Fig. 1. Schematic representation of an animal cell with the potential means of regulating intracellular pH. (1), metabolic interconversion of acids and bases. (2), buffering; HA represents a weak acid or base with a dissociation constant in the physiological pH range. (3), transport of acids and bases across cell membranes; carbonic anhydrase (CA) catalyzes the hydration of CO₂ to yield H₂CO₃, which then dissociates to H⁺, HCO₃^-, and CO₃^2- (an abbreviated reaction is shown).