Sec 2 G3 Revision Paper 2024 Mark Scheme (1)

Sec 2 G3 Revision Paper 1 2024 Science EOY Mark Scheme Section A 1 2 3 4 5 6 7 8 9 10 C C B A A B A D A D 11 12 13 14 15 16 17 18 19 20 B C A D B C D B A D 21 22 23 24 25 26 27 28 29 30 B B B A B B D B B C Section B B1a It is renewable/does not produce pollution/clean energy Reject sustainable without explanation. 1 B1b gravitational potential energy à kinetic energy à electrical energy One energy conversion – 1m each Accept also gravitational potential energy à kinetic energy of water à kinetic energy of turbine à electrical energy -1m if students wrote additional incorrect energy conversions to demonstrate how electrical energy is used without context. 2 B1c The water pressure increases with depth/water pressure is highest/water pressure is higher at the base and hence the base need to be thicker to resist the pressure to avoid breaking. Reject atmospheric pressure 1 B2a Q and R 1 B2b P 1 B2c Particles will be closely packed in a disorderly arrangement and the particles will slide past each other in a random manner. Note all keywords to be present. 1 1 B2di X and Z 1 B2dii Accept if students wrote 1- or -1 for this time only. Reject if no square brackets given. Reject if the gained electron is not of a different symbol. 1 X

B3a Smooth and white surface is a poor absorber of infrared radiation/ This slows down heat gain by the rate of radiation. 1 B3b Polystyrene foam contains many air pockets; and air is a poor conductor of heat. Polystyrene foam is a poor conductor of heat/This reduces heat gained by the refrigerator through conduction/ This reduces heat gained by the refrigerator through convection 1 1 1 B3c The air near the cooling coil/at the top cools and contracts, causing its density to increase and sinks to the bottom. The warmer air at the bottom, which is less dense, rises to the top and get cooled This cycle of sinking and rising repeats and set up the convection currents in the air which cools the refrigerator. Reject float. 1 1 1 B3d To be placed at the top shelf of the refrigerator. 1 B4a A: Oesophagus/Gullet/Esophagus B: Rectum 1 1 B4b physical digestion: Chewing of food breaks the food pieces down in smaller sizes and mixes the food with saliva to increase action by enzymes. chemical digestion: Carbohydrase/Amylase in saliva breaks down carbohydrates in the food to simpler carbohydrates/simpler sugars. 1 1 B4c The stomach is partially removed surgically; as only the amount of amino acids had significantly decreased from 8.7 units to 4.1 units before and after removal of organ. With parts of the stomach removed, rate of protein digestion to form partially digested protein is slower / lesser protease produced by stomach to digest proteins in a same amount of time. 1 1 1 polystyrene foam air pockets cooling coil smooth white surface for both inner wall and outer wall

B4d Side effect: The patient will lose the good bacteria in his gut/small intestine/ The patient will have lower ability to absorb nutrients and mineral salts. Explanation: Bacteria will be killed by antibiotics. OR Side effect: The patient will have lowered immunity/be less able to fight off certain diseases. Explanation: Bacteria will be killed by antibiotics/ Bacteria to evolve resistance to antibiotics rapidly 1 1 1 1 B5a oxygen 1 B5b Glucose will move from a region of higher concentration to a region of lower concentration / blood in capillary to body cells via diffusion. 1 1 Section C C1a C: magnesium carbonate D: water E: carbon dioxide 1 1 1 C1b Similarity: both reactions produces magnesium nitrate/salt/ both reactions produce a gas. Difference: The first reaction in Fig. C1.1 produces carbon dioxide gas/water but the second reaction produces hydrogen gas./ 1 1 C1ci He can add a few drops of bromothymol blue to both solutions. If the final colour of the solution is green, solution is A. If the final colour of the solution is blue, solution is B. OR He can add a few drops of red cabbage solution to both solutions. If the final colour of the solution is purple, solution is A. If the final colour of the solution is yellow, solution is B. Reject methyl orange and universal indicator. Students must state correct indicator to get the credit for subsequent colour changes/ 1 1 1 C1cii Quicklime is an alkaline substance as it turns two indicators (bromothymol blue and red cabbage solution) blue. Quicklime will neutralize the acidic soil/ Quicklime will increase the pH of soil to 7.0/Quicklime will reduce acidity in soil. 1 1 C2a Mangrove tree makes food using carbon dioxide and water in the presence of light through photosynthesis. 1 C2b Structural adaptation. Mangroves has exposed roots that allows it to obtain oxygen gas as the water has low oxygen content/ The roots allows it to anchor the tree in the mud./ The roots allows the tree to be stable/withstand strong tides. 1 1

C2c Worm acts as a decomposer that feeds on the remains of dead organisms. They break down the faeces of organisms and return the nutrients to the environment to create a cyclical flow of nutrients in an ecosystem. 1 1 C2di Mangrove tree à mangrove crab à plover bird à monitor lizard à crocodile Decayed leaf à mangrove crab à plover bird à monitor lizard à crocodile Decayed leaf à worm à archer fish à otter à crocodile Decayed leaf à worm à plover bird à monitor lizard à crocodile Accept any answers with 5 levels in the food chain 1 C2dii It is the least energy efficient food chain. / 90% energy is lost in each trophic level and as the number of tertiary consumers increase, little energy is transferred to the last consumer in the food chain. / More energy is lost. 1 C2e Mutualism exists between plover bird and crocodile. Bird benefits: Crocodile protects the plover bird from predator/ monitor lizard./ Plover bird eats from the leftover food stuck between the teeth of the crocodile. Crocodile benefits: Crocodile gets its teeth cleaned by the bird/reduce possibility of tooth decay by removing food from teeth. Students must describe how both organisms benefit to get 1 m. 1 1 C2f The pets when released into the wild, will become an invasive species that can feed on existing populations in the ecosystem, which can destabilise the ecosystem./result in the ecosystem becoming imbalanced/disrupt the eocsystem /introduce competition./disrupt communities by causing one group of organisms to decrease and hence affect the numbers of the other organisms with feeding relationships. Students can get 1m if they use predator prey relationships to explain how introducing new species affects the organisms in the whole food web and causes it to be destabilised. 1 C3a IB is larger; as resistors are connected in parallel so the total/circuit/effective resistance decreases and current is larger OR Resistors in series in IA so total/circuit/effective resistance increases 1 1 C3b Wire E1 : 1.5 V Wire E2 : 0.5 V Penalize if no units are given 1

C3bii Resistance of wire E1 = voltage / current = 1.5 V / 0.3 A = 5.00 W Resistance of wire E2 = voltage / current = 0.5 V / 0.3 A = 1.67 W Wire E1 has a higher resistance than wire E2. Students must apply the formula correctly, and use the correct set of data. Penalise if answers are in fractions. Award if students did not include units. 1 1 C3biii E1 (Allow accurate/logical ECF) 1 C3biv Ensure that the wires are not exposed to prevent electric shocks. 1 C3ci 1 C3cii Chemical Change. Liquid water decomposed to form different gaseous products, hydrogen gas and oxygen gas / Decomposition of liquid water is an irreversible process. 1 1 C4a Osmosis 1 C4b As the concentration of sugar solution increases from A to C, the length of potato increases. As the concentratio