Biology 9700/32 May/June 2024: question paper and mark scheme

Question

Some fruits contain protease enzymes. These enzymes can denature the proteins in milk, causing the milk to clot. You will investigate the effect of protease concentration on the time taken for milk to clot. You will use your results to estimate the concentration of protease in a fruit extract. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 P 100% protease solution none 50 M milk none 30 W distilled water none 100 fruit extract containing unknown U none 20 protease concentration If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection. You will need to make different concentrations of protease solution, using proportional dilution of the 100% protease solution, P. You will need to prepare 10 cm3 of each concentration, using P and W. Table 1.2 shows how to prepare one of the concentrations of protease you will use. Decide which other concentrations of protease you will use. (a) (i) Complete Table 1.2 to show how you will prepare the concentrations of protease you will use. Table 1.2 percentage concentration volume of P volume of W of protease / cm3 / cm3 100 10.0 0.0 [2] Carry out step 1 to step 8. step 1 Stir the 100% protease solution, P. In the beakers provided, prepare the concentrations of protease as shown in Table 1.2. step 2 Label test-tubes with the concentrations of protease stated in Table 1.2. step 3 Put 2 cm3 of milk, M, into each labelled test-tube. step 4 Put 1 cm3 of the 100% protease solution, P, into the appropriately labelled test-tube. Start timing. step 5 Hold the test-tube at an angle and slowly rotate the test-tube as shown in Fig. 1.1. Hold a piece of black card behind the test-tube and observe the thin layer of milk on the side of the test-tube. step 6 As soon as a number of small clots appear, stop timing and record the value in (a)(ii). If there are no clots after 180 seconds, stop timing and record as ‘more than 180’. milk drains back small clots stick smoothly from to the sides of the the sides of the test-tube test-tube no clotting clotting Fig. 1.1 step 7 Repeat step 4 to step 6 with each of the other concentrations of protease you prepared in step 1. Record your results in (a)(ii). step 8 Repeat step 2 to step 7 using clean test-tubes. (ii) Record the two sets of results in an appropriate table. [5] (iii) Suggest one source of error in the procedure described in step 6 of this investigation. …… [1] (iv) Suggest why the procedure was repeated. …… [1] (v) To estimate the concentration of protease in fruit extract U, you will need to test a sample of the extract. State the volume of fruit extract U that you will use. (vi) Record the time taken for clots to appear using fruit extract U. time taken = …… [1] (vii) Use your results from (a)(ii) and (a)(vi) to estimate the concentration of protease in fruit extract U. concentration of protease in fruit extract U = …… % [1] (viii) With reference to your estimate in (a)(vii), suggest how you would modify this procedure to obtain a more accurate value for the concentration of protease in fruit extract U. …… [2] (b) The effect of pH on the activity of the protease enzyme actinidin in fruit extract was investigated. Table 1.3 shows the results of the investigation. Table 1.3 pH protease activity / μmol min–1 mg–1 1.8 0.00 4.0 20.25 5.1 24.00 6.1 28.25 7.4 22.50 8.5 6.75 (i) Plot a graph of the data shown in Table 1.3 on the grid in Fig. 1.2. Fig. 1.2 [4] (ii) Use the data in Table 1.3 and your graph in Fig. 1.2 to explain the effect of pH on the activity of protease. …… [3] [Total: 21]

Question

K1 is a slide of a stained transverse section through a plant leaf. (a) (i) Draw a large plan diagram of the region of the leaf on K1 indicated by the shaded area in Fig. 2.1. Use a sharp pencil. Use one ruled label line and label to identify a vascular bundle. draw this region Fig. 2.1 [5] (ii) Observe the trichomes on the leaf on K1. Select a group of four adjacent cells that includes three epidermal cells and one trichome. Each cell must touch at least one other cell. • Make a large drawing of this group of four cells. • Use one ruled label line and label to identify the cell wall of the trichome. [5] (iii) The presence of trichomes on K1 suggests the leaf is from a plant that is a xerophyte. State one other observable feature that suggests the leaf is from a plant that is a xerophyte. …… [1] (b) (i) Fig. 2.2 is a scanning electron micrograph of an open stoma. P R S Q Fig. 2.2 Line P–Q represents the width of the paired guard cells that form the stoma. Line R–S represents the width of the stoma. Calculate the width of the stoma as a percentage of the width of line P–Q. Show your working and give your answer to two significant figures. answer = …… % [4] (ii) Fig. 2.3 and Fig. 2.4 are photomicrographs of the leaf surface from different plants. Fig. 2.3 Fig. 2.4 Identify three observable features that are different between the leaf surface in Fig. 2.3 and the leaf surface in Fig. 2.4. Record these three observable features in Table 2.1. Table 2.1 feature Fig. 2.3 Fig. 2.4 1 2 3 [4] [Total: 19]