Surface area to volume

• Why do larger organisms require specialised exchange surfaces ?


  • Small surface area to volume ratio means they cannot exchange all the substances they need across body surfaces
• Why do larger organisms require mass transport systems ?

  • Diffusion is not sufficient enough to quickly transport substances long distances
  • Mass transport systems transport substances between the organisms specialised exchange surfaces which are usually very far apart
• Why do small organisms not require specialised exchange surfaces ?

  • Distance between the cells and the outside world is very small.
  • So diffusion between cells and outside world happens quickly
• What does SA : V


  Surface area to volume ratio

  • How many times larger the surface area is than the volume
• How to calculate surface area ?


  Find area of single face

  • Multiply by number of faces
• How does the surface area to volume ratio affect the transport of molecules ?

  • The lower the surface area to volume ratio, the further the distance molecules need to travel to reach all parts of the organism
• What is the relationship between an organisms size and its surface area to volume ratio?

  The larger the organism : the lower the surface area to volume ratio