During gas exchange in the human respiratory system, which of the following components carries the highest percentage of carbon dioxide in blood?
Correct: A
Approximately 70% of CO2 is transported as bicarbonate ions (HCO3⁻) in plasma, formed via CO2 reacting with water in red blood cells. Carbaminohemoglobin carries ~23%, and dissolved CO2 accounts for ~7%. Carbonic acid conversion is part of the bicarbonate pathway but is not the primary form.