Answer:
Hemoglobin is an iron-containing protein present in the blood that functions for transportation of oxygen to different body cells..
Each hemoglobin molecule have tetrahedral structure consist of four heme groups surrounded by a globin group. Heme, is composed of porphyrin (ringlike organic structure) which is attched to an iron atom. There are four iron atoms in each molecule of hemoglobin that binds with four oxygen atoms and globin carry two linked pair of polypeptide chain.
The oxygen reversibly binds with the polypeptide chain and the process called oxygenation.