So anytime the copper in this diagram abstracts an electron, it binds an electron, it is reduced. So it goes from its oxidized form to its reduced form. And this is exactly what happens in this diagram when this copper B gains an electron. And it also happens when this copper A gains an electron. Now, notice in the diagram we actually have two of these cytochrome C molecules in their reduced form. And that's because what happens is first a single cytochrome binds onto this section, giving off an electron.