ACJC 2023 H2 Bio Prelim Paper 2 Answers

This document consists of 29 printed pages and 2 blank pages. [Turn over A Anglo-Chinese Junior College JC2 Biology Preliminary Examination Higher 2 CANDIDATE NAME FORM CLASS TUTORIAL CLASS INDEX NUMBER BIOLOGY Paper 2 Structured Questions Candidates answer on the Question Paper. No Additional Materials are required. 9744/02 23 August 2023 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. 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 Examiners’ use only 1 / 8 2 / 11 3 / 10 4 / 8 5 / 11 6 / 10 7 / 10 8 / 12 9 / 10 10 / 5 11 / 5 Total / 100

2 Anglo-Chinese Junior College 2023 J2 H2 9744 Paper 2 Preliminary Examination For Examiner Use Answer all questions. 1 The cell surface membranes of different cells have a similar basic structure, but the proportions of the various molecules present vary between membranes and even between the inner and outer layers of a membrane. Fig. 1.1 shows the structure of a typical cell surface membrane. Fig. 1.1 (a) With reference to Fig. 1.1, (i) identify molecules A and B and describe their respective functions. A: Cholesterol; Function: Regulates/maintains membrane fluidity and permeability; B: Channel protein; Function: Provides hydrophilic channel for charged ions/ polar molecules to move across the membrane; R! polar ions [M] …………………………………………………………………………………………............ [4] (ii) State one way in which the outer layer of the membrane is different from the inner layer. Presence of glycoprotein / glycolipid in the outer layer of membrane where none occur on the inner layer of the membrane; A! oligosaccharides face outwards …………………………………………………………………………………………............ [1] (iii) Describe the significance of the difference stated in your answer for (a)(ii). Oligosaccharides on glycoprotein/glycolipid facing exterior of cell involved in: 1. Cell-cell adhesion; 2. Cell-cell recognition; 3. Acting as receptors to allow signal molecules to bind; no ecf. …………………………………………………………………………………………............ [1]

3 [Turn over Anglo-Chinese Junior College 2023 J2 H2 9744 Paper 2 Preliminary Examination For Examiner Use Fig. 1.2 shows an organelle which contains an extensive network of internal membranes. Fig. 1.2 (b) With reference to Fig. 1.1, suggest if molecule B will be found in the internal membranes found within the organelle shown in Fig. 1.2. Explain your answer. 1. Yes, molecule B will be found; 2. E.g. of channel proteins embedded in thylakoid membrane: ATP synthase allow protons to diffuse down the electrochemical potential gradient / other channel proteins that allow diffusion/movement of molecules etc.; R! proton pump ……………………………………………………………………………………………………….. [2] [Total: 8]

4 Anglo-Chinese Junior College 2023 J2 H2 9744 Paper 2 Preliminary Examination For Examiner Use 2 One mechanism for bacterial resistance to antibiotics is through the action of efflux pumps, which are proteins found on the bacterial cell surface membrane. Table 2.1 shows the intracellular concentrations of an antibiotic in two strains of bacteria, after exposure to the antibiotic for 24 hours. Table 2.1 strain of bacteria intracellular concentration of antibiotic / mg L–1 antibiotic-resistant 0.008 antibiotic-susceptible 0.125 (a) Explain why antibiotics do not harm the human cells when used to treat humans. Generally, certain antibiotics target the : 1. peptidoglycan cell wall, which is absent in human cells; 2. 70S ribosomes, but the ribosomes in human cells are mainly 80S; 3. bacterial enzymes involved in DNA replication / transcription , which have a different 3D conformation from that found in human cells; AVP: antibiotics bind to a transport protein only found in bacterial cells to enter bacterial cells / transport protein absent in human cells; ……………………………………………………………………………………………………….. [2] (b) Describe how the efflux pumps are held in position within the membrane. 1. Formation of hydrophobic interactions between hydrophobic R groups of amino acid residues of efflux pumps / proteins and hydrophobic hydrocarbon tails/fatty acid chains of phospholipid molecules / hydrophobic core of phospholipid bilayer; 2. Formation of ionic bonds /hydrogen bonds between charged/polar R groups of amino acid residues and phosphate groups of phospholipid molecules; ……………………………………………………………………………………………………….. [2] (c) With reference to Table 2.1, explain how the presence of efflux pumps allow bacteria to be resistant to the antibiotic. 1. * The antibiotic-resistant strain of bacteria had a lower intracellular concentration of antibiotic of 0.008 mgL–1 after exposure to the antibiotic OR The antibiotic-resistant strain of bacteria had a low intracellular concentration of antibiotic of 0.008 mgL –1 after exposure to the antibiotic compared to that of the antibiotic-susceptible strain which had a intracellular concentration of 0.125 mgL–1; 2. The efflux pump is a carrier protein which actively transports the antibiotic; 3. out of the bacteria, against / regardless of the concentration gradient of the antibiotic; 4. with the expenditure / hydrolysis of ATP; 5. The efflux pump changes its 3D conformation to carry the antibiotic across the cell surface membrane; * MP1 compulsory, max 4m ……………………………………………………………………………………………………….. [4]

5 [Turn over Anglo-Chinese Junior College 2023 J2 H2 9744 Paper 2 Preliminary Examination For Examiner Use (d) Some strains of this bacteria show resistance to the antibiotic while other strains are susceptible, even though they both belong to the same species. Suggest explanations for this observation. 1. Spontaneous mutation occurred only in some strains but not others , affecting gene(s) which confer resistance to the antibiotic; 2. The gene(s)/allele(s)/sequence conferring resistance to the antibiotic may be found on plasmids instead of the bacterial chromosome; 3. which are not always distributed to daughter cells during binary fission / which are only passed from some cells to others through horizontal gene transfer; 4. the two strains are not sufficiently different genetically / morphologically / phylogenetically to be considered distinct species; max 3m ……………………………………………………………………………………………………….. [3] [Total: 11]

6 Anglo-Chinese Junior College 2023 J2 H2 9744 Paper 2 Preliminary Examination For Examiner Use 3 Fig. 3.1 shows models of a haemoglobin molecule and part of a keratin molecule. Fig. 3.1 (a) Outline the main structural differences between these two proteins, visible in Fig. 3.1. 1. Haemoglobin is a globular / spherical / rounded in structure while keratin is long / fibrous; 2. Haemoglobin consists of four