2023 ACSBR 2EXP EOY ANS KEY

Anglo-Chinese School (Barker Road) A Methodist Institution Founded in 1886 LOWER SECONDARY SCIENCE DEPARTMENT OF SCIENCE Name: ( ) Class: SEC 2 SEC 2 SCIENCE 2023 EOY PAPER ANSWERS Section A Qn Answer A1 D A11 A A21 C A2 A A12 C A22 C A3 A A13 A A23 B A4 D A14 A A24 D A5 B A15 A A25 B A6 B A16 C A26 D A7 D A17 B A27 A A8 B A18 D A28 C A9 A A19 B A29 C A10 B A20 D A30 A (Penalise 1 mark throughout the whole paper for no working in a calculation question.) Qn Answer Mks Remarks B1(a) (simple) Distillation 1 penalise for spelling mistake (b) 100 oC 1 reject: no units (c) (in from bottom, out from top) 1 (d)(i) The water vapour formed will escape/not be trapped/not be collected. 1 accept OWTTE as long as the idea that the water vapour would have escaped is present in the answer. BOD: steam escaped (d)(ii) White residue/solid/crystal remains in the dish. 1 reject: white salt / salt / white powder Students must include colour

B2(a)(i) K 1 (a)(ii) N 1 (a) (iii) L and M 1 (b) sodium 1 B3(a)(i) OP 1 BOD: O (a)(ii) Q (or QP) 1 (a)(iii) T (or OPR) 1 (b) Virtual / upright / laterally inverted / same size as object / same distance between object to mirror and mirror to image 1 B4(a) The smaller object will exert a greater pressure / depth / depth of impact when dropped onto the sand. 1 Accept: ● relationship statement ● “deeper” impact ● Statement written must correlate dependant and independent variables reject: ● aim ● impact ● volume ● surface (b)(i) Zero error 1 (b)(ii) Weight = 3.0 – 0.2 = 2.8 N OR Weight = (3.0 - 0.2) x 2 = 5.6 N 2 (1 m for answer, 1 m for correct unit) (c) Pressure = F / A = 2.8 N / (1 cm x 1 cm) = 2.8 N/cm2 or 28000 Pa (N/m2) 1 (1 m for correct answer. Ignore if units are not given) Penalize if wrong units are given. Note: Pascal = N/m2 Allow ECF (d) Yes. (No marks) As object X has a smaller area in contact with the sand than object Y, [1] 1 1 Reject: discussion based on size only without mention of area in contact

it will exert a greater pressure on the sand. [1] Hence, the depth of impact on sand for object X should be larger than for object Y. B5(a) Carbon dioxide: white precipitate observed / solution turned chalky / cloudy Hydrogen: insert lighted splint 1 1 BOD: ● “use lighted splint”. reject: ● “lighted splint test”. Students need to describe the test. (b) Alkaline 1 Reject: ● It is an alkali./ It is alkali. ● it has a pH higher than 7. (c) Hydrochloric acid + calcium carbonate 🡪 calcium chloride + carbon dioxide + water 2 (1m: water 1m: correct word equation - only award if all products are correct) B6(a) The teeth in the mouth cuts and crushes / chews the food into smaller pieces; OR The stomach churns food into smaller pieces; 1 BOD: mouth chews (no mention of teeth) accept: to increase surface area to volume ratio (instead of smaller pieces) Reject: to increase surface area (b) ● Proteins are first being digested in the stomach by proteases present in gastric juice into partially digested proteins/amino acids; [1] ● The small intestine also contains proteases , and will continue to digest proteins to produce amino acids.; [1] 1 1 1m: stomach, small intestine 1m: proteases, amino acids Accept: Proteins are digested in the stomach and small intestines by proteases into amino acids. (c) observations ● Iodine solution remains yellow-brown.; [1] explanations 1 1 BOD: yellow / brown Reject: remain the same, orange BOD: glucose / maltose

● Carbohydrase catalyse the breakdown of starch into simple sugars ; [1] ● With absence of starch (or all starch has been broken down), [1] iodine solution did not change colour and remains yellow-brown 1 (d) ● No. (No marks) ● Diabetes is a disease where the sugar level in the blood is too high [1]; ● Since pasta contains a high proportion of/mainly starch(carbohydrates) / this will cause a large amount of simple sugars to be absorbed into the blood [1] after digestion ; 1 1 BOD: Diabetics cannot eat too much sugar. B7(a)(i) Label both ovaries [1] and both oviducts [1] 2 BOD: label only 1 ovary, 1 oviduct (ii) oviduct: Site of fertilisation / moves the (fertilised) egg to the uterus. 1 Ovary: Releases mature eggs or ovum OR Produces female sex hormones that controls sexual development in the body. 1 reject: produces mature egg (b)(i) Any section on both of the fallopian tubes 1 (ii) Advantage: Reliable method to prevent pregnancies Disadvantage: Irreversible process 2 Accept: as long as students wrote about no pregnancies C1(a) Plastic / rubber / ceramic; It is a poor conductor/good insulator of heat.; 2 (b) Process: convection; Explanation: When the water at the bottom is heated up , it expands and become less dense, hence, rises. ; The cooler, denser water, then sinks to the bottom to get heated up.; 3 (c)(i) It is the amount of electrical energy converted to heat energy per unit time (per second). 1 (ii) Time taken to boil 6 cups of water = 6 x 1 min = 6 min = 6/60 = 0.1 hr; [M] Energy required to boil 6 cups of water = 0.5 kW x 0.1 hr = 0.05 kWh; [A] 2 (iii) Cost of electricity = 0.05 kWh x 25 cents = 1.25 cents; [A] 1 allow ecf

(d) The water molecules changed from sliding over one another to moving at high speed in constant random motion. 1 BOD: no constant random motion is mentioned C2(a)(i) (ii) (voltmeter to be placed in either position) 1 1 (voltmeter to be placed in either position) (b)(i) 2 [1m: resistors connected in series; 1m: all other components correctly drawn and connected properly] (ii) The bulb will shine brighter in the parallel circuit.; [1] Because the effective (total) resistance in a parallel circuit is lower, [1] and hence, a higher current will flow through the circuit.; [1] 3 (c)(i) Fuse 1 (ii) When a large amount of current flows through the device (fuse) and is larger than its current rating, [1] a short, thin wire in the fuse heats up and melt causing the circuit to break/open [1] This protects the device from damage from excessive/high current flow. 1 1 reject: fuse blow C2(a)(i) Increase in average RBC count = 6.6 – 5.0 = 1.6 million cells per microlitre 1 BOD: 6.55 - 5.0 = 1.55 Reject: if students read day 8 as 6.5 (ii) They need to increase the number of red blood cells OR 1

in their body to increase the rate of oxygen being transported; to all parts of their bodies, as there is a lack of oxygen at high altitudes.; 1 BOD: need more oxygen in the high altitudes (on the mountains) (b)(i) A: vein/veins B: artery/arteries 1 1 Penalise for spelling mistake (ii) Blood vessel C has a higher concentration of oxygen compared to [1] surrounding tissue cells/body tissues, This causes oxygen to move out via diffusion [1] OR oxygen diffuses out of blood vessel C to the tissues 1 1 (c) 2 (Labels include: “cell membrane”, “nucleus” and “cytoplasm” labelled.) [2m for all 3 correct structures, 1m for 2, 0m for only 1] [1m] Clearly defined lines – no shading, solid lines used 0 for plant cell drawn