6   2 The diagram shows an RNA virus that causes influenza. (Source: © Kateryna Kon/Shutterstock) (a) Influenza cannot be treated with antibiotics. Explain why antibiotics cannot be used to treat influenza. 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Turn over 7   (b) The surface of this virus capsid is covered with ‘spike’ proteins. The diameter of the capsid of this virus is 240 nm. 240 nm b = 20.0 nm h = 22.4 nm Diagram of the surface of the virus showing each spike protein as a triangle The diagram shows the area occupied by one spike protein Calculate the maximum number of spike proteins that can be packed on the surface of one virus particle. The formula for calculating the surface area of a sphere is 4πr2 The formula for calculating the area of a triangle is h b × 2 (3) Answer .............................................................. 8   (c) Changes in the RNA of influenza produce new strains of the virus with an altered spike protein. Devise a procedure to determine the similarity of the strains of influenza in saliva samples collected from different people. 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(Total for Question 2 = 9 marks) Turn over 9   3 Eukaryotic cells contain membrane‑bound organelles. (a) The photograph, obtained using an electron microscope, shows an organelle. X (Source: © Science History Images/Alamy Stock Photo) (i) Label a part of this organelle where carbon fixation occurs. (1) (ii) Give the name of the component labelled X. (1) .................................................................................................................................................................................................................................................................................... (iii) Describe how the structure of a membrane in the part labelled X is related to its function. 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(b) The graph shows the changes in biomass, gross primary productivity and the energy used in respiration during succession from grassland to mature forest. 80 60 40 20 0 9 8 7 6 5 4 3 2 1 0 Time / years Energy / a.u. respiration gross primary productivity biomass (i) Add shading to the graph to show the area that represents net primary productivity. (1) Turn over 11   (ii) Describe what is meant by the term succession. 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(iii) Deduce the effect of succession on the level of carbon dioxide in the atmosphere. 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(Total for Question 3 = 13 marks)