`ATP` formation in chloroplast and mitochondrion is explained by

Options

A. Lock and Key Theory of Fisher
B. Chemiosmotic Theory of Mitchell
C. Lipmann and Lohmann Theory
D. Chemical coupling theory

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the explanation for ATP formation in chloroplasts and mitochondria. We need to identify the theory that describes this process.

2. **Identifying Key Theories**:
- **Lock and Key Theory**: Proposed by Emil Fischer, it describes the specificity of enzymes and substrates but does not explain ATP formation.
- **Chemoosmotic Theory**: Proposed by Peter Mitchell in 1961, this theory explains ATP synthesis through a process involving proton gradients and ATP synthase.
- **Lippmann and Lohmann Theory**: Lippmann discussed the chemical energy of ATP, while Lohmann discovered ATP, but neither directly explains ATP formation in chloroplasts and mitochondria.
- **Chemical Coupling Theory**: This theory relates to oxidative phosphorylation but does not specifically address ATP synthesis in chloroplasts and mitochondria.

3. **Selecting the Correct Theory**: Among the options, the **Chemoosmotic Theory** by Peter Mitchell is the only one that accurately describes ATP formation in chloroplasts and mitochondria through the mechanism of proton electrochemical coupling and the action of ATP synthase.

4. **Conclusion**: Therefore, the correct answer to the question is the **Chemoosmotic Theory** proposed by Peter Mitchell.

### Final Answer:
ATP formation in chloroplasts and mitochondria is explained by the **Chemoosmotic Theory** by Peter Mitchell.

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