YTSS 2024 P2 MS ANS

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 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 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 3bi 3 purple : 2 red 1

3 Qn Answer Key 3bii • small sample size • fertilisation is a random process / fusion of sex gametes are random • 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 + QV • 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 4ci (3.10 – 1.55) / 15 = 0.10 au / oC OR (3.10 – 1.50) / 15 = 0.11 au / oC 1 1 1 1 4cii • at optimum temperature which ranges from 20/21 oC to 28/29/30 oC, rate of enzyme reaction is the fastest. • after 28 oC, enzymes start to denature, loss of (shape of) active site • slower rate of, enzyme activity / less / no enzyme-substrate complex formation 1 1 1 4ciii similar shape but below sunny day curve 1 5ai • a technique used to transfer genes from one organism to another OR • 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. • 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 1

4 Qn Answer Key 5b • A and B kill larvae , GM increases, yield of / food from (potatoes) + QV • A, is best at killing insects / kills most insects / works fastest to kill insects • A, should be grown / will provide most food 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 • In Fig 6.1, the anthers mature before the stigma, while in Fig. 6.2, the stigma mature only after the anthers have withered • to ensure that pollen cannot be transferred to the mature stigma of the same flower 1 1 6c • (embryo in) seed develops from the zygote that is formed by fusion of two gametes / fertilisation • both gametes are genetically, dissimilar / different / from two parents 1 1 7a • Correct scale • Correct order of trophic level (from bottom, A à I à S à 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 and is stored in, fat/fatty/adipose, tissues, increasingin concentration, in the bodies of small fishes 1 1 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 8c • as grapes age, the concentration of amylase and reducing sugar increase (only trend) • +QV • amylase digests / catalyse the digestion of + starch (in grapes) + into maltose + which is a reducing sugar 1 1 1 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

5 Qn Answer Key 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 X and Y chromosome Health: Down syndrome / chromosomal mutation Due to trisomy at chromosome 21 1 1 1 cii Sickle cell anemia • red blood cells becomes sickle-shaped due to the abnormal haemoglobin OR • red blood cells unable to absorb oxygen efficiently in the lungs OR Albinsim • body cells cannot produce pigment (1 mark for disease, 1 mark for any description) 1 1 1 1 10a • (drinking of water causes) increase in blood water potential, detected by receptors hypothalamus • causes decrease in release of ADH into blood (in first hour) to be transported to the kidneys • cells in the walls of collecting duct becomes less permeable to water, less water is selectively reabsorbed into the blood • volume of urine produced will increase, (so) decrease in blood water potential / blood water potential returns to, set point / norm / normal, concentration of ADH increases back to norm at 9au from 1h to 3h 1 1 1 1 10b • (osmoregulation) is the maintenance of a constant body water potential • by controlling the water potential and solute concentration in the blood. 1 1 10c Similarities • Both involves a stimulus • Both bring about a response Differences • Nervous control involves nerve impulses while endocrine control involves hormones 1 1 1 1

6 Qn Answer Key • Nervous control are usually quick responses while endocrine control are usually slow responses • Nervous control requires transport by the neurones while endocrine control requires transport by the blood • Nervous control responses are short-lived while endocrine control responses