What are the overall products of the light-dependent reactions?

• A. ADP and Pi only
• B. Glucose and O2
• C. ATP, NADPH, and O2
• D. NADH and FADH2

Answer: (C)

The main idea is that the light-dependent reactions produce ATP, NADPH, and oxygen. In the thylakoid membranes, light energy drives the flow of electrons, with water split to supply those electrons and to release O2 as a byproduct. The electron transport creates a proton gradient that powers ATP synthase to make ATP, and electrons are finally transferred to NADP+, forming NADPH. These outputs—ATP, NADPH, and O2—are the energy carriers and the byproduct needed to drive the next stage of photosynthesis. Glucose is produced later in the Calvin cycle, not during these reactions, and NADH and FADH2 are carries of electrons from respiration, not from photosynthesis. ADP and Pi are substrates used to make ATP, not the end products of the light-dependent stage.