Oxygen transport:  98% as oxyhemoglobin, 2% dissolved as a gas in plasma. The binding of iron to oxygen is a reversible reaction which is determined by the concentration of oxygen, the pH, and other factors we will discuss in more detail later.
	Iron will also bind to carbon monoxide (CO) in competition with oxygen. The strength of the bond with CO (called carboxyhemoglobin) is about 10 times that of the bond with oxygen. CO comes from polluted air resulting from incomplete combustion such as autos, woodstoves, etc. Removal of CO requires breathing clean air, or high concentration oxygen, or being placed in a hyperbaric (high pressure) chamber of pure oxygen.