Which poisoning reduces the amount of oxygen in the bloodstream and the atmosphere?

• A. Carbon monoxide poisoning
• B. Anemia
• C. Hypoxia
• D. Cyanide poisoning

Answer: (A)

Main idea: a poison can reduce oxygen delivery by both binding to the blood’s oxygen-carrying system and occupying space in the air. In carbon monoxide poisoning, carbon monoxide binds to hemoglobin with far greater affinity than oxygen, forming carboxyhemoglobin. This blocks oxygen from attaching to hemoglobin and being transported to tissues, so oxygen delivery to cells drops. At the same time, CO in the environment reduces the amount of breathable oxygen by occupying part of the air that would normally be oxygen, lowering the overall oxygen content in the atmosphere. Anemia lowers the blood’s oxygen-carrying capacity due to less hemoglobin, but it isn’t a poison and doesn’t alter the ambient oxygen level. Cyanide poisoning stops cells from using oxygen but doesn’t reduce the amount of oxygen available in the bloodstream or in the air. Hypoxia is a result of insufficient oxygen delivery to tissues, not a poisoning that lowers oxygen in blood and air. So carbon monoxide poisoning best fits the description.