AQA A Level Biology 7402/3 Paper 3 Question Paper June 2021 Version 1.0 Final

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AQA A-Level Biology 7402/3 Paper 3 Question Paper June 2021 Version 1.0 Final / AQA A-Level Biology 7402-3 Paper 3 Question Paper June 2021 Version 1.0 Final / AQA A-Level Biology Paper 3 Question Pap... er June 2021 Version 1.0 Final Time allowed: 2 hours Materials For this paper you must have: •a ruler with millimetre measurements •a scientific calculator. Instructions •Use black ink or black ball-point pen. •Fill in the boxes at the top of this page. •Answer all questions in Section A. •Answer one question from Section B. •You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages. •If you need extra space for your answer(s), use the lined pages at the end ofthis book. Write the question number against your answer(s). •Show all your working. •Do all rough work in this book. Cross through any work you do not want to be marked. Information •The marks for the questions are shown in brackets. •The maximum mark for this paper is 78. Please write clearly in block capitals. Centre number Candidate number Surname Forename(s) Candidate signature I declare this is my own work. A-level BIOLOGY Paper 3 AQA 2 *02* IB/H/Jun21/7402/3 Do not write outside the box Section A Answer all questions in this section. You are advised to spend no more than 1 hour and 15 minutes on this section. 0 1 In one species of squirrel, Sciurus carolinensis, fur colour is controlled by one gene, with two codominant alleles. CG represents the allele for grey fur colour, and CB represents the allele for black fur colour. Table 1 shows the three possible phenotypes. Table 1 Genotype Phenotype CGCG Grey fur CGCB Brown-black fur CBCB Black fur 0 1 . 1 In a population of 34 S. carolinensis, 2 had black fur. Use the Hardy–Weinberg equation to estimate how many squirrels in this population had brown-black fur. Show your working. [2 marks] Answer 3 *03* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 0 1 . 2 The actual number of squirrels in this population that had brown-black fur was 16. Use all of the information to calculate the actual frequency of the CG allele. Do not use the Hardy–Weinberg equation in your calculation. Give your answer to 2 decimal places. [1 mark] Answer 0 1 . 3 S.carolinensis were first introduced to the UK from North America in the 1870s. They are now widely distributed across the UK. S.carolinensis from both North America and the UK show exactly the same genotypicand phenotypic variation. An identical mutation causing black fur has also been found in several other species closely related to S. carolinensis. Use this information to deduce which one of the following conclusions is most likely true. Tick (✓) one box. [1 mark] A The mutation that caused black fur happened after S.carolinensis was introduced to the UK from North America. B The mutation that caused black fur happened in a common ancestor of S. carolinensis and other closely related species. C The mutation that caused black fur happened independently in S. carolinensis and all other closely related species. D The phenotypic variation shown in S. carolinensis and other closely related species is caused by genetic drift. Question 1 continues on the next page 4 *04* IB/H/Jun21/7402/3 Do not write outside the box The mutation that caused the CB allele was due to a 24 base-pair deletion from the CG allele. 0 1 . 4 The protein coded for by the CB allele is 306 amino acids long. Calculate the percentage reduction in size of the protein coded for by the CB allelecompared with the protein coded for by the CG allele. Give your answer to 3 significant figures and show your working. [2 marks] Answer In S. carolinensis, fur colour depends on the distribution and relative amounts of light pigments and dark pigments in the hairs of the fur. Figure 1 shows how the protein produced from the CG allele can result in the production of a light pigment or a darkpigment. Figure 1 5 *05* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box The deletion mutation in the CB allele results in the production of a receptor protein that does not have glutamic acid. The lack of glutamic acid in the receptor protein has the same effect as αMSH leaving the receptor protein. 0 1 . 5 Use Figure 1 and this information to suggest why S. carolinensis with the genotype CBCB have black fur rather than grey fur. [3 marks] Turn over for the next question 9 6 *06* IB/H/Jun21/7402/3 Do not write outside the box 0 2 . 1 Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). [4 marks] 7 *07* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box HIV-1 is the most common type of HIV. HIV-1 binds to a receptor on TH cells called CCR5. Current treatment for HIV-1 involves the use of daily antiretroviral therapy (ART) to stop the virus being replicated. Only 59% of HIV-positive individuals have access to ART. Scientists have found that two HIV-1-positive patients (P and Q) have gone into remission (have no detectable HIV-1). This happened after a blood stem cell transplant (BSCT). • Patient P was given two BSCTs, and patient Q was given one BSCT. • All BSCTs came from a donor with TH cells without the CCR5 receptor. • In addition, patient P had radiotherapy, and patient Q had chemotherapy. Both of these treatments are toxic. • Both patients (P and Q) stopped receiving ART 16 months after BSCT. 18 months after stopping ART, both patients had no HIV-1 RNA in their plasma, no HIV-1 DNA in their TH cells and no CCR5 on their TH cells. 