Which one of the following is correct about circadian rhythm?
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Circadian rhythm is dependent on exogenous clock is restricted to birds and mammals
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Circadian rhythm is not exactly of 24 hours
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Circadian rhythm is necessary as the earth is tilted on its axis
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Circadian rhythm has period of exactly 24 hours in animals
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Circadian rhythm has period of 1 year
A circadian rhythm is any biological process that displays an endogenous, entrainable oscillation of about 24 hours. These rhythms are driven by a circadian clock, and rhythms have been widely observed in plants, animals, fungi and cyanobacteria. The term circadian comes from the Latin circa, meaning around (or approximately), and diem or dies, meaning day. The formal study of biological temporal rhythms, such as daily, tidal, weekly, seasonal, and annual rhythms, is called chronobiology. Although circadian rhythms are endogenous they are adjusted (entrained) to the local environment by external cues called zeitgebers, commonly the most important of which is daylight.