NYGH 2013-S3EOY-Bio P1 & P2 Ans

1    NANYANG GIRLS’ HIGH SCHOOL End-of-Year Examination 2013 Secondary Three BIOLOGY Paper 1 1 B 7 A 13 C 19 C 25 C 2 D 8 C 14 B 20 D 26 B 3 B 9 C 15 B 21 A 27 C 4 B 10 D 16 C 22 C 28 C 5 A 11 A 17 C 23 D 29 D 6 D 12 B 18 B 24 B 30 A Paper 2 - Section A Qn Answers Marks A1a Plant: S / chloroplast , Animal: T / flagellum/tail; 1 A1b Allows organism to move towards an area where sunlight is available/ escape from predators/ move away fr om undesirable conditi ons/ search for nutrients/food; Allow: ECF from (a) Reject: increases mobility – does not explain how it increases survival. 1 A1c 1m – drawing of infolding/ invagination + explanation/labeling; 1m – drawing of vesicle formed; 2 A1d Foreign particles would combine with vesicles released from structure Q/ GA; Foreign particles will (combine and) be digested by (enzymes in) lysosomes; Foreign particles will be (digested and) sent to Q/R; Foreign particles will be digested by enzymes; 1 Foreign particle

2    A2a 2 A2b Ester bond + circle (see A2a); Allow: ECF from A2a, circles COO- for ester bond 1 A2c Benedict’s solution can be used; since fructose is a reducing sugar; Take Solution C and make a series of dilutions of known concentrations; Carry out Benedict’s test for each known concentration + record colour/amount of precipitate; Carry out Benedict’s test for Solutions A and B + observe colour /amount of precipitate OR compare colour/amount of precipitate to Solution C; Max 3marks if student only describes comparison of Solution A and B against colour and amount of precipitate of Solution C: - Benedict’s solution can be used; - since fructose is a reducing sugar; - Carry out Benedict’s test for Solutions A, B and C + observe colour /amount of precipitate OR compare colour/amount of precipitate to Solution C; Max 1mark if student uses potato strip experiment as potato strips have a certain amount of fructose concentrati on which is unknown and will affect the accuracy of the results. Also, length/mass of potato strip may be the same after immersion in all 3 solutions and experiment will be inconclusive. Reject: - compare time taken to form bric k-red precipitate (concentration not determined by time taken, but by colour and amt of precipitate formed) - darker colour/ lighter colour of precipitate formed - experiments involving Visking Tubings (Concept error as fructose is a monosaccharide, unlike sucrose which is a disaccharide. Fructose will diffuse in/out of V.T. freely and there will be no change in turgidity of V.T.) 4

3    A3ai Draw narrow curve, pH range between 1- 6, optimum pH 2 must be labeled. (note: actual pH range is from 1-3) 1 A3aii Increase in rate of reaction less steep than pepsin; Enzyme active over a wider range of pH values than pepsin; Optimum enzyme activity over a range of 3 pH units, larger than pepsin that is only 1 pH unit; Alcalase works best in alkaline conditions/ pH 6-8 while pepsin works best in acidic conditions/ pH 2; Any 1 point 1 A3b Addition of more enzymes/ substrates/increase in temperature. Reject: change temp to optimum/ increase or decrease temp to optimum 1 A4a Must label both correctly for 1m X = Granum / thylakoid Y = Stroma; 1 A4b Z = Starch grain; Reject: vacuole (Q asked for ONLY found in chloroplast in day time) 1 A4c There is no membrane in the isolated state,; There is no capturing of electrons released; Electrons caused the glow; Reject: Electrons not released (False as chlorophyll is still excited with light) 3 A5a bi 1 1 A5bii Seed develops root-like structure / root to penetrate the stem; Accept: Seed germinated / seed grow 2 To reach sucrose / amino acids (located in the phloem); Accept: To reach food in the phloem Accept: ECF from Q(b)(i) A6a Insulin is released at B ; When blood glucose goes higher than norma l, body will release insulin to let liver cells absorb more glucose. (1m) 1 1 A6b At time D, the person may be fasting / exercising vigorously and this leads to a drop in the blood glucose level below the normal range; When blood glucose level drops below normal, pancreas will release glucagon. Glucagon promotes conversion of glycogen to glucose, bring the level back to the norm ; 1 1 (bi) Phloem (a) Xylem

4    A7a When blood vessels are damaged, damaged tissues and blood platelets release thrombokinase. Thrombokinase converts prothrombin into thrombin (calcium ions must be present for this to occur); Thrombin catalyses the conversion of fibrinogen to insoluble threads of fibrin; Fibrin threads entangle blood cells and the whole mass forms a clot. The clot seals the wound, preventing entry of microorganisms; 3 A7b The inner lining of blood vessels is extremely smooth, thus prevents the adhesion of platelets; Heparin, an anti-clotting substance, is present in blood; 1 1 A7c The chance of a clot (thrombus) forming is increased when fat is deposited inside the vessel walls; This roughens the inner lining, causing platelets to adhere, disintegrate and initiate the clotting mechanism Accept: lining becomes rough [no mark given if no explanation is given] 1 A8a Blood passes through the heart twice as it moves from the pulmonary circulation and into the systemic circulation; Accept: Blood flows through the heart twice in one (complete) circuit 1 A8b Closed circulatory systems have the blood closed at all times within vessels of different size and wall thickness; 1 A8c In an open circulatory system, blood is pumped from the heart through blood vessels but then it leaves the blood vessels [1 mark] and enters body cavities, where the organs are bathed in blood, or sinuses (spaces) within the organs; Blood flows slowly in an open circulatory system because there is no blood pressure after the blood leaves the blood vessels [1 mark]; [max 1 mark] 1 A8d Jellyfish do not have a circulatory system because it has no heart and blood; Jellyfish is in contact with water and absorb oxygen through diffusion; [max 1 mark] 1 A9a Must state both structures C & D; Reject: Lung which is A 1 A9b No need to explain as Q is on “Suggest what happens” Lungs remain deflated / lungs collapse / lungs will not inflate; (during inspiration when the diaphragm is pulled down, air now enter through the open wound into the space between the lungs and ribcage) Accept: Intercostal muscles injured so difficulty in breathing Reject: Fractured rib “prevent” chest from expanding (cos diaphragm still able to contract) Reject: Lung punctured (Q: only chest punctured) 1

5    Paper 2 - Section B Qn Answers Marks B1a At O to Q there was no digestion of proteins in the buccal cavity and oesophagus. Section R is the stomach where pepsin digests some of the proteins. Section S and T represents the duodenum and ileum where enzymes from the pancreas and intestinal glands convert it into amino acids. Digestion is completed at Section T. 3 B1b Milk contains proteins, fats and milk sugar lactose(carbohydrate). When milk passes through section O – Q, nothing will be digested as milk do not contain starch. When milk passes through section R, so me proteins will be digested by pepsin secreted from the stomach. The fats and milk sugar remain undigested. The pancreas secretes enzymes to digest ion of proteins, carbohydrates and fatty acids and releases the enzymes into the duodenum. A person with pancreatic failure will not be able to release these enzymes. At sections S and T, there will be incomplete digestion of protein, carbohydrates and fats as there are less enzymes acting on them at the same given time. 3 2 2 B2a One – The pulmonary artery connecting the heart and lungs was not developed (pulmonary atresia.); this makes it impossible for the heart to pump b