Hemoglobin is a protein normally in the blood at concentrations of 12-20 grams per deciliter. The erythrocyte (red blood cell, RBC) are one of the 211 cell types in a human body. The RBC cytoplasm dry-weight is 90% hemoglobin. For “cellular combustion” of metabolites, oxygen is transported from the lungs by hemoglobin. The diagram below is of hemoglobin binding oxygen. 
“Hemoglobin”
