ectotherms and endotherms

• endotherms

  • organisms that use a variety of mechanisms to control their body temperature within a normal range, despite changes in the external temperature (warm blooded)
• ectotherms

  • organisms that are not able to control their body temperature as effectively as endotherms. This is because they rely on external sources of heat.
  • this also means that their body temperature fluctuates with the external temperature. They use a variety of behavioural mechanisms to control thei body temperature (cold blooded)
• ectotherms temperature control (behavioural responses)

  • moving to a sunny area
  • lie on a warm surface
  • expose a greater surface area to the sun
  • move out of the sun
  • move underground
  • reduce the body surface exposed to the sun
• ectotherm examples

  • snakes: behavioural adaption - basks in sun. They are often found lying on an exposed path beside vegetation - absorb heat directly from sun
  • horned lizard: behavioural adaption - can change its shape by expanding or contracting its ribcage - expanding ribcage increases the surface area exposed to the sun, so more heat absorbed
• ectotherm advantages

  • less food used in respiration
  • more energy and nutrients gained from food can be converted to growth
  • they need to find less food
  • they can survive for long periods without food
• ectotherms disadvantages

  • they are less active in colder temperatures
  • at risk from predators while cold - unable to escape and cannot take advantage of food while they're cold
• endotherms behavioural adaptions (too hot)

  • hide away from sun in the shade or in a burrow
  • orientate body to reduce surface area exposed to sun
  • remain inactive and spread limbs out to enable greater heat loss
  • wet skin to use evaporation to help cool body. cats lick themselves and elephants spray water over their bodies.
• endotherms behavioural adaptions (too cold)

  • lie in the sun
  • orientate body towards sun to increases surface area exposed
  • move about to generate heat in the muscles or in extreme conditions, roll into a ball shape to reduce surface area and heat loss
  • remain dry
• endotherms physiological adaptations (too hot)


  skin

  • sweat glands secrete fluid onto skin surface; as this evaporates it uses heat from blood as latent heat of vaporisation
  • hairs and feathers lie flat to reduce insulation and allow greater heat loss
  • vasodilation of arterioles and precapillary sphincters directs blood to skin surface so more heat so more heat radiated away from blood
• endotherms physiological adaptations (too hot)

  gas exchange system

  • some animals pant, increasing evaporation of water from surface of lungs and airways. evaporation uses heat from blood as latent heat of vaporisation.
• endotherms physiological adaptations (too hot)

  liver

  • less respiration takes place, less heat released
• endotherms physiological adaptations (too hot)


  skeletal muscles

  • fewer contractions mean less heat released
• endotherms physiological adaptations (too hot)


  blood vessels

  • dilation to direct blood to the extremities so that more heat can be lost
• endotherms physiological adaptations (too cold)


  skin

  • less sweat is secreted, so less evaporation means less heat is lost
  • hairs and feathers stand erect to trap air, which insulates the body
  • vasoconstriction of arterioles and precapillary sphincters leading to skin surface
• endotherms physiological adaptations (too cold)


  gas exchange system

  • less panting, so less heat is lost
• endotherms physiological adaptations (too cold)


  liver

  • increased respiration in liver cells means more energy from food converted to heat
• endotherms physiological adaptations (too cold)


  skeletal muscles

  • spontaneous muscles contractions (shivering) release heat
• endotherms physiological adaptations (too cold)


  blood vessels

  • constriction to limit blood flow to extremities, so blood not cooled too much - frostbite
• sphincters open = vasodilation

  sphincters closed = vasoconstriction