WJEC Biology for AS Level Student Book: 2nd Edition

(a) (i) Describe the effect of lead nitrate on the growth of the seedling roots. (3) (ii) Suggest the role of lead nitrate in producing this effect. (1) (iii) Describe the mechanism that might produce the observed results. (3) (b) Suggest two ways in which the experiment could be made more accurate. (2) (c) It could be argued that the different responses to different lead nitrate concentrations were not related to the lead nitrate, but to some other factor. A control experiment was, therefore, necessary. (i) What is the purpose of a control experiment? (1) (ii) Suggest a suitable control experiment for this investigation. (2) (Total 12 marks) 3 Milk can be made lactose-free by passing it down a column of the enzyme lactase, immobilised in alginate beads, as shown in Image 3.1. An experiment was carried out to determine the optimum size of alginate beads. Using the same volumes of reagents, three bead diameters were prepared: 3 mm, 6 mm and 12 mm. The beads were placed in columns. The same volume of milk, 5 cm 3 , was run into each column at the same rate. (a) (i) Name one additional factor that should be kept constant during the experiment. (1) (ii) Describe a suitable control for this experiment. (1) (iii) Suggest the effect the diameter of the beads would have on the percentage yield of product and justify your answer. (3) (iv) Explain the result you would expect if the flow rate were decreased. (1) (v) Suggest why immobilised lactase is more resistant to thermal denaturation than lactase in solution. (3) (b) Name the two monosaccharides produced by the breakdown of lactose. (1) (c) State two advantages of using immobilised enzymes in industrial processes. (2) (Total 12 marks) Image 3.1  1.4 Enzymes and biological reactions 93