Which of the following is NOT a form that CO2 is transported to the lungs?

Carbon dioxide (CO2) is primarily transported in the blood in three ways: dissolved in plasma, bound to hemoglobin, and as bicarbonate ions. While carbonic acid (H2CO3) is an intermediate in the conversion of CO2 to bicarbonate, it is not a major form in which CO2 is transported to the lungs.

When CO2 diffuses into red blood cells, it can react with water to form carbonic acid, which quickly dissociates into bicarbonate and hydrogen ions. This process facilitates the transport of CO2. However, once formed, carbonic acid does not remain in its acidic form in the bloodstream for very long; it primarily exists as bicarbonate ions. Thus, while carbonic acid plays a role in the transport of CO2, it is not a significant or direct method of transport to the lungs.

In contrast, the other options represent how CO2 is effectively transported: as bicarbonate, which is the main form; as carbamino compounds bound to hemoglobin; and as dissolved CO2 in the plasma, which constitutes a smaller portion of total CO2 transport. Therefore, identifying carbonic acid as not being a primary form of CO2 transportation helps clarify its lesser role in this