Cyanide poisoning disrupts cellular respiration by preventing cells from using oxygen.

• A. Carbon Monoxide Poisoning
• B. Methemoglobinemia
• C. Opioid Overdose
• D. Cyanide Poisoning

Answer: (D)

This question tests how certain poisons disrupt cellular respiration by blocking the cell’s ability to use oxygen itself. Cyanide acts by binding to cytochrome c oxidase (complex IV) in the mitochondrial electron transport chain, effectively halting oxidative phosphorylation. When this final step of the chain is blocked, cells can’t extract energy from oxygen even though oxygen is available in the blood. As a result, ATP production drops and the cell shifts to anaerobic glycolysis, leading to lactic acidosis and rapid organ dysfunction, especially in high-energy-demand tissues like the brain and heart.

Other options don’t directly prevent cells from using oxygen. Carbon monoxide and methemoglobinemia impair oxygen delivery by altering hemoglobin’s ability to carry or release oxygen, while an opioid overdose primarily reduces oxygen delivery by suppressing breathing.