What are Circadian Cycles?

A circadian rhythm is an approximate daily periodicity, a roughly-24-hour cycle in the biochemical, physiological or behavioural processes of living beings, including plants, animals, fungi and cyanobacteria. The term "circadian", coined by Franz Halberg, comes from the Latin circa, "around", and diem or dies, "day", meaning literally "approximately one day." The formal study of biological temporal rhythms such as daily, tidal, weekly, seasonal, and annual rhythms, is called chronobiology.
Circadian rhythms are endogenously generated, and can be entrained by external cues, called Zeitgebers. The primary one is daylight. These rhythms allow organisms to anticipate and prepare for precise and regular environmental changes

1. Wikipedia (2008). Circadian Cycles. Retrieved January 1,2009, from http://en AAAAAAAAAAAAAAAA.jpg.wikipedia.org/wiki/Circadian_cycles