20 8 The activity of enzymes is affected by a number of factors. (a) Explain why increasing the temperature of an enzyme-controlled reaction changes the rate of reaction. 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Turn over 21 (b) A student investigated the activity of the enzyme catalase in potato. This enzyme is found in potato cells. It catalyses the conversion of hydrogen peroxide to oxygen and water. The diagram shows the apparatus used to collect the data. beaker containing water retort stand burette oxygen potato hydrogen peroxide rubber tube (i) Describe how two named variables, other than the potato, can be controlled in order to obtain valid results. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 22 (ii) The graph shows the results of the investigation. 300 270 240 210 180 150 120 90 60 30 0 50 45 40 35 30 25 20 15 10 5 0 Time / seconds Volume of oxygen produced / cm3 Determine the initial rate of reaction from this graph. (1) Answer .............................................................. Turn over 23 (iii) Explain why the rate of reaction decreases over time. 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(c) The student used this apparatus to investigate the effect of using increasing numbers of potato cubes on the rate of reaction. The potato was cut into 1 cm3 cubes to be used in five trials. In the first trial, one cube was added to the flask and the volume of oxygen produced in 30 seconds was measured. The hydrogen peroxide was then replaced. This was repeated in the other four trials using 2, 3, 4 and 5 cubes of potato. Explain the results you would expect from this investigation. 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(Total for Question 8 = 13 marks) 24 BLANK PAGE