RI 2023 Prelim H2 Biology P1234 Answers

H2 Biology ● RI Prelim 2023 PAPER 1 1. B 7. B 13. D 19. C 25. D 2. B 8. A 14. C 20. A 26. C 3. B 9. D 15. D 21. B 27. A 4. A 10. A 16. D 22. A 28. C 5. C 11. C 17. D 23. C 29. C 6. D 12. D 18. D 24. C 30. C PAPER 2 1(a) Name the structures A, B and C. [2] A mitochondria; B centrioles; C lysosome/Golgi vesicle/ secretory vesicle; A: vesicle 2 marks if all correct, 1 mark if 2 correct (b) Name one organelle that would also be present in a prokaryotic cell. [1] Ribosome; R: 80S ribosome (c) Describe the structure of B and its role. [4] 1. A pair of hollow cylinders made up of 9 triplets of microtubules (hollow tubes made of protein tubulin) each; 2. The tw o rod-like cylinders are positioned at right angles to each other; 3. Found in a region called centrosome which is microtubule organising centre (MTOC); MAX 2m 4. During mitosis/ meiosis/ nuclear division, centrioles replicate and move to opposite poles of cells; 5. To determine polarity of the cell; 6. They help to organize microtubules to form spindle fibre; 7. To ensure proper separation of chromosomes during nuclear division; MAX 2m

(d) Sodium ions cross cell surface membranes using facilitated diffusion or active transport. Explain why sodium ions cross cell surface membranes by these mechanisms and not by simple diffusion. [3] 1. Sodium ions are charged and hydrophilic; 2. They cannot pass through the hydrophobic core* of the phospholipid bilayer of membrane; 3. So must pass through transport proteins/carrier proteins w ith hydrophilic pore/channel embedded on cell surface membrane involved in facilitated diffusion or active transport. [Total: 10] 2(a) Describe two differences in DNA behaviour during binary fission in a prokaryotic cell and mitosis in a eukaryotic cell. [2] Binary fission Mitosis 1. DNA replication of circular bacterial chromosome occurs during binary fission; DNA replication of chromosomes occurs during the S phase of interphase prior to mitosis; 2. Circular chromosome does not condense prior to separation; All chromosomes in the nucleus will condense during prophase*; 3. Chromosome does not attach to spindle fibres; Chromosomes attach to spindle fibres via kinetochore proteins; 4. Single chromosome does not line up across the equator of the cell; Chromosomes line up in a single row at the metaphase plate; 5. Chromosome does not separate into chromatids; Chromosomes separate into sister chromatids during anaphase*; 6. AVP (b) Suggest why the flasks were incubated at 35°C. [1] This is the optimum temperature for the bacterial enzymes resulting in its fastest rate of growth/ division; Fig. 2.2 is a graph which shows the results of the investigation. Fig. 2.2 number of living bacteria remaining after 3 hours (x 106) concentration of antibiotic / µg cm-3 This is not a flat line. The number of living bacteria decreases from 38 x