Lesson 2 of 8

Alveoli

Goal: Explain how alveoli are adapted for gas exchange.

Puzzles for this lesson

Alveoli are tiny air sacs, bunched like grapes at the end of each bronchiole. Gases swap between the air and the blood here.

Oxygen diffuses from the air into the blood. Carbon dioxide diffuses from the blood into the air.

A very large surface area. There are millions of alveoli, so there is a lot of wall for gases to cross.
Very thin walls. The wall of an alveolus is one cell thick, so the gases have only a short way to go.
A good blood supply. Each alveolus is wrapped in tiny blood vessels called capillaries. The blood carries the oxygen away, so more keeps diffusing in.

Your turn

This lesson’s activity starts here in a moment.

I can give three adaptations of alveoli.I can say which way oxygen and carbon dioxide move.

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Gas exchange Taking in one gas and giving out another

Bronchi Two tubes that carry air from the trachea into the lungs

Alveoli Tiny air sacs at the ends of the bronchioles

For teachers: AQA 3.8.3 · Cambridge 8Bs.04