Which product is produced by the light-dependent reactions of photosynthesis?

• A. Oxygen gas only
• B. ATP and NADPH
• C. Glucose
• D. CO2

Answer: (B)

Light-dependent reactions convert light energy into chemical energy in the form of ATP and NADPH, and they also split water to release oxygen. The ATP provides energy and NADPH provides reducing power for the next stage of photosynthesis, the Calvin cycle, where CO2 is fixed into sugars. Oxygen is produced as a byproduct of water splitting, but ATP and NADPH are the primary energy carriers generated by these reactions. Glucose is formed later in the Calvin cycle, not directly by the light-dependent reactions. CO2 is a reactant in photosynthesis, not a product. Therefore, ATP and NADPH best represent the products of the light-dependent reactions.