DHS 2023 H2 Biology Prelim Practical ans

© DHS 2023 9744/04 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 BIOLOGY Paper 4 Practical Candidates answer on the Question Paper 9744/04 29 August 2023 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the question paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in brackets [ ] at the end of each question or part question. Shift Laboratory For Examiner’s Use 1 23 2 13 3 19 Total 55 This s consists of 15 printed pages (including this cover page) and 1 blank page.

2 © DHS 2023 9744/04 BLANK PAGE

3 © DHS 2023 9744/04 [Turn over 1 Enzyme E catalyses the hydrolysis of starch to maltose. The progress of this enzyme‑catalysed reaction can be followed by measuring the time taken for the substrate, starch, to disappear. You will investigate the effect of compound C, C1, on the hydrolysis of starch. If any solution comes into contact with your skin, wash off immediately under cold water. You will need to dilute the 2.0% compound C solution, C1, which reduces the concentration by a factor of ten between four successive dilutions, to give C2, C3, C4 and C5. Once the dilution has been completed, there is a volume of 10.0 cm3 for each solution in each vial. (a) (i) Complete Table 1.1 to show how you will make the concentrations of the compound C solutions, C2, C3, C4 and C5. Table 1.1 Label of compound C solution Percentage concentration of compound C solution Label of compound C solution to be diluted Volume of compound C solution to be diluted / cm3 Volume of distilled water to make up the dilution / cm3 Total volume / cm3 C1 2.0 10.0 0.0 10.0 C2 0.2 C1 1.0 9.0 10.0 C3 0.02 C2 1.0 9.0 10.0 C4 0.002 C3 1.0 9.0 10.0 C5 0.0002 C4 1.0 9.0 10.0 [3] (ii) Describe a suitable control for the experiment and explain its purpose. …........................................................................................................................................... …........................................................................................................................................... …........................................................................................................................................... . .................................................................................................................................. ..[2] 1. [Description of control] A suitable control would be to replace compound C solution with an equal volume of distilled water; 2. [Purpose of control] To show that change in amylase activity is due to the presence of compound C; 1. Correct concentrations; 2. Correct volume of solutions and label of compound X; 3. Correct precision;

4 © DHS 2023 9744/04 (b) A student suggested the hypothesis that: ‘the higher the concentration of compound C, the slower the breakdown of starch.’ The student carried out some preliminary tests to find the volumes of amylase and starch solutions to use when testing this hypothesis. The student found that the best volumes of compound C, amylase and starch solutions to use were in a ratio of 1 : 2 : 6. Use the results of the tests to plan and carry out an investigation to provide results that will enable you to support or reject this hypothesis. If the complete breakdown of starch takes more than 180 seconds, record as ‘more than 180’. In addition to the 10 cm 3 of compound C solutions prepared according to Table 1 (without the control), you are provided with: • only 20 cm3 of amylase in a container, labelled E • only 60 cm3 of starch in a container, labelled S Using the specimen tubes and the other apparatus provided, plan and carry out a method to obtain results to support or reject the student's hypothesis. You may use the space below to make any notes. Read through (b)(i), (b)(ii) and (b)(iii) before proceeding.

5 © DHS 2023 9744/04 [Turn over (i) State the dependent variable. …........................................................................................................................................... . .................................................................................................................................. ..[1] (ii) Other than the volumes of solutions, state an additional variable to be controlled and explain how this variable can be controlled. …........................................................................................................................................... …........................................................................................................................................... …........................................................................................................................................... . .................................................................................................................................. ..[2] (iii) Outline the steps in your method that you used to collect results. …........................................................................................................................................... …........................................................................................................................................... …........................................................................................................................................... …........................................................................................................................................... …........................................................................................................................................... . .................................................................................................................................. ..[3] (iv) Record your results in a suitable format in the space provided. Concentration of compound C / % Time taken for complete hydrolysis of starch / s 2.0 0.2 0.02 0.002 0.0002 1. Correct table headings with proper units; 2. Correct precision; 3. Correct trend (decreasing time taken with increasing concentration of compound C); [3] Time taken for complete hydrolysis of starch / time taken for iodine solution to remain brown; 1. Using a 3 or 5 cm3 syringe; prepare a solution of 1.0 cm3 of compound C, 2.0 cm3 of amylase and 6.0 cm3 of starch in a test-tube; (appropriate volumes according to the 1:2:6 ratio) 2. Using a Pasteur pipette/dropper, take a sample of mixture every 20 seconds and place it on a spotting tile; (fixed time interval + spotting tile) 3. Using a Pasteur pipette/dropper, add three drops of iodine to sample and record the time using a stopwatch at which the mixture remains brown; 1. State suitable value of temperature of water bath where the test tubes containing the compound C, amylase and starch solutions will be immersed in; 2. Temperature can be controlled using hot and cool water, measured using a thermometer;

6 © DHS 2023 9744/04 (v) State whether or not your results in (b)(iii) support the student’s hypothesis. Give a reason for your decision. …......................................................