Biological rhythms

Biological rhythms are the repeating cycles of activity which occur in living organisms. The best-known example is the daily of circadian rhythm, which fits the cycle of day and night. Most forms of life have natural rhythms which fit them to natural changes in their environment. Animals are most active in part of the day, and rest or sleep at other times. They may be:
Plants undergo daily cycles as well. Photosynthesis has parts which need light, called light-dependent reactions, and parts which can continue at night (light-independent reactions).
Many other important cycles are also studied, including: