Protons in Cellular Respiration

[jellyksong]

Where do the protons in oxidative phosphorylation come from?
(The proton gradient is formed to make ATP through ATP synthase)
I know in plants the proton gradient is made by splitting water (hydrogen specifically).
Does it come from NADH & FADH2 in this case?

Originally I thought that they only provided the electrons for the ETC, but it not them, then where else can the electrons come from? This was unclear in my Barron's AP Bio book.

Thanks!

[JackBean]

The protons are there all the time, the water is autohydrolyzed.
And the electrons are from the molecules, which you oxidize of course.