Exchange Surfaces
Biology: Edexcel IGCSE, topic 3.2.7
Exchange Surfaces
Exchange surfaces are surfaces that are adapted to maximise the efficiency of gas and solute (a substance dissolved in a liquid) exchange across them. Exchange surface such as alveoli have the following adaptations:
Large surface area
- A large surface area allows more of a substance to diffuse at the same time.
- Alveoli create a large surface area for gas exchange in the lungs.
Thin membrane
- A thin membrane reduces the diffusion distance.
- The walls of the alveoli are one cell thick.
Blood supply
- Where substances are exchanged through blood in animals, exchange surfaces are densely packed with blood vessels:
- These blood vessels replenish the blood supply to maintain a high concentration gradient by bringing in new blood as diffusion starts to even out the concentrations.
- There are many capillaries around the alveoli.
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.
Kept clear
- Any particles of dust will block an exchange surface and reduce the rate of exchange.
- Goblet cells and cilia cells line the airways to prevent this.
- Goblet cells produce sticky mucus that traps particles and cilia cells waft the mucus up and out of the airway.
Test yourself on Exchange Surfaces
How are alveoli adapted for gas exchange?