In the context of photosynthesis, what is the largest source of electrons used to reduce NADP\(^+\) to NADPH?

• A. Oxygen (O\(_2\))
• B. Carbon dioxide (CO\(_2\))
• C. Glucose (C\(_6\)H\(_{12}\)O\(_6\))
• D. Water (H\(_2\)O)

Answer: (D)

Verified step by step guidance

1. Understand the role of NADP\(^+\) in photosynthesis: NADP\(^+\) is an electron carrier that gets reduced to NADPH during the light-dependent reactions of photosynthesis. NADPH is then used in the Calvin cycle to help synthesize glucose.
2. Identify the source of electrons in the light-dependent reactions: Electrons are needed to reduce NADP\(^+\) to NADPH. These electrons are provided by a molecule that undergoes oxidation during the process.
3. Recall the process of photolysis: In the light-dependent reactions, water (H\(_2\)O) is split into oxygen (O\(_2\)), protons (H\(^+\)), and electrons through a process called photolysis, which is driven by light energy absorbed by photosystem II.
4. Connect the electrons from water to NADP\(^+\) reduction: The electrons released during the splitting of water are transferred through the electron transport chain, ultimately reducing NADP\(^+\) to NADPH.
5. Conclude that water (H\(_2\)O) is the largest source of electrons: Among the options provided, water is the molecule that donates electrons during photosynthesis, making it the correct answer.