Final answer:
Option (C), More than 95 percent of the protein in a red blood cell is hemoglobin, a molecule essential for the transport of oxygen and carbon dioxide in the blood.
Step-by-step explanation:
More than 95 percent of the protein in a red blood cell is hemoglobin. Hemoglobin is a large molecule composed of proteins and iron. It consists of four folded chains of a protein called globin, with each chain bound to a red pigment molecule called heme.
The key function of hemoglobin in red blood cells is to carry oxygen from the lungs to body tissues and to transport carbon dioxide from the tissues back to the lungs. Hemoglobin is the reason red blood cells are able to bind to over a billion oxygen molecules, owing much to the iron in hemoglobin, which is essential for oxygen binding and gives blood its characteristic red color.