2020 PSLE Science Mozzie Question That Rattled Students

The question below is a good example of a PSLE Science question that requires more critical and creative thinking rather than domain knowledge.

Can your P6 child answer this question?

(a) Oil is sprayed on stagnant water as shown.

Explain how this prevents mosquito from breeding. [1]

(b) Malaria is a disease spread by mosquito A. Children infected with malaria are found to be bitten more often by mosquito A.

Joel wanted to find out if children infected with malaria are more attractive to mosquito A due to a certain smell that they produce. He used the set-up shown with 20 of mosquito A in box P.

Joel counted the number of times mosquitoes landed on the shirt for 3 minutes. He repeated the experiment using another shirt worn by an uninfected child in box Q.

(i) State a hypothesis on how the smell on a shirt affects its attractiveness to mosquito A. [1]

(ii) Joel used a white shirt instead of a black shirt for the experiment. Suggest why using a white shirt allows him to obtain more accurate results. [1]

(iii) Joel recorded his results in the table.

Scientists are able to store the smell produced by infected people in a container. Suggest how Joel could use this smell and his results to reduce the number of bites on people. [1]

Once of the most commonly-heard feedback from students and parents for this question is that students had not been taught in school the knowledge required to solve part (b) of this question. If they mean that they had never encountered a similar question in school, well, that might probably be true.

This, however, is an application question that actually does not require much science knowledge per se. Of the three parts, only part (i) requires some sort of scientific understanding. Parts (ii) and (iii) can be answered with common sense. Indeed, the question tag 'suggest' in both questions tells you that some creative and critical thinking are required as well.

Question (a)

Knowledge required:

  • How mosquito larvae breathe in water

  • How oil affects mosquito larvae


Mosquito larvae breathe through breathing tubes that protrude from the surface of water. The oil forms a barrier that prevents the larvae from obtaining air through their breathing tube, causing them to die.

Question (b)(i)

Knowledge required:

  • What the word hypothesis means

Critical thinking required:

  • Based on the set-up, what is the objective of the experiment?


A shirt that has the smell produced by children infected with malaria is more attractive to mosquito A than a shirt that does not have that smell.

Question (b)(ii)

Knowledge required:

  • What colour are mosquitoes?

Critical thinking required:

  • How will using a black shirt affect the experiment?


Mosquitoes are black in colour. A white shirt provides contrast that makes the mosquitoes more visible, and therefore more easily counted. A black shirt on the other hand makes mosquitoes harder to spot.

Question (b)(iii)

Critical thinking required:

  • What can we conclude from Joel's results?


Joel's results shows that mosquito A are attracted to the smell produced by infected people. This smell could be released in an unoccupied part of a house to lure the mosquitoes away from where people actually are.

That wasn't so difficult now, was it?

All it took was a little bit of logical thinking!

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