This is where protons re-enter into the mitochondrial matrix.

Question

what is the term used for this HELP

Answer 1

Protons are pumped out of the mitochondrial matrix as the electrons from NADH/FADH2 (electron transporters) pass along the complexes of the electron transport chain (ETC). This builds an electrochemical gradient across the inner mitochondrial membrane (aka builds energy), which powers the ATP synthase (where ATP is made via oxidative phosphorylation in cell respiration). When the protons re-enter the mitochondrial matrix through the ATP synthase it provides the energy for the phosphorylation of ADP to form ATP.