Specialised Exchange Surfaces

• What is an exchange surface?

  A part of an organism over which substances are exchanged with the environment 
• The small protrusions of the lining of the small intestines are called villi. These have a large surface area which increases the area over which we can absorb nutrient molecules.
• Root hair cells absorb water and mineral ions from the soil.
• State and explain three features that most exchange surfaces have in common. 

  Feature 1 - Large surface area

  Explanation 1 - Lots of molecules can diffuse across at the same time

  Feature 2 - Surfaces are very thin

  Explanation 2 - Substances only have to diffuse a short distance

  Feature 3 - Surfaces are permeable 

  Explanation 3 - Substances are able to pass through the surface
• State and explain three features of alveoli that make them good exchange surfaces?

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

  Explanation 1 - Lots of molecules can diffuse across at the same time

  Feature 2 - Surfaces are very thin (only 1 alveolar cell and 1 capillary cell thick)

  Explanation 2 - Substances only have to diffuse a short distance

  Feature 3 - Surfaces are permeable

  Explanation 3 - Oxygen and carbon dioxide are able to diffuse across
• Which adaptation in plants contributes to the efficient exchange of gases?

  The flattened shape of their leaves