YCKSS Pure Biology Prelim 2024 Paper 1 & Paper 2 Answer

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

1(a)(i) root hair cell + long and narrow protrusion 1 1(a)(ii) 1 soil water has a higher water potential than the cell sap of root hair cell / cell A 2 hence, water molecules moved from soil water to the cell sap of root hair cell / cell A via osmosis through a partially permeable membrane 3 cell sap of root hair cell now has a higher water potential than cell sap of cortical cells leading to water molecules moving into the cell sap of cortical cells 4 this process continues until water molecules reaches the xylem vessel 3 1(b)(i) still air: graph C moving air: graph B 1 1(b)(ii) 1 In the presence of moving air, there is a greater mass of water los t from 0 to 30 minutes, where the greatest mass of water lost is (6.1 – 2.1 =) 4.0 g at 30 min 2 Moving air removes the layer of water vapour immediately outside the leaves, reducing / lowering the concentration gradient of water vapour between the intercellular air spaces and the atmospheric air compared to the plant in still air 3 Hence, there is a higher net rate of water vapour diffusing out of the intercellular air spaces (through the stomata) to the atmospheric air in the plant exposed to moving air 3 1(c)(i) 252 1 1(c)(ii) any three from: 1 (carbon dioxide /  14C) enters (leaf), through stoma(ta) / by diffusion and diffuses into the chloroplast 2 photosynthesis occurs and radioactive carbon dioxide is converted to glucose in the presence of light energy and chlorophyll 3 excess glucose is then converted to sucrose for transportation 3 [Total: 12] 2(a) D 1 2(b)(i) 1 test-tube 3 contained bile but test-tube 2 did not. Bile emulsifies large fat droplets into smaller fat droplets 2 increases surface area to volume ratio of fats for a faster rate of digestion by lipase into fatty acids and glycerol in test-tube 3 than 2 3 since fatty acids are acidic, hence, pH in test -tube 3 decreases faster / at an earlier time than test-tube 2 3 2(b)(ii) any one from: 1 shows that bile, does not (chemically) digest fats / does not make solution acidic ; 2 shows that, lipase / enzyme, is required (for breakdown of fats into fatty acids and glycerol) 1

2(c)(i) line drawn showing that decrease after optimum is steeper than increase ; 1 line does not have to start at the origin or end at the x-axis label line to point where line meets the x -axis and label indicating that all the lipase is denatured / AW ; 2 line must meet the x-axis 2 [Total: 7] 3(a) 1 light is refracted / bent by cornea 2 ciliary muscles / body contract + suspensory ligaments become slack 3 lens becomes more convex + light rays refracted / bent (more) by lens formed on retina 3 3(b) lens bends / refracts light rays too much so they meet before retina / drawn on diagram ; 1 [Total: 4] 4(a)(i) 1 Amino groups of excess amino acids are deaminated and converted to urea 1 4(a)(ii) 1 The molecule of urea is transported by the hepatic vein from the liver / organ D to the right atrium of the heart via the vena cava 2 From right atrium, the molecule of urea then enters right ventricle and exit to the lungs via the pulmonary artery and returns to the left atrium of the heart via pulmonary vein 3 From left atrium, the molecule of urea then enters the left ventricle and exit the heart via the aorta to the kidney via the renal artery 3 4(b)(i) 1 ultrafiltration happens at the glomerulus / K where the high hydrostatic pressure of blood forces small molecules such as water / glucose / urea / ions into proximal convoluted tubule / L 2 selective reabsorption occurs at proximal convoluted tubule / L, where all glucose and amino acids are reabsorbed while urea and some water are not reabsorbed if no description of ultrafiltration and selective reabsorption is mentioned = 1m 2 all enzymes dentaured

4(b)(ii) 1 An increased concentration of ADH stimulates the increased permeability of the collecting duct to water molecules 2 Hence, more water molecules are reabsorbed into the blood capillaries, resulting to a lower volume of water in the collecting duct 2 [Total: 8] 5(a) Any one from: 1 Inhibits the synthesis of bacterial cell walls 2 Inhibit cell membrane function 3 Inhibits protein synthesis in ribosome 4 Inhibits enzyme action in cytoplasm 1 5(b)(i) [(100 – 180) / 180] x 100% = – 44% 1 1 5(b)(ii) Any three from: 1 daily doses / use (of erythromycin), peak, 1989 / at 2.8 doses per 1000 people 2 (bacterial) infections (resistant to erythromycin) peak, in 1993 / at 180 bacterial infections per 1000 people 3 no record of resistant infections, until 1991 / from 1983 to 1989 / first 6 years 4 delay (of 4 years) between peak of doses and peak of (resistant) infections 3 5(b)(iii) any two from: 1 fewer doses of erythromycin used 2 development of new, antibiotics / treatments / vaccines (or any example that would cause a reduced usage of antibiotics) 3 more, awareness / education about, overuse of antibiotics / antibiotic resistance 4 improved, detection / screening (of pathogens to avoid spread) (reference to improved, cleanliness / hygiene or more people vaccinated / population has reached herd immunity) 5 isolating infected individuals 2 5(c) any one from: 1 vaccines are able to stimulate the production of WBCs in the body which provides longer term of protection against the disease while antibiotics does not provide long term protection as it does not stimulate the production of WBCs 2 vaccines are able to provide protection against bacteria and viruses while antibiotics are only able to provide cure for bacterial infections 3 vaccines help to provide prevention to the onset of a disease while antibiotics help to cure a bacterial infection after the onset of the disease 1 [Total: 9] 6(a)(i) X: nucleus Y: mRNA Z: ribosome 3

6(a)(ii) 1 Gene controlling the production of insulin is transcribed into an mRNA in the nucleus 2 mRNA diffuses / exit the nucleus and attaches to the ribosome in the cytoplasm where it is translated into a polypeptide 2 6(a)(iii) sequence of nitrogenous bases / nucleotides on the mRNA 1 6(a)(iv) 1 (the sequence of amino acids) determines the specific shape of the antibodies produced 2 so that it is complementary / specific, to the shape of the antigens found on (surface of) pathogens to destroy them 2 6(b) 1 The same restriction enzyme is used to cut the insulin gene, and the bacterial plasmid to create complementary ‘sticky ends’ 2 The cut insulin gene and cut plasmid are mixed with DNA ligase to join the complementary ‘sticky ends’ 2 [Total: 10] 7(a)(i) 7(b) (a) red line all plots correct award 1m line drawn award 1m (c) blue line award 1m as long as graph is above red graph + end at same point 2 × × × × × × × ×

7(a)(ii) 0 to 2 minutes: 1 During vigorous exercise, muscle tissues contract more vigorously and the demand of energy of muscle cells increases. 2 However, the supply of oxygen to the muscles cells is unable to meet the increased demand of oxygen of the muscle cells. 3 Hence, m uscle cells undergo anaerobic respiration and produces lactic acid which lowers the pH from 7.07 to 6.55. 2 to 30 minutes: any two from: 1 After exercise, the pH increases gradually from 6.55 to 7.06 because lactic acid is transported away from the muscle cells to the liver. 2 Lactic acid is oxidised to harmless substances in the liver. 3 During this time, breathing rate and heart rate remained high to take in more oxygen for oxidation of lactic acid and to transport lactic acid at a faster rate to the liver