Here's a breakdown:
* Cyclic photophosphorylation:
* Only Photosystem I (PSI) is involved.
* Electrons excited in PSI cycle back to PSI, generating ATP.
* No water is split, and no NADPH is produced.
* This process primarily occurs when the plant has a low supply of NADP+ and high supply of ATP.
* Noncyclic photophosphorylation:
* Both Photosystem I (PSI) and Photosystem II (PSII) are involved.
* Electrons excited in PSII are passed through an electron transport chain to PSI, eventually reducing NADP+ to NADPH.
* Water is split to release electrons for PSII and oxygen as a byproduct.
* This process produces both ATP and NADPH.
In summary: The key difference is that in cyclic photophosphorylation, the electron from PSI is recycled back to PSI, while in noncyclic photophosphorylation, it is used to reduce NADP+ and eventually generate NADPH.
