Redox reactions. Illustration of the process of molecules (orange, left) gaining or losing an electron (e, small sphere), resulting in the formation at right of a positive ion (anion, yellow) and a negative ion (cation, red). The loss of electrons is known as oxidation. The gain of electrons is known as reduction. Collectively known as redox reactions, these electron transfers are fundamental to chemical and biochemical processes such as electron transport pathways. For this artwork with labels, see image C023/8721.