Exchange surfaces

• Specialised exchange surfaces allow efficient transport of substances from one area to another
• Exchange surfaces usually have:

  • short distance for diffusion
  • a large surface area
• Root hair cells on plants

  Specialised to take up water and nutrients from the soil

  • They have a large surface area and thin walls (diffusion occurs quicker)
• The walls of the nephrons in the kidneys

  Have thin walls and a very large surface area as they are required to efficiently reabsorb substances like water and glucose
• In the lungs . . .

  • Oxygen is transferred to the blood, Carbon dioxide is transferred to the lungs
  • This takes place across microscopic sized alveoli which are covered in tiny capillaries that supply the blood
• In the small intestine . . .

  • Cells have projections called villi
  • Digested food is absorbed over the membrane of these cells into the bloodstream
• The gills . . .

  • Water with oxygen passes through the gills
  • Each gill has plates called gill filaments and upon these are gill lamellae
  • Diffusion of oxygen into the blood and Diffusion of carbon dioxide into water takes place.
• In the leaves . . .

  • Carbon dioxide diffuses through the stomata for photosynthesis whilst oxygen and water vapour moves out through them