How does oxygen primarily travel in the bloodstream?

• A. Dissolved in plasma
• B. Bound to hemoglobin in red blood cells
• C. As bicarbonate ions
• D. In the form of oxygen gas

Answer: (B)

Oxygen primarily travels in the bloodstream bound to hemoglobin in red blood cells. Hemoglobin, a protein found in red blood cells, has a high affinity for oxygen, allowing it to bind to oxygen molecules as blood passes through the lungs where the oxygen concentration is high. This binding facilitates efficient transport of oxygen to tissues throughout the body, where it is released for use in cellular respiration.

Although a small amount of oxygen is dissolved directly in the plasma, this method accounts for only about 1.5% of the total oxygen transport in the blood. The majority, approximately 98.5%, is carried in the form of oxyhemoglobin, allowing for efficient delivery to the body's cells.

This mechanism is advantageous because hemoglobin can carry multiple oxygen molecules at once, dramatically increasing the blood's oxygen-carrying capacity compared to what would be possible if oxygen were only dissolved in plasma. Additionally, while bicarbonate ions play a crucial role in carbon dioxide transport, they are not involved in oxygen transport. Consequently, hemoglobin’s role is critical for maintaining adequate oxygen levels in tissues.