Which of the following correctly describes the path of an electron from a molecule of water to the formation of glyceraldehyde-3-phosphate (G3P) during photosynthesis?

• A. Water → Calvin Cycle → Photosystem II → NADPH → G3P
• B. Water → NADPH → Photosystem II → Calvin Cycle → G3P
• C. Water → Photosystem II → Electron Transport Chain → Photosystem I → NADP⁺ → NADPH → Calvin Cycle → G3P
• D. Water → Photosystem I → Electron Transport Chain → Photosystem II → NADPH → Calvin Cycle → G3P

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the role of water in photosynthesis. Water molecules are split during the light-dependent reactions in a process called photolysis, which occurs in Photosystem II. This releases electrons, protons, and oxygen.
2. Step 2: Trace the path of the electrons after they are released from water. The electrons are transferred to Photosystem II, where they are excited by light energy and passed through the Electron Transport Chain (ETC).
3. Step 3: Follow the electrons as they move through the ETC. The energy from the electrons is used to pump protons across the thylakoid membrane, creating a proton gradient. The electrons eventually reach Photosystem I, where they are re-energized by light.
4. Step 4: After being re-energized in Photosystem I, the electrons are transferred to NADP⁺, forming NADPH. NADPH is a crucial molecule that carries high-energy electrons to the Calvin Cycle.
5. Step 5: In the Calvin Cycle, NADPH provides the electrons needed to reduce carbon dioxide into glyceraldehyde-3-phosphate (G3P), a three-carbon sugar that serves as a precursor for glucose and other carbohydrates.