2022 HCI JC2 H2 Biology Prelims Paper 2 MS

HWA CHONG INSTITUTION / 2022 H2 BIOLOGY / Preliminary Examination Paper 2 / MS HWA CHONG INSTITUTION (COLLEGE SECTION) 2022 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 2 MARK SCHEME QUESTION 1 (a) Describe the main features of amylose visible in Fig. 1.1 [2] 1 Ref to α (1, 4) glycosidic bonds between glucose units ; 2 Ref to helical structure, with 6 glucose units per turn ; (b) Explain how the structure of amylose makes it suitable for its function. [2] 1 Ref to large amylose, thus insoluble in water, does not exert osmotic influence in the cell ; 2 Ref to hundreds to thousands of glucose, thus a large source of carbon ; 3 Ref to α (1, 4) glycosidic bonds, being easily hydrolysed ; 4 Ref to amylose being helical and thus compact ; 5 Ref to anomeric carbon involved in glycosidic bond formation, thus unreactive / chemically-stable ; (c) Suggest how double helix structure of amylose is formed. [1] Ref to via hydrogen bonds between adjacent amylose molecules ; (d) (i) State two way in which the structure of collagen differs from the structure of starch. [2] Collagen Starch 1 a Made up of amino acids 1 b Made up of α-glucose ; 2 a Linked by peptide bonds 2 b Linked by α(1,4) glycosidic bonds ; 3 a Triple helix tropocollagen 3 b Helical amylose, highly branched amylopectin ; 4 a ref to unbranched 4 b Ref to branched ; 5 a Ref to extensive hydrogen bonds / cross-links / staggered arrangement 5 b absent ; (ii) Explain how one of the differences stated in (d)(i) allows collagen to perform its function. [2] 1 Ref to glycine-X-Y, glycine with small R group can fit in / packed tightly together ; A: hydroxylproline having OH group for hydrogen bonding 2 Ref to providing high tensile strength ; 3 Ref to extensive hydrogen bonds within tropocollagen, between NH group of Gly in one α-chain and CO group of another amino acid in next α-chain ; 4 Ref to providing high tensile strength ;

HWA CHONG INSTITUTION / 2022 H2 BIOLOGY / Preliminary Examination Paper 2 / MS 5 Ref to covalent cross-links present within/between tropocollagen, between CO end of one molecule and NH end of another or ref to staggered arrangement stabilised by hydrophobic interactions ; 6 Ref to conferring greater tensile strength ; [Total: 9] QUESTION 2 With reference to Fig. 2.1, (a) (i) explain why calcium ions do not pass through the phospholipid bilayer. [2] 1 Calcium ions are water soluble/ hydrophilic; 2 unable to pass through hydrophobic core of the phospholipid bilayer which consists of hydrocarbon fatty acids chains; (ii) state and describe the process by which calcium ions are moved across the membrane. [4] 1 Active transport; Any 3 2 Intracellular Ca2+ binds to the binding sites of the calcium pump/ carrier protein; R: active site R: channel protein 3 Upon binding