∞ generated and posted on 2016.01.26 ∞
Gain of an electron.
Electrons can be gained by atoms either in full or in part. When electron carriers such as NAD+ and FAD carry electrons, they are said to be in a reduced form, i.e., NADH or FADH2 (each carrying two extra electrons).
When hydrogens are added to carbon-containing compounds, such that C-H bonds are formed, the resulting compounds can be said to have been reduced (where the electrons forming those bonds are held closer to the C and H than they are held by those same atoms in C-O or H-O bonds). See by contrast oxidation.
Reducing electrons in biological systems often are energetic electrons, though much less so when oxygen or nitrogen are what is being reduced. Compounds which are reduced, such as fats, glucose, or electron-rich minerals, can serve as important sources of energy for organisms.
When a substance is reduced it has gained electrons. When oxygen or other oxidizing agents steal electrons, they in turn are reduced. When oxygen serves as a final electron acceptor it is reduced in the process, in this case forming the reduced molecule, H2O, i.e., water.