Identify a respiratory pigment, and then describe its structure and how this relates to its function. What will be an ideal response?

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Hemoglobin, hemocyanin and myoglobin are all respiratory pigments, but hemoglobin is the most
common respiratory pigment in vertebrates. Hemoglobin consists of four polypeptide chains (the
globin portion), and attached to each chain is an iron-porphyrin (heme). An iron atom is attached to
each heme, and one O2 molecule attaches to each iron. As a result, each molecule of hemoglobin has
the potential to bind four molecules of O2.The extent to which hemoglobin binds O2 depends on
several factors, one of which is the partial pressure of O2. Where the PO2 is high (e.g., in the
pulmonary capillaries), hemoglobin “loads up” with oxygen, and where the PO2 is low (e.g., deep in
the tissues far from the lungs), hemoglobin “unloads” its O2. In addition, where the PCO2 is high (e.g.,
deep in the tissues), the CO2 reacts with water to form bicarbonate and hydrogen ions. The resulting
decrease in pH causes hemoglobin to unload its O2. As a result, hemoglobin doesn’t unload its O2 until
the hemoglobin is close to rapidly respiring cells.