Exchange surfaces

• How easily stuff moves between an organism and it’s environment depends on its surface area to volume ratio
• Cells use diffusion to take in substances they need and get rid of waste products 


  eg

  • oxygen and carbon dioxide are transferred between cells and the environment during gas exchange
• example

  a hippo can be represented by a 2cm x 4cm x 4 cm block

  area of surface found by: L x W

  (4 x 4)x2 (top and bottom)

  + (4 x 2) x4 ( the sides) =64 Cm^2

  volume found by: LxWxH

  volume: 4 x 4 x 2 = 32CM ^2

  so ratio: 64:32 or 2:1
• Multicellular organisms need exchange surfaces 


  mticellular organisms have a small surface area compared to their volume so not enough substances can diffuse so they have adapted:

  • thin membrane do substances have a short distance to diffuse
  • large surface area so lots of substances can diffuse at once
  • exchange surfaces in animals have lots of blood vessels to get stuff in and out of blood quick
  • gas exchange surfaces in animals are often ventilated- air moves in and out