<P> The photosystem II complex replaced its lost electrons from an external source; however, the two other electrons are not returned to photosystem II as they would in the analogous cyclic pathway . Instead, the still - excited electrons are transferred to a photosystem I complex, which boosts their energy level to a higher level using a second solar photon . The highly excited electrons are transferred to the acceptor molecule, but this time are passed on to an enzyme called Ferredoxin - NADP reductase which uses them to catalyse the reaction (as shown): </P> <Dl> <Dd> NADP + 2H + 2e → NADPH + H </Dd> </Dl> <Dd> NADP + 2H + 2e → NADPH + H </Dd> <P> This consumes the H ions produced by the splitting of water, leading to a net production of 1 / 2O, ATP, and NADPH + H with the consumption of solar photons and water . </P>

In noncyclic photophosphorylation the source of electrons is ____