What is the internal timekeeper of physical and physiological activity in organisms called?

The internal timekeeper of physical and physiological activity in organisms is called the circadian rhythm. This biological clock regulates various processes, such as sleep-wake cycles, hormone release, and metabolism, typically following a roughly 24-hour cycle. It is influenced by external cues like light and temperature, helping organisms adapt to their environment. Disruptions to circadian rhythms can lead to various health issues.