What describes the Haldane effect?

• A. Decreased O2 enhances CO2 transport.
• B. Increased O2 enhances CO2 transport.
• C. CO2 transport is unaffected by O2 levels.
• D. Carbon dioxide binds more strongly to plasma albumin.

Answer: (A)

The Haldane effect describes how the oxygenation state of hemoglobin influences its capacity to carry carbon dioxide. When hemoglobin is deoxygenated (low O2), it binds CO2 more readily—forming carbaminohemoglobin—and promotes the conversion of CO2 to bicarbonate, increasing CO2 transport from tissues to the lungs. As blood reaches the lungs and hemoglobin loads oxygen (becomes oxygenated), its affinity for CO2 decreases, releasing CO2 for exhalation. So, decreased O2 enhances CO2 transport. The idea that CO2 transport is unaffected by O2 levels isn’t correct, and the dominant CO2 carriers involve hemoglobin and bicarbonate, not primarily binding to plasma albumin.