Exchange Surfaces

• Exchange Surface

  • Three key features:
  • Good Blood Supply
  • Large Surface Area
  • Thin Walls
  • As an organism increases in size, SA:V decreases; negative correlation
  • Small Organisms
  • Achieve efficient internal transport by just diffusion
  • High SA:V
  • Short diffusion distance
  • Low activity
  • Lower O_2 and glucose demand
  • Diffusion gradients maintained
  • Multicellular Organisms
  • Low SA:V
  • Diffusion too slow and distances too far
  • Greater metabolic activity (endothermic higher than exo)
  • Have specialised exchange surfaces; large SA
• Gas Exchange

  • O_2 + CO_2 exchange between organism and environment
  • Over specialised exchange surface
  • May be cell wall/membrane or single cell layer
  • Gases pass over exchange surface by diffusion
  • Mechanisms on either exchange surface side to maintain steep diffusion gradient of molecules/ions
  • Gas exchange surfaces are moist
  • Allow water to diffuse across
  • Not included as useful feature
  • Slows diffusion
  • Single-celled organisms
  • Larger SA:V
  • Less active
  • Gas exchange occurs over plasma membrane
  • Adequate to supply needs
  • Multi-cellular organisms
  • Smaller SA:V
  • High oxygen requirements