What happens in light reaction (Photo chemical reaction)

Options

A. Formation of ATP and `NADPH_(2)`
B. Formation of ATP
C. Formation of sugar
D. Breakdown of sugar

Answer

**Step-by-Step Solution:**

1. **Understanding Light Reactions**: Light reactions, also known as photochemical reactions, occur in the thylakoid membranes of chloroplasts during photosynthesis. They require light energy to initiate the process.

2. **Absorption of Light**: The process begins when chlorophyll and other pigments absorb sunlight. This energy excites electrons in the chlorophyll molecules.

3. **Water Splitting**: The excited electrons are transferred to an electron transport chain. To replace these lost electrons, water molecules (H₂O) are split in a process called photolysis. This reaction produces oxygen (O₂), protons (H⁺), and electrons.

4. **Formation of NADPH**: The electrons move through the electron transport chain, and their energy is used to reduce NADP⁺ (nicotinamide adenine dinucleotide phosphate) to NADPH. This molecule acts as a reducing agent in the subsequent dark reactions of photosynthesis.

5. **ATP Formation**: As protons (H⁺) are pumped across the thylakoid membrane, a proton gradient is created. Protons flow back into the stroma through ATP synthase, a protein complex that synthesizes ATP from ADP and inorganic phosphate (Pi) in a process known as chemiosmosis.

6. **Summary of Products**: The light reactions result in the formation of two important energy carriers: ATP and NADPH. These molecules are essential for the Calvin cycle, where carbon fixation occurs.

7. **Conclusion**: Thus, the correct answer to the question "What happens in light reaction?" is the formation of ATP and NADPH2.

**Final Answer**: The correct option is A: formation of ATP and NADPH2.

---