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TEMPERATURE REGULATION. Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. This process is one aspect of homeostasis :.
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Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. • This process is one aspect of homeostasis:
Endotherms create most of their heat via metabolic processes, and are colloquially referred to as warm-blooded. • Ectotherms use external sources of temperature to regulate their body temperatures. They are colloquially referred to as cold-blooded despite the fact that body temperatures often stay within the same temperature ranges as warm-blooded animals.
Ectotherms • Are animals whose regulation of body temperature depends on external sources, such as sunlight or a heated rock surface. • Ectothermic animals include most fish, amphibians, and reptiles as well as most invertebrates.
Ectotherms • Many ectotherms do, however, control body temperature through behaviour. • The well-known image of the lizard sunning itself on a rock provides a good example. • Most ectothermic organisms are able to maintain body temperatures both higher and more constant than the air or water around them.
Endotherms • An endotherm is an animal that produces most of its own heat metabolically. • Endotherms produce their own heat through the metabolic breakdown of food. • Of course, practically all endothermic animals depend on environmental heat at some point in their lives. • All birds and mammals are endotherms.
Transfer of Heat • Heat can be gained or lost from a body in four ways. • Conduction • Convection • Radiation • Evaporation
Conduction • Conduction occurs when two object at different temperatures are in contact with each other. • Heat flows from the warmer to the cooler object until they are both at the same temperature. • Conduction is the movement of heat through a substance by the collision of molecules.
Convection • Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy. • The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas. • The denser cold liquid or gas falls into the warm areas. In this way, convection currents that transfer heat from place to place are set up.
Radiation • Radiation is a method of heat transfer that does not rely upon any contact between the heat source and the heated object. • For example, we feel heat from the sun even though we are not touching it. • Heat can be transmitted though empty space by thermal radiation.
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Cooling the Body. • When the ambient (outside) temperature is above body temperature, then radiation, conduction and convection all transfer heat into the body rather than out. • Since there must be a net outward heat transfer, the only mechanisms left under those conditions are the evaporation of perspiration from the skin and the evaporative cooling from exhaled moisture.
Evaporation • Energy is required to change from liquid to gas (evaporation). • Latent heat of evaporation is the energy used to change liquid to vapour. • When evaporation does happen, the molecules that leave the liquid body takes a lot of heat with it, therefore the average temperature of the liquid decreases.
The temperature does not change during this process, so heat added goes directly into changing the state of the substance. • Evaporation is therefore a cooling process. • Evaporation depends on heat, humidity, and air movement.
Many animals use counter-current heat exchange to maximise heat exchange. • Read text page 322. • Watch this you tube. (2.53 mins) • http://www.youtube.com/watch?v=3tqjITi8S8s
