NCERT Solutions Curiosity Chapter 10 .5.1 — In-text Questions

Book page 19710 Updated on2026-09-05

Q1.

You may find two different types of worm-like creatures (Fig. 10.5). They are larva and pupa, two distinct life stages during the development of mosquito. What differences do you observe in the shape of larvae and pupae?

Answer

Both wriggle in the water, but a hand lens shows they are quite different.

Feature	Larva	Pupa
Overall shape	Long, slender and worm-like, clearly divided into segments	Short and comma-shaped — a big rounded head-end with a small curved tail
Head	A small distinct head at one end	Head and chest fused into one large rounded part
Body covering	Bristles or hair-like projections along the body	Smooth, without bristles
How it hangs in water	Hangs head-down from the surface	Floats head-up, curled like a comma
How it moves	Wriggles actively from side to side — hence “wriggler”	Tumbles or somersaults away when disturbed; otherwise fairly still
Does it feed?	Yes, it feeds and grows	No — it is a resting stage in which the body is being rebuilt

Safety first: observe them in the container with a hand lens, do not touch the water with bare hands, and report to your teacher. Then empty the water on to dry ground.

Q2.

Mosquito larvae and pupae observed in water bodies repeatedly come to the water surface. What can be the reason for this?

Answer

They come up to breathe.

Mosquito larvae and pupae live in water but require air to respire. They cannot take in the air dissolved in the water the way a fish does, so they must move to the surface of the water for air. Each has a short breathing tube which it pokes just above the water film before sinking again.

Live in water + need air → must keep returning to the surface

Why this single fact is so useful: it is the weak point in the mosquito's life. Anything that seals the water surface off from the air will kill every larva and pupa in that container, without harming anyone outside it. The next question shows exactly how that is done.

Q3.

How can the life cycle of a mosquito be disrupted?

Answer

Break the cycle at any one stage and no adult mosquito is produced. The easiest stages to attack are the ones that live in water.

Stage attacked	What to do	Why it works
Egg	Do not let water stagnate; empty coolers, pots, trays, tyres and tanks every week; cover water storage	The female has nowhere to lay her eggs
Larva and pupa	Spray a thin layer of kerosene oil on standing water that cannot be emptied	The layer cuts them off from the air and they die
Larva	Keep guppy or gambusia fish in ponds and tanks	The fish eat the larvae
Adult	Use mosquito nets, screens on windows, full-sleeved clothes, repellents; keep the surroundings clean	Fewer bites, so fewer diseases spread and fewer eggs laid

Did you know? This is why municipal workers fog the drains and spray oil on ponds before the monsoon, and why schools hold a “dry day” once a week to empty every container.

Q4.

I have seen my mother spraying kerosene oil on stagnant water. Why does she do so?

Answer

To kill the mosquito larvae and pupae growing in that water. The book gives the reason in one clear sentence.

Kerosene oil forms a thin layer over the water surface.
This layer separates water from air, and does not allow larvae and pupae to inhale air.
As a result, they die.

Why kerosene spreads like that: kerosene is lighter than water and does not mix with it, so even a small quantity spreads out into a film covering the entire surface. The larva pushes its breathing tube up as usual, meets oil instead of air, and cannot breathe.

A caution worth adding: kerosene should be used only on water that nobody will drink or use — a blocked drain, a disused pit, a waterlogged corner. Never on a drinking-water tank or a pond used by cattle. For household containers, the safest step is simply to empty and dry them.

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