Science Applications Set B

Qn	Answer	Remarks/Explanation
1a	Yes. Like poles of a magnet repels. The like pole of the magnet must be facing the like pole of the rod. Only a magnet can repel another magnet.
1b	Heating a magnet causes it to demagnetize. When the rod is heated, it gradually becomes less strong. The repulsion is no longer as great as before do it moves towards the magnet.	When explaining, always try to give : (1) comparison, if there is (2) relevant concept (3) link back to the question
2a	Released – Bulb B lit up Pushed – Bulb A lit up
2b	Bulb A is brighter. The circuit that bulb A is in has 3 batteries in series thus more electricity is flowing through it. There are only 1 battery in the circuit for Bulb B.
3a	When the salt water is heated by the sun, the water evaporated and becomes water vapour. The water vapour rises and comes into contact with the cooler aluminium foil. It loses heat and condenses into water droplets. The water droplets would then slide down the aluminium foil into the part that collects drinkable water.
3b	Set up B. Water vapour can condense on 2 surfaces instead of 1 in set up A. With more condensation, more water can be collected more quickly.
3c	Liquid à Gas à Liquid
4a	The water in wet substance P evaporated the water vapour rises to touch the cooler dry cloth. It then loses heat and condenses back into water making the cloth damp.
4b	Some of the heat in the surrounding air was lost to the water in wet substance P causing the water to evaporate. With less heat, the temperature in set up A drops.
4c	Draw some tiny water droplets onto the top surface of the mineral water bottle.
5a	i) lungs ii) diaphragm
5b	The balloon will inflate.
5c	When the plunger is pulled back, air from the surroundings is drawn into the balloon causing it to inflate.
6a	Draw the line below that a leaf A from the same starting point.
6b	i) Exchange of gases could not take place as the stomata were also blocked by the oil. ii) The plant was not able to get rid of excessive water through the stomata.
9a	6g per m2
9b	Too much fertilizer can cause the weight of the vegetables to become less. Too much fertilizer will affect the growth of vegetables negatively.
10a	P has the shortest bar. Followed by R and Q.
10b	Q
10c	The water in R that evaporated could escape through the opening. However the water that evaporated in Q could not escape. Thus rate of evaporation would be lower in Q so there is more water left.
11	Fish S. Its outer covering is not able to help the fish camouflage itself from being spotted by predators amongst the water plants. R has spots and T has spots and stripes which can help them blend in with the surroundings.
14a	The box has wheels which help to reduce friction with the table top thus less force is needed to move the box and the iron block.
14b	Magnet
15a	Mrs Lim
15b	Mrs Lim’s bamboo pole holders are not covered. Thus when it rained, some water may be collected inside the pole which can become good breeding grounds for mosquitoes.
19a	No. She is testing the number of batteries, but she did not change the number of batteries in her set up. Her experimental set up does not support her aim.
19b	Chemical energy à electrical energy à kinetic energy à sound energy
20a	As a 2cm ring was cut, the xylem was also removed. Water cannot be transported to the leaves above B so they cannot make food. Thus they to wither and droop.
20b	The leaves between Part A and B could get water to make food. Since a 2cm ring was cut at B, food from the leaves cannot be transported upwards. So the food is transported downwards and stored in X making it heavier.
26a	When water drips into the cup, it becomes heavier until it moves downwards. When this happens, the rod would move upwards and hit against the wooden block. At the bottom, when the water flows out of the cup, it becomes lighter again so the rod moves up, back to the original position. It starts all over again.
26b	More clicks will be heard.
26c	More clicks will be heard. If the rod was fixed at B, the distance between the fulcrum and the effort is longer so less effort is needed, thus the cup will fill and refill more quickly.	This is part of simple machines which is not tested anymore.
29a	The size of the cage
29b	Ladybird Q. The decrease of both aphid A and B was the greatest when Q was introduced into the cage.

Science Applications Set A

Qn	Answer	Remarks/Explanation
14a	Heat travels from a warmer place to a cooler place. When he applied alcohol on his forearm, his warmer forearm loses heat to the alcohol. The alcohol gains heat and vaporizes. He felt the cooling sensation because the part of his skin lost heat to the alcohol.	When explaining, always try to give : (1) comparison, if there is (2) relevant concept (3) link back to the question
14b	The temperature will drop. Heat travels from a warmer place to a cooler place. Joseph’s tea will lose heat to the cooler alcohol so the temperature drops.	When explaining, always try to give : (1) comparison, if there is (2) relevant concept (3) link back to the question
15a	Blood vessel B has thicker walls than blood vessel A. Blood vessel A has a tissue that prevents blood from flowing backwards, but blood vessel B does not.
15b	Blood vessel B. It has thicker walls which can withstand the high pressures from the fast flowing blood pumped from the heart.
16a	The travellator. The plant transport system comprises of 2 separate set of tubes that moves up and down the plant.
16b	Heart
17a	A and B / AB
17b	The heat from the surroundings
17c	Mark on the y axis any where between -10 to 0.
19	(1)	There is no way a question like this will appear in the PSLE. It is too tedious.
20	(4)
21	(4)
22a	Photosynthesis
22b	Light, Water, Carbon dioxide and nitrogen
22c	When the tree is young, it is not as tall. Thus it is near the forest floor where there is less light. The leaves need to be bigger so that it can trap more sunlight. When the tree is grown, it is taller and thus the leaves are found in the area where there is more light, so the leaves become smaller.
23a	Heat the air in flask X over a flame. OR Cool the air in flask Y will some ice.	Be specific. Don’t just say heat or cool the air.
23b	Matter expands when heated. When the air in flask X is heated, it expands and move up the tube, pushing the ink drop towards Y. OR Matter contracts when cooled. When the air in flask Y is cooled, it contracts. Thus there is more space in the tube causing the ink drop to move towards Y.	When explaining, always try to give : (1) comparison, if there is (2) relevant concept (3) link back to the question
24	(4)
25a	Highest – Gold Lowest – Silver
25b	Aluminium. It has a lower melting point than iron, thus it would be easier to melt the aluminium to make it into the cans.
26	(1)
27	(4)
28	(1)
29a	Join the left dot to dot 1. Joint the right dot to dot 4.
29b	Eliza can control the same lamp from 2 different locations. The 2nd switch allows her to switch off the light from on top of the stairs after she has walked up. Otherwise, she will have the climb the stairs in darkness.
31a	Draw B between the Y axis and line for A.
31b	The air in container A and container B will gain heat from the lamp. The clear plastic sheet will prevent some heat from escaping from the opening thus more heat is retained in container B. This causes the temperature to rise faster than air in container A.	When explaining, always try to give : (1) comparison, if there is (2) relevant concept (3) link back to the question