Where does the gas exchange take place?

- air travels through your nose to lungs
- begins at trachea
- divides into 2 tubes
- smallest tubes are called bronchi
- have branches like a tree
- branches empty air into very thin wall sacks called alveoli
- walls are so thin that gases like carbon dioxide and oxygen can pass through
- called diffusion- movement of particles from areas of high and low concentration
- alveoli are surrounded by capillaries
- walls of those vessels are very thin too
- blood cells trade carbon dioxide for oxygen
- carbon dioxide is let out, oxygen is kept in

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