How does water function in the process of photosynthesis, particularly in the production of ATP, NADPH, and sugars?

• A. Water is only used to cool the chloroplasts and does not participate in the production of ATP, NADPH, or sugars.
• B. Water directly combines with carbon dioxide to form glucose during the light-independent reactions.
• C. Water is converted into oxygen and glucose during the light-dependent reactions.
• D. Water provides electrons during the light-dependent reactions, enabling the formation of ATP and NADPH, which are then used to synthesize sugars in the Calvin cycle.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the role of water in photosynthesis. Water is a key reactant in the light-dependent reactions of photosynthesis, which occur in the thylakoid membranes of the chloroplasts.
2. Step 2: Break down the light-dependent reactions. Water molecules are split through a process called photolysis, driven by light energy absorbed by chlorophyll. This splitting produces oxygen gas (O₂), protons (H⁺), and electrons.
3. Step 3: Explain the electron transport chain. The electrons provided by water are transferred to the photosystem II reaction center and then move through the electron transport chain. This movement generates a proton gradient across the thylakoid membrane, which is used to produce ATP via chemiosmosis.
4. Step 4: Discuss the formation of NADPH. The electrons eventually reach photosystem I, where they are energized again by light. These high-energy electrons are used to reduce NADP⁺ to NADPH, a molecule that carries energy and reducing power for the Calvin cycle.
5. Step 5: Connect to the Calvin cycle. ATP and NADPH produced in the light-dependent reactions are utilized in the Calvin cycle (light-independent reactions) to convert carbon dioxide (CO₂) into glucose and other sugars, completing the process of photosynthesis.