NYGH 2020-S3EOY-Bio P1 and P2 Ans

2020 End-of-Year Examination Secondary Three IP 1 Nanyang Girls’ High School IP Biology [Turn Over 南洋女子中学校 NANYANG GIRLS’ HIGH SCHOOL End-of-Year Examination 2020 Secondary Three IP BIOLOGY Paper 1 1. B Chloroplast is a double membrane bound organelle, Cell membrane has a phospholipid bilayer. 2. C Fact. 3. B Largest and heaviest organelle is the nucleus, this is followed by mitochondria and then lysosome all of which are membrane-bound organelles. Lastly ribosomes is the smallest and lightest. 4. A Fact. A nucleotide consists of 3 components: deoxyribose, phosphate group and a nitrogenous base. 5. B UCG CGC CGG UCG GCG CGC CGC UUA Find GCG from the coding strand. 6. C A gene codes for one polypeptide. Since there are 2 different polypeptides, 2 different genes are involved. 3 consecutive bases on the mRNA codes for 1 amino acids. Hence to code for a polypeptide consisting of146 amino acids, the gene required will be 438 bases long. 7. C If there are 7 adenines on strand 2, this would mean there are 7 thymines on strand 1. If there are 3 guanines on strand 2, this would mean there are 3 cytosines on strand 1. Since each strand consists of 27 bases, then the number of guanines present in strand 1 = 27 – 11 -7 – 3 = 6 1 2 3 4 5 6 7 8 9 10 B C B A B C C C B A 11 12 13 14 15 16 17 18 19 20 B C B D B B C B C B 21 22 23 24 25 26 27 28 29 30 A B D D D A C C D B

2020 End-of-Year Examination Secondary Three IP 2 Nanyang Girls’ High School IP Biology [Turn Over 8. C Gametes do not consist of homologs. A pair of homologous chromosomes can have different alleles e.g. the allele for blood type found on the maternal chromosome is IB but that found on the paternal chromosome is IA. But on the same position on both the maternal and paternal chromosome, the gene there codes for blood type. 9. B Only during prophase does the nuclear membrane breaks down and spindle fibres formed. 10. A T is in metaphase, hence anaphase should follow. P is in anaphase and decondensing of chromosomes only happen during telophase. 11. B Ratio of long wing: short wing produced is 1:1. Hence number of long-winged flies is also 150. 12. C People who are heterozygous for sickle-cell anaemia are not resistant. They have a higher chance of surviving malaria than people who do not have the mutated allele. Diet does not cause sickle-cell anaemia. 13. B P(non-taster) x P(boy) = 0.5 x 0.5 = 0.25 14. D Good solvent property (water is a universal solvent) is important as it allows mineral salts to dissolve so that they can be transported up the xylem. High latent heat of vaporisation is not important for the function of transport in the xylem. Having high adhesive forces (between unlike molecules) and cohesive forces (between like molecules) allow water to flow as a stream up the xylem. 15. B 5 peptide bonds are formed; hence 5 condensation reactions. Since there are 5 different amino acids, there will be 5 different R groups. Amino group and carboxyl groups are common for all amino acids; what they differ in is the R group. 16. B Sucrose is a non-reducing sugar. 17. C Having a high concentration of magnesium ions in the cell sap will reduce diffusion rate. 18. B When there is no net osmosis, the concentration of the solution that the strip is immersed in will correspond to the concentration of the cell sap. If there is no

2020 End-of-Year Examination Secondary Three IP 3 Nanyang Girls’ High School IP Biology [Turn Over change in the length, then the final length: initial length is 1. So read, when y=1, x = 0.25. 19. C Osmosis occurs. Net movement of water into the potato cells, resulting in a rise in the volume of the sugar solution. 20. B Enzyme is the lock and substrate is the key. 21. A Denaturation is an irreversible change. 22. B 1: as substrate concentration increases, the rate of reaction continues to increase. This shows that substrate concentration is limiting. 2: cannot be concluded since there was no mention of change in temperature or pH. 3: further increase in concentration of substrate no longer increases the rate of reaction. This means that other factor is limiting the rate of reaction. 23. D Fact. 24. D X: lacteal Y: blood capillary Lacteal transports fat while blood capillary transports water soluble nutrients. 25. D Fact. 26. A The tube with enzyme and alkali shows the greatest rate of digestion. Duodenum is the part of our alimentary canal that is alkaline. 27. C When packed together these cells will form air spaces within the leaf. Hence it is a spongy mesophyll cell. 28. C At Q and S, with the increase in light intensity, the rate of photosynthesis increases. Hence light is still the limiting factor. 29. D Calcium hydroxide is used to remove carbon dioxide. 30. B Rate of oxygen production indicates the rate of photosynthesis. Rate of production of oxygen is highest at red and violet light and lowest in green light.

2020 End-of-Year Examination Secondary Three IP 4 Nanyang Girls’ High School Paper 2 Answer Guidance 1(a) Structure A Function Nucleus Controls activities of the cells Nuclear envelope/nuclear membrane Controls the movement of substances into and out of the nucleus Structure C Function Lysosome Contains enzymes to digest substances Vacuole Stores food substances Vesicle/Secretory vesicle Transports substances for secretion out of the cell 1 for correct structural identification and correct function 1 for correct structural identification and correct function Both identification and function must be correct for each organelle (b) Mitochondria are oriented in different directions/ planes with respect to one another 1 (c) Magnification = Length of DE/ Actual Length of DE Actual Length [acceptable length is 2.1 cm + 0.1 cm] = 2.1 cm/10 000 = 0.00021 cm 1 for substitution of measurement with correct precision 1 final answer total: 5

2020 End-of-Year Examination Secondary Three IP 5 Nanyang Girls’ High School IP Biology [Turn Over Answer Guidance 2(a) cell J: anaphase cell K: metaphase 1 for both stages correctly identified R spelling error (b) spindle fibres shorten sister chromatids are pulled apart with centromeres leading sister chromatids/ daughter chromosomes migrate to opposite poles of the cell 1 1 1 total: 4 Answer Guidance 3(ai) The sudden spontaneous change in gene structure/ sequence of gene or chromosome number 1 (aii) Exposure to radiation e.g. UV rays/ gamma rays Exposure to chemical mutagens e.g. tar in cigarette smoke/ mustard gas/ formaldehyde/ cancer causing agents 1 1 (b) Infant B has one more chromosome than infant A/ Infant B has 47 chromosomes while infant A has 46 chromosomes. Infant B has 3 chromosome 13, infant A has 2 chromosome 13. Infant B has 2 X chromosomes while infant A has 1 X and 1 Y chromosome. 1 for number 1 for chromosome type R: infant B is a female and infant A is a male. total: 5

2020 End-of-Year Examination Secondary Three IP 6 Nanyang Girls’ High School IP Biology [Turn Over Answer Guidance 4(a) Let XH represents the normal allele Let Xh represents the allele that causes Duchenne Muscular Dystrophy Parental Phenotype: normal, female x normal, male Parental Genotype: XHXh x XHY Gametes: Offspring Genotype: XHXH XHY XHXh XhY Offspring Phenotype: normal, female normal, male normal female affected, male 1 for defining the alleles 1 for identifying genotype x must be written once 1 gamete + show random fertilisation 1 genotype 1 matching phenotype R: carrier as phenotype (bi) 0.50 or 50% or 1/2 1 (bii) Fertilisation is random/ The sample size is too small so the actual ratio is different from the expected 1 to