NCERT Solutions Curiosity Chapter 9 .2.1 Respiration in humans — In-text Questions

Book page 1299 Updated on2026-09-05

Q1.

How is this oxygen used in the body? Are breathing and respiration different?

Answer

The oxygen we inhale is used to break down glucose and release energy. Food is first digested into simple substances like sugar (glucose); oxygen then helps break this glucose down inside the body. That process is called respiration.

Glucose + Oxygen → Carbon dioxide + Water + Energy

Yes, breathing and respiration are different.

Point	Breathing	Respiration
What it is	Inhaling and exhaling air	Breaking down glucose with oxygen to release energy
Type of process	A physical process	A chemical process
Where it happens	In the respiratory system — nose, windpipe, lungs	Inside the body, in all its parts
What it gives	Brings oxygen in, removes carbon dioxide	Releases the energy that lets us walk, run, play and think

Why it happens: breathing only delivers the oxygen and carries away the waste gas. The useful work — getting energy out of food — is done by respiration. Breathing is the transport; respiration is the purpose. Both are essential for survival.

Q2.

It is difficult to live without food for a week; without water for a day or two, but without breathing, we usually cannot survive more than a few minutes. Why is that?

Answer

Because the body can store food and water, but it cannot store oxygen.

Food is stored in the body, so energy can be drawn from those stores for days.
Water is held in the body and is lost slowly, so a person can manage a day or two.
Oxygen, however, is used up every single second by every part of the body to release energy from glucose, and there is no store of it anywhere.

The moment breathing stops, the supply of oxygen stops. Respiration in the body slows down at once, energy is no longer released, and delicate organs such as the brain begin to fail within minutes.

Why it happens: respiration is not something the body does now and then — it goes on non-stop in every part of the body, awake or asleep. A process that never pauses needs a supply that never pauses.

Q3.

Have you noticed tiny hair inside your nostrils?

Answer

Yes. There are tiny hair inside the nostrils. These hair, along with mucus, trap dust and dirt from the air we breathe in, so that clean air goes down to the lungs.

Dusty air enters nostrils
↓ tiny hair + sticky mucus catch the dust
Cleaner air → nasal passages → windpipe → lungs

Why it happens: the delicate alveoli deep inside the lungs have no way of cleaning themselves. So the air must be filtered before it gets there, and the nose is the filter. This is why we should breathe through the nose and not through the mouth — the mouth has no such filter.

Did you know? The nose also warms and moistens the air on the way in, so cold dry air does not shock the lungs.

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