The lock and key principle is related to

Options

A. Dark reaction
B. Enzyme action
C. Chemical action
D. Hormonal action.

Answer

**Step-by-Step Solution:**

1. **Understanding the Lock and Key Principle**: The lock and key principle is a model that explains how enzymes interact with substrates. It was proposed by Emil Fischer in 1899.

2. **Identifying the Components**: In this model, the enzyme is likened to a lock, while the substrate is compared to a key. The enzyme has a specific active site that is shaped to fit a particular substrate.

3. **Binding Process**: When the substrate (the key) fits into the active site of the enzyme (the lock), they form an enzyme-substrate complex. This specific fit is crucial for the enzyme to catalyze a reaction.

4. **Chemical Reaction**: Once the enzyme-substrate complex is formed, the enzyme facilitates a chemical reaction, resulting in the formation of products. Importantly, the enzyme remains unchanged after the reaction.

5. **Eliminating Incorrect Options**:
- **Dark Reaction**: This is related to photosynthesis and not specifically about enzyme action.
- **Chemical Action**: This term is too broad and does not specifically refer to the enzyme action.
- **Hormonal Action**: This does not relate to the lock and key principle.

6. **Conclusion**: The correct answer to the question is "enzyme action," as the lock and key principle specifically describes how enzymes function.

**Final Answer**: The lock and key principle is related to enzyme action.

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