Biology – Photosynthesis as an energy transfer process | e-Consult
Photosynthesis as an energy transfer process (1 questions)
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Here's a comparison and contrast of cyclic and non-cyclic photophosphorylation:
| Photosystem II (PSII) Involvement | Yes | No |
| Photosystem I (PSI) Involvement | Yes | Yes |
| NADPH Production | Yes | No |
| ATP Production | Yes | Yes |
| Electron Flow | Non-cyclic: PSII -> ETC -> PSI -> NADP+ | Cyclic: PSI -> ETC -> PSI |
| Overall Purpose | Produce ATP and NADPH for carbon fixation. | Produce ATP only, to meet the energy demands of the Calvin cycle when NADPH is in short supply. |
Key Differences: The most significant difference is the involvement of PSII and the production of NADPH. Non-cyclic photophosphorylation utilizes both PSII and PSI, generating both ATP and NADPH. Cyclic photophosphorylation only involves PSI, resulting in ATP production without NADPH. The choice between the two pathways is regulated by the ratio of ATP and NADPH within the chloroplast. If there's a surplus of ATP and a shortage of NADPH, the plant will favour cyclic photophosphorylation to maintain ATP levels.