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 aero