Hinglish

Respiration in Humans

Class 7 Science · Chapter 9: Life Processes in Animals · NCERT Curiosity section 9.2.1

Learn

We can live without food for some time and without water for a day or two, but without breathing only a few minutes. Air enters through the nostrils, where hairs and mucus trap dust, passes through the windpipe, which branches into the two lungs, and ends in millions of tiny air sacs, the alveoli. The rib cage protects the lungs.

Meher builds a model: a bottle with its bottom covered by a rubber sheet, and two balloons on a Y-tube inside. Pulling the sheet down inflates the balloons; letting it go deflates them. In our body, when we inhale, the ribs move up and out and the dome-shaped diaphragm moves down, making room for air. When we exhale, the ribs move down and in and the diaphragm moves up, pushing air out.

Blowing through a straw turns lime water milky, but pumping ordinary air through does not: exhaled air has more carbon dioxide. Inhaled air has about 21% oxygen and 0.04% CO₂; exhaled air about 16–17% oxygen and 4–5% CO₂. In the alveoli, oxygen passes into the blood and carbon dioxide passes out.

The blood carries oxygen to every cell, where it breaks down glucose to release energy: this chemical process is respiration. Breathing (moving air in and out) is physical; respiration is chemical. The heart, blood and blood vessels form the circulatory system that carries oxygen and nutrients. Smoking damages the lungs, and passive smoking harms people nearby too.

glucose + oxygen → carbon dioxide + water + energy

Explore: in or out?

  1. Sort each change.

Remember

  • Air: nostrils → windpipe → lungs → alveoli, where oxygen enters blood and CO₂ leaves.
  • Breathing is physical; respiration (glucose + oxygen → CO₂ + water + energy) is chemical.

Quick check

When we breathe in, the diaphragm …

  1. moves down
  2. moves up
  3. stays still
  4. disappears
Answer

moves down. This increases space in the chest so air flows in.

Think about it

After a race you breathe faster and deeper. Why?

One answer

Working muscles need more energy, so they respire faster and need more oxygen and must get rid of more carbon dioxide.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.