Final answer:
In the CO₂/HCO₃ buffer system, when PCO₂ levels increase, bicarbonate (HCO₃) decreases due to the conversion of excess CO₂ to carbonic acid. The decrease in bicarbonate results in a decrease in pH. However, the excess CO₂ is exhaled, keeping the partial pressure of CO₂ relatively unchanged.
Step-by-step explanation:
In the CO₂/HCO₃ buffer system, when the PCO₂ levels increase, the bicarbonate (HCO₃) decreases. This is because the excess CO₂ reacts with water to form carbonic acid (H₂CO₃), which then dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻). The hydrogen ions decrease the pH of the system, resulting in a decrease in bicarbonate levels. However, in order to maintain balance, the excess CO₂ is released in the lungs and exhaled into the atmosphere, keeping the partial pressure of CO₂ (PCO₂) relatively unchanged.