Acidosis and alkalosis are best defined as fluctuations in blood pH and CO2 content due to changes in:

• A. Bohr effect
• B. O2 content
• C. Bicarbonate buffer
• D. Carbonic anhydrase

Answer: (C)

Acid-base disturbances hinge on the bicarbonate buffering system in the blood. The pH is set by the ratio of bicarbonate (HCO3–) to dissolved CO2 (as carbonic acid). When bicarbonate buffering changes, you shift that ratio and thus the pH, producing metabolic acidosis (low pH due to excess acid or loss of buffering) or metabolic alkalosis (high pH due to excess base or loss of acid). CO2 content is linked because it reflects respiratory input to the system and is part of the same equilibrium that the bicarbonate buffer moderates; the body compensates between the lungs and kidneys to restore the proper balance.

The bicarbonate buffer is the best descriptor here because it directly explains why fluctuations in pH accompany changes in buffering capacity, whereas changes in oxygen content or the Bohr effect describe other physiological relationships, and carbonic anhydrase is an enzyme that participates in the reaction but does not define the condition itself.