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.
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