T3W2 4E Pure Biology Prelim 2023 MS

1 Preliminary Examination 2023 Secondary 4 Express Biology 6093 Mark Scheme Paper 1 1 2 3 4 5 C A B A D 6 7 8 9 10 B A C B D 11 12 13 14 15 C B C B D 16 17 18 19 20 C A C C C 21 22 23 24 25 A A B A B 26 27 28 29 30 B A D A D 31 32 33 34 35 A A C A D 36 37 38 39 40 A A D B D Section A 1 (a)(i) Tissue; reject: incorrect spelling max 1 1 (a)(ii) circular / round shape + label ‘chloroplast’; circular / round shape (larger than drawing of chloroplast) + label ‘nucleus’; large, central oblong shape + label ‘large central vacuole’; line around cell wall (inner) + label ‘cell surface membrane’ reject: incomplete line / broken line/ wrong proportional w.r.t other organelle drawn max 1 1 1 1 4 (a)(iii) Label a pair of guard cell; accept: one guard cell max 1 1 (b) Presence of thin film of moisture; Water evaporates from the thin film of moisture and moves into the intercellular air spaces; AW Presence of intercellular air spaces; 1 1 1

2 Accumulation of water vapour, creating a water vapour concentration gradient between leaf and the surrounding air; max 1 4 2 (a) Similarity: Lactic acid is produced as a by-product/ product ; AW Difference: Carbon dioxide is produced in bacteria but is not produced in muscle cell of human ; AW 1m ea max 1 1 2 (b) From t = 0 to t = 40h, concentration of lactose decreases gradually; AW From t = 40 to t = 48h, concentration of lactose remains unchanged; AW max 1 1 2 (c) Measure 2cm3 of milk and add equal amount of Benedict’s solution; Mix well and heat in a boiling water bath for 5 minutes; max 1 1 2 (d)(i) Mutation / Gene mutation ; There is a change in the allele / gene / base sequence / DNA ; This result in change in the 3- dimensional shape of active site of the enzyme; The substrate / lactose is unable to fit into the active site max 1 1 1 1 3 (d)(ii) Yes; Lactose concentration in yogurt is much low than milk; AW reject: no lactose max 1 1 2 3 (a)(i) Structure A: network of capillaries; Maintains the concentration gradient for the absorption of digested food sustances by the continual transport of digested food substances away; AW Structure B: one cell thick epithelium; Digested food substances take a shorter time to diffuse through, speed up the rate of absorption; max 1 1 1 1 4 (a)(ii) Alveolus / Alveoli; max 1 1 (b)(i) Excess amino acids are transported to the liver for deamination; The amino group will be removed and convert into urea; Urea will be transported to the kidney and excreted from the body in urine; The remaining deaminated amino acids will be convert into glucose. max 1 1 1 3 (b)(ii) Regulation of blood glucose concentration / carbohydrate metabolism; Production of bile / metabolism of fats; Detoxification / Break down alcohol; Break down of red blood cells/ iron storage; Protein synthesis; 1 1 1 1 1

3 Any 1 = 1m max reject: answers from the same catergory /deamination of amino acids/ metabolism of proteins 1 (c) Each transaminase has a unique 3-dimensional active site; which is only binds/ complementary / fits / matches the shape of one type of amin acids; to form an enzyme-substrate complex. max 1 1 2 4 (a)(i) D: aorta / aortic arch; E: pulmonary artery; max 1 1 2 (a)(ii) Any one from similarity and one from difference; max Aorta Pulmonary Artery Similarity Transport blood away from heart Presence of semi-lunar valve Difference Transport oxygenated blood; AW Transported deoxygenated blood; AW Blood at higher pressure than pulmonary artery Blood at lower pressure than aorta; 2 (b)(i) Fatty substances such as cholesterol and saturated fats may deposit on the inner surface of the coronary arteries; This is known as atherosclerosis; This narrows the lumen of these arteries and increases blood pressure; Rough inner surface may develops which increase the risk of a blood clot being trapped in the artery; completely block off the artery. max 1 1 1 3 (b)(ii) inflating the balloon : push / compress the fats to widen the lumen of the blood vessel; leaving the hollow metal mesh in the blood vessel: maintain the lumen for blood flow; max 1 1 2 5 (a) Organism (a named organism from Fig 5.1) that feeds on another organism (a named organism from Fig 5.1) e.g. Yellow-vented bulbuls feeds on ladybirds accept any correct example from Fig. 5.1 max 1 1 (b) Energy decreases down a food chain; There will be insufficient energy/not enough energy to sustain; the organisms beyond the fifth link. max 1 1 2 (c) Population of brown hawk owls may decrease after some time; 1

4 Pesticides on rain tree will be consumed by the primary consumers As the pesticides cannot be excreted and will accumulate on the bodies of the primary consumers; This results in the pesticides being passed along the food chains. Increasing the concentration in the bodies of the organisms along the trophic levels; Brown hawk owls is the top /apex consumer in many of the food chains, hence will accumulate large amount of pesticides from eating the affected prey; The brown hawk owls may be poison eventually by the pesticides. max 1 1 1 1 1 1 4 (d) Accurate drawing of the number (represent by rectangle); Label of each rectangle with the correct trophic level; max 1 1 2 6 (a) Label of axis; Appropriate scale; Accurate plot; max 1 1 1 3 (b) Total volume of water lost: 740 + 160 + 1560 + 540 = 3000 cm3 Percentage lost through faeces: 160 / 3000*100 = 5.33% (3 s.f) reject: no unit max 1 1 (c) Volume of water lost through sweat will decrease; Sweat gland will become less active hence less sweat will be produced; Less evaporation of water, and less latent heat of vaporization lost; Volume of water lost through urine will increase; Less water lost through sweat, the water potential in blood will increase; Less ADH will be released, resulting in less water reabsorbed at the collecting duct; 1m for suggesting the two ways max 1 1 1 1 4 (d) 190 000 – 740 = 189 260 cm3 ; 189 260 cm3 of water will be reabsorbed along the tubules by osmosis; max 1 1 2 7 (a) The nuclei of the sperm cell and egg cell will fuse; to form a fertilized egg / zygote The fertilized egg will divide by mitosis; to form a ball of cells known as an embryo; Meiosis is involved in the formation genetically dissimilar egg and sperm cells which increase variation in the species. This will increase the chance of survival of the species during the change in the environment; Meiosis is involved in the formation of the haploid; egg and sperm cells, this maintains the normal diploid number of chromosomes in the species. max 1 1 1 1 1 5

5 (b) Function of the amniotic sac Encloses the fetus in the amniotic cavity, containing amniotic fluid; Function of amniotic fluid (Any 2) It supports and cushions the fetus before birth; It is a shock absorber; It protects the fetus against physical injury / mechanical shock as it cannot be compressed; It allows the fetus a certain degree of movement, which promotes muscular development; It lubricates, and reduces friction in the birth canal; max 1 1 1 1 1 1 3 (c) Sexual reproduction Asexual reproduction Involves 2 parents Involves only 1 parent Produce genetically dissimilar offsprings Produce genetically similar offsprings Any two = 2m max 2 8 E (a) When blood glucose level is higher than norm, insulin will be secreted by islets of Langerhans in the pancreas; Insulin will be transported in blood stream to liver; Any 2 from: It will