During the light-dependent reactions of photosynthesis, which energy carriers are produced using light energy?

• A. ADP and NADH.
• B. GTP and NADPH.
• C. FADH2 and NADH.
• D. ATP and NADPH.

Answer: (D)

Light energy in the light-dependent reactions is used to power the production of two key energy carriers: ATP and NADPH. Photosystems harvest light to excite electrons and drive their flow through an electron transport chain embedded in the thylakoid membrane. This electron movement pumps protons across the membrane, creating a proton gradient that ATP synthase uses to convert ADP into ATP—a process called photophosphorylation. At the same time, electrons are transferred to NADP+, forming NADPH via NADP+ reductase. The ATP and NADPH produced provide the energy and reducing power needed for carbon fixation in the Calvin cycle. Oxygen is released as a by-product from water splitting, but the energy carriers generated from light energy are ATP and NADPH. NADH and FADH2 come from cellular respiration, not the light reactions, and GTP is produced in other metabolic contexts.