• All Notes
• Biology
• Exchange and Transport
• Exchange Surfaces
• Exchange Surfaces

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