Features of Gas Exchange Surfaces (Cambridge International IGCSE Biology)

Spec point — 11.1.1 · Describe the features of gas exchange surfaces in humans, limited to: large surface area, thin surface, good blood supply and good ventilation with air

Features of gas exchange surfaces

• All gas exchange surfaces have features in common

• These features maximise the rate of gas exchange taking place; 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

Exam Hint You may notice that several of the features of alveoli that aid their function are the same as those that make villi, or root hair cells, suited to their function, e.g.

• large surface area
• good blood supply
• steep concentration gradient

These structures are all examples of exchange surfaces; they allow the efficient movement of substances across their surface by diffusion, active transport and/or osmosis. So, if you learn the features of one exchange surface, you also know the features of the others!