0 2 . 2 Use the information given to evaluate the use of BSCT to treat HIV infections. [5 marks] 9 8 *08* IB/H/Jun21/7402/3 Do not write outside the box 0 3 Scientists investigated movement in adult pine beetles. Adult beetles emerge from cracks in tree bark. The scientists released a newly emerged adult beetle, G, from the centre of a sample area that had a single light source coming from one direction. They made a drawing of the beetle’s path of walking. They repeated this with three more beetles, J, P and R. Figure 2 shows the scientists’ results. Figure 2 0 3 . 1 Name the type of behaviour shown by beetles G, J, P and R, and suggest one advantage to adult beetles of the type of behaviour shown. [2 marks] Behaviour Advantage 9 *09* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box Question 3 continues on the next page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED 10 *10* IB/H/Jun21/7402/3 Do not write outside the box At higher temperatures and higher light intensities, adult pine beetles normally • move more • fly rather than walk. When preparing to fly, these adult beetles walk slowly. The scientists investigated the movement of adult beetles at different temperatures, and in the light and the dark. They created a box that was half in the light and half in the dark. They released an adult beetle at the midpoint of the central dividing line between light and dark areas. They recorded the path of the beetle’s movement and its location after 5 minutes. From this, they calculated the mean speed of movement. They repeated the experiment with many beetles and at several temperatures. Figure 3 shows the scientists’ results. Figure 3 11 *11* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 0 3 . 2 After studying these experiments, a student concluded: •there is a significant change in movement between 35 °C and 37.5 °C •between 35 °C and 37.5 °C, more beetles move away from the light •between 35 °C and 37.5 °C, more beetles have a slower walking speed. Suggest reasons why these conclusions might not be valid. [3 marks] Turn over for the next question 5 12 *12* IB/H/Jun21/7402/3 Do not write outside the box 0 4 Freshwater marshes have one of the highest rates of gross primary production (GPP) and net primary production (NPP) of all ecosystems. Carbon use efficiency (CUE) is the ratio of NPP:GPP. Freshwater marshes have a high CUE. 0 4 . 1 Use your knowledge of NPP to explain why freshwater marshes have a high CUE and the advantage of this. Do not refer to abiotic factors in your answer. [2 marks] Explanation Advantage 0 4 . 2 Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions. Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions. [2 marks] 13 *13* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box A student investigated the growth rate of a freshwater marsh plant. The growth rate (R) of a plant can be determined using this equation. R = (InW2 − In W1)t Where ln = natural logarithm t = duration of the investigation in days W1 = plant biomass at the start of the investigation W2 = plant biomass at the end of the investigation The student used the equation above; however, she substituted height for biomass. This was because she did not want to destroy the plants to measure their biomass. 0 4 . 3 State the assumption the student has made and suggest why this assumption might not be valid. [2 marks] 0 4 . 4 At the end of the investigation, the student noted the freshwater marsh plant had grown 268 mm in height, and now measured 387 mm. She calculated the rate of growth (R) to be 0.097 mm m–1 day–1 Use this information and, substituting height for biomass, use the equation to calculate the duration of the student’s investigation. Give your answer to the nearest full day. Show your working. [2 marks] days 8 14 *14* IB/H/Jun21/7402/3 Do not write outside the box 0 5 . 1 The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how. [2 marks] 0 5 . 2 As humans age, there is a decrease in body protein. Give the name of one body protein that could have resulted in: [2 marks] reduced muscle power reduced immunity Scientists investigated the effect of two types of dietary protein on the ability of old men to produce body proteins. Table 2 shows information about the two types of dietary protein investigated. Table 2 Physiological factor Name of dietary protein Casein Whey Rate of absorption of dietary protein / mmol dm–3 amino acids in blood plasma h–1 3.05 4.33 Stimulation of protein synthesis Higher rate Lower rate Breakdown of body proteins No effect Inhibitory effect 15 *15* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box Figure 4 shows the percentage of protein absorbed that becomes body protein in old men following a meal of casein or whey. Figure 4 A statistical test confirmed that the difference between the results shown in Figure 4 was significant. 