Requirements for efficient exchange
Respiring cells require a continuing supply of oxygen, while the carbon dioxide formed during respiration must be removed. Exchange surfaces therefore need to allow gases to diffuse quickly enough to meet these demands.
Features that increase diffusion
| Feature | Effect on gas exchange |
|---|---|
| Large surface area | More area is available for gas molecules to cross at the same time. |
| Short diffusion distance | The pathway that gas molecules must travel across the exchange surface is brief. |
| Steep concentration gradient | A large difference in gas concentration across the surface promotes rapid net diffusion. |