In the light reactions of photosynthesis, water is required to supply two of which particles that are transferred to P680\(^+\)?

• A. Oxygen atoms
• B. Electrons
• C. Protons
• D. ATP molecules

Answer: (B)

Verified step by step guidance

1. Understand the context: The light reactions of photosynthesis occur in the thylakoid membranes of chloroplasts. These reactions involve the absorption of light energy to drive the transfer of electrons and the production of ATP and NADPH.
2. Identify the role of water: Water (H₂O) is split during the process of photolysis in the light reactions. This occurs at Photosystem II, where the enzyme complex splits water molecules into oxygen (O₂), protons (H⁺), and electrons.
3. Focus on P680: P680 is the reaction center chlorophyll molecule in Photosystem II. When P680 absorbs light energy, it becomes excited and loses an electron, becoming P680⁺. To stabilize P680⁺, electrons from the splitting of water are transferred to it.
4. Clarify the particles supplied by water: The splitting of water provides electrons to P680⁺, which are essential for the continuation of the light reactions. Protons (H⁺) are also released into the thylakoid lumen, contributing to the proton gradient used for ATP synthesis.
5. Summarize the answer: Water supplies electrons to P680⁺ during the light reactions of photosynthesis. These electrons are critical for the electron transport chain and the production of energy molecules like ATP and NADPH.