Trace elements function primarily as catalysts in enzyme systems; some metallic ions, such as iron and copper, participate in oxidationreduction reactions in energy metabolism. Iron, as a constituent of haemoglobin and myoglobin, also plays a vital role in the transport of oxygen. Related Theory Essential trace elements of the human body include zinc ( Zn), copper (Cu), selenium (Se), chromium (Cr), cobalt (Co). lodine (I). manganese (Mn), and molybdenum (Mo).