Chemiosmotic theory of ATP synthesis in chloroplasts & 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 concept of creating a proton gradient across a membrane.

2. **Role of Electrochemical Gradient**: ATP synthesis is driven by an electrochemical gradient, which is established by the accumulation of protons (H⁺ ions) on one side of the membrane.

3. **Location of ATP Synthesis**:
- In **chloroplasts**, this process occurs across the thylakoid membrane during photosynthesis.
- In **mitochondria**, it occurs across the inner mitochondrial membrane during cellular respiration.

4. **Proton Gradient Generation**: The accumulation of protons creates a proton gradient, which is essential for ATP synthesis. This gradient results in a difference in charge and concentration across the membrane.

5. **ATP Synthase Function**: The ATP synthase enzyme (composed of F0 and F1 subunits) utilizes the energy from the flow of protons back across the membrane (down their gradient) to synthesize ATP from ADP and inorganic phosphate.

6. **Conclusion**: The chemiosmotic theory of ATP synthesis in chloroplasts and mitochondria is fundamentally based on the establishment of a proton gradient.

### Final Answer:
The chemiosmotic theory of ATP synthesis in chloroplasts and mitochondria is based on the generation of a proton gradient across the membranes.

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