Here's a breakdown:
* Light-dependent reactions: This stage uses light energy to split water molecules (H₂O). This process releases oxygen (O₂) as a byproduct and generates ATP (energy) and NADPH (a reducing agent).
* NADPH is crucial because it carries high-energy electrons and a hydrogen atom, which are then used in the light-independent reactions (Calvin cycle).
In summary: The addition of hydrogen happens during the light-dependent reactions when water is split, and the resulting hydrogen atoms are carried by NADPH to fuel the light-independent reactions.
