Heat Exchange

• Heat transfer depends on the temperature gradient between the internal and external environments
• An organism that's hotter than its surroundings loses heat in 4 ways (organism that's cooler gains heat in the same ways):

  • conduction
  • convection
  • radiation
  • evaporation
• Conduction

  • hotter object to cooler object by direct contact
  • water conducts heat faster than air
  • small SA:V ratio reduces area in contact with the environment
• Convection

  • currents of air remove heat energy from surface of organism
  • the faster the rate of current, the faster heat is transferred
• Evaporation

  • water turns to water vapour, absorbing heat
  • convection increases the rate of evaporation
• Radiation

  • emission of electromagnetic 'heat' waves
  • radiation and absorption is greater with dark colours and large SA