What is an exchange surface?

A part of an organism over which substances are exchanged with the environment.

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What exchange surface is shown above?

Alveoli.

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What is the role of alveoli?

To exchange gases with the environment.


Specifically to absorb oxygen from the atmosphere into the bloodstream, and to get rid of carbon dioxide from the bloodstream - releasing it to the atmosphere. 

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Name 4 exchanges surfaces.

  1. Alveoli.
  2. Villi.
  3. Root hair cells.
  4. Leaves.

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What exchange surface is being shown here?

Villi.

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What is the role of villi?

To absorb nutrients (such as glucose, amino acids, and vitamins) from the small intestines, into the bloodstream. 

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What is the role of root hair cells?

To absorb water and mineral ions from the soil.

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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.


  1. Surfaces are very thin: substances only have to diffuse a short distance.


  1. Surfaces are permeable: substance are able to pass through the surface.

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What affect does a good blood supply have on the rate of diffusion across exchange surfaces?

A good blood supply (or supply of 'internal medium') will increase the rate of diffusion across an exchange surface. 


This is because having a good blood supply helps maintain a strong concentration gradient between the blood and the 'external medium' (for example, the air in the alveoli, or the nutrients in the small intestine).


The higher concentration gradient results in faster diffusion.

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State and explain five features of alveoli that make them good exchange surfaces.

  1. There are many alveoli - this gives a large total surface area, so lots of molecules can diffuse across at the same time.
  2. Alveoli walls are are very thin - the walls are only 1 alveolar cell thick, so substances only have to diffuse a short distance.
  3. Alveoli walls are permeable - oxygen and carbon dioxide are able to diffuse through the walls.
  4. Good supply of blood ('internal medium') - maintains a strong concentration gradient as oxygenated blood is constantly being replaced with deoxygenated blood.
  5. Good supply of air ('external medium') - maintains a strong concentration gradient as air in the alveoli is constantly being replaced with oxygen-rich air from the lungs.

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