20 7 The photograph shows sweet red peppers growing on a plant. © Janet Horton / Alamy Stock Photo Unripe sweet red peppers contain the enzyme catalase. As these peppers ripen, the activity of catalase decreases. The equation summarises the reaction catalysed by catalase. hydrogen peroxide water + oxygen (a) The diagram shows the structure of catalase. one of four protein subunits one of four haem groups Turn over 21 Explain why the enzyme catalase is described as having a tertiary and quaternary structure. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 22 (b) The activity of catalase can be measured by collecting the oxygen produced during the reaction. The diagram shows apparatus that can be used to collect the oxygen produced. oxygen collected by displacing water in a test tube tank of water flask containing reaction mixture (i) When measuring the activity of enzymes, the initial rate of reaction should be measured. Explain why the initial rate of reaction should be measured. 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Turn over 23 *(ii) Devise an investigation, using this apparatus, to show that as sweet red peppers ripen the activity of catalase decreases. 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(Total for Question 7 = 11 marks)