In many chemical reaction where more complex molecules are being made
it is necessary to add hydrogen ions (Reduce a compound).
In photosynthesis it is necessary to reduce carbon dioxide to turn it
into glucose. This process is carried out by (nicotinamide adenine dinucleotide
phosphate) NADPH2
Making NADPH2 requires energy
(in the form of high energy electrons) and H+ ions.
NADPH can be converted into NADPH2
in photosynthesis by adding electrons, knocked out of chlorophyll by sunlight,
and also adding H+ ions from water.