Alveoli: Adaptations for Gas Exchange (Edexcel IGCSE Biology)

Alveoli

Spec point — 2.48 · explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries

• The alveoli are highly adapted and specialised for gas exchange

  • There are many rounded alveolar sacs which give a very large surface area to volume ratio
  • Alveoli (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, meaning there is a steep concentration gradient for diffusion of gases
  • A good blood supply ensures a constant supply of blood high in carbon dioxide and low in oxygen, again to maintain concentration gradients for diffusion
  • A layer of moisture on the surface of the alveoli helps diffusion as gases dissolve

Alveoli are specifically adapted to maximise gas exchange