Exchange Surfaces

Exchange surfaces are adapted to maximise effectiveness.

An effecive echange surface allows enough of a substance to pass through it.

The size and complexity of an organism increases the difficulty of exchanging materials.

The effectiveness of an exchange surface is increased by:

• Being thin, to provide a short diffusion path
• Having a large surface area, so lots of a substance can pass through at once
• Animals have lots of blood vessels, so there is an efficeint blood supply
• Gas exchange surfaces in animals are often well ventilated 

Gas Exchange in Humans:

• The surface are of the lungs is increased by millions of air sacs called alveoli
• The alveoli are specialised to maximise the difusion of oxygen and carbon dioxide.
• They have:
  • An ernormous surface area
  • A moist lining for dissolving gases
  • Very thin walls
  • A good blood supply

Solute Excahnge in Humans: 

• The surface area of the small intestine is increased by villi.
• The villi porvides a large surface area with an extensive network of capillaries to absorb the products of digestions efficiently, by diffuision and active transport.
• They have:
  • A single layer of surface cells
  • A very good blood supply to assist quick absorbtion.