Which of the following best describes the primary function of the light-dependent reactions in photosynthesis?

• A. To release oxygen by splitting carbon dioxide
• B. To break down glucose into pyruvate
• C. To fix carbon dioxide into glucose
• D. To convert solar energy into chemical energy in the form of ATP and NADPH

Answer: (D)

Verified step by step guidance

1. Understand that photosynthesis consists of two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). The light-dependent reactions occur in the thylakoid membranes of chloroplasts.
2. Recognize that the primary function of the light-dependent reactions is to capture solar energy and convert it into chemical energy. This chemical energy is stored in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).
3. Learn that during the light-dependent reactions, sunlight excites electrons in chlorophyll molecules, initiating a chain of reactions in the photosystems (Photosystem II and Photosystem I).
4. Understand that water molecules are split during these reactions, releasing oxygen gas (O₂) as a byproduct. The electrons from water replenish the chlorophyll molecules, and protons contribute to the formation of a proton gradient used to synthesize ATP.
5. Recognize that ATP and NADPH produced in the light-dependent reactions are then used in the Calvin cycle (light-independent reactions) to fix carbon dioxide into glucose, completing the process of photosynthesis.