Hemoglobin and chlorophyll have similar structures. The main difference is that hemoglobin is built around iron (Fe), where as chlorophyll is built around magnesium,(Mg). The primary function for hemoglobin is to transport oxygen from the lungs to other parts of the body. Hemoglobin is composed of four elements-carbon, hydrogen,oxygen and nitrogen. All four are organized around iron. Chlorophyll is composed of the same elements,which are organized around magnesium.