CO2 is primarily transported in the arterial blood as
**Core Concept**
The primary mechanism of CO2 transport in the bloodstream involves the bicarbonate buffering system, which plays a crucial role in maintaining acid-base balance. This system involves the reaction of carbon dioxide with water to form carbonic acid, which is then converted to bicarbonate ions and hydrogen ions.
**Why the Correct Answer is Right**
The correct answer is **D. Bicarbonate (HCO3-)**. This is because in the arterial blood, CO2 reacts with water to form carbonic acid (H2CO3), which is then rapidly converted to bicarbonate ions (HCO3-) and hydrogen ions (H+) by the enzyme carbonic anhydrase. The majority of CO2 is transported bound to hemoglobin in the form of carbaminohemoglobin, but a significant portion is also transported as bicarbonate ions in the plasma. The bicarbonate buffering system is essential for maintaining acid-base balance in the body.
**Why Each Wrong Option is Incorrect**
**Option A:** **Dihydrogen phosphate (H2PO4-)** - This is incorrect because dihydrogen phosphate is a component of the phosphate buffer system, not the primary mechanism of CO2 transport.
**Option B:** **Proton (H+)** - This is incorrect because while hydrogen ions are produced in the reaction of CO2 with water, they are not the primary form of CO2 transport in the arterial blood.
**Option C:** **Bicarbonate (HCO3-)** is the correct answer, so there is no incorrect option to provide.
**Clinical Pearl / High-Yield Fact**
The bicarbonate buffering system is essential for maintaining acid-base balance in the body. An increase in CO2 levels can lead to an increase in bicarbonate ions, which can be excreted by the kidneys to maintain acid-base balance.
**Correct Answer: D. Bicarbonate (HCO3-)**