How is oxygen primarily transported in the blood?

Oxygen is primarily transported in the blood bound to hemoglobin, a protein found in red blood cells. Hemoglobin has a strong 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 method of transport is highly efficient, as each hemoglobin molecule can carry up to four oxygen molecules, significantly increasing the blood's oxygen-carrying capacity compared to other methods.

While oxygen can dissolve in plasma and be transported in this form, this amount is relatively small and insufficient for the metabolic needs of the body. Oxygen dissolved in plasma accounts for only a minor fraction of the total oxygen transport in the blood. Additionally, transport through white blood cells is not a mechanism associated with oxygen; these cells have roles primarily related to the immune system and do not participate in oxygen transport. Overall, the binding of oxygen to hemoglobin is the key mechanism that enables efficient oxygen delivery to tissues.