Light reactions: electron flow in photosystems.
Light energy from a photon is passed among chlorophyll molecules.
The energy is eventually captured in an electron from water in
The splitting of the electron donor, water, releases oxygen.
The electron passes through an electron transport chain (ETC).
The energy from the electron is used to generate ATP.
Another photon excites chlorophyll molecules of Photosystem I.
Energy is passed among electrons to a 2nd ETC.
Energy from this 2nd ETC is stored in the electron acceptor NADPH.
As electrons pass along the ETC, protons are pumped from the stroma
into the thylakoid space, forming a H^+ gradient.
The protons diffuse back to the stroma by chemiosmosis, and powers the
ATP synthase to make ATP.
These light reactions store chemical energy in NADPH and ATP, which
are used in the Calvin cycle.