gas exchange- size and surface area

• what is metabolic rate?

  the amount of energy expended by that organism in a time period (usually daily)
• what is metabolic demand?

  how much oxygen and nutrients an organism needs to take in daily to respire enough to maintain the metabolic rate
• the greater the mass of an organism the higher that organisms metabolic rate will be
• Unicellular organisms:

  • Large S.A : V - surface area is large enough to absorb nutrients
  • diffusion distance is short - to get from the outside to the centre of the organism quickly
  • Advantage - can exchange materials directly with the environment as the whole cell is exposed to the outside
  • disadvantage - lose heat and energy quickly, cannot survive extreme temperatures
• Multicellular organisms

  • small S.A : V - more cells to receive substances
  • large diffusion distance - why there are exchange systems
  • advantage - lose less heat energy (can survive colder temperatures)
  • disadvantage - some cells are not exposed so an internal transport system is needed
• small animals lose heat energy easily so they need more energy and a higher metabolic rate to maintain a constant internal temperature
• there are behavioural adaptations to do with an animals actions to something external in order to survive
• physical adaptations are structural features of an organism that help it to survive