Energy required for ATP synthesis in PSII comes from

Options

A. proton gradient
B. electron gradient
C. reduction of glucose
D. oxidation of glucose

Explanation

To answer the question "Energy required for ATP synthesis in PSII comes from", we need to understand the process of photosynthesis, particularly the role of Photosystem II (PSII) in the light-dependent reactions.

### Step-by-Step Solution:

1. **Understanding Photosystem II (PSII)**:
- PSII is a crucial component of the light-dependent reactions of photosynthesis. It is located in the thylakoid membranes of chloroplasts and contains chlorophyll and other pigments that capture light energy.

2. **Photolysis of Water**:
- In PSII, light energy is used to split water molecules (H2O) in a process known as photolysis. This reaction produces oxygen (O2), protons (H+), and electrons (e-). The equation for this reaction can be simplified as:
\[ 2H_2O \rightarrow 4H^+ + 4e^- + O_2 \]

3. **Electron Transport Chain**:
- The electrons released from water are then transferred through a series of proteins in the thylakoid membrane known as the electron transport chain. As the electrons move through this chain, they lose energy.

4. **Proton Gradient Formation**:
- The energy lost by the electrons is utilized to pump protons (H+) from the stroma into the thylakoid lumen, creating a proton gradient (higher concentration of protons inside the thylakoid lumen compared to the stroma).

5. **ATP Synthesis**:
- The proton gradient created across the thylakoid membrane is essential for ATP synthesis. As protons flow back into the stroma through ATP synthase (a protein complex), the energy released during this process is used to convert ADP and inorganic phosphate (Pi) into ATP.

6. **Conclusion**:
- Therefore, the energy required for ATP synthesis in PSII primarily comes from the proton gradient established by the movement of protons across the thylakoid membrane.

### Final Answer:
The energy required for ATP synthesis in PSII comes from the **proton gradient**.

---