• The surfaces where gas exchange occurs in an organism are very different and different organisms have evolved different mechanisms for getting the gases to the gas exchange surface depending on size, where they live etc.
• All gas exchange surfaces have features in common
• These features allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time
• They include:
  • Large surface area?to allow faster diffusion of gases across the surface
  • Thin walls?to ensure diffusion distances remain short
  • Good ventilation with air?so that diffusion gradients can be maintained
  • Good blood supply?to maintain a high concentration gradient so diffusion occurs faster

The alveolus is the gas exchange surface in humans