Which of these are respiratory poisons or inhibitor of ETC?

Options

A. Cyanides
B. Antimycin A
C. Carbon monoxide
D. All of these

Explanation

To determine which of the given substances are respiratory poisons or inhibitors of the electron transport chain (ETC), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of the Electron Transport Chain (ETC)**:
- The ETC is a series of protein complexes located in the inner mitochondrial membrane that facilitate the transfer of electrons from electron donors to electron acceptors, ultimately leading to the production of ATP.

2. **Identify the Inhibitors**:
- We need to identify which of the provided substances act as inhibitors of the ETC. The options given are:
- Cyanide
- Anti-mycin A
- Carbon monoxide
- All of these

3. **Analyze Each Substance**:
- **Cyanide**: This is a well-known respiratory poison that binds to cytochrome oxidase (complex IV) in the ETC, preventing the transfer of electrons to oxygen.
- **Anti-mycin A**: This antibiotic specifically inhibits the electron transport at the level of cytochrome c reductase (complex III), blocking electron flow in the chain.
- **Carbon Monoxide**: Similar to cyanide, carbon monoxide binds to cytochrome oxidase, inhibiting the transfer of electrons to oxygen.

4. **Conclusion**:
- Since all three substances (cyanide, anti-mycin A, and carbon monoxide) inhibit the electron transport chain at different points, they all act as respiratory poisons.

5. **Final Answer**:
- Therefore, the correct option is **"All of these"**.