Specialised Exchange Surfaces

• What is an exchange surface?

  A part of an organism over which substances are exchanged with the environment.
• Where are alveoli found?

  Lungs
• The small protrusions of the lining of the small intestines are ___called . These have a large _____ area which increases the area over which we can absorb nutrient molecules.

  villi

  surface
• Root hair cells absorb ____ and _____ ions from the soil.

  water

  mineral
• State and explain three features that most exchange surfaces have in common. 

  1. Large surface area.

  • Lots of molecules can diffuse across at the same time.

  2. Surfaces are very thin.

  • Substances only have to diffuse a short distance

  3. Surfaces are permeable.

  • Substances are able to pass through the surface.

  4. Good blood supply (good supply of 'internal medium').

  • Maintains a strong concentration gradient as blood is constantly replaced.
• State and explain three features of alveoli that make them good exchange surfaces. 

  1. There are lots of alveoli, giving a large total surface area.

  • Lots of molecules can diffuse across at the same time.

  2. Surfaces are very thin (only 1 alveoli cell and 1 capillary cell thick).

  • Substances only have to diffuse a short distance.

  3. Surface area permeable.

  • Oxygen and carbon dioxide are able to diffuse across.