Cyanide kills the organisms/stop cell activity by

Options

A. (a) reducing water potential
B. (b) decreasing diffusion of oxygen
C. (c) interfering in respiratory mechanism by preventing transfer of electron from copper of cyt `a_3` to oxygen
D. (d) coagulating proteins of carriers in ETC

Answer

**Step-by-Step Solution:**

1. **Understanding Cyanide's Mechanism of Action:**
- Cyanide is a toxic agent that affects cellular respiration by interfering with the electron transport chain (ETC).
- It specifically binds to the copper site of cytochrome c oxidase, which is part of Complex IV of the ETC.

2. **Identifying the Role of Cytochrome c Oxidase:**
- Cytochrome c oxidase is responsible for the final step in the electron transport chain, where electrons are transferred to molecular oxygen.
- This transfer is crucial for the production of ATP through oxidative phosphorylation.

3. **Impact of Cyanide Binding:**
- When cyanide binds to cytochrome c oxidase, it inhibits the transfer of electrons to oxygen.
- This blockage prevents the cells from utilizing oxygen, leading to a state of hypoxia (oxygen deprivation).

4. **Consequences of Hypoxia:**
- As the cells are deprived of oxygen, they cannot perform aerobic respiration effectively.
- This ultimately leads to cell death due to the lack of energy production.

5. **Evaluating the Options:**
- Option A (reducing water potential) is incorrect because cyanide does not affect water potential directly.
- Option B (decreasing diffusion of oxygen) is also incorrect; cyanide does not reduce the amount of oxygen available but prevents its use.
- Option C (interfering in respiratory mechanism by preventing transfer of electron from copper of cytochrome A3 to oxygen) is correct as it accurately describes cyanide's action.
- Option D (coagulating proteins of carriers in ETC) is incorrect as cyanide does not work by coagulating proteins.

6. **Conclusion:**
- The correct answer is Option C, as it accurately describes how cyanide inhibits cellular respiration by preventing the transfer of electrons to oxygen.