Exchange Surfaces
Biology: Edexcel IGCSE, topic 3.3.2
Exchange Surfaces
Multicellular organisms have specialised surfaces because they can't rely on diffusion to reach all their cells. Exchange surfaces are adapted to maximise the efficiency of gas and solute (a substance dissolved in a liquid) exchange across them.
Large surface area
- A large surface area allows more of a substance to diffuse at the same time.
Thin membrane
- A thin membrane reduces the diffusion distance.
Blood supply
- Where substances are exchanged through blood in animals, exchange surfaces are densely packed with blood vessels:
- These blood vessels replenish (restore) the blood supply. They do this to maintain (keep up) a high concentration gradient by bringing in new blood as diffusion starts to even out the concentrations.
Ventilation
- In animals, if a gas is exchanged, the surface is ventilated (through breathing) to maintain a high concentration gradient and increase the rate of exchange.
Test yourself on Exchange Surfaces
Why is a thin membrane a useful adaptation of an exchange surfaces?