Most of oxygen is transported by `"_____________"`.

Answer

To answer the question "Most of oxygen is transported by __________," we can follow these steps:

1. **Understand the Context**: Recognize that the question is asking about how oxygen is transported in the blood.

2. **Identify the Methods of Oxygen Transport**: There are two primary methods by which oxygen is transported in the blood:
- A small amount of oxygen (approximately 1.5%) is dissolved in the plasma.
- The majority of oxygen (approximately 98.5%) is transported bound to a specific protein.

3. **Identify the Protein Involved**: The protein that binds most of the oxygen in the blood is called hemoglobin.

4. **Conclude the Answer**: Therefore, the correct answer to the question is that most of the oxygen is transported by hemoglobin.

Final Answer: Most of oxygen is transported by **hemoglobin**.