Exchange surfaces

• Exchange Surfaces


  How easily stuff moves between an organism and its environment depends on its surface area to volume ratio
• Organisms Exchange Substances with their Environment
• Cells can use diffusion to

  1. Take in substances they need

  2. Get rid of waste products
• Substances exchanged by diffusion

  • Oxygen and carbon dioxide
  • Urea (a waste product produced from the breakdown of proteins)
• How easy it is for an organism to exchange substances with its environment

  • Depends on the organism's surface area to volume ratio (SA: V)
• A ratio shows how big one value is compared to another
• The larger an organism is, the smaller its surface area is compared to its volume
• Calculating surface area to volume ratio

  1. Find surface area using LENGTH x WIDTH

  2. Find volume using LENGTH x WIDTH x HEIGHT

  3. Divide surface area by volume to get ratio
• Surface area to volume ratios

  • Hippo: 2:1
  • Mouse: 6:1
• Multicellular organisms


  • Have a smaller surface area compared to their volume, so need exchange surfaces for efficient diffusion
• Exchange surfaces


  • Have a thin membrane for short diffusion distance
  • Have a large surface area for lots of diffusion
  • Have lots of blood vessels to get stuff into and out of the blood quickly
  • Are often ventilated to allow air movement in and out
• A large surface area is a key way that organisms' exchange surfaces are made more effective
• Calculating surface area to volume ratio of a bacterial cell

  1. Find surface area using LENGTH x WIDTH

  2. Find volume using LENGTH x WIDTH x HEIGHT

  3. Divide surface area by volume to get ratio