What is true concerning hemoglobin.

A protein molecule present in the RBCs, which helps in the transportation of oxygen from the lungs to the different parts of the body and brings back carbon dioxide, that is, collected from different parts of the body back to the lungs is known as hemoglobin.  

The general features of hemoglobin are that it comprises four molecules of protein in the form of globulin chains. In adults, the molecules of hemoglobin comprise two beta-globulin chains and two alpha globulin chains, while in infants and fetuses, the beta chains are least found, and is substituted by two gamma chains.  

Each globulin chain comprises an essential iron-containing compound porphyrin, which is termed as heme. Together both iron and heme play an essential role in circulating oxygen and carbon dioxide in the blood. This iron gives the red appearance to the blood.  

when it is at an intermediate population density