0 5 . 3 Suggest which type of dietary protein would be better for old men to eat to cause a net gain of body proteins. Use the information provided to explain your answer. [3 marks] 7 16 *16* IB/H/Jun21/7402/3 Do not write outside the box 0 6 Plants transport sucrose from leaves to other tissues for growth and storage. SUT1 is a sucrose co-transporter protein. Scientists investigated whether the cells of tobacco plant leaves used SUT1 to transport sucrose to other tissues. 0 6 . 1 The scientists used a radioactively labelled DNA probe to show that the cells of tobacco plant leaves contained the SUT1 gene. Describe how they would do this. Do not include PCR in your answer. [4 marks] 17 *17* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 0 6 . 2 To study the role of SUT1 in tobacco plants, scientists reduced the expression of the SUT1 gene. When the SUT1 gene is transcribed, the SUT1 mRNA produced is called ‘sense’ SUT1 mRNA. The scientists genetically modified plants by inserting an extra gene so that this also allowed the production of ‘antisense’ SUT1 mRNA. The scientists had two types of tobacco plants: • type A – plants that were genetically modified • type B – plants that were not genetically modified. Suggest how the production of ‘antisense’ SUT1 mRNA in type A plants would reduce the expression of the SUT1 gene. [4 marks] Question 6 continues on the next page 18 *18* IB/H/Jun21/7402/3 Do not write outside the box 0 6 . 3 The scientists hypothesised that lower rates of sucrose transport from leaves would cause reduced growth. To test this hypothesis, the scientists provided leaves of type A and type B plants with labelled carbon dioxide (14CO2). To estimate sucrose transport out of leaves, they measured the percentage of 14C remaining in the leaves for 16 hours. Figure 5 shows their results. Figure 5 Calculate the ratio of percentage of 14C remaining in leaves of type B to type A plants16 hours after providing 14CO2 [1 mark] Answer 19 *19* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 0 6 . 4 In type B plants, the percentage of 14C remaining in the leaves does not reach zero per cent, as shown in Figure 5. Suggest two reasons why. [2 marks] 1 2 Question 6 continues on the next page 20 *20* IB/H/Jun21/7402/3 Do not write outside the box The scientists measured physiological differences between type A plants and type B plants. Table 3 shows the scientists’ results as they presented them. Table 3 Physiological factor Type of tobacco plant Type A Type B Rate of sucrose transport from leaf cells / μmol m–2 s–1 0.1 3.7 Leaf sucrose concentration / mmol m–2 22 4 Ratio of shoot:root dry mass 6:1 2:1 Rate of photosynthesis / μmol glucose m–2 s–1 4 14 21 *21* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box Sucrose is able to inhibit the production and activity of rubisco in leaves of a plant. Type A plants have decreased dry mass compared with type B plants. 0 6 . 5 Use all the information to suggest and explain how the physiological factors in Table 3 would contribute to the decreased dry mass observed in type A plants. [4 marks] Turn over for Section B 15 22 *22* IB/H/Jun21/7402/3 Do not write outside the box Section B Answer one question. You are advised to spend no more than 45 minutes on this section. 0 7 Write an essay on one of the topics below. Either 0 7 . 1 The importance of complementary shapes of molecules in organisms [25 marks] Or 0 7 . 2 The importance of ions in metabolic processes [25 marks] 23 *23* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 24 *24* IB/H/Jun21/7402/3 Do not write outside the box 25 *25* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 26 *26* IB/H/Jun21/7402/3 Do not write outside the box 27 *27* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 28 *28* IB/H/Jun21/7402/3 Do not write outside the box 29 *29* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 30 *30* IB/H/Jun21/7402/3 Do not write outside the box 31 *31* Turn over ► IB/H/Jun21/7402/3 Do not write outside the box 32 *32* IB/H/Jun21/7402/3 Do not write outside the box END OF QUESTIONS 25 33 *33* IB/H/Jun21/7402/3 Do not write outside the box There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED 34 *34* IB/H/Jun21/7402/3 Do not write outside the box Question number Additional page, if required. Write the question numbers in the left-hand margin. 35 *35* IB/H/Jun21/7402/3 Do not write outside the box Question number Additional page, if required. Write the question numbers in the left-hand margin. 36 *36* IB/H/Jun21/7402/3 Do not write outside the box Question number Additional page, if required. Write the question numbers in the left-hand margin. [Show More]

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