Light-dependent reactions of photosynthesis include splitting of water in the presence of sunlight and release of electrons. The electrons move from the reaction center of the PS-II via electron carriers to the PS-I. From the reaction center of PS-I, the electrons finally reach NADP reductase and reduce NADP into NADPH.
During this electron transfer via electron carriers, a proton concentration gradient is generated across the thylakoid membrane. The energy of this gradient is used to drive ATP synthesis. ATP and NADPH formed during the light-dependent phase of photosynthesis are then used during the reactions of the Calvin cycle.
