Exchange Surfaces

• In single-celled organisms, substances can diffuse directly into/out of the cell as they have a large surface area to volume ratio
• Multicellular organisms have a smaller surface area to volume ratio so they need exchange surfaces for efficient diffusion
• Exchange surfaces are adapted to maximise effectiveness:

  • They have a thin membrane so theres a short distance to diffuse
  • They have a large surface area so lots of a substance can diffuse at once
  • Exchange surfaces in animals have lots of blood vessels and are ventilated