What describes a free-running rhythm in biological terms?

A free-running rhythm refers to a biological rhythm that is generated and maintained by an internal biological clock, independent of external environmental cues. This rhythm typically oscillates with a period slightly longer or shorter than 24 hours, suggesting that while it is influenced by the body’s intrinsic timing mechanisms, it is not directly synchronized with external factors like light or temperature.

The internal biological clock, often referred to as circadian rhythms, enables organisms to anticipate and adapt to cycles of day and night or other consistent environmental changes without relying on direct sensory input from the environment. This means that even in constant conditions where external cues are absent, such as in controlled laboratory settings, the free-running rhythm persists, highlighting the autonomy of the biological clock.

In contrast to a free-running rhythm, rhythms that are highly influenced by environmental cues or fixed schedules do not capture the essence of an internal biological clock's independence, which is the defining feature of a free-running rhythm.