YTSS PURE BIO 2

1 YTSS 2024 Biology Prelim Paper 1 Answers 1 A 11 A 21 B 31 C 2 C 12 A 22 C 32 C 3 B 13 C 23 B 33 B 4 A 14 C 24 B 34 A 5 C 15 B 25 D 35 A 6 B 16 A 26 A 36 D 7 B 17 C 27 B 37 C 8 B 18 B 28 D 38 C 9 D 19 C 29 B 39 A 10 B 20 B 30 D 40 B

2 Paper 2 Answers Qn Answer Key Remarks Section A 1a • irregular shape of cell (membrane) / cell loses its circular/biconcave shape / affects the shape of RBC • cell swells / cell is larger / cell expands • contains less haemoglobin (any 2) 1 1 1 1b • Decrease in surface area to volume ratio • Slower rate of diffusion of oxygen into and out of RBC • Less oxygen can bind to haemoglobin • Not able to transport oxygen in the body efficiently (any 2) 1 1 1 1 1c Platelets (Blood) plasma White blood cells / lymphocytes / phagocytes (max 2 marks, minus 1 mark for each missing word / mistake) 2 2a Water Amino acids Sucrose (max 2 marks, minus 1 mark for each missing word / mistake) 2 2b Cell type A: sieve tube cell Cell type B: companion cell 1 1 2c • companion cell / cell type B, have (many mitochondria) • to provide energy to help sieve tube cells / cell type A transport food by active transport / translocation OR • companion cell / cell type B, provides nutrients and carries out metabolic processes • to keep, sieve tube cell / cell type A, alive 1 1 1 1 3a Phenotype of parents: purple purple Genotype of parents: Aa Aa Gametes: A a A a Genotype of F1 generation: AA Aa Aa aa Phenotype of F1 generation: purple purple purple red Ratio of F1 generation: 3 purple : 1 red 1 ½ ½ ½ ½ 1

3 Qn Answer Key Remarks ½ mark if no mention of purple/red 3bi 3 purple : 2 red 1 3bii • small sample size • random fertilisation of gametes OR random nature of fertilisation • mutation of gene for colour (any 2) 1 1 3c 1 AA : 2 Aa 2/3 x 660 = 440 1 1 3d • colours / shades / categories / phenotypes, not distinct / not discrete / overlap / form a (gradual) range / include intermediates • >1 / 4 / several / many, genes • environment affects, colour / phenotype (max 2 marks, any 2) 1 1 1 4a Light intensity / temperature / humidity / wind speed / volume of water (any 2) 2 4b • (as climate changes) increase in carbon dioxide concentration causes + average width of stomatal aperture to decrease / stomata to be less open • less water (vapour) will be, lost / evaporated / diffused out / transpired (though stomata) + this allows survival in, low water availability / dry conditions / this helps to conserve water 1 1 Minus ½ if never specify benefit of water 4ci (3.10 – 1.55) / 15 = 0.10 au / oC OR (3.10 – 1.50) / 15 = 0.11 au / oC 1 1 1 1 Minus ½ for no/wrong units Minus 1 for wrong dp. 4cii • optimum temperature • ranges from 20/21 oC to 28/29/30 oC • fastest rate of, enzyme activity / enzyme-substrate complex formation / effective collisions / product formation • after 28 oC, • enzymes start to denature • loss of (shape of) active site • slower rate of, enzyme activity / enzyme-substrate complex formation / effective collisions / product formation • (process is) photosynthesis (max 3 marks) ½ ½ ½ ½ ½ ½ ½ ½

4 Qn Answer Key Remarks 4ciii similar shape but below sunny day curve 1 Minus ½ if the lines intersect 5ai • a technique used to transfer genes from one organism to another • Individual genes may be cut off from the cells of one organism and inserted into the cells of another organism of the same or different species. OR • The transferred gene can express itself in the recipient organism. OR • To form a transgenic organism 1 1 1 5aii • to, test / compare, effect(iveness) of, genes / proteins / plants / varieties / A and B • to see which, (gene / plant / variety / of A and B), works, better / best • To compare possible side effects • To increase genetic variation (any 1) 1 1 1 5aiii To act as a control to show that non-GM potato plant is not able to kill any insects ½ ½ 5b • A and B kill larvae • GM increases, yield of / food from (potatoes) • A, is best at killing insects / kills most insects / works fastest to kill insects • A, should be grown / will provide most food (max 3 marks, any 3 points) 1 1 1 1 6a Fig. 6.1 - Pollen from the anthers, sticks to / clings onto, the (hairy) body of the bee Fig. 6.2 - Pollen on the insect’s (hairy) body is transferred to the stigma 1 1 6b The anthers and stigma mature at different timings In Fig 6.1, the anthers mature before the stigma to ensure that pollen cannot be transferred to the mature stigma of the same flower In Fig. 6.2, the stigma mature only after the anthers have withered ½ ½ ½ ½ 6c • (embryo in) seed develops from the zygote • zygote is formed by fusion of two gametes / fertilisation • both gametes are genetically, dissimilar / different / from two parents • male gamete / pollen, come from different plant • fruit pod formed from tissue of parent / female plant / carpel / fruit (coat) genetically identical to female parent ½ ½ ½ ½ ½

5 Qn Answer Key Remarks • fruit pod is formed by mitosis (max 2 marks, any 4) ½ 7a • Correct scale • Correct order of trophic level (from bottom, A → I → S → L) + label for trophic level 1 1 7b • mercury in the, river / water / invertebrate animals, may be, consumed / ingested, by small fishes • mercury cannot be excreted • is stored in, fat/fatty/adipose, tissues • Mercury, accumulates / increases in concentration, in the bodies of small fishes ½ ½ ½ ½ 8a • A: x-axis: age of grapes and days and y-axis: percentage concentration of reducing sugars • S: scale for x-axis (20 days for every 10 boxes) and scale for y-axis (2.0% for every 10 boxes) • P: correct plotting of all six points • L: best fit CURVE 1 1 1 1 8b correct age estimated from graph ≈ 64 days 1 Minus ½ mark for missing units 8c • as grapes age, the concentration of amylase and reducing sugar increase (only trend) OR • as grapes age from 14 days to 84 days, the concentration of amylase increase from 0.10 to 0.30 au and reducing sugar increase from 1.1 to 11.3 % (trend + data) • amylase digests / catalyse the digestion of + starch (in grapes) + into maltose + which is a reducing sugar 1 2 1 Minus ½ for any missing part, no

6 Qn Answer Key Remarks marks for 2 or more missing part 8d • Zero amount of / no reducing sugar, solution remains blue • Trace amount of reducing sugar, green ppt is observed OR Moderate amount of reducing sugar, orange ppt is observed OR • Large amount of reducing sugar, brick red ppt is observed (max 2 marks, any 2) 1 1 Missing precipitate /solution -minus 1m. 9a L – placenta Function - • diffusion of oxygen and digested food substances / named (e.g. glucose, amino acid) from maternal blood to foetal blood • diffusion of metabolic waste/named from foetal blood into maternal blood • diffusion of antibodies from maternal blood into foetal blood • produces progesterone to maintain uterine lining • blood barrier that protects foetus from high pressure of maternal blood/harmful microorganisms/incompatible blood group (1 mark for labelling) (max 2 marks for function, any 2 points) 1 1 1 1 1 1 9b M - urethra Function - transports urine from the urinary bladder to outside of the body 1 1 9ci Sex: male Due to presence of