Identify the true statements regarding the heme group ofmyoglobin and hemoglobin. 

A heme group contains four pyrrole rings, which are linked viamethene (methine) bridges.

The heme group is conjugated.

The globin chains of myoglobin and hemoglobin prevent theoxidation of Fe2 to Fe3 , which irreversibly binds oxygen.

The cooperativity of oxygen binding in hemoglobin arises fromelectronic interactions between heme groups.

The T state of hemoglobin has lower affinity for O2 than the Rstate because the Fe–Nporphyrin bonds are longer.

Hemoglobin contains four heme groups.

The iron in the heme group can form six bonds: The fifth is withan imidazole ring of a histidine and the sixth is with oxygen.