Biology 0610/53 October/November 2020: question paper and mark scheme

Question

Amylase is an enzyme that catalyses the break-down of starch into reducing sugars. Amylase is produced by seeds during germination. You are provided with extract U, which is made from germinating seeds. You are going to estimate the concentration of amylase in seed extract U by comparing it to known concentrations of amylase. Read all the instructions but DO NOT CARRY THEM OUT until you have drawn a table for your results in the space provided in 1(a)(ii). You should use the gloves and eye protection provided while you are carrying out the practical work. Step 1 Label four small beakers A, B, C, and D. Step 2 Use the syringes to add the volumes of 2% amylase and distilled water shown in Table 1.1 to each labelled beaker. Table 1.1 volume of 2% final percentage volume of distilled beaker amylase solution concentration of water / cm3 / cm3 amylase solution A 10.0 0.0 2.0 B 7.5 2.5 1.5 C 5.0 5.0 1.0 D 2.5 7.5 (a) (i) Complete Table 1.1 by calculating the final percentage concentration of amylase solution for beaker D. ……% [1] Step 3 Label five test-tubes A, B, C, D and U. Step 4 Use a syringe to add 2 cm3 of starch suspension to each of the labelled test-tubes. Step 5 Prepare a white tile by using a pipette to put drops of iodine solution in five columns labelled A, B, C, D and U, as shown in Fig. 1.1. There should be 8 drops of iodine solution in each column. A B C D U drop of iodine solution 1 2 3 time / minutes 4 5 6 white tile 7 8 Fig. 1.1 Step 6 Use a clean syringe to add 2 cm3 of amylase solution from beaker A to test-tube A and shake gently to mix. Step 7 Repeat step 6 using beakers B, C, D and U and test-tubes B, C, D and U. Step 8 Start the stop-clock. Step 9 After one minute use a clean pipette to remove one drop of solution from test-tube A and add it to the first drop of iodine solution, A1, on the white tile. Observe any colour change. Step 10 Repeat step 9 using: • the contents of test-tube B and iodine solution drop B1 • the contents of test-tube C and iodine solution drop C1 • the contents of test-tube D and iodine solution drop D1 • the contents of test-tube U and iodine solution drop U1. Step 11 Repeat steps 9 and 10 after two minutes using iodine solution drop A2, B2, C2, D2 and U2. Step 12 Continue to test the contents of the test-tubes at one minute intervals until a drop of the mixtures in the beakers has been added to all eight rows of iodine solution drops on the white tile. Step 13 Observe the colour of each drop of iodine solution on the white tile and determine the time at which the starch in each test-tube was broken down. In your table in 1(a)(ii), record the time taken for the starch to be broken down. If starch was still present in row 8 record the time taken as >8. (ii) Prepare a table to record your results. [4] (iii) Explain how you decided when all of the starch had been broken down in step 13. …… [1] (iv) Estimate the concentration of amylase in seed extract U using your results in 1(a)(ii). State the evidence that supports your choice. estimated amylase concentration of U …… evidence …… [1] (v) Describe how you would test for the presence of reducing sugars. State the result for a positive test. method …… positive test result …… [3] (b) Seeds contain starch as a store of energy. Amylase in the seeds catalyses the break-down of the stored starch into reducing sugars. Seeds use the reducing sugars to provide some of the energy required for germination. Plan an investigation to find out how temperature affects the activity of amylase in germinating seeds. …… [6] (c) A scientist investigated how the activity of amylase in a seed changed as it germinated. She measured the activity of amylase in a germinating seed over a period of 18 days. The results are shown in Table 1.2. Table 1.2 activity of amylase time / days / arbitrary units 0 0 3 0 6 40 9 240 12 240 15 120 18 65 (i) Plot a line graph of the data in Table 1.2. [4] (ii) Describe the pattern shown by the data in your graph. …… [2] (d) (i) The data in Table 1.2 did not enable the scientist to determine precisely when the amylase was most active. Explain why. …… [1] (ii) Suggest what further data is needed to be able to determine exactly when amylase was most active. …… [1] [Total: 24]

Question

Fig. 2.1 shows a photograph of two winged seeds from a sycamore tree. seed wing seed A B magnification ×4 Fig. 2.1 (a) (i) Make a large drawing of the two winged seeds shown in Fig. 2.1. Do not label your drawing. [4] (ii) Measure the length of line AB on the winged seed on Fig. 2.1. length of line AB …… mm Calculate the actual seed length using the equation and your measurement. Include the unit. length of line AB magnification = actual seed length [3] (b) Fig. 2.2 is a photograph of a seed from another type of tree. wing seed magnification ×1.5 Fig. 2.2 Describe one similarity and one difference between the seeds in Fig. 2.1 and the seed in Fig. 2.2. similarity …… difference …… [2] (c) Seeds such as those in Fig. 2.1 and in Fig. 2.2 can rotate when they fall, moving them further away from the parent tree. A student collected sycamore seeds with wings of different lengths. They dropped the seeds from the same height and measured the distance travelled by each seed. The results are shown in Fig. 2.3. 140 130 120 distance travelled by the seed 110 / cm 100 90 80 8 10 12 14 16 18 20 seed wing length / mm Fig. 2.3 (i) Estimate, using the graph, the distance travelled by a seed with a wing length of 15 mm. Show on your graph how you estimated this value. …… cm [2] (ii) Calculate the percentage increase in the distance travelled by a seed with a wing length of 18 mm compared to a seed with a wing length of 10 mm. Give your answer to two significant figures. Space for working. …… % [3] (iii) State two variables that should be kept constant in the investigation described in 2(c). 1 …… 2 …… [2] [Total: 16]