2026 CJC H2 Biology 9477 P3 QP

CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME CLASS 2T INDEX NUMBER BIOLOGY 9477/03 Paper 3 Long Structured and Free Response Questions 15 September 2026 2 hours Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your name, class and index number 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 this section on writing papers 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, fasten your answers for Section B securely. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 [32] 2 [12] 3 [11] 4 or 5 [20] TOTAL 75

2 This document consists of 26 printed pages and 0 blank page. [Turn over 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 3

3 Section A Answer all questions in this section. 1 The INSR gene encodes the insulin receptor, a transmembrane receptor protein found on the surface of many mammalian cells. The receptor binds to insulin and activates intracellular signalling pathways involved in regulating cellular metabolism. After transcription, the INSR pre-mRNA undergoes post-transcriptional processing. The pre-mRNA can be processed into many different mRNA molecules, which are translated to produce different isoforms of the insulin receptor. Figure 1.1 shows two pathways of post-transcriptional processing of INSR pre-mRNA in mammalian cells. Fig. 1.1 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 3

4 (a) (i) Outline the events involved in the expression of the INSR gene during post-transcriptional processing of the pre-mRNA. ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….……………………… [3] (ii) In normal hepatocytes, insulin activates target cells that promote increased glycogen synthesis. Outline how insulin results in the initiation of cell signalling in a hepatocyte. ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….……………………… [2] 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 3

5 (iii) With reference to Fig. 1.1, describe how the mechanisms of post-transcriptional processing result in different receptor isoforms IR-A and IR-B, and suggest how the structural difference between the two isoforms results in different cellular responses. ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….……………………… [4] Gene mutations that occur within the INSR gene can directly change the receptor structure and function. Analysis of tissue samples from patients with liver carcinoma identified three distinct somatic variants mapping to functional domains of the receptor. Table 1.1 shows three different somatic mutations identified in liver cells. Table 1.1 Variant Location on INSR Gene DNA change Outcome 1 exon 2 (extracellular domain) nonsense mutation introducing a stop codon within the exon not responsive to insulin 2 exon 17 (intracellular domain) missense mutation locking the kinase domain in an active conformation cellular effects are present without insulin 3 exon 13 missense mutation causing misfolding of a single α- helix less sensitive to insulin 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 3

6 (transmembrane domain) (iv) With reference to Table 1.1, suggest how the molecular mechanism of each mutation in variants 1 , 2 and 3 changes the structure and function of the insulin receptor, resulting in their observed outcomes. ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….………………………… ………………………………………………………………………………….……………………… [6] (b) The intracellular signalling cascade activated by the insulin receptor stimulates the conversion of excess blood glucose to glycogen within hepatocytes. (i) In the space provided below, draw the structural formula of 2 α- glucose residues to show the linkage formed at a branch point in glycogen, and label the bond. 9477 H2 Biology 2026 JC2 Preliminary Examination Paper 3

7 [2] (ii) Glycogen is a polysaccharide used for the storage of glucose in animals. It is found in the liver and skeletal muscles and is often compared to starch as a storage molecule. Table 1.2 compares some of the structural parameters of glycogen from human hepatocytes with starch from potato tubers. Table 1.2 structural parameter glycogen (human hepatocyte) starch (potato tubers) frequency of branch points 1 in every 8 to 12 glucose residues 1 in every 24 to 30 glucose residues mean number of non-reducing ends per molecule approx. 5.5 X 10 4 approx. 2.0 X 10 3 mean degree of polymerisation 1 X 10 7 1 X 10 5 With reference to Table 1.2, explain how the data support the id