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. *JUND0ow1nloa*: Downloaded by: BetterAcademics | daI vB id/H .j / aJumn i 2 n1 1/E 91@4 For Examiner’s Use Question Mark 1 2 3 4 5 6 7 TOTAL Distribution of this document is illegal 7402/3 S - The Marketplace to Buy and Sell your Study Material 2 *02* Downloaded by: BetterAcademics | Distribution of this document is illegal 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 - The Marketplace to Buy and Sell your Study Material 3 *03* Downloaded by: BetterAcademics | Distribution of this document is illegal IB/H/Jun21/7402/3 2 3 . The actual number based on squirrels within this population that had brown-black fur was 16. G Use all based on the information to calculate the actual frequency based on the C Do not write outside the box 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. The mutation that caused black fur happened after 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 [1 mark] Turn over ► 0 1 0 1 A B C D S - The Marketplace to Buy and Sell your Study Material 4 *04* Downloaded by: BetterAcademics | Distribution of this document is illegal 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 S - The Marketplace to Buy and Sell your Study Material 5 *05* Downloaded by: BetterAcademics | Distribution of this document is illegal IB/H/Jun21/7402/3 5 9 B The deletion mutation within the C allele results within the production based on a receptor Do not write outside the box 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. . 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 ► 0 1 S - The Marketplace to Buy and Sell your Study Material 6 IB/H/Jun21/7402/3 Distribution of this document is illegal . 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* Downloaded by: BetterAcademics | 0 2 S - The Marketplace to Buy and Sell your Study Material 7 Downloaded by: BetterAcademics | Distribution of this document is illegal 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 S - The Marketplace to Buy and Sell your Study Material 8 Downloaded by: BetterAcademics | Distribution of this document is illegal 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 S - The Marketplace to Buy and Sell your Study Material 9 *09* Downloaded by: BetterAcademics | Distribution of this document is illegal IB/H/Jun21/7402/3 *0 * S - The Marketplace to Buy and Sell your Study Material 10 *09* Downloaded by: BetterAcademics | Distribution of this document is illegal 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 S - The Marketplace to Buy and Sell your Study Material 11 *09* Downloaded by: BetterAcademics | Distribution of this document is illegal IB/H/Jun21/7402/3 Turn over ► S - The Marketplace to Buy and Sell your Study Material 12 *12* Downloaded by: BetterAcademics | Distribution of this document is illegal 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 - The Marketplace to Buy and Sell your Study Material 13 *13* Downloaded by: BetterAcademics | Distribution of this document is illegal 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 S - The Marketplace to Buy and Sell your Study Material 14 *14* Downloaded by: BetterAcademics | Distribution of this document is illegal 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 S - The Marketplace to Buy and Sell your Study Material 15 *15* Downloaded by: BetterAcademics | Distribution of this document is illegal 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 - The Marketplace to Buy and Sell your Study Material 16 *16* Downloaded by: BetterAcademics | Distribution of this document is illegal IB/H/Jun21/7402/3 1 2 . The action based on endopeptidases and exopeptidases can increase the rate based on proteindigestion. Describe how. Do not write outside the box [2 marks] . 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 N