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 (3.1