QTSS Prelim 2024 Sec 4E Science (Biology) P1 and 4 [5087] Ans

Preliminary Examination 2024 Secondary Four Express Science (Biology) 5087/01/04 Answers 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. B A D D C A B B D B 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. C A C C C A A A C A Paper 4 Qn Answers Marks 1. (a) mass decrease of beet root in test-tube A decreases [1] explanation: beetroot cells has higher water potential compared to 30% sucrose solution [1]. Water move out of beet root by osmosis [1] 3 (b)(i) Cell membrane of beet root cells were damaged by heat The purple colour in the beet root move out to the surrounding water causing it to turn purple. [1] 1 (ii) The colour of liquid in test-tube B will remain unchanged/will not turn purple.[1] The beet root cells will become turgid but will not burst because there is cell wall to protect the cell from bursting. [1] 2 Total 6 2 (a) There are more albumen still present in test-tube B than C at the end of experiment.[1] As temperature is higher in test-tube C, enzymes and substrate gain kinetic energy which increases the effective collisions between the molecules thus increasing rate of digestion of albumen. [1] (Do not write temperature affect rate of digestion) 2 (b) As temperature increases beyond optimum temperature, pepsin gets denatured; [1] Heat destroys the chemical bonds as a result pepsin loses its 3D structure and its active site [1]. Pepsin cannot bind to the complementary shape found on the albumen to form the enzyme-substrate complex. [1] As a result, albumen remains undigested in test-tube D. [1] 4

2 Queenstown Secondary School [Turn over (c)(i) Polypeptides/amino acids 1 (ii) Pepsin is a prote ase which digests protein found in albumen into polypeptides/amino acids. 1 Total 8 3 (a (i) Left atrium contracts, blood is pushed into the left ventricle [1] 1 (ii) If the flap B is not closed properly, some blood will backflow into left atrium when left ventricle contracts.[1] Less oxygenated blood is sent out to aorta and to other parts of body [1]. OR Pressure of blood is also reduced [1]. 2 (iii) Left ventricle has a thicker muscular wall to push blood at high speed & pressure so that it can be transported to all parts of body efficiently [1]. 1 (b) Blood in the coronary artery is at higher pressure [1] OR higher oxygen content [1] than blood in the coronary vein. 1 Total 5 4 (a) Anaerobic respiration is the breakdown of glucose in the absence of oxygen to release energy and lactic acid 1 (b) Glucose decreases rapidly from 0-10 minutes (during exercise) and lactic acid concentration increases from 0 to 10 minutes.[1] During vigorous exercise in the first 10 minutes, muscles cells carry out aerobic respiration and anaerobic respiration to release large amount of energy to carry out the vigorous activities .[1] The rapid rate of aerobic respiration causes the level of glucose decreases so rapidly during exercise and anaerobic respiration releases lactic acid which causes the increased in lactic acid concentration [1] 3 (c) During resting, lactic acid is removed from cells and transported to the liver [1] to be converted to glucose and little energy[1] 2 Total 6 5 (a) X: by droplets (1) Y: by direct contact (1) Z: by contaminated food and water (1) 2 (b) Washing hands with soap and water or rub with disinfectant after touching objects suspected to be contaminated with the bacteria (1). Keep a safe distance from others, thus avoiding close contact with people (1). 2 (c) The food was not covered and was left exposed to the environment (1). Hence, the food could have become contaminated with pathogens (1). As he did not reheat the food, Larry probably ate the live pathogens together with his food . 2 Total 6

3 Queenstown Secondary School [Turn over 6 (a) Scale (at least 75% of space given) -1 Line join points – 1 Axis (correct labels, labels at fixed intervals) – 1 Points (correctly plotted) – 1 4 (b) Between 0830 hrs to 1030 hrs + rate of transpiration increases from 5.0 mg/min to 12.8 mg/min 1030 hrs up till 1230 hrs + transpiration rate drops from 12.8 mg/min to 12.0 mg/min 2 (c) Light intensity increases; More photosynthesis + stomata opens bigger ;, higher rate of transpiration OR Temperature gets higher as morning gets later/sun rises higher; Increased rate of evaporation of water from mesophyll cell surface, more water vapour to diffuse out ; 2 Total 8 7 (a) A [1] shortest food chain/least trophic levels so less energy is lost in between the trophic levels [1] 2 (b) Pyramid of number – represents the number of living thing in the food chain creating an inverted pyramid shape this is due to there being only one singular bush tree in which the green flies feed on. [1] Pyramid of biomass - represents the total mass of each trophic level so creating a pyramid this is due that bush tree in the lower trophic level has a broader base as it provide food for the animals which prey on them. [1] 2 Total 4 5 9 12.8 12.4 12 11 8 7 4.5 0 2 4 6 8 10 12 14 830 930 1030 1130 1230 1330 1430 1530 1630 rate of transpiration (g/min) Time (hrs) Rate of transpiration (g/min)

4 Queenstown Secondary School [Turn over 8 (a) X: oestrogen Y: progesterone 2 (b) X causes repair and growth / thickening of uterus lining.[1] Y maintains the thickness of uterus lining.[1] 2 (c) uterus lining thickness maintains at thickest for embryo implantation and growth [1] concentration of oestrogen and progesterone remains high [1] 2 Total 6 9 (a) Noah inherited a recessive allele each from both father and mother. He is homozygous recessive, pp, so he expressed PKU His father and mother are both heterozygous, Pp, so they do not express the PKU 2 (b) Noah (pp) p p Rachel (Pp) P Pp Pp p pp pp Correct genotype of offspring (F2) (based on pupils’ answers in parents’ genotype) ; [1] Correct phenotype of F2 ; [1] Correct phenotype ratio of F2 [1] Probability of child getting PKU is 50% [1] 4 Total 6 Section B 8 (a) • From 0000 to 0600 h, sugar concentration in the leaves decreases; [1] No sunlight during the period, photosynthesis did not occur; sugar in the leaves was oxidised/ used during respiration [1] • From 0600 to 1500 h, sugar concentration in the leaves increases to maximum of 20 units/ highest [1] As light intensity increases to noon, the rate of photosynthesis increases. Thus, more sugar is produced [1] • From 1500 to 2400 h, sugar concentration in the leaves decreases from 20 to 9 units [1] Light intensity decreases in the night, rate of photosynthesis decreases. Thus, lesser sugar is produced [1] [Students must explain the relationship between light intensity and rate of photosynthesis] 6

5 Queenstown Secondary School [Turn over (b) When more sugar is made in the leaves, more sugar will be present in the stem; [1] More sugar will be translocated/transported to other parts of the stems through the phloem in the stem. This causes the increase in the sugar in stem.[1] 2 (c) Any two of the following: • oxidised to released energy during respiration; • component of cellulose cell walls; • combined with nitrogen to form amino acids; • stored as starch 2 Total 10 9 a • A is Respiration. • Respiration is a chemical process that releases energy from food substances in all living cells through oxidation process and in the process releases carbon dioxide into the environment. [1] • This process increases the