Why is $H_{2}O$ an essential ingredient for photosynthesis in organic chemistry?

• A. $H_{2}O$ is the primary source of carbon atoms for glucose synthesis.
• B. $H_{2}O$ provides electrons through photolysis, which are necessary for the light-dependent reactions.
• C. $H_{2}O$ acts as a catalyst in the Calvin cycle.
• D. $H_{2}O$ is used to transport glucose out of the chloroplast.

Answer: (B)

Verified step by step guidance

1. Understand the role of water in photosynthesis: Water is crucial in the light-dependent reactions of photosynthesis, where it undergoes photolysis.
2. Explore photolysis: During photolysis, water molecules are split into oxygen, protons, and electrons. This process is driven by light energy absorbed by chlorophyll.
3. Identify the importance of electrons: The electrons released from water are essential for the electron transport chain in the light-dependent reactions, which ultimately leads to the production of ATP and NADPH.
4. Clarify the misconception: Water is not the primary source of carbon atoms for glucose synthesis; carbon dioxide is. Water's role is primarily in providing electrons and protons.
5. Summarize the correct answer: Water provides electrons through photolysis, which are necessary for the light-dependent reactions, supporting the synthesis of energy carriers used in the Calvin cycle.