Specialised exchange surfaces

• Role of alveoli

  Absorb oxygen from the atmosphere into the bloodstream and to get rid of carbon dioxide from the bloodstream
• Role villi

  Absorb nutrient from the small intestines into the bloodstream
• Role of root hair cells

  Absorb water and mineral ions from soil
• Three things in common that exchange surfaces have

  Large surface area

  Surfaces are very thin

  Surfaces are permeable
• Why is a large surface area important

  Lots of molecules can diffuse across at the same time
• Why are thin surfaces important

  Substances only have to diffuse a short distance
• Why are permeable surfaces important

  Substances can pass through the surface
• Why is having a good blood supply important

  Increases the rate of diffusion

  Higher concentration gradient results in faster diffusion
• 5 features of alveoli

  Lots of alveoli- large surface area

  One cell thick- short diffusion distance

  Permeable walls

  Good supply of blood

  Good supply of air