No, Photosystem II (PSII) does not directly produce NADPH.
PSII plays a critical role in photosynthesis, primarily focusing on splitting water molecules and releasing electrons, protons (H+), and oxygen. The electrons released from water molecules replenish the electron deficiency in PSII caused by light energy. These electrons are then passed along an electron transport chain. This electron transport chain ultimately feeds into Photosystem I (PSI). It is PSI that is primarily responsible for generating NADPH.
Here's a breakdown of how it works:
- Photosystem II (PSII): Absorbs light energy, splits water molecules (photolysis), releases electrons, protons (H+), and oxygen. Electrons are passed to plastoquinone (Pq).
- Electron Transport Chain: Electrons move from Pq to cytochrome b6f complex, and then to plastocyanin (Pc). This process also pumps protons (H+) into the thylakoid lumen, creating a proton gradient used to generate ATP through chemiosmosis.
- Photosystem I (PSI): Accepts electrons from Pc. PSI absorbs light energy and re-energizes the electrons. These energized electrons are then passed to ferredoxin (Fd).
- NADPH Production: Ferredoxin (Fd) then transfers the electrons to NADP+ reductase, which uses them to reduce NADP+ to NADPH.
Therefore, while PSII initiates the electron flow necessary for NADPH production, the direct production of NADPH is the responsibility of Photosystem I (PSI) and NADP+ reductase. PSII contributes by providing the initial electrons and indirectly contributing to the proton gradient that drives ATP synthase.
