18 7 Starch changes the colour of iodine solution from yellow-brown to blue-black. The enzyme amylase hydrolyses starch. The initial rate of reaction of starch hydrolysis was investigated. A test tube contained 25 cm3 of starch suspension to which 1 cm3 of 1% amylase solution was added. A sample was immediately taken from this test tube and added to iodine solution. The light absorbance of this mixture was measured. This was repeated every 30 seconds during the investigation. The results are shown in the graph. Light absorbance / a.u. 0 5 10 15 Time / minutes 0.8 0.6 0.4 0.2 0.0 (a) (i) Name a piece of apparatus that would be used to measure the light absorbance of this mixture. (1) ..................................................................................................................................................................................................................................................................................... Turn over 19 (ii) Calculate the initial rate of reaction for this experiment. (3) Answer................................................................................ (iii) Draw a line on the graph to show the expected trend if a 5% amylase solution was used instead. (1) (b) Explain why the light absorbance of the mixture changed over time. (3) ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... 20 (c) A student placed the same volume of starch suspension into two bags made of Visking tubing. Each bag had a different length and width. The thickness of the Visking tubing for each bag was the same. The membrane of the Visking tubing is partially permeable. The same volume and concentration of amylase solution was added to the starch suspension. Each bag was sealed and placed into test tubes containing the same volume of water, as shown in the diagram. Visking tubing water starch and amylase solution Tube A Tube B The water was tested at regular intervals for the presence of maltose. Turn over 21 Maltose was detected in the water in tube A before it was detected in the water in tube B. Assess the factors that would cause maltose to be detected in tube A before tube B. 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(Total for Question 7 = 12 marks)