2015 HCI H1 Biology Prelims P1&P2 Answers

HWA CHONG INSTITUTION / 2015 JC2 H1 BIOLOGY / PRELIMINARY EXAMINATION / MARK SCHEME 1 HWA CHONG INSTITUTION 2015 JC2 H1 BIOLOGY PRELIMINARY EXAMINATION PAPER 1 & 2 MARK SCHEME 1 D 11 D 21 D 2 D 12 D 22 C 3 B 13 A 23 A 4 D 14 B 24 A 5 B 15 C 25 A 6 A 16 A 26 D 7 C 17 B 27 D 8 D 18 B 28 C 9 C 19 C 29 D 10 A 20 B 30 A STRUCTURED QUESTIONS Question 1 (a) Describe the role of haem group in haemoglobin. [2] 1. Haem group in haemoglobin consists of an iron ion held in a porphyrin ring structure 2. Ref to iron ion bind with oxygen (b) Discuss the advantages of having four subunits in haemoglobin. [3] 1. Binding of four oxygen molecules per haemoglobin results in increased oxygen carrying capacity 2. Ref to cooperative binding 3. Change in 3D conformation in one subunit results in changes in 3D conformation of the other subunits (c) Explain how the differences in haemoglobin structure of the Greylag and Andean geese contribute to their different oxygen affinities. [4] 1. Ref. to different amino acid sequence in the for Greylag goose and Andean goose haemoglobin 2. Different R-groups interactions results in the different specific 3D conformation 3. Haem groups are more exposed to bind to oxygen in Andean goose 4. Ref to different subunit interactions and different extend of cooperativity [Total: 9] Question 2 (a) (i) Account for the trends shown by the distribution of the two types of bacteria after six m o n t h s . [ 3 ] 1. Aerobic bacteria decrease with depthfrom mean number of bacteria per gram of stored soil of 12.5 x 107 to 0.9 x 107

HWA CHONG INSTITUTION / 2015 JC2 H1 BIOLOGY / PRELIMINARY EXAMINATION / MARK SCHEME 2 2. Anaerobic bacteria increase with depth from mean number of bacteria per gram of stored soil of 0.6 x 107 to 8.8 x 107 3. Oxygen content of soil decreases with depth as aerobic bacteria requires oxygen for respiration 4. Less oxygen available as the final electron acceptor in ETC, decrease in ATP synthesis (ii) Describe how aerobic bacteria are structurally adapted for cellular respiration. [2] 1. Presence of cytoplasmic membranes in aerobic bacteria. Hence, increase surface area 2. For more embedding of electron transport chain and ATP synthase to allow electron transfer / to drive oxidative phosphorylation of ADP to ATP (b) (i) State with evidence from Fig. 6.1 which depth, A or B, were samples taken from a greater depth. [2] 1. Depth B 2. Bacteria in samples taken from depth B shows a lowered mean dehydrogenase activity with 1.5 to 2.4 au compared to 3.2 to 5.7 au in samples taken from depth A (ii) Explain the roles of dehydrogenase in Krebs cycle of the aerobic bacteria. [2] 1. ref to substrate and ref oxidation / loss of protons and electrons 2. ref to reduction of coenzyme NAD and FAD and formation of NADH and FADH2 [Total: 9] Question 3 3 (a) State the