2016 HCI H1 Biology Prelims P1&P2 Answers

1 HWA CHONG INSTITUTION 2016 JC2 H1 BIOLOGY PRELIMINARY EXAMINATION PAPER 1 & 2 MARK SCHEME MULTIPLE CHOICE QUESTIONS 1 B 11 B 21 B 2 B 12 A 22 D 3 D 13 D 23 A 4 D 14 A 24 A 5 C 15 A 25 D 6 D 16 A 26 D 7 C 17 D 27 B 8 D 18 C 28 B 9 A 19 C 29 A 10 B 20 C 30 C STRUCTURED QUESTIONS QUESTION 1 (a) Explain the role of helicase in DNA replication. [2] 1. separates/unwinds / unzips strands / helix / breaks H-bonds 2. so nucleotides can attach / parental DNA strands can act as templates (b) Explain how cytarabine prevents DNA replication. [2] 1. similar structure to cytosine added instead of cytosine 2. prevents complementary base pairing / prevents strand elongation With reference to Fig. 1.2, (c) (i) state the duration of metaphase in the cell. [1] 18min (ii) complete line Y on the graph. [1] horizontal until 18 minutes, then decreases as straight line to 0 μm at 28 minutes

2 (iii) account for your answer in (c)(ii). [ 3 ] 1. chromosomes / pairs of sister chromatids align singly at the metaphase plate during metaphase of mitosis 2. hence, from 0 minute to 18 minutes, the distance of each chromatid and the pole to which it is moving was constant at 20 μm 3a. sister chromatids separate at the centromere to become daughter chromosomes 3b. and migrate towards the opposite poles in anaphase 4. hence, the distance of each chromatid / daughter chromosome and the pole decreased from 20 μm to 0 μm from 18 minutes to 28 minutes at the end of anaphase 5. each chromatid / daughter chromosome did not move / remain at the pole in telophase 6. hence, the distance of each chromatid / daughter chromosome was constant at 0 μm [Total: 9]

3 QUESTION 2 (a) (i) State precisely where RuBP and GP are located in the chloroplast. [1] Stroma (ii) Explain why the concentration of RuBP changed between 200 and 275 seconds. [2] 1. during this period, CO 2 concentration is lower 2. since less CO 2 fixed by RuBP / CO2 combining with RuBP / RuBP converted to GP 3. moreover, RuBP is regenerated from triose phosphate (b) Suggest how the decrease in the concentration of GP leads to a decrease in harvest for commercial suppliers of Chlorella. [2] 1. a decrease in the concentration of GP will lead to less triose phosphate / glyceraldehyde-3-phosphate being produced 2. so less conversion of triose phosphate to carbohydrates / lipids / amino acids / proteins (c) In the light dependent stage, illumination of chloroplasts is important for maintaining the high pH in the stroma. Explain how the illumination of chloroplasts maintains the high pH in the stroma. [3] 1. illumination of chloroplasts excite and displace electrons from special chlorophyll a / photosystem / ref. to photoactiva