Final answer:
In the light-dependent reactions of photosynthesis, energy from light is used to extract electrons from water and create a proton gradient. This proton gradient is then used to synthesize ATP and reduce NADP+ to NADPH.
Step-by-step explanation:
In the light-dependent reactions of photosynthesis, the energy of light is used to extract electrons from water in a process called photosystem II (PSII). These electrons then travel through the chloroplast electron transport chain (ETC) to photosystem I (PSI), which reduces NADP+ to NADPH.
As the electrons move through the proteins between PSII and PSI, they lose energy. This energy is used to move hydrogen atoms from the stroma to the thylakoid lumen, creating a proton gradient.
The ATP synthase enzyme uses this proton gradient to synthesize ATP, while NADPH is used as a reducing agent in the Calvin cycle to produce glucose.