The main function of bicarbonate is to:

• A. Osmotic pressure
• B. Balanced body pH levels
• C. Muscular function
• D. Cardiac rhythm and contractility

Answer: (B)

The main concept being tested is that bicarbonate acts as a key buffer to keep body fluids, especially blood, at a stable pH. In the bloodstream, bicarbonate (HCO3-) pairs with hydrogen ions (H+) to form carbonic acid (H2CO3), which rapidly breaks down into CO2 and water. The CO2 is then exhaled by the lungs, so the respiratory system helps control acidity. The kidneys also regulate bicarbonate levels by reabsorbing or excreting it, fine-tuning the pH balance over longer periods. This buffering system keeps arterial pH around 7.35–7.45, which is essential for enzyme activity and metabolic processes.

Osmotic pressure is driven by the total concentration of solutes like sodium, chloride, and other electrolytes, not specifically bicarbonate. Muscular function and cardiac rhythm depend more directly on ions such as calcium, potassium, and magnesium, rather than bicarbonate’s buffering role.