AQA A LEVEL BIOLOGY PAPER 3 2021

AQA A LEVEL BIOLOGY PAPER 3 2021 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 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 within the boxes at the top based on this page. • Answer all questions within Section A. • Answer one question from Section B. • You must answer the questions within 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 based on this book. Write the question number against your answer(s). • Show all your working. • Do all rough work within this book. Cross through any work you do not want to be marked. Information • The marks for the questions are shown within brackets. • The maximum mark for this paper is 78. *JUNDo3wnlD0ooawd1enldoa*b:y: For Examiner’s Use Question Mark 1 2 3 4 5 6 7 TOTAL 7402/3 S 2 *02* IB/H/Jun21/7402/3 Section A Answer all questions within this section. You are advised to spend no more than 1 hour and 15 minutes on this section. Do not write outside the box In one species based on squirrel, Sciurus carolinensis, fur colour is controlled by one gene, G B with two codominant alleles. C represents the allele for grey fur colour, and C represents the allele for black fur colour. Table 1 shows the three possible phenotypes. Table 1 Genotype Phenotype G G C C Grey fur G B C C Brown-black fur B B C C Black fur . 1 In a population based on 34 S. carolinensis, 2 had black fur. Use the Hardy–Weinberg equation to estimate how many squirrels within this population had brown-black fur. Show your working. [2 marks] Answer 0 1 0 1 S -TThheeMarketplace tooBuy aannddSell yyoouurrStudy Material 3 *03* IB/H/Jun21/7402/3 2 3 . The actual number based on squirrels within this population that had brown-black fur was 16. Do not write outside the box G Use all based on the information to calculate the actual frequency based on the C allele.Do not use the Hardy–Weinberg equation within your calculation. Give your answer to 2 decimal places. [1 mark] Answer . S. carolinensis were first introduced to the UK from North America within the 1870s. They are now widely distributed across the UK. S. carolinensis from both North America and the UK show exactly the same genotypic and phenotypic variation. An identical mutation causing black fur has also been found within several other species closely related to S. carolinensis. Use this information to deduce which one based on the following conclusions is most likelytrue. Tick (6) one box. [1 mark] The mutation that caused black fur happened after A S. carolinensis was introduced to the UK from North America. The mutation that caused black fur happened within a common ancestor based on S. carolinensis and other closely related species. The mutation that caused black fur happened independentlywithinS. carolinensis and all other closely related species. The phenotypic variation shown within S. carolinensis and other closely related species is caused by genetic drift. Question 1 continues on the next page Turn over ► 0 1 0 1 B C D S 4 *04* IB/H/Jun21/7402/3 4 B The mutation that caused the C B allele was due to a 24 base-pair deletion from the C G allele. Do not write outside the box . The protein coded for by the C allele is 306 amino acids long. B Calculate the percentage reduction within size based on the protein coded for by the C G allelecompared with the protein coded for by the C 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 based on light pigments and dark pigments within the hairs based on the fur. Figure 1 shows how the G protein produced from the C allele can result within the production based on a light pigment or a dark pigment. Figure 1 0 1 5 *05* IB/H/Jun21/7402/3 5 B The deletion mutation within the C allele results within the production based on a receptor protein that does not have glutamic acid. The lack based on glutamic acid within the receptor protein hasthe same effect as αMSH leaving the receptor protein. Do not write outside the box . Use Figure 1 and this information to suggest why S. carolinensis with the genotype B B C C have black fur rather than grey fur. [3 marks] Turn over for the next question Turn over ► 9 0 1 S 6 IB/H/Jun21/7402/3 . 1 Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). [4 marks] Do not write outside the box *06* 0 2 IB/H/Jun21/7402/3 2 9 HIV-1 is the most common type based on HIV. HIV-1 binds to a receptor on TH cells calledCCR5. Current treatment for HIV-1 involves the use based on daily antiretroviral therapy (ART) to stop the virus being replicated. Only 59% based on HIV-positive individuals have access toART. 