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These are roughly 24-hour cycles in the biochemical, physiological, or behavioral processes of living entities, influenced by external cues like sunlight.

Faster cycles than circadian, completing more than one cycle within a 24-hour period, such as stages of sleep in humans.

Biological rhythms with a frequency longer than 24 hours, such as menstrual cycles in humans or seasonal migration in birds.

These animals are active during the day and rest at night, like squirrels and humans.

Animals that are active at night and sleep during the day, such as owls and most bat species.

These animals are most active during the twilight hours of dawn and dusk, like rabbits and some species of deer.

Biological rhythms that occur when natural environmental time cues are absent, showing the internal origin of circadian clocks.

A German term for 'time giver', used to describe any external or environmental cue that entrains biological rhythms to the Earth's 24-hour light/dark cycle.

The alteration of the timing of a biological rhythm, such as due to jet lag or shift work in humans, which is an adjustment of the internal clock to new environmental time cues.

Refers to an individual's natural inclination towards the timing of their daily periods of activity and rest, such as being a 'morning person' or 'night owl'.

A tiny region in the brain's hypothalamus considered the body's master circadian pacemaker that regulates the timing of many biological rhythms.

A hormone secreted by the pineal gland in response to darkness, it helps regulate circadian rhythms and promote sleep.

These genes are responsible for producing the proteins that control circadian rhythms, found in nearly all tissues and organs in animals.

The process of synchronizing biological rhythms to an external rhythm, such as the light-dark cycle.