Biology · Class 7–10

The Respiratory System

See how air travels from your nose to the tiny air sacs in your lungs, and how oxygen reaches your blood.

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🧠 Remember it

The Respiratory System

Air's path: Nose → Trachea → Bronchi → Bronchioles → Alveoli. Gas exchange happens in the alveoli — "Alveoli = Air sacs where air swaps": O₂ in, CO₂ out.

🌏 In real life

Blow onto a cold mirror and it fogs up — you are breathing out water vapour and CO₂ that your cells produced while releasing energy from food.

📝 Quick notes

  • Air enters through the nose (where it is filtered and warmed) → pharynx → larynx → trachea (windpipe).
  • The trachea branches into two bronchi, then finer bronchioles, ending in air sacs called alveoli.
  • Alveoli have very thin walls and a rich blood supply — O₂ diffuses into the blood and CO₂ diffuses out.
  • The diaphragm and rib muscles change the chest volume to draw air in (inhale) and push it out (exhale).

🎯 Test yourself

Where does the exchange of gases take place in the lungs?

In the alveoli (the tiny air sacs).

Learn it fully — free

See the animated, step-by-step The Respiratory System lesson on Syllab

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