exchanging substances

• name two gases that are exchanged in a leaf.

  oxygen, water vapour and carbon dioxide
• what is the function of alveoli?

  alveoli /rapid transfer oxygen to the blood and the removal of waste carbon dioxide from the blood.
• how are alveoli adapted for their function?

  they have a large surface area, a moist lining for dissolving gases, very thin walls and a good blood supply
• State and explain three features that most exchange surfaces have in common

  • large surface area - lots of molecules can diffuse at once
  • surfaces are very thin - substances only have to diffuse a short distance
  • surfaces are permeable - substances are able to pass through the surface
• State and explain three features of alveoli that make them good exchange surfaces. 

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

  - Lots of molecules can diffuse across at the same time

  • Surfaces are very thin (only 1 alveolar cell and 1 capillary cell thick)

  - Substances only have to diffuse a short distance

  • Surfaces are permeable - Oxygen and carbon dioxide are able to diffuse across