Why can deoxygenated blood carry more carbon dioxide than oxygenated blood?

Deoxygenated blood can carry more carbon dioxide than oxygenated blood primarily because deoxyhemoglobin is a better buffer of hydrogen ions. As blood passes through tissues, carbon dioxide diffuses into red blood cells, where it can be converted to bicarbonate, increasing acidity and, subsequently, the production of hydrogen ions. Deoxyhemoglobin, which forms when hemoglobin releases oxygen, has a greater affinity for hydrogen ions, allowing it to buffer these ions more effectively. This interaction promotes the conversion of carbon dioxide to bicarbonate, facilitating the transport of carbon dioxide away from tissues.

When hemoglobin is in the deoxygenated state, it favors the uptake of carbon dioxide via the reaction with water to form bicarbonate and hydrogen ions. This means that deoxyhemoglobin not only plays a critical role in maintaining acid-base balance but also enhances the blood’s capacity to carry carbon dioxide, which is particularly advantageous for efficient gas exchange in the lungs and tissues.

In contrast, the other options relate to various aspects of hemoglobin’s function but do not directly address the role of hydrogen ion buffering in enhancing carbon dioxide transport capacity. Therefore, understanding the buffering capacity of deoxyhemoglobin crucially elucidates why deoxygenated blood can carry more carbon dioxide.