2025 ASRJC H2Bio PE P2 (ANS)

ASRJC BIOLOGY DEPT 9744/2025/J2PRELIM/P2 [Turn over H2 ANDERSON SERANGOON JUNIOR COLLEGE HIGHER 2 2025 JC2 PRELIMINARY EXAMINATIONS CANDIDATE NAME CLASS INDEX NUMBER BIOLOGY 9744/02 PAPER 2 SHORT STRUCTURED QUESTIONS Candidates answer on the Question Paper. No Additional Materials are required. 22 AUGUST 2025 FRIDAY 2 HOURS READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graph Do not use paper clips, highlighters, glue or correction fluid. Answer all questions. 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 31 printed pages and 1 blank page. For Examiner’s Use 1 / 9 2 / 9 3 / 11 4 / 10 5 / 10 6 / 9 7 / 10 8 / 10 9 / 10 10 / 7 11 / 5 Total /100

2 ASRJC BIOLOGY DEPT 9744/2025/J2PRELIM/P2 Answer all the questions. 1 Stem cells are found throughout the human body. Lgr5 + stem cells are found in the lining of the small intestine. Fig. 1.1 is a flow chart showing stages in the development of one of the daughter cells produced by the mitotic division of an Lgr5+ stem cell. Fig. 1.1 (a) Explain why Lgr5+ stem cells are required in the lining of the small intestine. [3] any two from: I repair cells 1. to replace (old / worn-out / dead / short-lived) cells / repair (damaged) tissue ; 2. (damaged by) movement of food through intestine / presence of pathogens, 3. stem cells divide and differentiate to become specialised ; A form different types of cells 4. cells (produced by stem cells) are genetically identical so the function of the small intestine can continue 5. idea of self-renewal of stem cells/ stem cells divide via mitosis to maintain the, pool / number, of stem cells ; (I increase in number of stem cells) 6. AVP idea that allows growth (of small intestine) during development (R growth of cells)

ASRJC BIOLOGY DEPT 9744//2025/J2PRELIM/P2 Fig. 1.2 shows one of the specialised cells, goblet cell that develops from Lgr5+ stem cells in the small intestine. Fig. 1.2 (b) Identify the structures labelled A and B, as shown in Fig. 1.2. For each structure, state its function and one identifying feature that can be seen in Fig. 1.2. structure A Golgi body/ Golgi apparatus function: -To chemically modify, sort proteins/polypeptides and lipids A any suitable type of modification or a description e.g. glycosylation / addition of sugars forming tertiary or quaternary structures -package proteins/polypeptides and lipids into vesicles (for transport) -To maintain the plasma membrane (through fusion of vesicle membrane with plasma membrane) -To form lysosomes identifying feature: - A stack of flattened, elongated, single membrane-bound sacs/ cisternae - (At the cis face) transport vesicles (from RER and SER) continuously fuse and release proteins and lipids into the lumen of the Golgi body./ At the trans face, secretory vesicles, Golgi vesicles and lysosomes continuously bud/ pinch off. - Presence of lumen ___________________ structure B: nuclear envelope/ accept nucleus function for nuclear envelope: To regulate entry and exit of specific molecules (state 2 examples e.g. DNA nucleotides, RNA nucleotides, DNA polymerase, RNA polymerase, helicase, ligase, mRNA, tRNA, rRNA etc) function of nucleus storage of DNA/ genetic information site of transcription

4 ASRJC BIOLOGY DEPT 9744/2025/J2PRELIM/P2 Function must match that of structure identified identifying feature (same for both): double membrane surrounding the nucleolus (darkly stained region) has numerous tiny openings called nuclear pores. Accept presence of nucleolus (darkly stained region) [Total: 9]

ASRJC BIOLOGY DEPT 9744//2025/J2PRELIM/P2 2 Neutrase® is an enzyme that is used to hydrolyse proteins in solution. When the enzyme is mixed with a 2% protein solution the reaction mixture changes from white to colourless. A student carried out an experiment to find the effect of copper sulfate and potassium sulfate on the activity of Neutrase®. The student made four reaction mixtures in test-tubes A to D. Test-tubes A to C contained equal volumes of protein solution and 0.1cm 3 of solutions of copper sulfate or potassium sulfate. Test-tube D contained the same volume of protein solution and 0.1 cm3 of water. 0.5 cm3 of a 1% Neutrase® solution was added to test-tube A and immediately placed into a colorimeter. The colorimeter was used to measure the intensity of light that is absorbed by the solution (absorbance) over 100 seconds. The procedure was repeated with the other reaction mixtures, B, C and D. The results are shown in Fig. 2.1. Fig. 2.1 (a) Suggest and explain why measuring the absorbance of the reaction mixture over 100 s is a suitable method for determining the activity of Neutrase® Any two: 1. Neutrase® breaks down (hydrolyses) protein into peptides / amino acids (Accept: increase in solubility). 2. During the reaction, more light passes through the solution / more light is transmitted / less light is absorbed. 3. The idea that 100 seconds is a sufficient duration to observe the progress of the reaction / for complete reaction. [2] (b) With reference to Fig. 2.1,

6 ASRJC BIOLOGY DEPT 9744/2025/J2PRELIM/P2 (i) describe the effects of copper sulfate solution and potassium sulfate solution on the activity of Neutrase®. Trend: 1. Copper sulfate decreases (or equivalent wording) the activity of Neutrase (reference to either A or B); 2. 0.01 mol dm⁻³ CuSO₄ has a greater decrease / smaller effect on the activity of Neutrase than 0.05 mol dm⁻³ (high concentration) (reference to A and B); 3. Potassium sulfate has little / no effect on Neutrase activity (reference to C) as the rate of decrease of absorbance is almost the same / similar to water added to the reaction (reference to D); Quote data: 4. Data quote showing absorbance for two different lines at the same time , hence either compare • A/B and C to explain point 1 (lesser decrease in absorbance for 0.05 mol dm⁻³ CuSO4) • A and B to show that absorbance of explain point 2 5. One time and two absorbance readings from different lines on the graph with the unit for time used once anywhere in the answer — allow ‘at the end’ to refer to 100 seconds (Students may have difficulties linking the gradient of graph to rate of reaction.) [4] (ii) suggest explanations for the effects described in (b)(i). 1. Copper (sulfate) i