Christ Church Pure Biology Prelim 2024 Paper 1 & Paper 2 Answer

Christ Church Secondary School Preliminary Examinations Science Department Secondary Four Express Biology 1 Paper 1 [40 marks] Q Ans Q Ans Q Ans Q Ans 1 D 11 D 21 C 31 A 2 A 12 D 22 B 32 D 3 A 13 B 23 D 33 D 4 D 14 C 24 B 34 B 5 B 15 B 25 C 35 D 6 B 16 B 26 B 36 A 7 B 17 C 27 C 37 A 8 C 18 B 28 B 38 C 9 C 19 D 29 C 39 D 10 B 20 D 30 A 40 B Paper 2 Section A [70 marks] Answer Remarks Marks 1 (a) 1 testosterone 2 sperm 1 mark each R semen R hormone 2 (b) X: Sperm Duct Explanation: - Man is infertile / cannot reproduce - Sperms cannot travel to the urethra and out of the body 1 1 1

Christ Church Secondary School Preliminary Examinations Science Department Secondary Four Express Biology 2 (c) [1] When the valves malfunction/not working, backflow of blood occurs / blood flow backwards. [2] Blood vessels swell up and blood accumulates. [3] Accumulation of blood raises the temperature of the area/cells/tissues surrounding the testes. [4] The high temperatures causes lower sperm production and poor quality of sperms. 4 Total 9 Answer Remarks Marks 2 (a) [1] Cells in the trachea / bronchial tubes secretes mucus. [2] Mucus traps bacteria / germs / pathogens. [3] Cilia sweep the mucus containing bacteria / germs / pathogens upwards and out of the body / prevent it from entering lungs. 3 (b) [1] Vaccine contains an agent that resembles a pathogen. [2] Which stimulate white blood cells to produce antibodies. [3] These antibodies kill pathogens that cause infectious diseases. 3 (c) [1] Virus does not have cellular structures that antibiotic target. [2] Antibiotic acts on bacterial cell walls but viruses do not have cell walls. [3] Antibiotic break up cell membranes but viruses do not have cell membranes. [4] Antibiotic act on ribosomes inhibiting protein synthesis and growth but viruses do not have ribosomes and they do not grow. Any two points 2 Total 8

Christ Church Secondary School Preliminary Examinations Science Department Secondary Four Express Biology 3 Answer Remarks Marks 3 (a) [1] Blood flow remains constant and then increases. [2] Blood flow remains at 4/5 %. [3] Increase in blood flow from 25-27°C [4] to a maximum / 100% at 41°C. AW Any three points 3 (b) [1] Rise in temperature detected by receptor in skin and generate nerve impulses. [2] Nerve impulses generated travelled to the brain via the sensory neurone. [3] Impulses from the brain travelled to the muscles in the arterioles / shunt vessels via motor neurone. [4] Arterioles dilate / vasodilation OR shunt vessels constrict to increase more blood flow into capillaries / near the surface of the skin Any three points 3 (c) 46% 1 (d) [1] Higher concentration of capsaicin on the skin surface (than in the cells) [2] Capsaicin diffuse through the cells / passes through / across cell membranes to the cells by [3] diffusion. A down a concentration gradient A from high to low concentration 3 (e) [1] Hormones is by chemical means while nerve co-ordination involves nerve impulses. [2] Hormones are transported in the blood / circulatory system while nerve co- ordination are transported by the neurones. [3] The (effects) by hormones are slower than nerves. [4] The (effects) by hormones are longer- lasting than nerves. Any two points 2 Total 12

Christ Church Secondary School Preliminary Examinations Science Department Secondary Four Express Biology 4 Answer Remarks Marks 4 (a)(i) Mutation is spontaneous / random change in the structure of the gene or the number of chromosome. 1 (a)(ii) formaldehyde; radiation; x-ray; tar 1 (a)(iii) Parent without MSUD has a child who has MSUD; Parent 1 and 2 without MSUD have child 5 with MSUD; Parent 7 and 8 without MSUD have child 12 with MSUD. 1 (a)(iv) Correct genotype of parents and gametes: N + n and N + n Correct genotypes of offspring: NN / Nn / Nn / nn Correct phenotypes of offspring. Probability that the child will have MSUD: 0.25 / ¼ / 25% R ratio 4 (b)(i) liver 1 (b)(ii) [1] Toxic substance P passes through the (glomerulus) in the kidney. [2] Not all of the toxic substance P is reabsorbed back into the blood capillaries and end up in the urine. [3] Only some of the toxic substance P is reabsorbed into the blood capillaries. Any two points 2 b(iii) [1] proteins are broken down into amino acids / proteins are made up of / contain amino acids. [2] must keep amino acids in low amount / amino acids do not build up / less amino acids produced. [3] so that toxic substance P does not build up in the body and cause damage to cells / tissues / organs. AW AW 3 Total 13

Christ Church Secondary School Preliminary Examinations Science Department Secondary Four Express Biology 5 Answer Remarks Marks 5 (a)(i) AAC-ACG-UCC-CAG 1 (a)(ii) asparagine – threonine – serine – glutamine 1 (b)(i) B Explanation: Amino acids is absorbed by the blood capillaries in the villi. 1 1 b(ii) [1] (Pancreatic enzymes) Protease active site is complementary to the shape of the proteins. [2] Only proteins can bind / fit to the protease (enzyme) / other molecules cannot bind / fit to the enzyme active site. [3] Lesser proteins is broken down (digested) into amino acids and lesser absorption of amino acids into the blood stream. [4] lesser amino acids results in stunted growth and poor muscle development. [5] amino acids are building blocks needed for muscle and tissue repairs / growth of new cells. Any four points 4 Total 8

Christ Church Secondary School Preliminary Examinations Science Department Secondary Four Express Biology 6 Answer Remarks Marks 6 (a) Circle any one of the vascular bundles. Label xylem. 2 (b) [1] cell vacuoles / cells have a higher water potential [2] cells absorbed water by osmosis / down a water potential gradient [3] causes cells to become turgid / have turgor pressure. [4] presence of cell wall which is inelastic and prevent the cells from bursting. Any three points 3 (c) Describe: [1] Q has sucrose / 13C in shoot and root [2] T has no sucrose / 13C in shoot and root [3] R has sucrose / 13C in root but not in shoot [4] S has sucrose / 13C in shoot but not in root Explain: [5] there is no transport of sucrose / 13C where phloem is removed. [6] phloem transport sucrose / 13C in both directions; upwards and downwards. [7] leaf carry out photosynthesis and produce glucose and convert to sucrose for transport. [8] sucrose is then transported to the roots and shoots. Any two points Any three points 5 Total 10 xylem

Christ Church Secondary School Preliminary Examinations Science Department Secondary Four Express Biology 7 Answer Remarks Marks 7 (a)(i) Scale; Best-Fit line; Axis Titles; Plotting points 4 (a)(ii) [1] As the time increases, the partial pressure of oxygen levels decreases from 75 mmHg to 55 mmHg / by 20 mmHg. [2] Every 6 hours, the partial pressure of oxygen levels decreases by 5 mmHg. AW 2 (b) [1a] walls of alveolus has a thin film of moisture [1b] to allow gases to dissolve to diffuse into the blood capillary [2a] walls of alveolus is made up of one cell thick [2b] to allow faster diffusion of gases [3a] alveolus is surrounded by a dense network of blood capillaries. [3b] to transport gases quickly to maintain a steep concentration gradient of gases. Any four points 4 Total 10 Time (hours) partial pressure of oxygen levels (mmHg) 6 12 24 48 50 60 70 80 X X X X X

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