Gas exchange

Inhaled and exhaled air

Compared to atmospheric air, exhaled air contains:

  • less oxygen
  • more carbon dioxide
  • more water vapour
Table with 4 colums and 4 rows. The columns are labelled Gas, Atmospheric air %, Exhaled air %, and Change %. The rows are labelled Nitrogen, Oxygen, Carbon dioxide, and Water vapour.

The composition of inhaled air differs to exhaled air, this is because of gas exchange in the alveoli.

Gas exchange in the lungs

Gas exchange in the lungs happens in the alveoli. Some of the features of alveoli include:

  • thin walls (just one cell thick) to reduce the diffusion distance
  • large surface area for maximum exchange of gases
  • moist surface for the dissolving of gases in alveolar air so that they can diffuse across the alveolar walls
  • rich blood supply to remove diffused gases and maintain a concentration gradient for further diffusion
Diagram showing deoxygenated blood entering the alveoli and oxygenated blood leaving through the other side.

Rhys is out of breath after walking to his camping destination. His science app, Alfred, helps him to breathe correctly by explaining the process of gas exchange.