**Core Concept**
Carbon dioxide (CO2) transport in the blood is a critical process for maintaining acid-base balance. The main mechanism involves the conversion of CO2 to bicarbonate ions (HCO3-) in the presence of carbonic anhydrase, an enzyme found in red blood cells.

**Why the Correct Answer is Right**
The correct answer involves the enzyme carbonic anhydrase, which catalyzes the reversible reaction between CO2 and water to form carbonic acid, which then dissociates to form bicarbonate ions (HCO3-) and hydrogen ions (H+). This process is facilitated by the enzyme carbonic anhydrase, which is abundant in red blood cells. The bicarbonate ions are then transported to the lungs, where they are converted back to CO2 and exhaled. This mechanism allows for efficient CO2 transport and helps maintain acid-base balance in the body.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the correct mechanism or component involved in CO2 transport.
* **Option B:** This option is incorrect because, although hemoglobin does bind CO2, it is not the primary mechanism for CO2 transport in the blood.
* **Option C:** This option is incorrect because it does not accurately describe the process of CO2 transport in the blood.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the enzyme carbonic anhydrase plays a crucial role in CO2 transport in the blood, and its inhibition can lead to impaired acid-base balance and respiratory alkalosis.

**Correct Answer: D. Bicarbonate ions (HCO3-)**