Which substance is considered an acid in the body that affects pH?

Which substance is considered an acid in the body that affects pH?

• A. CO2 is considered an acid in the body.
• B. O2 is considered an acid in the body.
• C. N2 is considered an acid in the body.
• D. H2O is considered an acid in the body.

Answer: (A)

Acidity in body fluids is largely governed by carbon dioxide, which acts as an acid when dissolved in water. CO2 + H2O forms carbonic acid (H2CO3), which then dissociates into hydrogen ions (H+) and bicarbonate (HCO3−). The added H+ lowers pH, so CO2 levels directly influence acidity. This is why CO2 is called a volatile acid tied to respiration: more CO2 lowers pH, less CO2 raises it. The body uses the bicarbonate buffering system to moderate this, and ventilation adjusts CO2 levels to help keep pH within a narrow range. Oxygen and nitrogen don’t release H+ in normal physiology, and water is neutral overall, so they don’t primarily determine body pH.

Acidity in body fluids is largely governed by carbon dioxide, which acts as an acid when dissolved in water. CO2 + H2O forms carbonic acid (H2CO3), which then dissociates into hydrogen ions (H+) and bicarbonate (HCO3−). The added H+ lowers pH, so CO2 levels directly influence acidity. This is why CO2 is called a volatile acid tied to respiration: more CO2 lowers pH, less CO2 raises it. The body uses the bicarbonate buffering system to moderate this, and ventilation adjusts CO2 levels to help keep pH within a narrow range. Oxygen and nitrogen don’t release H+ in normal physiology, and water is neutral overall, so they don’t primarily determine body pH.