By Jacob Stutsman, Updated Aug 30, 2022
The pH scale quantifies a solution’s acidity by measuring its hydrogen‑ion concentration. Biological systems depend on a narrow pH range; even modest deviations can disrupt cellular processes, enzyme activity, and organ function.
In aqueous chemistry, acids raise the concentration of hydrogen ions (H⁺) while bases increase hydroxide ions (OH⁻). The scale ranges from 0 to 14, with 7 considered neutral at 77 °F. Each unit change represents a tenfold difference in ion activity.
Organisms maintain pH homeostasis through buffering systems and respiratory or renal adjustments. The bicarbonate buffer, for example, reacts with CO₂ to form carbonic acid, which dissociates into H⁺ and HCO₃⁻. Enzymatic catalysis can reverse the reaction, allowing the body to fine‑tune acidity or alkalinity. These mechanisms keep systemic pH within tight limits.
Human blood is tightly regulated between 7.35 and 7.45. Deviations—acidosis (pH < 7.35) or alkalosis (pH > 7.45)—affect protein charge, red‑blood‑cell separation, and the function of organs such as the heart and kidneys. Chronic shifts can also alter bone mineralization, impacting bone density.
The stomach’s hydrochloric acid (pH 1–2) initiates protein denaturation and enzymatic digestion. Antacids neutralize excess acid, providing relief for gastro‑esophageal reflux or peptic ulcers.
Acidic waters (pH < 4.5) disrupt osmotic balance in fish and other aquatic organisms, forcing cells to absorb H⁺ at the expense of Na⁺, leading to respiratory failure and mortality. Slightly alkaline conditions can also impair ion transport and metabolic processes.
Understanding how pH shifts affect biological systems is essential for medical, environmental, and industrial applications.
