Features

• There are two stages in photosynthesis: the light reactions, which require light to take place, and the light-independent reactions, which do not involve light. During the light reactions, water molecules are broken up to release hydrogen ions, molecules of oxygen and electrons that are used by the electron transport chain in the membrane of the thylakoid, a structure inside the chloroplasts of plant cells.
  
  

Function

• During the final stage of the light reactions, an enzyme called NADP reductase catalyzes the reduction (addition of electrons) to a molecule of nicotinamide adenine dinucleotide phosphate or NADP+. The NADP+ accepts two electrons and a hydrogen ion to become NADPH. Later on during the light-independent reactions the NADPH will donate a hydrogen and two electrons to a molecule of 1,3-bisphosphoglycerate, which will (after some further modifications) be used to synthesize a glucose or sugar molecule.
  
  

Considerations

• Ultimately, the hydrogen for the plant comes from water -- a molecular compound with the formula H2O. Water molecules that are broken up during the light reactions yield the oxygen that all humans and animals breathe.