How is oxygen transported in the blood?

Answer 1

Hemoglobin is the compound in red blood cells that carries oxygen from the lungs to body cells. The oxygen combines readily with the ion in hemoglobin, and hemoglobin can carry more than twenty times its own volume in oxygen. After releasing oxygen to the cells, hemoglobin collects carbon dioxide and carries it to the lungs where it is exhaled.

Answer 2

Every blood cell contains a chemical called hemoglobin. The hemoglobin molecule contains a single atom of Iron. This Iron atom is in such an oxidation state and is presented in such a way that it has a weak affinity to oxygen molecules. This is not a real bond (ionic or covalent) but an 'understanding' between the filled orbital of oxygen and the unfilled orbitals on the iron. When the blood reaches its target tissue the oxygen hunger of the cells is greater than the oxygen affinity in the blood and the oxygen gets sucked off the blood and replaced by carbon dioxide. Carbon dioxide has oxygen in it of course and these oxygen molecules 'stick' to the iron. It is not as great an attraction as to pure oxygen but is the absence of the real stuff it'll be content with carbon dioxide. When the blood gets back to the lungs where there is real oxygen to be had the carbon dioxide is spuriously rejected and real oxygen taken up again.