HCI 2023 JC2 9744 H2 Bio Prelim P2 MS (Sharing)

HWA CHONG INSTITUTION / 2022-2023 H2 BIOLOGY / Preliminary Examination Paper 2 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2023 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 2 MARK SCHEME QUESTION 1 (a) Explain why scientists keep the protoplasts in a solution that has the same water potential as the cell. [2] any two: 1 to prevent, lysis or to prevent, shrinking 2 ref. to no net movement, of water (occurs) 3 prevent movement of water, by osmosis (b) The cellulose microfibrils visible in Fig. 1.2 will form cellulose fibres. Each cellulose molecule is a polymer of β-glucose. (i) Define the term polymer. [1] a macromolecule, that is made up of many monomers (ii) Explain how the structure of a cellulose molecule allows for the formation of the cellulose microfibrils and fibres. [3] cellulose chain max 2 1 monomers joined by β(1,4) glycosidic bonds 2 adjacent, monomers, rotated through 180° 3 straight chain cellulose microfibril and fibres max 2 4 parallel molecules, of cellulose 5 hydrogen bonds form, between the OH groups of neighbouring chains 6 (as such) formation of cross links 7 microfibrils associate with other non-cellulose polysaccharides, and are arranged in larger bundles to form macrofibrils 8 many macrofibrils bundle together to form a cellulose fibre 9 idea that between adjacent cellulose molecules, beginnings and ends in different places (c)(i) Explain why the mAb ZAC-3 produced against the core polysaccharide and lipid A components will not act against the O-polysaccharide of the LPS molecules. [2] any two: 1 (mAbs) specific / different, antigen-binding sites 2 (each mAb has) specific / different, 3D conformation 3 ZAC-3 has complementary shape to core polysaccharide and lipid A Or 2D6 complementary shape to O-polysaccharide

HWA CHONG INSTITUTION / 2022-2023 H2 BIOLOGY / Preliminary Examination Paper 2 / MS 2 (ii) The results of the tests showed that both mAbs were effective in causing agglutination (clumping) of bacteria and in preventing their motility. This suggests they may be useful for preventing cholera and for treating the disease. Justify the claim that mAb 2D6 and mAb ZAC -3 are useful for preventing cholera and for treating the disease. [3] any three: general points 1 (agglutination / motility prevented, so) bacteria less able to, colonise intestine 2 less / no, choleragen released 3 bacteria passed out in faeces not able to cause disease in others 4 ref. to phagocytosis more effective prevention / treatment 5 (to prevent disease) needs to be given, at early stages 6 passive immunity 7 idea that in addition to immune response (so increased effect) 8 ref. to quicker recovery (if a person has cholera) 9 useful when, there is antibiotic resistance / antibiotics cannot be given specific mAb 10 mAb ZAC-3