<P> The light - harvesting system of PS I uses multiple copies of the same transmembrane proteins used by PS II . The energy of absorbed light (in the form of delocalized, high - energy electrons) is funneled into the reaction center, where it excites special chlorophyll molecules (P700, maximum light absorption at 700 nm) to a higher energy level . The process occurs with astonishingly high efficiency . </P> <P> Electrons are removed from excited chlorophyll molecules and transferred through a series of intermediate carriers to ferredoxin, a water - soluble electron carrier . As in PS II, this is a solid - state process that operates with 100% efficiency . </P> <P> There are two different pathways of electron transport in PS I. In noncyclic electron transport, ferredoxin carries the electron to the enzyme ferredoxin NADP reductase (FNR) that reduces NADP to NADPH . In cyclic electron transport, electrons from ferredoxin are transferred (via plastoquinone) to a proton pump, cytochrome . They are then returned (via plastocyanin) to P700 . </P> <P> NADPH and ATP are used to synthesize organic molecules from CO . The ratio of NADPH to ATP production can be adjusted by adjusting the balance between cyclic and noncyclic electron transport . </P>

Which events take place in the light dependent reactions of photosynthesis