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1 Centre Number Surname 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. Candidate Signature Candidate Number Other Names Date For Teacher s Use Section Mark PSA Stage 1 Skills Stage 2 Skills Section A General Certificate of Education Advanced Subsidiary Examination June 2013 Section B TOTAL (max 50) Human Biology HBI3T/P13/test Unit 3T AS Investigative Skills Assignment Written Test For submission by 15 May 2013 For this paper you must have: l the task sheet, your results and your calculations l a ruler with millimetre measurements l a calculator. Time allowed l 1 hour 15 minutes 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. Information l The marks for questions are shown in brackets. l The maximum mark for this paper is 36. l You are expected to use a calculator where appropriate. 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 HBI3T/P13/test

2 2 Section A These questions are about your investigation into the effect of time of day on mitosis. Use your Task Sheet, your results and your graph to answer the questions. Answer all questions in the spaces provided. 1 You left roots in acid at 60 ºC for 4 minutes (steps 2 and 3). The acid kills the cells. 1 (a) Suggest how acid kills the cells. 1 (b) Suggest why it is necessary to kill the cells. 2 Root tips grow rapidly. This makes them suitable for use in this investigation. Explain why. 3 You squashed the root tip between two slides to spread out the cells (step 6). Why was this important?

3 3 4 When you examined the tissue, you could see the chromosomes if the cell was in mitosis (step 8). What happens to the chromosomes during mitosis to make them visible? 5 You counted cells that were showing signs of mitosis. Many cells were not in mitosis. 5 (a) In what stage of the cell cycle were these cells? 5 (b) What happens to DNA during this stage? 6 You calculated percentages of cells in mitosis (Candidates Results Sheet: Stage 2). Explain the advantage of using percentages of cells rather than numbers of cells. Turn over for the next question Turn over

4 4 7 A student carried out a similar investigation to you. His initial results are shown in the table. He calculated the mean number of cells showing chromosomes. The mean for his own results and for the teacher are shown in the table. Mean number of cells showing chromosomes (± standard deviation) Student s result Teacher s result 10.8 (± 0.9) 12.7 (±1.3) Do his results show that time of day affects mitosis? Explain your answer. 8 The student also recorded the number of cells in each stage of mitosis. The table shows how he presented his initial and processed results. Stage of mitosis Number of cells in each stage of mitosis Percentage of cells in each stage of mitosis Prophase Metaphase 219 Anaphase Telophase

5 5 8 (a) Where in the cell are the chromosomes located during metaphase? 8 (b) Complete the table to show the percentage of cells that were in metaphase. 8 (c) In the student s investigation the mean time for these cells to complete one mitotic division was 90 minutes. He recognised that he could use the percentage values from his table to calculate the time cells spent in each stage of mitosis. Use the data in the table to calculate the time in seconds spent in prophase. Show your working.... seconds 8 (d) A mitotic index can be calculated for a tissue. This is a measure of the rate of mitosis. Mitotic index = number of dividing cells total number of cells The student counted a total of 863 cells. Use the formula and data from the table to calculate the mitotic index for the root tips. Show your working.... mitotic index 16 Turn over

6 6 Resource Sheet Resource A Too much exposure to ultraviolet rays (UV) from the sun can cause skin cancer. Sunscreen is a cream that is supposed to protect the skin from UV. Some sunscreen creams contain a substance called retinyl palmitate (RP) to absorb this UV. Scientists investigated whether cream containing RP reduced skin cancer caused by UV. They used 6 groups of 100 laboratory animals, and put a cream containing a different concentration of RP on the skin of animals in each group. The scientists exposed all the animals to the same very intense UV and checked them regularly for signs of skin cancer. The table shows their results. Concentration of retinyl palmitate / % Mean time taken to develop skin cancer / days

7 7 Resource B The mitotic index is a measure of the rate of mitosis in a tissue. The larger the mitotic index the faster the rate of mitosis. A scientist calculated the mitotic index for samples of skin taken from a patient with skin cancer. He took one skin sample from a healthy area of the patient s skin and one from an area affected by the cancer. He took these samples at regular intervals. The scientist discovered that cell division in the patient s skin cells follows a pattern that repeats every 24 hours. The scientist s results for one day are shown in the graph Skin cells taken from an area of skin with cancer 0.20 Mitotic index Skin cells taken from an area of healthy skin :00 04:00 08:00 12:00 16:00 20:00 24:00 Time of day / hours Turn over for question 9 Turn over

8 8 Section B Use the information in the Resource Sheet to answer the questions. Answer all the questions in the spaces provided. Use Resource A to answer Questions 9 to Describe the effect of different concentrations of retinyl palmitate on the development of cancer. 10 The scientists used groups of 100 animals. Suggest two reasons why they used such large groups Tests like these are usually carried out on animals such as rats, mice or rabbits. 11 (a) Apart from ethical reasons suggest one reason why rats, mice or rabbits are a suitable choice for testing a sunscreen intended to be used by people.

9 9 11 (b) Explain why carrying out these tests on humans would be unethical. 12 The scientists tested one group of animals with UV but with cream containing no retinyl palmitate. Explain why. 13 An alternative ingredient in sunscreen creams is titanium oxide. Suggest two properties this ingredient should have to make it an effective alternative to retinyl palmitate Turn over

10 10 Use Resource B to answer Questions 14 to The graph shows mitotic indices over 24 hours. 14 (a) When was there the greatest difference in mitotic index between skin cells from areas with cancer and skin cells from healthy areas? Time of day / hours (b) (i) Sometimes the mitotic index for skin cells from an area of healthy skin was higher than the mitotic index for skin cells from an area of skin with cancer. For how long did this happen? 14 (b) (ii) Use your answer to 14 (b) (i) to calculate the percentage of the 24-hour period this time represents.... % 15 The scientists could not calculate the standard deviation. Explain why.

11 11 16 Skin cancers are malignant. Explain the meaning of the term malignant. 17 Some skin cancers are treated by radiotherapy. Radiotherapy is more damaging to cells when they are in mitosis. Doctors discussed the timing of radiotherapy sessions to maximise success when treating patients with skin cancer. When do the data suggest would be the best time of day to maximise success? Explain your answer. (4 marks) 20 END OF QUESTIONS Copyright 2013 AQA and its licensors. All rights reserved.