What is the normal pH range for human blood?

• A. Approximately 7.0 to 7.2
• B. Approximately 7.35 to 7.45
• C. Approximately 7.8 to 8.0
• D. Approximately 7.55 to 7.65

Answer: (B)

Blood pH must stay in a very narrow, slightly alkaline window to keep enzymes and metabolic processes functioning properly. The body maintains this tight balance using buffers in the blood, plus regulation by the lungs (removing carbon dioxide) and the kidneys (excreting hydrogen ions and reabsorbing bicarbonate). Because the pH scale is logarithmic, even small shifts in hydrogen ion concentration can significantly alter enzyme activity, protein charge, and how readily oxygen is released from hemoglobin. That means a tiny drift outside this delicate range can disrupt countless cellular reactions and organ functions. The correct choice reflects this small, physiologically acceptable window, while ranges that are too acidic or too alkaline point to acidosis or alkalosis, conditions that destabilize biology and can be life-threatening.