JPJC 2023 J2 H2 BI Prelim P3 ANS

9744 / 03 [Turn over NAME : CLASS : JURONG PIONEER JUNIOR COLLEGE JC2 Preliminary Examinations 2023 BIOLOGY Higher 2 9744/03 18 September 2023 Paper 3 Long Structured and Free-response Questions 2 hours Candidates answer on the Question Paper. Additional Materials: Answer Booklet READ THESE INSTRUCTIONS FIRST Write your class and name 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. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question on the separate Answer Booklet provided. 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 Examiner’s Use 1 2 3 Section B Total This document consists of 20 printed pages.

2 JPJC/JC2 H2 Biology/Prelim/2023 Section A Answer all the questions in this section. 1 Reindeer are semi-domesticated ruminants that have adapted to challenging environment characterised by long winters and marked annual fluctuations in daylight. Comparative genome analyses revealed several genes that may have promoted the adaptation of reindeer, such as those involved in vitamin D metabolism (POR ), circadian rhythm (GR1A1), and tolerance to cold-triggered pain (SCN11A1). (a) A study was carried out to examine the gene involved in vitamin D metabolism ( POR) and the POR enzyme, which is an important enzyme in the vitamin D metabolic pathway. Vitamin D is made in the skin under the influence of UV light and is important in promoting calcium absorption and the mineralisation of bone for the rapid and robust growth of the antlers, which are important for various aspects of reindeer behaviour and reproductive success. Samples were taken from the reindeer, as well as roe deer and goats to examine for POR enzyme activity in a reconstituted system consisting of the enzyme and substrate. Fig. 1.1 With reference to Fig. 1.1, suggest how reindeer are able to produce sufficient vitamin D for their antler growth despite long winters with low amount of sunlight. ..................................................................................................................................... [2] 1. Reindeer has high enzyme activity of 32 arbitrary units, (25 a.u. more than roe deer, 30 a.u. more than goat) ; 2. Idea of reindeer has evolved / adapted + (a) efficient vitamin D metabolism pathway / (b) enzymes with high catalytic activity to maximise (OWTTE) the amount of vitamin D produced / (c) pr ocure/obtain high (OWTTE) levels of vitamin D with low levels of sunlight ;

3 JPJC/JC2 H2 Biology/Prelim/2023 [Turn over (b) The reindeer do not exhibit 24-hour activity rhythms, and evidence suggests absent circadian activity, which is a useful adaptation in Arctic conditions. Explain how DNA methylation and histone modification had altered the gene expression of GR1A1. ..................................................................................................................................... [4] DNA methylation [2] 1. physically blocks the binding of general transcription factors (GTFs) / RNA polymerase to the promoter of GR1A1 ; 2. preventing formation of the transcription initiation complex, preventing transcription of GR1A1 ; OR 3. leads to recruitment of transcriptional repressors / histone deacetylases / other repressive chromatin remodelling complexes, resulting in more compact chromatin and tighter nucleosomes / DNA more tightly coiled around nucleosomes, preventing transcription of GR1A1; histone modification [2] 4. Histone deacetylation results in DNA winding more tightly around the nucleosomes / the chromatin condenses ; 5. GTFs and RNA polymerase are unable to recognise and bind to the promoter (of GR1A1), preventing formation of the transcription initiation complex, preventing transcription of GR1A1 ;

4 JPJC/JC2 H2 Biology/Prelim/2023 Two subspecies of reindeer, Rangifer tarandus, live in North America. Members of the different subspecies belong to the same species but have some morphological differences and are found in different geographical locations. Table 1.1 compares the features of the two North American reindeer subspecies. Table 1.1 (c) During the last ice age, an ice sheet separated southern and northern populations of R. tarandus to result in the two different subspecies. Explain how this ice sheet affected the evolution of R. tarandus to result in the two different subspecies. ..................................................................................................................................... [4] Selection 1. The (sub)populations were exposed to different environments and were thus subjected to different selection pressures e.g. environment / habitat / climate / food / vegetation ; 2. S ince there was variation within the (sub-)populations due to different mutations, individuals with favourable characteristics were at a selective advantage (or vice versa) and evolutionary changes/changes in allele frequency occurred independently in each (sub)population ; 3. Giving rise to morphological / ecological / behavioural differences ; Isolation 4. The (sub)populations become geographically isolated leading to allopatric speciation ; 5. T he (sub)populations did not interbreed (reproductive isolation) and thus gene flow was disrupted between populations (resulting in different subspecies) ;

5 JPJC/JC2 H2 Biology/Prelim/2023 [Turn over (d) Assess the relative importance of natural selection and genetic drift in producing: (i) the different colours of fur of the two subspecies of reindeer ..................................................................................................................................... [2] 1. natural selection was more important than genetic drift ; 2. reindeer with dark colour / fur was selected for in the woods / warm / shade ; OR 3. reindeer with light colour / fur was selected for in the barren ground / cold / tundra; 4. act as camouflage to protect against (named) predators ; (ii) the different body sizes of the two subspecies of reindeer. ..................................................................................................................................... [2] 1. genetic drift was more important than natural selection ; 2. as small size in north was not adaptive / beneficial ; 3. small animals lose heat faster / harder to keep warm ; 4. Smaller fat reserves are unfavourable with unstable food supply ; 5. Different body sizes are due to food shortage in the tundra and plentiful food supply in the south ; (e) Hybridisation has occurred between individuals of the two subspecies which now live in the area previously covered by the ice sheet. Comment on how the hybrid populations compare to the pure subspecies in terms of genetic variation and potential to adapt to climate change. ..................................................................................................................................... [4] 1. Hybrid populations have more genetic variation / alleles ; 2. As the gene pool contains genes / alleles from both (sub)species ; 3. More potential to adapt / can adapt better to climate change (in future) ; 4. Genes / alleles for migration may let some individuals find new habitats ; 5. They may have genes / alleles to allow them to survive in warm and cold / different temperatures ; (f) Outline how molecular techniques could be used to test the hypothesis that migratory