Cyanide is metabolic poison as it:

Options

A. Inhibits the enzymes of TCA cycle
B. Inhibits the enzymes cytochrome oxidase and blocks tissue respiration
C. Inhibits glycolysis
D. Stops protein synthesis

Answer

### Step-by-Step Solution:

1. **Understanding Cyanide's Role**: Cyanide is known as a metabolic poison. To understand why, we need to look at its effects on cellular respiration.

2. **Identifying the Enzyme**: One of the key enzymes involved in the electron transport chain during cellular respiration is cytochrome oxidase. This enzyme plays a crucial role in the transfer of electrons.

3. **Mechanism of Action**: Cyanide inhibits the activity of cytochrome oxidase. When this enzyme is inhibited, the electron transport chain cannot function properly.

4. **Consequences of Inhibition**: The inhibition of cytochrome oxidase leads to a blockage of tissue respiration. Without proper electron transfer, cells cannot produce ATP efficiently, which is essential for energy.

5. **Eliminating Incorrect Options**:
- Option A states that cyanide inhibits an enzyme of the TCA cycle, which is incorrect.
- Option C suggests it inhibits glycolysis, which is also incorrect.
- Option D mentions protein synthesis, which is unrelated to cyanide's action.

6. **Conclusion**: Therefore, the correct answer is that cyanide is a metabolic poison because it inhibits the enzyme cytochrome oxidase, blocking tissue respiration.

### Final Answer:
Cyanide is a metabolic poison as it inhibits the enzyme cytochrome oxidase and blocks tissue respiration.

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