Question

How is the ratio of NADPH and ATP adjusted to the needs of a plant cell?

Answer 1

The NADPH and ATP ratio is maintained by cyclic electron flow and cyclic photophosphorylation. Under certain conditions, the photoexcited electrons follow an alternate pathway called cyclic electron flow, which uses photosystem I (P700) but not photosystem II (P680). This process produces ATP without the production of NADPH or O2. This process is called cyclic photophosphorylation. The chloroplast opt for this process when the level of ATP supply decreases and the level of NADPH increases and thus maintain NADPH and ATP ratio.