* Water as a reactant: In the light-dependent reactions of photosynthesis, water molecules are split apart. This process, called photolysis, is driven by the energy from sunlight absorbed by chlorophyll. The splitting of water releases electrons, hydrogen ions (H+), and oxygen gas (O2).
* Electrons: The electrons are used to power the electron transport chain, which generates ATP (energy) and NADPH (a reducing agent).
* Hydrogen ions: The H+ ions contribute to the proton gradient that drives ATP synthesis.
* Oxygen: This is released as a byproduct of photosynthesis.
* Water as a product: During the Calvin cycle, the light-independent reactions of photosynthesis, carbon dioxide is converted into sugar. This process requires energy (from the ATP produced in the light-dependent reactions) and reducing power (from NADPH). Ultimately, the hydrogen ions released from water during photolysis are used to create glucose molecules.
In summary:
* Water is consumed in the light-dependent reactions as a source of electrons and protons.
* Water is produced in the Calvin cycle as a byproduct of the reduction of carbon dioxide.
So, while water appears on both sides of the equation, it's not the same water. It's being broken down and used on one side, and reformed as a byproduct on the other.
