There are lots of transitional organisms in the fossil record though it does take very specific and precise conditions for a fossil to be preserved, a deer that dies in a field will not end up in the fossil record so we are looking at a small sampling of the evidence (and a good thing too or there wouldn't be anywhere to walk with all the bones laying around)
Answer: Protons contribute towards making ATP by producing proton-motive force that provides energy for ATP synthesis.
Explanation: In the respiratory chain, the transfer of electrons from one complex to another is accompanied by pumping of protons out of the matrix. This creates a difference in proton concentration and separation of charge across the mitochondrial inner membrane. The electrochemical energy inherent in this difference in proton concentration called proton-motive force is used to drive ATP synthesis as protons flow back passively into the matrix through a proton pore.
