Exchange substances

• 1. The job of the lungs is to transfer oxygen to the blood and remove waste carbon dioxide from it
  2. to do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place
  3. the Aleppo are specillised to maximise the diffusion of O2 and CO2
• How alveoli are specillised

  • big surface area
  • moist lining for dissolving gases
  • very thin walls
  • a good blood supply
• Villi 


  The inside of the small intestine is covered in millions of tiny projections called villi

  1. they increase the surface area in a big way so digested food is absorbed much quicker into the blood
  2. they have: a single layer of surface cells, a very good bloody supply to assist quick absorption