Adaptations of the Alveoli (Edexcel GCSE Biology: Combined Science)

• The lungs are the gas exchange surface in humans and so are adapted to maximise the exchange of gas by diffusion
• Inside the lungs there are many rounded alveolar sacs which give a very large surface area to volume ratio
• These alveoli are highly specialised structures
  • They (and the capillaries around them) have thin, single layers of cells to minimise diffusion distance
  • Ventilation maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space
  • A good blood supply ensures constant supply of blood high in carbon dioxide and low in oxygen
  • A layer of moisture on the surface of the alveoli helps diffusion as gases dissolve

Alveoli are specifically adapted to maximise gas exchange