Exchange surfaces

Diffusion distance

  • single celled organism

    • no part of the organism is far from the plasma membrane where oxygen is absorbed so diffusion distance is short

    • large surface area:volume ratio so oxygen and carbon dioxide can be easily exchanged

    • large SA:V ratio

    • low metabolic activity

    • diffusion can supply the needs of the organism

  • multicellular organism

    • small SA:V ratio

    • high metabolic activity

    • diffusion distance too large for effective supply of oxygen

Specialised exchange surfaces

  • increased surface area

    • more efficient diffusion

  • good blood supply

    • maintains steep concentration gradient

  • ventilation/support

    • also maintains a steep concentration gradient

  • short diffusion distance/thin layers

    • fast and efficient diffusion

EXAM Q: explain how the following features contribute to the efficiency of the gas exchange surface in the lungs

  • the lungs consist of millions of alveoli

    • large surface area

  • capillary wall only one cell thick

    • short diffusion distance

  • gas exchange surface is well ventilated

    • brings oxygen/removes carbon dioxide

    • maintains concentration gradient

exchange surfaces