• G. W. Stout
  • N. P. O. Green
Part of the Macmillan Master Series book series (MACMMA)


  • Negative feedback This opposes any detected tendency away from the optimal level and returns it to the optimal level.

  • Positive feedback This reinforces a particular tendency so that it moves further and further away from the level at which it is normally held.

  • Homeostasis The maintenance of the internal environment within certain narrow limits.

  • Ectotherm An organism that relies on heat derived from the environment to raise its body temperature.

  • Endotherm An organism that maintains a fairly constant temperature independent of the environmental temperature. It generates heat, which must be conserved, via a high metabolic rate.

  • Core temperature The temperature of the tissues below a level of 2.5 cm beneath the surface of the skin.

  • Basal metabolic rate (BMR) The amount of heat energy per unit mass released in a resting, fasting organism.

  • Glycogenesis The conversion of carbon residues arising from metabolism to glycogen.

  • Glycogenolysis The conversion of glycogen to glucose.

  • Organisms are able to maintain their internal environment in a steady state despite constant fluctuations in the external environment. This is called homeostasis. It provides cells with optimum conditions in which to function effectively and efficiently and provides organisms with varying degrees of independence of their environments.

  • Fluctuations either side of the optimal level (reference or set point) of a particular condition are detected by receptors which stimulate control centres in the brain to counteract, correct and return that condition towards its optimal level. This is known as negative feedback and leads to the stability of systems. Positive feedback is rare in biological systems and generally leads to instability.


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Copyright information

© G. W. Stout and N. P. O. Green 1986

Authors and Affiliations

  • G. W. Stout
  • N. P. O. Green

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