Iron is primarily transported in plasma by which of the following proteins?

The primary protein responsible for transporting iron in plasma is transferrin. Transferrin is a glycoprotein that specifically binds to ferric iron (Fe3+) and facilitates its transport in the bloodstream to various tissues, including the liver, spleen, and bone marrow, where it is utilized for processes such as hemoglobin synthesis and erythropoiesis.

While hemosiderin and ferritin are involved in iron storage within the body, they do not function as transport proteins in the plasma. Hemosiderin serves as a storage form of iron that accumulates when there is excess iron, and ferritin serves as a soluble, readily accessible storage form, but neither transports iron in the circulation. Hemoglobin is a protein found within red blood cells that binds oxygen for transport but does not play a role in iron transport in the plasma.

Thus, transferrin is the correct answer, as it is the key transport molecule for iron in the plasma, ensuring the safe delivery and availability of iron throughout the body for essential physiological functions.