Photosystems II and I

Photosystem II

1) Light-harvesting complex (or antenna complex)
Directly absorbs photons
Energy transferred via resonance energy transfer

2) Reaction center
P680→〖P680〗^∗
〖P680〗^∗ is relatively unstable, so energy is transferred quickly
Electron transfers to primary electron acceptor and captured
Water is oxidized to replace the electron on 〖P680〗^+, producing oxygen gas in the process
Energy used to make H^+ electrochemical gradient
Excited electrons travel from PSII to PSI

Photosystem I

- Primary role to make NADPH
- Addition of H^+ to NADP^+ contributes to H^+ gradient by depleting H^+ from the stroma

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