Final answer:
The correct reactants of the light-dependent reactions are sunlight, which is absorbed by chlorophyll, and water. During these reactions, sunlight is utilized to split water, producing oxygen and allowing the formation of ATP and NADPH, which are the energy carriers for the light-independent reactions.
Step-by-step explanation:
The reactants of the light-dependent reactions in photosynthesis are not carbon dioxide and water (A), glucose and oxygen (B), or ATP and NADPH (C). Instead, the correct reactants are derived from option (D), which are sunlight and water. The energy from sunlight is captured by chlorophyll and other pigments located within the thylakoid membranes of chloroplasts.
During the light-dependent reactions, sunlight is absorbed and used to split water molecules into oxygen, protons, and electrons. Oxygen is released as a byproduct, while the protons and electrons contribute to the formation of ATP and NADPH, respectively. These molecules of ATP and NADPH then serve as energy carriers and are utilized in the subsequent light-independent reactions (Calvin cycle) to help synthesize glucose.
Therefore, in answering the student's question, the proper reactants of the light-dependent reactions are sunlight and water, which I would clarify as the reactant elements. However, the presence of chlorophyll is also essential for these reactions to occur. Hence, the most accurate answer would be the combination of sunlight and chlorophyll that captures the light energy to initiate the processes that use water as a direct reactant.