1. Specialised exchange surfaces

• Need for specialised exchange surfaces

  • In microscopic organisms = Amoeba → O2 + Waste CO2 can be exchanged with external environment by diffusion through cell surface
  • Small diffusion distance
  • 2 reasons why diffusions enough to supply needs o single-celled organism:
  • their metabolic activity is low = O2 demands + Co2 production low
  • SA: Vol ratio is large
  • The bigger me organism--> the higher metabolic activity, high energy demands, larger diffusion distances, smaller SA: vol
• SA : vol ratios

  • Bigger the organisms = smaller SA: VoI ratio becomes = diffusion of substances from outside to centre of body longer = impossible /hard to absorb enough o2 through available SA to meet bodies needs
• Specialised exchange surfaces

  1. Increased SA --> provides area needed for exchange + overcomes limitations of SA: vol of larger organisms
  2. Thin layers --> shorter diffusion distances = makes process fast and efficient
  3. Good blood supply --> the steeper conc gradient = the faster diffusion. Good blood supply ensures substances constantly delivered + removed from exchange surfaces = maintains steep conc gradient for diffusion
  4. Ventilation to maintain diffusion gradient → for gases, ventilation system helps maintain conc gradients + make process more efficient