Free radicals

Free radicals are atoms, molecules, or ions with at least one unpaired electron, which makes them typically very reactive. Some of them are reactive oxygen species, but not every reactive oxygen species is a free radical—hydrogen peroxide, for example, is not. In small amounts, they participate in signaling processes, while an excess of them leads to oxidative stress and cell damage. Plants limit their effects using enzymes and antioxidants, including vitamin C and carotenoids.