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Homeostasis describes the processes that exert positive and negative control over the variables in a system. In biology, there are four categories of homeostatic control.


These processes regulate and maintain the internal environment of a cell or an organism. Each process involves:

1) A sensory device that monitors the value of a variable
2) An input from the sensor to an effector whenever the value changes beyond a set threshold
3) An effector that restores the value of the variable to normal and stops the original input (negative feedback)

Examples of physiological homeostasis include the control of blood sugar levels, heart rate, and body temperature.


These are the processes that control disturbances in developmental conditions, ensuring that the fitness of the organism is not impaired.


This describes the tendency for species to resist the effects of artificial selection, in order to maintain genetic composition.


There are some ecological processes that are considered homeostatic, such as the regulation of population density and diversity.