(1) Red blood cells Explanation: Hemoglobin is the ironcontaining oxygen-transport metalloprotein in the red blood cells of all vertebrates. Hemoglobin in the blood carries oxygen from the respiratory organs to the rest of the body where it releases the oxygen to burn nutrients to provide energy to power the functions of the organism, and collects the resultant carbon dioxide to bring it back to the respiratory organs to be dispensed from the organism.