What are the end products of the light-dependent reactions of photosynthesis?

• A. ATP, NADPH, and oxygen.
• B. Glucose and oxygen.
• C. NADH and CO2.
• D. ATP alone.

Answer: (A)

Light-dependent reactions convert light energy into chemical energy and release a byproduct as oxygen. In the thylakoid membranes, water is split by the oxygen-evolving complex, releasing oxygen gas. Electrons flow through an electron transport chain, creating a proton gradient that drives ATP synthase to make ATP. At the same time, electrons are transferred to NADP+, forming NADPH. These three outputs—ATP, NADPH, and O2—are the end products of the light-dependent stage, with ATP and NADPH providing the energy and reducing power for the subsequent Calvin cycle to fix CO2 into sugars.

Glucose isn’t produced directly here; it’s the result of using ATP and NADPH in the Calvin cycle. NADH isn’t generated in this stage (plants produce NADPH instead). CO2 isn’t a byproduct; it’s a substrate used in the Calvin cycle. ATP alone would be incomplete because the light-dependent reactions also generate NADPH and O2.