specialised exchange surfaces

• what is an exchange surface

  a part of an organism over which substances are exchanged with the environment
• what is the role of a 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
• 4 exchange surfaces

  • alveoli
  • villi
  • root hair cells
  • leaves
• what is the role of villi

  to absorb nutrients (such as glucose, amino acids, and vitamins) from the small intestines, into bloodstream
• what is the role of a root hair cell

  to absorb water and mineral ions from the soil
• 3 features most exchange surfaces have in common

  • large surface area: lots of molecules can diffuse across at the same time
  • surfaces are very thin: substances only have to diffuse a short distance
  • surfaces are permeable: substance are able to pass through the surface
• what effect 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 have a good blood supply helps maintain a strong concentration gradient between the blood and the 'external medium' (e.g. the air in the alveoli or the nutrients in the small intestine)
  • the higher concentration gradient result in faster diffusion
• 5 features of alveoli that make them good exchange surfaces

  • there are many alveoli - this gives a large total surface area so lots of molecules can diffuse across the same time
  • alveoli walls are very thin - the walls are only 1 cell thick, so substances only have to diffuse a short distance
  • alveoli walls are permeable - oxygen and carbon dioxide are able to diffuse through the walla
  • good supply of blood - maintains a strong concentration gradient as blood is constantly replaced