The circadian rhythm describes the internal biological clock that controls an organism's daily activity cycles. It is well-known that in many species, activity does in fact follow daily patterns. This applies to activities such as feeding or sleeping, as well as to physiological attributes such as metabolic rate, body temperature, blood pressure, and hormone levels. Most animal and plant species have daily rhythms and even fairly simple creatures like bacteria have been known to have natural daily cycles.

Experiments in which organisms are placed in constantly light or constantly dark environments frequently indicate that daily periodicity in activity patterns persists even when the normal day-night cues from sunlight are removed. These circadian rhythms are important in allowing for the timing of important daily activities.

Circadian Cycles

Circadian rhythms typically describe a twenty-four-hour cycle that corresponds to the length of the day on Earth. However, for almost...