Specialised exchanged surfaces

• Why diffusion is enough to supply single-celled organisms:

  • Low metabolic activity
  • SA:V ratio is very large
• How to work out SA:V ratios

  Surface area - 4 x pi x rsquared

  Volume - 4/3 x pi x rcubed

  Ratio = SA/V
• Features of efficient gas exchange surfaces:

  • Increased surface area
  • Thin layers
  • Good blood supply
  • Ventilation maintaining a diffusion gradient
• Features of efficient gas exchange surfaces - Increased surface area:

  • Overcomes limitations of SA:V ratio of larger organisms
  • E.g. root hair cells - plants, villi - small intestine
• Features of efficient gas exchange surfaces - Thin layers:

  • Short diffusion distances - Fast efficient
  • E.g. alveoli - lungs, villi - small intestine
• Features of efficient gas exchange surfaces - Good blood supply:

  • Substances constantly delivered or removed - maintains steep concentration gradient for faster diffusion
  • E.g. alveoli - lungs, gills - fish, villi - small intestine
• Features of efficient gas exchange surfaces - Ventilation to maintain diffusion gradient:

  • For gases
  • Maintains concentration gradients
  • More efficient processes
  • E.g. alveoli and gills - fish