Exchange Surfaces

  • All living cells need to be able to take up and excrete substances from and to their environment.

  • Cells need:
    • Water for many different things
    • Minerals for many different things
    • Oxygen for respiration
    • Glucose for energy
    • Fats for membranes
    • Proteins for growth and repair
  • Specialised cells in multicellular organisms may also need to take up other molecules.

  • Many of these substances can be produced inside the cytoplasm as part of metabolism, but the basic building blocks must still be taken up from the environment.

  • Cells may need to excrete:
    • Carbon Dioxide
    • Oxygen
    • Ammonia
  • Again, specialised cells in multicellular organisms may also need to excrete special molecules.

  • Single-celled organisms can exchange all the substances they need to via their outer surfaces; however, most multicellular organisms require special Exchange Surfaces.

  • This is because single-celled creatures have a very high surface-area-to-volume ratio, so have lots of available surface to exchange substances. Multi-celled creatures on the other hand tend to have a low surface-area-to-volume ratio, meaning their outer surfaces cannot exchange substances fast enough for all their cells.
  • Exchange surfaces have a number of adaptations to make them efficient:
    • Thin barriers to minimise the diffusion distance
    • A high concentration gradient to the substance
    • A large surface area
  • Exchange surfaces are found in abundance in nature. For example:
    • The Nephron in the Kidney
    • The root hairs of plants
    • The Hyphae of fungi
Written by Sam Adam-Day.