Final answer:
Iron is the essential mineral that plays a key role in oxygen transport in the blood through its presence in hemoglobin.
Step-by-step explanation:
The mineral that plays a key role in oxygen transport in the blood is iron. Hemoglobin, which is the protein in red blood cells that carries oxygen to the body's tissues, contains iron at its core. This iron reversibly associates with oxygen, allowing for efficient transport. Iron is absorbed as heme iron from animal sources or as non-heme iron from plant sources, although heme iron is absorbed more efficiently. In the body, iron is stored in various forms and transported to where it is needed using a protein called transferrin. When there is a deficiency in other trace minerals like copper, which is involved in the oxidation of iron from Fe²+ to Fe³+, the iron transport for heme synthesis can be adversely affected.