Human iron metabolism energy as ATP from a multi-step process known as cellular respiration, more specifically from oxidative phosphorylation at the mitochondrial cristae. Iron is present in the iron-sulfur clusters and heme groups of the electron transport chain proteins that generate a proton gradient that allows ATP synthase to synthesize ATP (chemiosmosis). Heme groups are part of hemoglobin, a protein found in red blood cells that serves to transport oxygen from the lungs to the tissues. Heme groups are also present in myoglobin to store and diffuse oxygen in muscle cells. The human body needs iron for oxygen transport. Oxygen (O) is required
Packed red blood cells are used in these situations, since they are unlikely to cause a reaction. A potentially fatal reaction is possible if the recipient has pre-existing antibodies, and uncrossmatched blood is only used in dire circumstances. Since O negative blood is not common, other blood types may be used if the situation is desperate. Most frequently, whole blood is collected from a blood donation and is spun in a centrifuge. The red blood cells are denser and settle to the bottom, and the majority of the liquid blood plasma remains on the top. The plasma is separated and the red blood cells