How is most oxygen transported in the blood?

Most oxygen in the blood is transported bound to hemoglobin, which is a protein found in red blood cells. Hemoglobin has a high affinity for oxygen, allowing it to pick up oxygen in the lungs and deliver it to tissues throughout the body where it is needed for cellular metabolism.

When oxygen enters the bloodstream in the lungs, the majority (approximately 98.5%) is taken up by hemoglobin molecules, forming oxyhemoglobin. This is an efficient method of transport, as it allows for a large amount of oxygen to be carried effectively, even at relatively low concentrations in the plasma. Each hemoglobin molecule can bind up to four oxygen molecules, maximizing the potential for oxygen delivery to tissues.

While some oxygen is indeed dissolved in plasma, this constitutes a very small percentage of oxygen transport. The options mentioning carbonic acid and the cytoplasm of red blood cells also pertain to the transport of carbon dioxide rather than oxygen. Understanding this distinction is crucial for grasping the mechanisms of gas transport in the circulatory system.