Question

In photosynthesis, what determines whether linear versus nonlinear e- flow occurs at any point in time?

Answer 1

Linear electron flow is the electrons that pass through the two photosystems from water to NADP+ pathway is sometimes called linear photophosphorylation. That's because electrons travel in a line from water through PSII and PSI to NADPH. The electrons then flow down the chain to PSI, as usual, driving proton pumping and the production of ATP. The products of linear electron flow are NADPH and ATP. These products are passed on to the Calvin cycle which is part of the light-independent stages

Cyclic electron flow are the electrons excited from P700 in PSI are passed from Fd to the cytochrome complex and back to P700 also known as nonlinear electron flow. In higher plants, the generation of proton gradient across the thylakoid membrane (ΔpH) through cyclic electron flow (CEF) has mainly two functions:

(1) To generate ATP and balance the ATP/NADPH energy budget, and

(2) To protect photosystems I and II against photoinhibition