Final answer:
The primary role of the carbonic-acid-bicarbonate buffer system is pH regulation in blood, which maintains the body's acid-base balance through a reaction involving carbon dioxide, carbonic acid, and bicarbonate ions.
Step-by-step explanation:
The primary role of the carbonic-acid-bicarbonate buffer system is B) pH regulation in blood. This system is crucial for maintaining the acid-base balance within the human body. Metabolic processes release carbon dioxide (CO2), which dissolves in the blood and forms carbonic acid (H2CO3) through a reaction with water. This carbonic acid can then dissociate into bicarbonate ions (HCO3-) and hydrogen ions (H+). Bicarbonate ions are supplied by the kidneys and serve as a buffer by absorbing excess hydrogen ions, which might otherwise lead to a change in pH. A stable pH is necessary for vital biological functions and to prevent harmful conditions caused by acid-base imbalances.
In the carbonic-acid-bicarbonate buffer system, the bicarbonate ions (HCO3-) act as a buffer by neutralizing excess acids or bases in the blood. Conversely, carbonic acid can release hydrogen ions if the blood becomes too basic. This dynamic balance effectively minimizes pH fluctuations, maintaining a stable environment for the body's cells. The byproduct of this buffering action, CO2, is exhaled through the lungs, whereas the bicarbonate ions are regulated by the kidneys to ensure the buffer system operates efficiently.