2026 RI H2 Biology Prelims P2 Answers

© RI 2026 Preliminary Examination 9477/02 [Turn over RAFFLES INSTITUTION 2026 Year 6 Preliminary Examination Higher 2 BIOLOGY 9477/02 Paper 2 Structured Questions 16th September 2026 2 hours Candidates answer on the Question Paper. No Additional Materials are required. 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. 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 The number of marks is given in brackets [ ] at the end of each question or part question. FOR EXAMINER’S USE Q1 Q2 Q3 Q4 Q5 Q6 10 10 11 12 13 9 Q7 Q8 Q9 TOTAL 8 12 5 90 This document consists of 23 printed pages and 1 blank page. CIVICS GROUP CANDIDATE NAME ANSWERS INDEX NUMBER 6 S 0 3 2 2 6

2 © RI 2026 Preliminary Examination 9477/02 For Examiner’s Use [Turn over 1 Some enzymes digest protein by hydrolysing the peptide bonds between amino acids. The extent to which a protein is digested is called the degree of hydrolysis (DH). The DH value may be calculated from the equation: DH = 100 X number of peptide bonds hydrolysed ___________________________________ total number of peptide bonds present (a) A protein made up of 151 amino acids was digested. The DH value of the digested protein was 18%. Calculate the number of peptide bonds that have been hydrolysed. [1] Total peptide bonds in protein = 151 - 1 = 150 AND number hydrolysed = 18% x 150 = 27 peptide bonds; [1 mark for correct answer AND working shown] (b) The enzyme trypsin hydrolyses proteins into short peptide chains. Fig. 1.1 illustrates the mode of action of trypsin. Fig. 1.1 (i) With reference to Fig. 1.1, explain the mode of action of trypsin. [4] 1. Effective collisions between active site of enzyme and substrate to form enzyme- substrate* complex; 2. The active site undergoes conformational changes to a more precise fit/fit more tightly around the peptide bond (A: substrate) via induced fit* model; 3. Lowers the activation energy*; 4. by placing strain on the target peptide bond/substrate; OR R-groups of amino acid residues in active site participate in direct catalysis; OR Raffles Institution Internal Examination

3 © RI 2026 Preliminary Examination 9477/02 [Turn over For Examiner’s Use orientation of substrate in active site to facilitate hydrolysis; 5. Shorter peptides which are no longer complementary to active site are released and enzyme is unchanged and can be used again; (ii) Trypsin can hydrolyse more than one type of protein. Explain why it is possible for trypsin to act on different types of protein. [1] Trypsin's active site* is complementary in conformation/shape* to a peptide bond*; (c) Proteases are present in some washing powders used for cleaning clothes. They digest protein- based stains such as those caused by blood, egg and sweat. Fig 1.2 shows the effect of pH on the activities of trypsin and pepsin. Fig. 1.2 Two identical samples of a protein, A and B, were each mixed with an excess of trypsin and left for the same length of time. Sample A was kept at pH 8, and sample B was kept at pH 6. All other conditions were kept the same and under optimal conditions. Predict and explain how the degree of hydrolysis (DH) of sample B would compare with sample A. [4] 1. Predict (compulsory point): Sample B (pH 6) would have a lower DH value than sample A (pH 8); 2. pH 8 (sample A) shows enzyme activity at 100% that is higher than the enzyme activity of 27% at pH 6 (sample B); 3. Changes in pH changes the ionisation of R groups* on amino acids; 4. disrupts ionic bonds and hydrogen bonds* that stabilizes the active enzyme* conformation/changes the active site conformation; 6 4 100 80 60 40 20 pH relative activity / % pepsin trypsin 0 2 8 10 12 14 0

4 © RI 2026 Preliminary Examination 9477/02 For Examiner’s Use [Turn over 5. At pH 6 active site* becomes less complementary in shape* to the substrate thus fewer enzyme-substrate* complexes formed; AVP: Lower pH/increase proton concentration change the specific* charge of the R groups* of the catalytic residues* in the active site* so catalytic activity of the enzyme is reduced; [Total: 10] 2 Fig. 2.1 is a transmission electron micrograph of a cell from the stem of the sago pondweed, Stuckenia pectinata. Fig. 2.1 (a) State the evidence from Fig. 2.1 that shows that the cell is from the stem and not from the mesophyll of a leaf of S. pectinata. [1] No chloroplasts present; (R: air spaces, guard cells, chlorophyll, stroma, thylakoid membranes) (b) Identify structure C and explain why it is so darkly stained. [2] 1. Nucleolus; 2. It contains a high concentration of a named structure e.g. ribosomal RNA (rRNA) / ribosomal proteins / ribosomal subunits / ribonucleoproteins; (c) (i) From Fig. 2.1, name and identify (using letters A to G) a membrane that carries out active transport. [1] cellulose cell wall air space G F A B C D E magnification x2500

5 © RI 2026 Preliminary Examination 9477/02 [Turn over For Examiner’s Use name of membrane: cell surface membrane; (A: tonoplast/vacuole membrane) (R: nuclear envelope, inner mitochondria membrane) letter on Fig. 2.1: A; [1 mark for correct name AND letter] (ii) Describe active transport. [2] 1. Active transport is the transport of substances across the membrane against a concentration gradient* using protein carriers /pumps*; 2. Energy in the form of ATP* is required; (d) Fig. 2.2 shows the movement of vesicles within a plant cell during the development of a vacuole. Fig. 2.2 (i) Name the process that is occurring at X. [1] Pinocytosis/endocytosis; (R: phagocytosis) (ii) Some of the vesicles formed by the Golgi body pass to the vacuole. Amongst these vesicles, some contain proteins that have folded correctly while others contain proteins that have not folded correctly. The proteins that have not folded correctly pass to the vacuole where they are broken down. Waste management in plants involves two distinct pathways: the ubiquitin-proteasome pathway which operate exclusively in the cytosol and the nucleus, and the vacuolar pathway which is described above. cell surface membrane Golgi body rough endoplasmic reticulum vacuole multi-vesicular body key protein folded correctly protein not folded correctly

6 © RI 2026 Preliminary Examination 9477/02 For Examiner’s Use [Turn over Explain how proteins that have not folded correctly are broken down in the vacuole. [2] 1. (name of correct enzyme) proteases/peptidases/proteolytic enzymes that break peptide* bonds; 2. by hydrolysis* with the addition of water to form amino acids/smaller peptides; (R: if any other bonds not found