The heme group of hemoglobin differs from the porphyrin of chlorophyll in having:

Explanation

The haem group of hemoglobin is characterized by having iron as its central metal atom. In contrast, the porphyrin of chlorophyll has magnesium as its central atom. This distinction is crucial in differentiating the two compounds. While both structures feature four pyrrole rings and have their central atom coordinated with the nitrogen of each pyrrole ring, it is the type of metal atom that sets them apart.