Why is iron used in the body?
1.) So is iron the only element that can do that? If not, what is it about iron that makes it the only element found in hemoglobin?


No, iron is not the only metal that will fit inside the porphyrin structure. But its ability to be an electron acceptor and donor makes it very useful for oxygen and carbon dioxide to bind to the hemoglobin. Since iron is also very abundant, it was easy to incorporate it and utilize its properties.

Other macrocyclic structures include chlorophyll with magnesium in the center and vitamin B12 (cobalamin) with cobalt in the center.


  2.) What is it about being able to gain and lose electrons make it essential to life? I think it has something to do with oxygen being able to bind with iron. ... What is special about iron?


Iron is abundant. The iron in the hemoglobin can weakly bind both oxygen and carbon dioxide.

You can find more information on the Wikipedia page.