SA:Vol Ratio

• Describe the relationship between the size and structure of an organism and its SA:Vol ratio

  • As size increases SA:Vol ratio tends to decrease
  • More thin/flat/folded/elongated structures increases SA:Vol ratio
• What is the metabolic rate and how can it be measured?

  • Metabolic rate = amount of energy used up by an organism within a given period of time
  • Often measured by Oxygen uptake - as used in aerobic respiration to make ATP for energy release
• Explain the relationship between SA:Vol ratio and metabolic rate?

  As SA:V increases (Smaller Organisms) metabolic rate increases

  • Rate of heat loss per unit body mass increases
  • So organisms need a higher rate of respiration
  • To release enough heat to maintain a constant body temperature e.g. replace lost heat
• Explain the adaptations that facilitate exchange as SA:V reduces in larger organisms?

  1)Changes to body shape (E.g. long/thin)

  • Increases SA:V and reduces long diffusion pathway

  2)Development of systems, such as a specialised surface/organ for gaseous exchange e.g. lungs:

  • Increases internal SA:V and reduces long diffusion pathway
  • Maintain a concentration gradient for diffusion e.g. by ventilation/good blood supply