Final answer:
Hemoglobin is the protein in red blood cells that carries most of the oxygen in the blood, due to its four subunits, each containing a heme group with iron that binds oxygen.
Step-by-step explanation:
The Role of Hemoglobin in Oxygen Transport
The iron-containing protein found in red blood cells that transports the majority of oxygen carried in the blood is hemoglobin. Hemoglobin is crucial for the transportation of oxygen from the lungs to other parts of the body and the return of carbon dioxide from the tissues back to the lungs. This protein is composed of four symmetrical subunits and four heme groups, each of which contains one iron atom that can bind to an oxygen molecule. This binding capacity allows hemoglobin to carry a substantial amount of oxygen—each molecule can bind up to four oxygen molecules. Additionally, the iron in hemoglobin is responsible for the red color of blood when oxygenated, and the large number of hemoglobin molecules in each red blood cell allows for efficient oxygen transport.
There are other oxygen-binding proteins such as myoglobin, which is found in muscle tissue and stores oxygen for when tissues require a high delivery, and proteins like hemocyanin and hemerythrin in other organisms. However, in human red blood cells, hemoglobin is the primary molecule responsible for carrying oxygen.