ASRJC 2024 H2 Prelims P4 (A)

ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P4 CANDIDATE NAME I BIOLOGY 9744/04 Paper 4 Practical 28 August 2024 Wednesday Candidates answer on the Question Paper. 2 hours 30 minutes Additional Materials: As listed in the Confidential Instructions. READ THESE INSTRUCTIONS FIRST Write your name and class 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 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. 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. Shift Laboratory For Examiner’s Use 1 2 3 Total 55 H2 ANDERSON SERANGOON JUNIOR COLLEGE HIGHER 2 CLASS INDEX NUMBER CLASS

2 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P4 This document consists of 21 printed pages and 3 blank pages. Answer all questions. 1 Bromelain is a proteolytic enzyme, which catalyses the hydrolysis of proteins into amino acid s. This enzyme can be found in fruits, such as pineapple. Gelatin contains structural proteins derived from animal tissues high in collagen. After dissolving in warm water, it sets into a gel-like structure upon cooling. The action of bromelain on gelatin gel results in liquification of the gel. You will investigate the effect of different concentrations of pineapple bromelain on gelatin breakdown. You are required to: • make five boiling tubes of gelatin gel • obtain pineapple juice extract using the pineapple sample provided • prepare a range of pineapple bromelain concentrations • add each concentration of pineapple bromelain solution into a boiling tube of gelatin gel • measure volume of liquified gelatin after 10 minutes of incubation. You are provided with: • 1 pineapple sample of a fixed mass, in a petri dish labelled A • 100.0 cm3 distilled water W, in a container labelled W • 3.0 g gelatin powder, in a specimen tube labelled G. Read steps 1- 6. Proceed as follows. 1 Using the container labelled hot water, collect approximately 100 cm3 of hot water from where it is provided in the laboratory. 2 Add all of the gelatin powder in a specimen tube labelled G into a beaker labelled X. Pour 75.0 cm3 of hot water directly into beaker X. 3 Use a glass rod to mix gently, so as to minimise air bubbles from forming. Stir for at least 1 minute to allow the powder to dissolve completely to form a gelatin mixture. 4 Take up 10.0 cm3 of the gelatin mixture into a syringe. 5 Position the syringe so that the nozzle touches the side of one of the boiling tubes. 6 Gently push the plunger of the syringe so that the mixture runs slowly down the side of the boiling tube to the bottom. 7 Repeat step 6 for the remaining four boiling tubes.

3 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P4 [Turn over 8 To the beaker labelled ice-bath, add ice to approximately the 400 cm3 mark. Immediately, place all five boiling tubes into the beaker of ice. Ensure all tubes are positioned upright and incubate in the ice bath for at least 10 minutes to allow setting of the gelatin. During this incubation period, continue with step 10. (a) (i) Explain why it is necessary for the tubes to remain upright throughout the cooling period. so that gelatin solution remains evenly distributed along the length of the tube/ even surface formed after gel is set → allows surface area to volume ratio to remain constant, since differences in surface area of gelatin can affect gelatin breakdown by bromelain enzyme. [1] 9 After 10 minutes, check the consistency of the gelatin by tilting the mixture slightly. If the gelatin does not move, the gelatin gel is set. Otherwise, continue to incubate in the ice- bath for another 5 minutes. 10 Transfer the pineapple sample in the petri dish labelled A onto a white tile. Using a kitchen knife, cut the pineapple sample into small pieces. 11 Using a plastic spoon, add the small pieces of pineapple into the mortar. Add 6.0 cm 3 of distilled water W and crush the pineapple pieces using the pestle for 1 minute to form a mixture. 12 Use a plastic spoon to transfer the first half of the pineapple mixture onto a sieve to extract the pineapple juice. Using the pestle, grind the pineapple mixture on the sieve for 1 minute. Collect the pineapple filtrate F1 in the beaker labelled B. 13 Use a plastic spoon to transfer the pineapple mixture left on the sieve into the petri dish labelled A. 14 Repeat step 12 for the remaining half of pineapple mixture in the mortar. Before proceeding to step 16, you will need to obtain at least 10.0 cm3 filtrate. If less than 10.0 cm3 filtrate is obtained, proceed to step 15. 15 Use a plastic spoon to transfer the pineapple mixture on the petri dish from step 13 and pineapple mixture left on the sieve from step 14 to a filter bag. Squeeze the filter bag using your fingers to collect the pineapple juice in the beaker labelled B

4 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P4 16 You will carry out a serial dilution of pineapple filtrate F1 to reduce the concentration of pineapple bromelain solution by a factor of 2 between each of four successive dilutions to obtain F2, F3, F4 and F5. You are required to make a sufficient volume of each pineapple bromelain solution so that, once the serial dilution has been completed, there is a volume of at least 5.0 cm3 for each concentration prepared. Assume that the filtrate F1 obtained is considered pure pineapple juice. (ii) Complete Table 1.1 to show how you will make the concentrations of pineapple bromelain solutions F2, F3, F4 and F5. Table 1.1 1. Correct percentage concentrations of pineapple bromelain solution (3 sf) 2. Correct percentage concentrations of pineapple bromelain solution to be diluted (3 sf) 3. Correct volumes of pineapple bromelain solution and W (1 dp) pineapple bromelain solution F1 F2 F3 F4 F5 percentage concentration of pineapple bromelain solution 100 50.0 25.0 12.5 6.25 percentage concentration of pineapple bromelain solution to be diluted 100 50.0 25.0 12.5 volume of pineapple bromelain solution to be diluted/ cm3 5.0 5.0 5.0 5.0 volume of distilled water W to make the dilution/ cm3 5.0 5.0 5.0 5.0 [3] 17 Prepare pineapple bromelain solutions F2, F3, F4 and F5 in the plastic containers provided, as shown in Table 1.1. 18 Once the gelatin is set, label the different boiling tubes as F1, F2, F3, F4 and F5. Place the labelled boiling tubes of gelatin on the test-tubes rack. 19 Add in 4.0 cm3 of pineapple bromelain solution to each of the five tubes, F1, F2, F3, F4 and F5, respectively. Start timing immediately. 20 At the end of 10 minutes, pour the liquified gelatin with the pineapple bromelain solution into a measuring cylinder carefully and measure the volume collected. 21

5 ASRJC BIOLOGY DEPT 9744//2024/J2PRELIM/P4 [Turn over (iii) Record your results in an appropriate table. Percentag