Photosynthesis is an important circadian rhythm in plants. The two pathways of photosynthesis, photophosphorylation and the Calvin-Benson Cycle, proceed within the chloroplast. Because photophosphorylation requires light energy to proceed, both pathways of photosynthesis stop in the dark. It is therefore beneficial for plants to coordinate their photosynthetic activity and stomata activity with daily changes in light availability. The internal clock coordinating photosynthesis produces a circadian rhythm.
Photosynthesis dominates the metabolism of green plant cells.
Therefore it is not surprising that many other plant activities, such as the opening of stomata or the activity of Photosystem II, are synchronized with the rhythm of photosynthesis. Because these rhythms are synchronized, however, it can be difficult to separate factors that are controlling the photosynthetic rhythm from those that are merely synchronized with it. Scientists learn more about the circadian rhythms of photosynthesis by manipulating organisms and their environment, then measuring the corresponding changes in rhythm. Because circadian rhythms are repeating patterns, we can use principles of trigonometry to quantify them. Circadian rhythms produce repeating patterns over time.