How is oxygen primarily transported in the blood?

• A. Dissolved in plasma
• B. Bound to hemoglobin in red blood cells
• C. By white blood cells
• D. In the form of carbon dioxide

Answer: (B)

Oxygen is primarily transported in the blood bound to hemoglobin in red blood cells. Hemoglobin, a protein within red blood cells, has a high affinity for oxygen, allowing it to effectively pick up oxygen in the lungs and release it in tissues where it is needed for cellular respiration. This binding significantly increases the blood's capacity to transport oxygen compared to simply dissolving it in plasma.

While a small amount of oxygen does circulate dissolved in plasma, this alone is not sufficient to meet the metabolic demands of the body's tissues. The contribution from white blood cells is unrelated to the transport of oxygen; they have a different role primarily associated with immune responses. The form of carbon dioxide mentioned refers to how carbon dioxide is transported out of tissues back to the lungs for exhalation, which is a separate process from oxygen transport. Thus, the mechanism involving hemoglobin is crucial for efficient oxygen delivery throughout the body.