2024 ACSBR 2G3 SCI EOY Ans Key

Anglo-Chinese School (Barker Road) Secondary 2 Express Science End-of-Year Examination 2024 Section A A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 B A D C B C C B D C A11 A12 A13 A14 A15 A16 A17 A18 A19 A20 C C B C B C C C C C A21 A22 A23 A24 A25 A26 A27 A28 A29 A30 C D C D D D C D A B Qn Answers Remarks B1(a) substance element compound mixture solid P  powder Q  [1] for each row B1(b) Add mixture P and Q into water to dissolve solid P. [1] Filter the mixture [1] OR using a (filter) funnel and filter paper, [1] to collect powder Q as residue. [1] Note: Use of a magnet is not required since qn requires isolation of Q from P only. R: No water added, subsequent steps of filtration required the mixture to be in water to be mixed in water first. [0m] B1(c) substance chemical formula number of atoms nitrogen gas N2 2 ethene C2H4 6 sulfuric acid H2SO4 7 [1] for each row B2(a)(i) temperature of water [1] R: temperature without mentioning substance B2(a)(ii) 1) volume of water / amount of water 2) mass of salt / amount of salt 3) rate of stirring 4) size of salt (powder/granular) [State any one – [1] each R: Exact mass of salt shown in diagram Not a variable but a feature of the setup R: Type of salt B2(b) Z ; [1] The higher the temperature, the faster the salt dissolves [1] OR Rate of dissolving occurs faster rate at higher temperature [1]

Qn Answers Remarks B3(a) (a) MP1: Correct image (same size, laterally inverted, equidistant from mirror, label) Equidistance from the mirror. MP2: correct incident (from object to mirror) light ray and reflected (from mirror to eye) light ray indicated by arrows pointing correctly. MP3 [1] angle of incidence = angle of reflection is correctly depicted (visually judge) (b) laterally inverted Virtual Same size as object Same shape as object, upright [any 2 features] R: flipped, inverted, R: object distance to mirror = image distance to mirror (law of reflection, not property of image) R: size of image is proportional to object B4(a)(i) A [1] B4(a)(ii) C [1] B4(a)(iii) B [1] B4(b) Physical reaction does not form new substances but chemical does [1] OR Physical reaction does not involve rearrangement of particles but chemical reaction does. [1] Physical reactions are reversible but chemical reactions are not. [1] B5(a)(i) Fatty acids OR glycerol [1] R: Incorrect spelling B5(a)(ii) Fatty acids produced caused the pH of solution to decrease to 7 [1] OR pH drops below 7 OR pH drops / milk more acidic B.O.D: Neutralisation occurred R: Lipase is acidic B5(b)(i) Results are more reliable/consistent/precise OR Reduce human error, reduce random error [1] R: increase/ensure accuracy, increase fairness, reduce chance of human error image object eye plane mirror

Qn Answers Remarks B5(b)(ii) B, C, A B6(a)(i) transport/carry oxygen around the body R: Carry oxygenated blood – RBC is a component of blood and it carries oxygen and not blood B6(a)(ii) MP1: biconcave; MP2: To increase surface area to volume ratio for faster exchange of oxygen OR Increase surface area for increase exchange of gases/ diffusion / OWTTE OR MP1: No nucleus MP2: More space to store/bind to more oxygen [1] correct feature + [1] matched related function. R: incorrect spelling for key features – e.g. bioconcave B6(b) platelet(s) [1] R: wrong spelling B6(c)(i) B. C, G All 3 correct – [1] B6(c)(ii) A, D, E, F [2] – 4 correct [1] – 3 correct [0] – 2 or less B7(a) letter from Fig. 8.1 name function T [1] male sex glands makes the fluid for the sperm to swim in Z urethra [1] carries urine and sperm out of the body X Testis/testes/testicle produces male sex hormones and cells/sperms [1] R: spelling error B7(b) L → M →K → J → H → G MP1: M then K then J after L MP2: H then G at the end B7(c) deepening of voice growth of facial and pubic hair muscular development [2] – 3 correct [1] – 2 correct [0] – 1 or less R: 1m for every additional tick

Qn Answers Remarks C1(a) Solar energy → heat/thermal energy → kinetic energy → electrical energy [2] – all 3 correct [1] – 2 correct R: If only 1 answer is correct & if energy is not indicated R: trap heat C1 (b) Metal (names of specific metals will be accepted) [1] black/dark coloured/dull [1] R: reflect heat energy C1(c) Black/Dark/Dull coloured metals are good conductors and absorbers of heat energy [both reasons are needed [1] R: energy (must indicate that it is kinetic energy) C1(d) MP1: To reflect light (energy) or radiation to the water container [1] MP2: Use of concave mirrors allows the light rays to be concentrated /converged towards the water container in the middle. [1] OR MP2: Surrounding the water container with multiple concave mirrors also increases amount of light rays reflected to the water container. [1] C1(e) MP1: When the temperature increases, the molecules (BOD: particles) gain more kinetic energy/kinetic energy increases [1] MP2: Arrangement: from closely packed in disorderly manner to far apart in a random manner. [1] MP3: Movement: from sliding past one another (randomly) to moving at high speeds (randomly). [1] R: energy increase R: small gaps to large gaps R: move randomly to move randomly faster C2(a) May [1] C2(b) 4 [1] R: names of months March, May, June, August C2(c) electricity consumption / kWh rate /$ cost/ $ total cost / $ 348 0.2250 348 X 0.225 = 78.30 [1] 78.30 + 13.39 = 91.69 [1] 52 0.2575 52 X 0.2575 = 13.39 [1] Allow e.c.f for (ii) total cost R: 78.3 C2(d) • Turn/Switch off electrical appliances when not in use • Use a fan instead of air conditioner • Use more energy saving electrical devices • Reduce amount of time using electrical devices/appliances Any two reasonable responses [2] R: Do not repeat ways that are the same idea (e.g. turn off the lights & turn off the fans

Qn Answers Remarks C2(e) A switch opened/closed MP1: correct number of circuit components correct diagram for each component – 2 batteries, 1 bulb, 1 switch and wires MP2: all components are connected in series. [MP3: wires drawn with straight lines using ruler R: MP1 if casing drawn around the circuit diagram R: no wire in between cell and bulb C3(a)(i) oxygen C3(a)(ii) MP1: (Diffusion) involves the movement of particles/molecules [1] MP2: from a region of higher concentration to a region of lower concentration. R: Deduct 1m if an explanation is provided R: missing word (particles/molecules) C3(a)(iii) MP1: undergo photosynthesis to make food/produce oxygen MP2: provides energy for organisms in a food chain to support survival OR [related to energy transfer in a food chain] MP2: provide oxygen for respiration [related to cellular process rather than breathing] Substance should relate to its function R: oxygen for breathing e.g. green plants produces oxygen in photosynthesis for animals to respire (undergo respiration) C3(b)(i) 5.8 – 1.2 = 4.6 cm3 MP1: read values 5.8 and 1.2 from graph correctly MP2: correct calculation + answer with units (accept: cm3 & cm3/h) R: Deduct 1m if no calculation shown or no evidence of data from graph C3(b)(ii) xylem C3(c) MP1: Phloem was removed MP2: Sugars cannot be transported down the stem and accumulate above the cut BOD: food/glucose Note: sucrose is the accurate sugar molecule R: Starch (if mentioned in phloem)