a. It captures light energy and transfers it to the electron transport chain.
b. It provides replacement electrons to the reaction center chlorophyll in photosystem II.
c. It combines with carbon dioxide (CO2) to make glucose.
d. It provides a phosphate group to ATP.
At a fundamental level, water provides electrons to replace those removed from chlorophyll in photosystem II. Also, water produces oxygen as well as reduces NADP to NADPH (required in the Calvin cycle) by liberating H+ ions.
