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Solving the challenging 2022 PSLE Science mosquito question

Solving the challenging 2022 PSLE Science mosquito question

If you've been keeping up with recent PSLE Science questions, you probably realise that simply memorising facts won't guarantee you a top score. What students truly require is a deep understanding of the subjects they've studied and the ability to use these ideas in everyday situations. This understanding will not only enable them to tackle unconventional questions, like the 2022 Turkey Question we discussed in a prior article but also the 2022 mosquito question we're going to explore in this piece.

Challenging 2022 PSLE Science Mosquito Question

The picture shown at the top of this article shows an outdoor toilet with a mosquito trap. Mosquitoes are attracted to human waste and will lay eggs in the waste. The human waste gives out Gas X. A mosquito trap is installed next to the toilet. The mosquito trap has a tube which allows mosquitoes to enter from the surroundings. Air and the smell of human waste moves from the waste tank through the mosquito trap, as shown by the arrows.

  1. Why are mosquitoes attracted to the human waste to lay eggs?
  2. What group of organisms in the human waste releases Gas X? State the process that releases Gas X.
  3. Gas X also attracts mosquitoes. Suggest a possible reason.
  4. Why do the mosquitoes die quickly after entering the mosquito trap?


  1. After the mosquito eggs hatch, the larvae will need something to eat. In this case, they will feed on microorganisms found in human waste. This is why the mosquitos are attracted to human waste to lay eggs.
  2. The group of organisms in human waste that releases Gas X are called 'bacteria' and the process that releases the Gas X is called decomposition. 
  3. Gas X could be a term used for carbon dioxide. Animals breathe it out when they respire. Mosquitoes can sense this gas, and it helps them find animals to feed on.
  4. The oxygen in the toilet tank is used up in the decomposition process. So, when the air entered the mosquito trap, there wasn't enough oxygen left for the mosquitoes to breathe. This lack of oxygen caused them to die quickly.

As you can see this is not a straightforward question. In order to correctly answer these questions, students should be familiar with the following topics:

  • Mosquito life cycle: Students need to understand the basic stages of a mosquito's life, including the egg, larva, pupa, and adult stages.
  • Decomposition: They should have a grasp of what decomposition means - how organic matter breaks down into simpler substances by the action of microorganisms.
  • Respiration: A basic understanding of respiration in animals is necessary. This involves knowing that animals, including mosquitoes, breathe in oxygen and release carbon dioxide.
  • Oxygen depletion: Students should know that when organic matter decomposes, it uses up oxygen, and this can lead to areas with low oxygen levels.
  • Inference: The ability to make logical connections between the given information and the outcomes described in the question is essential. This involves critical thinking and analysis skills.

In summary, the best way to get a high score in PSLE science is to explore different parts of the subjects you've learned and solve lots of challenging questions. This will help you improve your problem-solving and thinking skills.

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