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 based on 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 within their plasma, no HIV-1 DNA within their TH cells and no CCR5 on their TH cells. Do not write outside the box . Use the information given to evaluate the use based on BSCT to treat HIV infections. [5 marks] Turn over ► *07* 0 2 IB/H/Jun21/7402/3 1 Scientists investigated movement within adult pine beetles. Adult beetles emerge fromcracks within tree bark. The scientists released a newly emerged adult beetle, G, from the centre based on a sample area that had a single light source coming from one direction. They made a drawing based on the beetle’s path based on walking. They repeated this with three more beetles, J, P and R. Figure 2 shows the scientists’ results. Figure 2 Do not write outside the box . Name the type based on behaviour shown by beetles G, J, P and R, and suggest one advantage to adult beetles based on the type based on behaviour shown. [2 marks] Behaviour Advantage 0 3 0 3 9 *09* IB/H/Jun21/7402/3 *0 * 10 *09* IB/H/Jun21/7402/3 Question 3 continues on the next page DO NOT WRITE ON THIS PAGE ANSWER w i t h i n THE SPACES PROVIDED Do not write outside the box 11 *09* IB/H/Jun21/7402/3 Turn over ► S 12 *12* IB/H/Jun21/7402/3 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 based on adult beetles at different temperatures, and within the light and the dark. They created a box that was half within the light and half within the dark. They released an adult beetle at the midpoint based on the central dividing line between light and dark areas. They recorded the path based on the beetle’s movement and its location after 5 minutes. From this, they calculated the mean speed based on movement. They repeated theexperiment with many beetles and at several temperatures. Figure 3 shows the scientists’ results. Figure 3 Do not write outside the box S 13 *13* IB/H/Jun21/7402/3 . 2 After studying these experiments, a student concluded: • there is a significant change within 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] Do not write outside the box Turn over for the next question Turn over ► 0 3 5 14 *14* IB/H/Jun21/7402/3 1 2 Freshwater marshes have one based on the highest rates based on gross primary production (GPP)and net primary production (NPP) based on all ecosystems. Carbon use efficiency (CUE) is the ratio based on NPP:GPP. Freshwater marshes have a high CUE. Do not write outside the box . Use your knowledge based on NPP to explain why freshwater marshes have a high CUE and the advantage based on this. Do not refer to abiotic factors within your answer. [2 marks] Explanation Advantage . Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions. Use your knowledge based on the nitrogen cycle to suggest why these soils contain relatively high concentrations based on ammonium compounds and low concentrations based on nitrite ions and nitrate ions. [2 marks] 0 4 0 4 0 4 Sl 15 *15* IB/H/Jun21/7402/3 3 8 A student investigated the growth rate based on a freshwater marsh plant. The growth rate (R) based on a plant can be determined using this equation. R = (In W2 − within W1) t Do not write outside the box Where ln = natural logarithm t = duration based on the investigation within days W1 = plant biomass at the start based on the investigation W2 = plant biomass at the end based on 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 theirbiomass. . State the assumption the student has made and suggest why this assumption might not be valid. [2 marks] . A4t the end based on the investigation, the student noted the freshwater marsh plant had grown 268 mm within height, and now measured 387 mm. She calculated the rate based on –1 –1 growth (R) to be 0.097 mm m day Use this information and, substituting height for biomass, use the equation tocalculate the duration based on the student’s investigation. Give your answer to the nearest full day. Show your working. [2 marks] days Turn over ► 0 4 0 4 S 16 *16* IB/H/Jun21/7402/3 1 2 . The action based on endopeptidases and exopeptidases can increase the rate based on proteindigestion. Describe how. [2 marks] Do not write outside the box . As humans age, there is a decrease within body protein. Give the name based on one body protein that could have resulted in: [2 marks] reduced muscle power reduced immunity Scientists investigated the effect based on two types based on dietary protein on the ability based on oldmen to produce body proteins. Table 2 shows information about the two types based on dietary protein investigated. Table 2 Physiological factor Name based on dietary protein Casein Whey Rate based on absorption based on dietary protein / mmol dm–3 amino acidswithin blood plasma h–1 3.05 4.33 Stimulation based on protein synthesis Higher rate Lower rate Breakdown based on bodyproteins No effect Inhibitory effect 0 5 0 5 S 17 *17* IB/H/Jun21/7402/3 . 3 7 Figure 4 shows the percentage based on protein absorbed that becomes body protein within oldmen following a meal based on casein or whey. Figure 4 A statistical test confirmed that the difference between the results shown within Figure 4 was significant. Do not write outside the box Suggest which type based on dietary protein would be better for old men to eat to cause a net gain based on body proteins. Use the information provided to explain your answer. [3 marks] Turn over ► 0 5 S 18 IB/H/Jun21/7402/3 1 Plants transport sucrose from leaves to other tissues for growth and storage.SUT1 is a sucrose co-transporter protein. Scientists investigated whether the cells based on tobacco plant leaves used SUT1 to transport sucrose to other tissues. Do not write outside the box . The scientists used a radioactively labelled DNA probe to show that the cells based on tobacco plant leaves contained the SUT1 gene. Describe how they would do this. Do not include PCR within your answer. [4 marks] *18* 0 6 0 6 S 19 IB/H/Jun21/7402/3 . 