es at the top of this page. l Answer all questions. l You must answer the questions in the space provided. Do not write around each page or on blank pages. l Do all rough work in this book. Cross through any work you do not want to be marked. Time allowed l 1 hour 15 minutes Information l The marks for questions are shown in brackets. l The maximum mark for this paper is 38. l You will be marked on your ability to: use good English organise information clearly use scientific terminology accurately. Details of additional assistance (if any). Did the candidate receive any help or information in the production of this work? If you answer yes give the details below or on a separate page. Yes No Teacher Declaration: I confirm that the candidateʼs work was conducted under the conditions laid out by the specification. I have authenticated the candidateʼs work and am satisfied that to the best of my knowledge the work produced is solely that of the candidate. Signature of teacher... Date... As part of AQA s commitment to assist students, AQA may make your coursework available on a strictly anonymous basis to teachers, examining staff and students in paper form or electronically, through the internet or other means, for the purpose of indicating a typical mark or for other educational purposes. In the unlikely event that your coursework is made available for the purposes stated above, you may object to this at any time and we will remove the work on reasonable notice. If you have any concerns please contact AQA. To see how AQA complies with the Data Protection Act 1988 please see our Privacy Statement at aqa.org.uk. BIO6T/Q12/test

2 2 Section A These questions relate to your investigation of the effect of temperature on respiration in yeast. Use your Task Sheet and your results to answer them. Answer all questions in the spaces provided. 5 You were told to leave the tubes in the water bath for 5 minutes (step 5). Explain why. (1 mark) 6 You were told to make sure that the water bath temperature stayed at 35 o C (step 6). Describe how you monitored the water bath temperature and kept it constant at 35 o C. 7 There was no control experiment in this investigation. Describe the control experiment you would set up. Explain why this control experiment would be important.

3 3 8 You were told not to shake the tubes again (step 9). Shaking the tubes would have caused the methylene blue to go blue again. Suggest why. 9 Respiration by the yeast caused the methylene blue to go colourless. Explain how. Turn over for the next question Turn over

4 4 10 A student carried out a similar investigation to yours but he used more temperatures. His results are shown in the graph. 5 4 Time taken for methylene blue to go colourless / minutes Temperature / ºC (a) Use the graph to describe the effect of temperature on the rate of respiration.

5 5 10 (b) Explain the shape of the curve between 10 and 40 o C. (3 marks) (Extra space) Turn over for the next question Turn over

6 6 RESOURCE SHEET Resource A A student investigated the rate of respiration of yeast cells. He set up a conical flask with a suspension of yeast in some apple juice. He took samples of the mixture at different times and found the number of yeast cells. His results are recorded in Figure 1. Figure 1 Time from start of investigation / days Mean number of yeast cells ( 10 6 ) per cm

7 7 Resource B A scientist investigated the use of a new source of carbohydrate in the production of ethanol for biofuel. He 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. He then measured the oxygen, carbon dioxide and ethanol concentrations over 8 hours. The results of his investigation are shown in Figure Figure Oxygen Ethanol Concentration / arbitrary units Carbon dioxide Time / hours Turn over

8 8 Section B Use the information in the Resource Sheet to answer the questions. Answer all questions in the spaces provided. Use Resource A to answer Questions 11 to The student set up a suspension of yeast in apple juice. Apple juice contains all the nutrients that yeast requires for growth. Name two types of nutrients present in the apple juice that are essential for the growth and reproduction of yeast cells The student counted the yeast cells in a sample of the suspension. Give one precaution the student should have taken to make sure he obtained a representative sample. Explain how this precaution would result in a representative sample. 13 Calculate the percentage increase of yeast cells between day 3 and day 4. Show your working. Answer...

9 9 14 The increase in the number of yeast cells was less between days 10 and 11 than it was between days 3 and 4. Give two reasons why Use Resource B to answer Questions 15 to The scientist used a container that was airtight. Give two explanations why the container had to be airtight (4 marks) Turn over

10 10 16 Explain the relationship between the concentration of oxygen and the concentration of carbon dioxide between 0 and 3 hours. 17 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. 18 (a) The scientist worked for a biofuel company. Give two suggestions for further work he should do to make sure that the results he presented to the company were reliable. Explain how each of your suggestions would make the results more reliable. Suggestion... Explanation... Suggestion... Explanation... (4 marks)

11 11 18 (b) The scientist recommended that when the ethanol is produced commercially as a biofuel the reaction should be stopped at 6 hours. Use Figure 2 to suggest why. 18 (c) The scientist s work was funded by a biofuel company. Explain why the source of funding can cause problems with scientific work. 24 END OF QUESTIONS Copyright 2012 AQA and its licensors. All rights reserved.