2025 RI H2 Bio Prelim P3 Questions 9477docx

© RI 2025 Preliminary Examination 9744/03 [Turn over RAFFLES INSTITUTION 2025 Year 6 Preliminary Examination Higher 2 BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 17th Sept 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Writing paper. READ THESE INSTRUCTIONS FIRST Write your index number, CT group & name in the spaces at the top of this page. 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. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question in the writing paper provided. 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, hand in your essay question SEPARATELY. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 15 printed pages. CIVICS GROUP CANDIDATE NAME INDEX NUMBER 5 S 0 3 2 Raffles Institution Internal Examination For Examiner’s Use Section A 1 / 31 2 / 8 3 / 16 Section B 4 or 5 / 20 Total / 75 TIMED PRACTICE – PAPER 3

2 © RI 2025 Preliminary Examination 9744/03 For Examiner’s Use Section A Answer all the questions in this section 1 Liver cells, or hepatocytes, are highly speciali sed and metabolically active. These cells are responsible for a vast array of vital functions, including the metabolism of carbohydrates, lipids, and proteins, detoxification of harmful substances, synthesis of plasma proteins, and bile production. Their constant activity makes them susceptible to damage from various factors such as viral infections (e.g., hepatitis), excessive alcohol consumption, and metabolic disorders like non-alcoholic fatty liver disease (NAFLD), which can impair their function and lead to serious health issues. Fig. 1.1 is a transmission electron micrograph showing a section of a human liver cell. Fig. 1.1 (a) (i) Name organelles A and B shown in Fig. 1.1. A ……………………………………………………………………………………………... B …………………………………………………………………………………………...[1] (ii) In liver cells, enzymes are attached to the membrane of smooth endoplasmic reticulum (SER). With reference to the functions of smooth endoplasmic reticulum, suggest the advantages of having enzymes attached to the membrane rather than free in the lumen of the SER. ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ……………………………………………………………………………………………..[2]

3 © RI 2025 Preliminary Examination 9744/03 [Turn over For Examiner’s Use Neutral lipids or non-polar lipids such as triglycerides and cholesterol esters are synthesised in the membrane of SER of the liver cell. Fig. 1.2 shows the formation of a lipid droplet (LD) from the endoplasmic reticulum membrane. Fig. 1.2 (b) (i) Describe the formation of the lipid droplet shown in Fig. 1.2. ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ……………………………………………………………………………………………..[3] (ii) Lipid droplets serve as energy storage within the cell. Based on the properties of the biomolecules involved, explain how a lipid droplet maintains its stable structure in the cytoplasm. ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ……………………………………………………………………………………………..[2]

4 © RI 2025 Preliminary Examination 9744/03 For Examiner’s Use (c) Prostaglandins are another type of lipid synthesised at the SER. Prostaglandins are small lipids produced in many tissues of the body. One role of prostaglandins is to cause inflammation at the site of an injury or infection. Inflammation is the normal first response of the immune system to injury or infection. Cyclooxygenase (COX) is an enzyme that catalyses one of the steps in the reaction pathway for the formation of prostaglandins from phospholipids. The reaction pathway occurs in the SER of cells. Part of the reaction pathway is shown in Fig. 1.3. Fig. 1.3 (i) Suggest an advantage for this reaction pathway occurring in the smooth endoplasmic reticulum of a cell rather than in the cytoplasm. ………………………………………………………………………………………………... ……………………………………………………………………………………………..[1] (ii) Inflammation may have side-effects, such as pain. Aspirin is a drug that can be used to reduce these side-effects by reducing the catalytic activity of the COX enzyme by modifying the R-group of one of the amino acids. Explain how modifying the R-group of an amino acid in the COX enzyme can reduce the catalytic activity of the enzyme. ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ……………………………………………………………………………………………..[3]

5 © RI 2025 Preliminary Examination 9744/03 [Turn over For Examiner’s Use A number of chemicals can disrupt mitochondrial respiration of the liver cell. Some of these are listed in Table 1.1. Table 1.1 chemical effect on mitochondrion oligomycin blocks proton flow through ATP synthase FCCP causes protons to leak out of the inter-membrane space back into the matrix without going through ATP synthase antimycin-A + rotenone stops electrons from being pass ed down the electron transport chain (rotenone and antimycin-A affects proteins along the electron transport chain) Scientists measured the oxygen consumption rate (OCR) of some cells. They then investigated how the OCR changed when oligomycin was added at 23 minutes, followed by FCCP at 56 minutes, followed by antimycin-A + rotenone at 93 minutes. Fig. 1.4 shows the results obtained. Fig. 1.4 (d) (i) With reference to events at the inner mitochondrial membrane, describe and explain each of these two statements: oligomycin causes a drop in OCR ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ……………………………………………………………………………………………..[3]

6 © RI 2025 Preliminary Examination 9744/03 For Examiner’s Use FCCP causes a rise in OCR ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ………………………………………………………………………………………………... ……………………………………………………………………………………………..[3] (ii) Suggest why the oxygen consumption rate of the cell never falls to zero in these cells. ………………………………………………………………………………………………... ……………………………………………………………………………………………..[1] During respiration, protons ‘leak’ through the inner mitochondrial membrane into the matrix. The OCR as a result of this leakage can be calculated by determining the difference between the OCR 20 minutes after the addition