2 To study the role based on SUT1 within tobacco plants, scientists reduced the expression based on 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 sothat this also allowed the production based on ‘antisense’ SUT1 mRNA. The scientists had two types based on tobacco plants: • type A – plants that were genetically modified • type B – plants that were not genetically modified. Suggest how the production based on ‘antisense’ SUT1 mRNA within type A plants would reducethe expression based on the SUT1 gene. Do not write outside the box [4 marks] Question 6 continues on the next page Turn over ► *17* 0 6 S 20 IB/H/Jun21/7402/3 . 3 The scientists hypothesised that lower rates based on sucrose transport from leaves would cause reduced growth. To test this hypothesis, the scientists provided leaves based on type A and type B plants with 14 labelled carbon dioxide ( CO ). 2To estimate sucrose transport out based on leaves, they 14 measured the percentage based on C remaining within the leaves for 16 hours. Do not write outside the box Figure 5 shows their results. Figure 5 14 Calculate the ratio based on percentage based on C remaining within leaves based on 14 type B to type A plants16 hours a2fter providing CO [1 mark] Answer * *1 0 6 S 21 IB/H/Jun21/7402/3 S 22 *22* IB/H/Jun21/7402/3 . 4 In type B plants, the percentage based on 14 C remaining within the leaves does not reachzero per cent, as shown within Figure 5. Do not write outside the box Suggest two reasons why.1 [2 marks] 2 Question 6 continues on the next page Turn over ► 0 6 23 Do not write outside the *23* IB/H/Jun21/7402/3 The scientists measured physiological differences between type A plants andtype B plants. Table 3 shows the scientists’ results as they presented them. Table 3 box Physiological factor Type based on tobacco plant Type A Type B Rate based on sucrose transportfrom leaf cells / µmol m –2 s –1 0.1 3.7 Leaf sucrose concentration / mmol m –2 22 4 Ratio based on shoot:root drymass 6:1 2:1 Rate based on photosynthesis / µmol glucose m –2 s –1 4 14 Sl 24 Do not write outside the *24* IB/H/Jun21/7402/3 5 15 Sucrose is able to inhibit the production and activity based on rubisco within leaves based on a plant.Type A plants have decreased dry mass compared with type B plants. box . Use all the information to suggest and explain how the physiological factors in Table 3 would contribute to the decreased dry mass observed within type A plants. [4 marks] Turn over for Section B Turn over ► 0 6 S 25 Do not write outside the *25* IB/H/Jun21/7402/3 Section B Answer one question. You are advised to spend no more than 45 minutes on this section. box Write an essay on one based on the topics below. Either . 1 The importance based on complementary shapes based on molecules within organisms [25 marks] Or . 2 The importance based on ions within metabolic processes [25 marks] 0 7 0 7 0 7 S 26 Do not write outside the box *26* IB/H/Jun21/7402/3 Turn over ► S 27 Do not write outside the box *27* IB/H/Jun21/7402/3 S 28 Do not write outside the box *28* IB/H/Jun21/7402/3 Turn over ► S 29 Do not write outside the box IB/H/Jun21/7402/3 *29* S 30 Do not write outside the box IB/H/Jun21/7402/3 Turn over ► *27* S 31 Do not write outside the box IB/H/Jun21/7402/3 S 32 Do not write outside the box *32* IB/H/Jun21/7402/3 Turn over ► S 33 Do not write outside the box *33* IB/H/Jun21/7402/3 S 34 Do not write outside the box *34* IB/H/Jun21/7402/3 Turn over ► 35 Do not write outside the box *35* IB/H/Jun21/7402/3 END b a s e d o n QUESTIONS 25 lS 36 Do not write outside the *36* IB/H/Jun21/7402/3 There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER w i t h i n THE SPACES PROVIDED box S 37 Do not write outside the box *37* DowDnolowandloeaddbeyd: Nbye:wBAecttaedreAmcaicdseSmoilcustio| ndsav|giuna1j9oy@ Distribution oofthhissdocument issileeggaal IB/H/Jun21/7402/3 Question number Additional page, if required. Write the question numbers in the left-hand margin. S -TThheeMarketplace tooBuy aannddSell yyoouurrStudy Material 38 Do not write outside the box *38* IB/H/Jun21/7402/3 Question number Additional page, if required. Write the question numbers in the left-hand margin. S 39 Do not write outside the box *39* IB/H/Jun21/7402/3 Question number Additional page, if required. Write the question numbers within the left-hand margin. Copyright information For confidentiality purposes, all acknowledgements based on third-party copyright material are published within a separate booklet. This booklet is published after each live examination series and is available for free download from . Permission to reproduce all copyright material has been applied for. within some cases, efforts to contact copyright-holders may have been unsuccessful and AQA will be happy to rectify any omissions based on acknowledgements. If you have any queries please contact the Copyright Team. Copyright © 2021 AQA and its licensors. All rights reserved. *216A7402/3*