/ ˌbaɪəˈlɑːdʒɪkl̩ ˈklɑːk /
An innate mechanism in living organisms that controls the periodicity of many physiological functions.
Regular internal rhythm of activity, produced by unknown mechanisms, and not dependent on external time signals. Such clocks are known to exist in almost all animals, and also in many plants, fungi, and unicellular organisms; the first biological clock gene in plants was isolated 1995 by a US team of researchers. In higher organisms, there appears to be a series of clocks of graded importance. For example, although body temperature and activity cycles in human beings are normally “set” to 24 hours, the two cycles may vary independently, showing that two clock mechanisms are involved.
Exposing humans to bright light can change the biological clock and help, for example, people suffering from seasonal affective disorder.