What is the function of water in photosynthesis?

While water does participate in the overall photosynthesis process, its primary role is not to combine with carbon dioxide. Instead, carbon dioxide is fixed during the Calvin cycle, which occurs after the light reactions. Water itself does not directly participate in this fixation process but is essential for supplying electrons.

Water does not absorb light energy; rather, it is chlorophyll and other pigments within the chloroplasts that capture light during photosynthesis. Water's role is to provide electrons, while the pigments are responsible for harnessing the energy from light to initiate the photosynthetic process.

Although hydrogen ions are involved in the dark reactions, or Calvin cycle, water does not transport them. Instead, the products of the light reactions, namely ATP and NADPH, carry the necessary energy and electrons to drive the Calvin cycle. Water's contribution is mainly through the supply of electrons and protons that support the light reactions.