And because these harmful byproduct molecules are actually oxygen derivative molecules we call them reactive oxygen species. Now, before we actually talk about these molecules in slightly more detail let's remember what happens on the normal conditions in complex four of the electron transport chain. So, remember, the entire point of the electron transport chain is to actually take those high energy electrons produced by creating the NADH molecules and fadh two molecules and using those electrons to create a proton gradient. And the final accept of electrons is diatomic oxygen. And in complex four of the electron transport chain a total of four electrons and four protons are combined into diatomic oxygen to completely reduce that diatomic oxygen into water molecules. And water molecules are harmless to the cell.