The chemiosmotic theory of ATP synthesis in the chloroplast and mitochondria is based on

Options

A. membrane potential
B. proton gradient
C. accumulate of `NA_""^(+)`
D. accumulation of `K_""^(+)`

Answer

### Step-by-Step Solution:

1. **Understanding Chemiosmotic Theory**: The chemiosmotic theory explains how ATP is synthesized in both chloroplasts and mitochondria. It is based on the movement of ions across a membrane, creating a gradient.

2. **Key Components**: The theory involves two main components:
- **Chemical (Chemio)**: Refers to the ions involved in the process, particularly protons (H+ ions).
- **Osmotic (Osmotic)**: Refers to the movement of these ions through a semi-permeable membrane, which is essential for creating a proton gradient.

3. **Proton Gradient Formation**: In mitochondria, protons are pumped from the mitochondrial matrix into the intermembrane space. This creates a higher concentration of protons in the intermembrane space compared to the matrix.

4. **ATP Synthase Function**: The protons then flow back into the mitochondrial matrix through ATP synthase, a protein complex that synthesizes ATP from ADP and inorganic phosphate (Pi) as the protons pass through it.

5. **Oxidative Phosphorylation**: This process of ATP synthesis driven by the proton gradient is known as oxidative phosphorylation. It is called so because it involves the use of oxygen to facilitate the production of ATP.

6. **Conclusion**: The chemiosmotic theory of ATP synthesis in chloroplasts and mitochondria is fundamentally based on the **proton gradient** (option B), which is crucial for the movement of protons through ATP synthase to generate ATP.