PRSS Sec 2 Science 2024 EOY (Ans Key)

1 Pasir Ris Secondary School SECONDARY 2E END OF YEAR EXAMINATION 2024 LOWER SECONDARY SCIENCE Papers 1 and 2 ANSWERS Note: for any sf/unit errors, penalise [½] up to a max of [2] for the entire paper. Paper 1 1 2 3 4 5 6 7 8 9 10 B D A C B A C A A D 11 12 13 14 15 16 17 18 19 20 C D D C B A D C D A 21 22 23 24 25 26 27 28 29 30 D B D C A D C C C D Paper 2 Section A 1 (a) 1 [1] (b) (i) It is insoluble [0.5] in solvent P [0.5]. [1] (ii) 4 [1] (iii) Spot 2 is a pure substance / is made up of one component. Spot 3 is a mixture / made of two components. Any one conclusion [1] 2 (a) The angle of incidence is equal to the angle of reflection. [1] The incident ray, reflected ray and normal at point of incidence all lie in the same plane. [1] (b) (i) concave mirror [1] (ii) upright [1] magnified [1] Accept: virtual

PRSS_2024_S2E_EOY_LSS_ANS 2 3 (a) Bacterial cell has cell wall ; R: unlabelled organelles [1] (b) Bacterial cell does not have nucleus ; [1] (c) Unable to make food ; Does not contain chloroplasts ; Unable to absorb light + photosynthesise ; Any 2 [2] 4 (a) [1] (b) B [1] (c) arrangement: very closely packed in an orderly manner [1] movement: vibrate about in their fixed positions [1] (reject: move) (d) Energy is needed to overcome forces of attraction. [1] 5 (a) (i) carbon dioxide gas [1] (reject formula) (ii) test: bubble the gas into limewater [1] observations: white precipitate forms in limewater [1] (b) sulfuric acid [1] copper carbonate + sulfuric acid → copper sulfate + water + carbon dioxide [1] (c) Place a moist blue and red litmus paper on the surface of the crystals. [0.5] Both litmus papers remain unchanged. [0.5] 6 (a) (i) Radiation ; [1] (ii) Solar panel can be painted black (A: any dark colour) / rough surface ; Dark / rough surfaces are good absorbers of (radiated) heat ; [1] [1] (iii) Metal + conducts heat fastest from the solar panel ; (R: no link to solar panel) [1] (b) Heat transferred from surrounding air to pack by conduction / convection ; Cooled air around pack is denser than air around apple ; Cooled air sinks to bottom of box to remove heat from apple ; Any 2 [2]

PRSS_2024_S2E_EOY_LSS_ANS 3 Section B 7 (a) (i) work is done when the man lifts the plant off the ground. [0.5] force is acted on the pot in the same direction as the movement [0.5] work is not done when the man carries the pot to the right of the room [0.5] force acted on the pot is not in the same direction as the movement [0.5] work is done when the man places the pot on the ground. [0.5] force is acted on the pot in the same direction as the movement [0.5] (ii) place wheels beneath the pot / make the floor smoother [1] accept any reasonable answer (b) (i) positive → negative (draw at least two arrows) [1] (ii) voltmeter placed parallel to the dry cells [1] ammeter placed in series any where in the circuit [1] (iii) chemical potential energy → electrical energy → kinetic energy → sound energy [2] [each energy 0.5m] (iv) refrigerator / electric iron / air conditioner etc (any one) [1] 8 (a) (i) Preservation (A: saving) of wildlife / natural resources ; [1] (ii) Energy-efficient appliances / use appliances only when needed / use less appliances ; A: OWTTE [1] (b) (i) Algae are producers / absorb light energy OR sunlight ; Produce food through photosynthesis ; Maintains other populations by providing energy as food ; Any 2 [2] (ii) Ref. to suitability of climate for 1. adaptive traits of algae ; 2. behavioural traits of algae ; [1] [1] (iii) Underwater plants are unable to photosynthesise ; Underwater plants may die due to lack of food / marine animals die due to lack of plants for food ; [1] [1] (iv) Algae does not obtain nutrients from other organisms ; Algae does not kill / consume other organisms ; [1] [1] 9 (a) Amylase / carbohydrase ; Simple sugars / maltose ; (A: glucose) (b) (i) Brown solution turns blue-black ; (ii) Sugar / maltose / product (particles) are small enough to pass through pores of the Visking tubing walls ; Higher concentration of sugar in the Visking tubing than outside ;

PRSS_2024_S2E_EOY_LSS_ANS 4 (c) (i) Percentage of undigested starch - decreases from 100 % to 77.5 % when in mouth and oesophagus ; - remains unchanged in the stomach ; - decreases from 75 % to 0 % in part X and large intestine ; [1] [0.5] [0.5] (ii) Physical digestion of starch ; (R: not chemical digestion) Starch is not chemically changed / digested / reacted + no new products ; [0.5] [0.5] (iii) Carbohydrase / amylase / enzymes are destroyed / denatured ; A: no carbohydrase produced in stomach [1] (iv) Absorption of digested food (substances) / nutrients (A: any end product of digestion) [1] 10 (a) (i) X – urethra Y – testis / testes [0.5] [0.5] (ii) Sperm ducts are cut and tied ; Semen ejaculated by males during intercourse do not contain sperms ; [1] [1] (iii) The male sex hormone is released into blood + transported around body ; R: male sex hormone is not released out of the body [1] (b) (i) 21 days ; (no unit – 0m) [1] (ii) Egg has died / deteriorated / degraded / disintegrated one day after ovulation (before day 20) ; No fertilisation occurred / fusion with sperm nuclei ; [1] [1] (c) (i) Spermicide ; [1] (ii) Improper use of condom + leakage of semen ; Semen containing virus / bacteria may be in contact with walls of vagina ; [1] [1] 11 (a) Higher amount / percentage / water potential of water in soil than root cells (A: cells within plant) ; R: water concentration Water moves into cells by osmosis ; Water (molecules) is small enough is pass through partial