PADI Divemaster Certification Practice Exam

Why is carbon monoxide considered toxic?

1. It reacts with water in the body

2. It bonds with hemoglobin more readily than oxygen

3. It causes blood to thicken

4. It displaces nitrogen from the bloodstream

The correct answer is: It bonds with hemoglobin more readily than oxygen

Carbon monoxide is considered toxic primarily because it binds with hemoglobin in the blood more readily than oxygen does. Hemoglobin is the protein in red blood cells responsible for transporting oxygen from the lungs to the rest of the body. When carbon monoxide is inhaled, it competes with oxygen for binding sites on hemoglobin. As a result, even small amounts of carbon monoxide can significantly reduce the blood's ability to carry oxygen, leading to hypoxia—an inadequate supply of oxygen to body tissues. This condition can have serious, potentially life-threatening effects on vital organs such as the heart and brain. Other options do not reflect the primary mechanism by which carbon monoxide exerts its toxicity. Carbon monoxide does not significantly react with water in the body, nor does it cause blood to thicken as one of its main effects. Additionally, it does not displace nitrogen from the bloodstream; rather, it competes with oxygen for binding sites on hemoglobin. Thus, the most relevant reason for the toxic nature of carbon monoxide is its ability to bond to hemoglobin more effectively than oxygen, which directly disrupts the oxygen transport function of the blood.