The path the air takes in the lungs is down the trachea, through the bronchi and bronchioles and into the alveoli.

It is in the alveoli that gas exchange takes place. The name gas exchange helps us to know what happens in the alveoli - oxygen and carbon dioxide (which are gases) are exchanged (or swapped) - oxygen is swapped for carbon dioxide. Oxygen in the lungs is swapped with carbon dioxide in the blood.

Alveoli are surrounded by a net of very thin blood vessels called capillaries. There is blood inside the capillaries. The oxygen moves into the blood and is then transported around the body by red blood cells.

The oxygen is used by body cells to do respiration. Respiration is a process that cells do to release the energy they need to do MRS C GREN.

The blood from around the body contains the toxic waste gas carbon dioxide, which is made by body cells doing respiration. The carbon dioxide moves out of the blood and into the air in the lungs. Carbon dioxide leaves the body when you breathe out.

Alveoli: Tiny air sacs where gas exchange takes place.

Capillaries: Tiny blood vessels that surround the alveoli.

Diffusion: When particles spread out to where there is least of them.

Gas exchange: Oxygen goes into the blood and carbon dioxide moves out of the blood.

Red blood cell: The cell that transports oxygen and carbon dioxide.