Explore this half-hour video to learn how metals allow the transfer of electrons through a process called oxidation-reduction, or "redox," when one species gains electrons while another loses them. Chemists take advantage of this process by using electron transfers to power the batteries in our flashlights, phones, or cars. In biochemistry, trace metals, such as cobalt in Vitamin B12, often drive chemical reactions that are essential for human health. Redox reactions also occur without metals, as is the case when lightening hair color.