2026 HCI 9477 H2 Bio Prelim P2 MS

HWA CHONG INSTITUTION (COLLEGE SECTION) 2026 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 2 MARK SCHEME QUESTION 1 (a)(i) Use Fig. 1.1 to explain what is meant by the term conjugated protein. [2] any two 1 ref to non-protein groups 2 ref to prosthetic group 3 ref to prosthetic group is, iron / Fe, ion 4 ref to prosthetic group attached by, covalent bonds / ionic interactions / hydrogen bonds (ii) Using the information provided about rubredoxin, state two other differences between the structures of rubredoxin and haemoglobin. [2] any two 1 ref to size: haemoglobin is a larger molecule while rubredoxin is smaller 2 ref to level of protein structure: haemoglobin has quaternary structure while rubredoxin has tertiary structure / does not have quaternary structure 3 ref to no. of prosthetic groups: haemoglobin has, more than one / four, prosthetic groups / iron ions while rubrodoxin has, only one, prosthetic group / iron ion 4 ref to haem group: haemoglobin has haem groups while rubredoxin does not have haem group 5 ref to iron ions held by: sulphur atoms in rubredoxin vs porphyrin ring / haem group in haemoglobin (b)(i) Calculate the volume of the inner sphere not occupied by Fe 3+ ions. [2] 1 (multiplication) Total volume of Fe 3+ ions = 4500 x 9.04 x 10 -4 nm 3 = 4.068 nm 3 2 (subtraction + correct s.f.) Vol not occupied = 268 nm 3 - 4.068 nm 3 = 263.9 nm 3 (A: 3 or 4 sf) (ii) Explain how hydrophilic and hydrophobic interactions contribute to the spherical shape of ferritin. [2] 1 ref to hydrophobic interactions / regions / R groups on the inside of the protein 2 ref to hydrophilic interactions / regions / R groups on the outside of the protein [Total: 8] QUESTION 2 (a) Describe stages A , B and C . Stage A : [2] 1 estrogen binds to complementary ligand-binding site of estrogen receptor / ER 2 ER undergoes change in conformation / dimerisation Stage B : [1] 3 estrogen-ER complex binds to estrogen response element (ERE) Stage C : [2] 4 estrogen-ER complex recruits / binds to M1 and M2 / mediator proteins 5 which bind to general transcription factors/ G at promoter, to form transcription initiation complex / result in transcription of target genes 6 ref. DNA bending / looping / folding to bring estrogen-ER complex close to the promoter HWA CHONG INSTITUTION / 2025-2026 H2 BIOLOGY / Preliminary Examination Paper 2 / MS 1

(b) With reference to Table 6.1, (i) explain how SERMs can be used in the treatment of breast cancer. [2] 1 SERMs are structurally similar to estrogen / competes with estrogen to bind to ligand-binding site of ER, and recruit M1 but not M2 2 prevent formation of complete / stable transcription initiation complex, hence reduces rate of transcription of genes involved in growth, proliferation and cell cycle progression / cancer-critical genes (ii) suggest why ERDRs might be more effective than SERMs. [2] 1 ERDR binds to ligand-binding site of ER and causes ER to undergo/ not undergo a change in 3D conformation / causes ER to be inactivated 2 *prevent movement of ERDR-ER complexes to the nucleus hence no transcription of genes, halting breast cancer development 3 whereas SERMs still allows for some transcription of gene, hence only slowing down breast cancer development [Total: 9] QUESTION 3 (a) With reference to Fig. 3.1, describe how an influenza virus enters the epithelial cell of the human respiratory tract. [3] 1 haemagglutinin binds to a sialic-acid receptor on the host cell surface 2 receptor-mediated endocytosis 3 membrane fusion allows viral material to be released into the cell (b) Other than the type of host cells they infect and their mode of entry into the respective host cells, compare the reproductive cycles of the influenza virus and HIV. [3] max two or one for differences (must be point-to-point) 1 ref to enzymes involved in replication of viral genetic material 2 ref to integration into host cell genome 3 idea of synthesis / production of viral genetic material for new virions 4 idea of synthesis / production of mRNA for viral protein synthesis 5 ref to processing of viral proteins 6 ref to mechanism involved in release of new virions max one or two for similarities 7 ref to use of host cell machinery for protein synthesis 8 ref to viral glycoproteins and host cell membrane 9 ref to mechanism of release of new viral progeny 10 idea of replication / synthesis of viral genetic material (c) With reference to Fig. 3.2, suggest how the novel H7N9 influenza virus could have arisen, and eventually infect humans. [4] any four 1 quotes / ref to different influenza virus strains may infect the same host 2 ref to correct description of antigenic shift 3 correctly quotes from Fig. 3.2 4 ref to correct description of antigenic drift HWA CHONG INSTITUTION / 2025-2026 H2 BIOLOGY / Preliminary Examination Paper 2 / MS 2

5 correctly describes how it changes the viral surface proteins [Total: 10] HWA CHONG INSTITUTION / 2025-2026 H2 BIOLOGY / Preliminary Examination Paper 2 / MS 3

QUESTION 4 (a) With reference to chromosomes 2 and 3 in Fig. 4.1, ● identify the type of chromosomal aberrations which has occurred ● explain how the identified chromosomal aberration could alter the function or expression of cancer-critical genes and contribute to the development of cancer. (i) Chromosome 2, which contains a tumour suppressor gene [3] Type of chromosomal aberration 1 ref to translocation of fragment 10/15 Effect on expression of gene an