2025 NJC H2 Biology Prelims Paper 4 QP

© NJC 2025 9744/04/SH2 Preliminary Examination [Turn over NATIONAL JUNIOR COLLEGE, SINGAPORE Senior High 2 Preliminary Examination Higher 2 CANDIDATE NAME BIOLOGY CLASS 2bi2_____ REGISTRATION NUMBER Biology Paper 4 Practical 9744/04 3 September 2025 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name, Biology class, and registration number 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 the brackets [ ] at the end of each question or part question. Shift 1 2 3 Laboratory BI23 BI24 CM43 CM44 For Examiner’s Use 1 35 2 20 Total 55 This document consists of 19 printed pages and 1 blank page.

2 © NJC 2025 9744/04/SH2/H2 Biology/Preliminary Examination Answer all questions. 1 Plants can be categorised into sun and shade plants. Sun plants need more sunlight than shade plants for photosynthesis. Sun plants are exposed to high sunlight intensity and hence are adapted against overheating and desiccation, while shade plants have little exposure to sunlight and hence are adapted to be more efficient in absorbing light for photosynthesis. Chloroplasts were isolated from these two types of plants and suspended in a buffer solution. You are required to: ● immobilise chloroplast in sodium alginate beads, and ● investigate the effect of immobilised chloroplast from sun and shade plants on the rate of photosynthesis. During the light-dependent stage of photosynthesis, hydrogen ions and electrons are transferred to hydrogen acceptor molecules, including NADP. Potassium permanganate can be used as an indicator to monitor the rate of the light-dependent stage of photosynthesis. When potassium permanganate is reduced, it turns from purple-pink to colourless. You are provided with: ● chloroplast suspensions S1 and S2 from the two types of plants ● sodium alginate solution, labelled A ● calcium chloride solution, labelled C ● dilute sulfuric acid, H2SO4 ● potassium permanganate solution, KMnO4 ● distilled water, labelled W ● a lamp. Dilute sulfuric acid and potassium permanganate are corrosive. If they come into contact with your skin, wash them off immediately under cold water. Read steps 1–18 before starting the investigation. Proceed as follows. 1 Put 20.0 cm3 of C into a small beaker. 2 Put 5.0 cm3 of A into a separate small container. 3 Stir the chloroplast suspension in S1 thoroughly. 4 Put 5.0 cm3 of S1 into the same container as A. Mix well. 5 Use a Pasteur pipette to collect about 2.0 cm3 of the mixture containing S1 and A. 6 Suspend the Pasteur pipette over the beaker containing C.

3 © NJC 2025 9744/04/SH2 Preliminary Examination [Turn over 7 Gently press the Pasteur pipette to release a drop of the mixture into C as shown in Fig. 1.1. The drop should form a bead that will sink to the bottom of the beaker. 8 Repeat step 7 to produce at least 40 beads. Fig. 1.1 9 Using a spatula, transfer 40 beads to the Petri dish to rinse with distilled water. 10 Set up a lamp. Place three test tubes on a test tube rack positioned 10 cm from the lamp. Do not switch on the lamp yet. 11 Put 4.0 cm3 of distilled water into each test tube. 12 Transfer 20 beads from the Petri dish to each of the two test tubes. The third test tube without any bead will be used as a colour standard. 13 Add 0.5 cm3 of H2SO4 to each test tube. 14 Add 0.5 cm3 of KMnO4 to each test tube. 15 Turn on the lamp and immediately start the stopwatch. You may use the white tile to assist with colour observation. 16 Record in (a)(i) the time taken for the purple-pink indicator to become colourless. If the purple-pink indicator solution has not become colourless after ten minutes, record the time as “more than 600”. 17 Repeat steps 1 to 16 with chloroplast suspension S2. 18 The rate of photosynthesis can be determined by calculating the reciprocal of the time taken for the purple-pink indicator solution to become colourless. rate of photosynthesis = 1000/t t = time in seconds

4 © NJC 2025 9744/04/SH2/H2 Biology/Preliminary Examination (a) (i) Record your results in a suitable format in the space provided, including the calculation of the mean rate of photosynthesis for the two chloroplast suspensions. [5] (ii) Based on your results for (a)(i), put a tick (✓) in one box to indicate which specimen tube contains chloroplast suspension taken from the sun plant. Give a reason for your answer. S1 S2 [2] (iii) Suggest a suitable control for this experiment to show that it is the chloroplast suspension that causes the decolourisation of the indicator. [1]

5 © NJC 2025 9744/04/SH2 Preliminary Examination [Turn over (iv) One significant source of error in this experiment is identifying when the indicator decolourises. Complete Table 1.1 to suggest: • how to make an improvement in identifying when the indicator decolourises • one other significant source of error in this experiment • how to make an improvement to reduce this other significant source of error. Table 1.1 significant source of error how to make an improvement identifying when the indicator decolourises [3]

6 © NJC 2025 9744/04/SH2/H2 Biology/Preliminary Examination (b) In another experiment, using sun and shade leaf extracts, a student investigated the effect of varying light intensity on the rate of photosynthesis of these plants, so as to determine their light compensation points. light intensity = 1/d2, where d represents the distance from the light source Compensation points can be investigated using bicarbonate indicator solution. It is very sensitive to changes in carbon dioxide levels. The indicator is red when equilibrated with atmospheric carbon dioxide. The colour changes to yellow when more carbon dioxide is added. The colour changes to purple when more carbon dioxide is removed. Table 1.2 shows the colour changes corresponding to the pH values. Table 1.2 yellow orange red magenta purple pH 7.6 pH 8.0 pH 8.4 pH 8.8 pH 9.2 Absorbance can be measured at 550 nm (wavelength of green light) using a colourimeter. The absorbance of green light increases with increased pH of bicarbonate indicator. Using this information and your own knowledge, plan an investigation to find out the light intensity at which sun and shade plants reach their light compensation points. You must plan to use: ● alginate beads containing sun and shade plants leaf extracts ● bicarbonate indicator solution ● colourimeter and cuvettes ● lamp. You may select from the following apparatus and plan to use appropriate additional apparatus: ● normal laboratory glassware, e.g. test-tubes, boiling tubes, beakers, measuring cylinders, glass rods, etc. ● syringes, Pasteur pipettes ● timer, e.g. stopwatch. Your plan should: ● have a clear and helpful structure such that the method you use is able to be repeated by anyone reading it ● identify the dependent variable and the independent variable ● identify the variables you will need to control ● use the correct technical and scientific terms ● indicate how any analysis of results will be carried out.

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