**Core Concept**
Carbon dioxide transport in blood is a crucial process that occurs in the body to maintain acid-base balance. The majority of CO2 is transported in a bound form to the blood, whereas a smaller amount is transported in an unbound form. This process is essential for the regulation of pH levels in the body.

**Why the Correct Answer is Right**
Carbon dioxide is transported in the blood as carbaminohemoglobin, a complex formed between CO2 and the hemoglobin in red blood cells. This process occurs in the lungs, where CO2 binds to the hemoglobin, forming carbaminohemoglobin. This bound form of CO2 is then transported to the tissues, where it is released and used for various metabolic processes. The binding of CO2 to hemoglobin also affects the oxygen-carrying capacity of the blood, making it an essential aspect of respiratory physiology.

**Why Each Wrong Option is Incorrect**
**Option A:** Carbon dioxide is not transported in the blood as bicarbonate ions in significant amounts. While bicarbonate ions do play a role in the transport of CO2, they are not the primary form of CO2 transport in the blood.
**Option B:** Carbon dioxide is not transported in the blood as a free gas. Although some CO2 is transported in this form, it is not the majority of CO2 transport.
**Option C:** Carbon dioxide is not transported in the blood as a complex with plasma proteins. While plasma proteins do play a role in the transport of various substances, they are not primarily involved in CO2 transport.

**Clinical Pearl / High-Yield Fact**
The transport of carbon dioxide in the blood is an essential aspect of acid-base balance, and disturbances in this process can lead to respiratory alkalosis or acidosis. Understanding the mechanisms of CO2 transport is crucial for diagnosing and managing various respiratory and metabolic disorders.

**Correct Answer:** A.