2026 ACJC H2 Biology Prelim P3 QP

Anglo-Chinese Junior College JC2 Biology Preliminary Examination Higher 2 CANDIDATE NAME FORM CLASS TUTORIAL CLASS INDEX NUMBER BIOLOGY Paper 3 Long Structured and Free-response Questions Additional Materials: Free-response Question Answer Booklet 9477/03 02 September 2026 2 hours 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 on the 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. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 19 printed pages. [Turn over For Examiners’ use only 1 / 30 2 / 8 3 / 12 4 / 5 / 25 Total / 75

2 Anglo-Chinese Junior College 2026 J2 H2 9477 Paper 3 Preliminary Examination

3 Section A 1 Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterised by cognitive decline and memory loss. A major hallmark of AD is the accumulation of amyloid-beta (A β) plaques in the brain. A β peptides are produced when the Amyloid Precursor Protein (APP) is cleaved abnormally by an enzyme complex called γ- secretase. Presenilin-1, encoded by the PSEN1 gene, forms the catalytic subunit of γ- secretase. Mutations in the PSEN1 gene are the most common cause of early-onset Familial Alzheimer’s Disease (FAD). To date, more than 300 mutations have been described in the PSEN1 gene. (a) Figure 1.1 shows a segment of the non-template DNA strand for both the wild-type PSEN1 allele and a patient's mutant allele. This segment codes for an essential hydrophobic transmembrane domain in the protein. Triplet base : 103 104 105 106 107 108 Wild-type allele : 5' - GGT ATC GTG ATT GTC ACC - 3' Mutant allele : 5' - GGT ATC GTG ATT GAC ACC - 3' Figure 1.1 Table 1.1 shows a section of the genetic code. Table 1.1 mRNA codon amino acid GGU glycine GAC aspartic acid GUC, GUG valine AUC, AUU isoleucine ACC threonine (i) Identify the type of mutation that has occurred at the DNA level in the patient's PSEN1 gene and determine its effect on the resulting amino acid sequence. ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . …………………………………………………………………………………………............ [2] [Turn over Anglo-Chinese Junior College 2026 J2 H2 9477 Paper 3 Preliminary Examination

4 (ii) Suggest how this change in the primary structure of the Presenilin-1 protein could disrupt its function within the hydrophobic core of the phospholipid bilayer. ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . …………………………………………………………………………………………............ [2] Anglo-Chinese Junior College 2026 J2 H2 9477 Paper 3 Preliminary Examination

5 (b) Figure 1.2 shows a pedigree of a family affected by a rare, aggressive form of FAD caused by a missense mutation in the PSEN1 gene. Figure 1.2 (i) Deduce the likely mode of inheritance of this form of FAD. Justify your answer. ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . ……………………………………………………………………………………………………. . …………………………………………………………………………………………............ [3] [Turn over Anglo-Chinese Junior College 2026 J2 H2 9477 Paper 3 Preliminary Examination

6 Anglo-Chinese Junior College 2026 J2 H2 9477 Paper 3 Preliminary Examination

7 To confirm the genetic status of the family members, gel electrophoresis coupled with Southern blotting was performed. The mutation in the PSEN1 gene eliminates a specific restriction site for the restriction enzyme, EcoRI . ● The wild-type PSEN1 allele yields two fragments of 3 kb and 2 kb when digested with EcoRI . ● The mutant allele yields a single fragment of 5 kb. Figure 1.3 shows the positions of the restriction sites on the wild-type and the mutant PSEN1 alleles, denoted by arrows, and the position where the radioactive probe binds to the two alleles. Figure 1.3 Figure 1.4 shows the Southern blot results for selected family members. Figure 1.4 [Turn over Anglo-Chinese Junior College 2026 J2 H2 9477 Paper 3 Preliminary Examination

8 (ii) Outline the steps required to perform the Southern blotting technique after the DNA fragments have been separated by gel electrophoresis to produce the results shown in Figure 1.4. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………............ [4] (iii) Complete Figure 1.4 by drawing the expected DNA band(s) for Individual A, given that Individual A is homozygous dominant for FAD. [2] Anglo-Chinese Junior College 2026 J2 H2 9477 Paper 3 Preliminary Examination

9 (c) For many years, the "Amyloid Cascade Hypothesis" suggested that the accumulation of A β plaques in the brain is the primary driver o