2026 CJC H2 Biology 9477 P4 ANS

NAME: ___________________________________________ CLASS: _________ INDEX: __________ CATHOLIC JUNIOR COLLEGE JC2 PRELIM EXAMINATION Higher 2 BIOLOGY 9477/04 Paper 4 Practical 27 th August 2026 2 hours 30 minutes Candidates answer on the Question Paper Additional Materials: As listed in Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your index number and name on all the work you hand in. Give details of the practical shift and laboratory, where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a 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. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 20 printed pages. [Turn over Shift Laboratory For Examiner’s Use 1 / 33 2 / 17 TOTAL / 50

2 Answer all questions 1 Urease is an enzyme that hydrolyses urea into ammonia and carbon dioxide. urea + water ammonia + carbon dioxide The formation of ammonia dissolves in aqueous solution forming ammonium ions. This causes the overall pH of the solution to increase which can be detected by using the indicator bromothymol blue. At pH 8.0, the indicator is blue. Fig. 1.1 shows the colour changes of bromothymol blue as pH increases. yellow green-yellow green blue-green blue Fig. 1.1 The point at which the colour changes to blue is the endpoint. Several minutes after the endpoint has been reached the blue colour may become darker, but this can be ignored. You will investigate the effect of changing the concentration of urease in alginate beads on the time taken to reach the endpoint using bromothymol blue. (a) EXPLAIN how reducing the concentration of urease is expected to affect the time taken to reach the endpoint. …………………………………………………………………….….……………………………… [2] ANS: 1. The time taken to reach the endpoint will increase / reaction will be slower or decrease ; there are fewer successful collisions between the urea substrate and the enzyme per unit time, to form enzyme-substrate complexes , 2. slowing down / decreasing the production of ammonia needed to raise the pH to the blue endpoint, hence decreases the rate of reaction /OWTTE You are provided with: ● a beaker, labelled hot water , in which to collect hot water at temperature of 50 º C to 55 º C. ● a beaker, labelled tap water , in which to collect tap water. ● a beaker, labelled water bath , needed for reaction. ● paper towels for blotting moisture from alginate beads. 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 4

3 You are also provided with the materials in Table 1.1: Table 1.1 labelled contents hazard volume / cm 3 E 2.0% urease solution harmful irritant 20 A 2.0% sodium alginate solution none 50 C 1.0% calcium chloride solution harmful irritant 100 S urea solution none 100 W distilled water none 100 U unknown concentration of urease none 10 B indicator bromothymol blue none 10 P alkaline solution harmful irritant 10 Urease solution E, calcium chloride C, and alkaline solution P are irritants. Suitable eye protection should be worn. If E, C, or P comes into contact with your skin, wash it off immediately under a tap. Bromothymol blue indicator solution is made up using ethanol and should be kept away from naked flames. Care should be taken when using hot water. (b) You will need to carry out a serial dilution of the 2.0% urease solution, E , to reduce the concentration by half between each successive dilution: E2 , E3 , E4 and E5 . You will need to prepare four concentrations of urease in addition to the 2.0% urease solution, E . After the serial dilution is completed, you will need to have 5 cm 3 of each concentration available to use. (i) Complete Fig. 1.2 to show how you will prepare for your serial dilution, ● stating, under each beaker, the volume and concentration of E available for use in the investigation. ● using one arrow, with a label above the beaker, to show the volume and concentration of E added to prepare the concentration. ● using another arrow, with a label above the beaker, to show the volume of distilled water, W , added to prepare the concentration. 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 4

4 Fig. 1.2 [3] Read steps 1 – 11 before starting the investigation. Proceed as follows. 1 Label and prepare beakers with the concentrations of urease solutions E2 , E3 , E4 and E5 in the small beakers provided, as stated in Fig. 1.2. Use one syringe to transfer the urease solutions in this step, washing the syringe between each use. Do not use this syringe for any solutions other than urease solution. 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 4

5 2 Preparation of alginate beads: ● Label 6 small plastic containers M1 , M2 , M3 , M4 , M5 , and MU to prepare the urease-alginate mixtures. ● Add 3.0 cm 3 of sodium alginate solution, A , into each plastic container using a clean syringe. ● Add 3.0 cm 3 of each enzyme solution E , E2 , E3 , E4 , E5 , and U , into the plastic containers M1 , M2 , M3 , M4 , M5 , and MU respectively. ● Mix each solution thoroughly with a glass rod, ensuring the rod is washed between each container. ● Place 15 cm 3 of calcium chloride solution, C , into a clean small beaker. Using 1 cm 3 syringe held vertically 5 cm above the beaker, draw up mixture M1