PSLE SCIENCE structured questions answering technique – Give a reason

This article is part 2 of the series in which part 1 can be seen here.

In this article we will discuss how to carefully answer PSLE science structured questions that asks you to give a reason.


Here is an example of a question.


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Observe –  balance tilts towards P

Data – 300cm3 of air versus 100cm3 of air



Start – more air

1. more mass

2. heavier

End – tilt towards P


Answer Guide

a. The side of the balance holding container P will tilt downwards, lower than the other side holding container Q.

b. More air is pumped into container P than Q. This increases it’s mass and weight. As there is more mass and weight, the balance at P is heavier. Since it is heavier, it will tilt towards P.


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Observe –  hot tea with crushed ice cool more quickly than no crushed ice

Data – at first same temperature, then one dropped more than the other


Start – crushed ice has more surface area,

1. more exposed surface area to tea

2. faster rate of heat loss

End – hot tea with crushed ice cool more quickly


Answer Guide

The crushed ice has more surface area than the non-crushed ice. The increased surface area causes more hot tea to be in contact with the ice than the other cup. More contact causes faster rate of heat loss and faster heat loss causes the hot tea to cool more quickly.

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Observe –  there are no information on mass on different planets

Data – Jane’s mass is 40kg


Start – Jane’s mass is 40kg

1. Mass is the amount of matter in an object

2. remains the same in different planets despite different gravitational force

End – Jane’s mass remains the same everywhere

Answer Guide

a. The gravitational force acting on objects are different in different planets.

b. 40kg. Mass is the amount of matter in an object. The amount of matter does not change regardless of the gravitational force. Therefore Jane’s mass remains the same in different planets.

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Observe – Cloth C allows least amount of water to pass through

Data – 100ml compared to 310ml and 540ml

Start – Cloth C allows least amount of water to pass through

1. It absorbed the water

2. Towel needs to be absorbent

End – Cloth C is the most suitable

Answer Guide

Based on results, Alice should use cloth C as a towel. A towel needs to be absorbent so that it can absorb water. Cloth C allows the least amount of water to pass through as compared to the others so it is the most absorbent.



Your turn to try

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a. Air, warmth, moisture

b. There was a substance to remove water vapour. Since there is no water, decay cannot occur and therefore the mushroom showed no signs of decay.


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Black plastic bag C. No light is allowed to pass through, however for the others, light is allowed to pass through. Since there is no light, there is no photosynthesis and the plant in bag C will respire instead. This will increase the amount of carbon dioxide.


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The sealed empty plastic bottle will float on water.


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K survives better. It has a smaller surface area to body than J. It will lose heat slower to the surrounding than J. Therefore keeping itself warm and sirviving better.


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It does not have a cell wall. Animal cells do not have cell walls whereas plant cells have. Therefore it is more an animal cell.


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Terrarium A will have a higher amount of carbon dioxide.  There is no light in the cupboard. The plant will not be able to photosynthesis. As a result, both the snail and plant respire to give out carbon dioxide which cannot escape due to the airtight container.

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The paper that was glued remained dry because it was not in contact with water. The cup did not allow air to escape when lowered into the container. Air occupied the space in the glass. So water was not able to enter and contact the paper.

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The boiling stopped for a while when she put some meat into the pot because the meat absorbed some of the heat. So there is less heat to heat the water. This causes the water to decrease in temperature temporarily. Hence it stopped boiling for a while.



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