When protons accumulate on one side of the membrane and then flow back across the membrane through ATP synthase it is called
a. chemiosmosis
b. electron transport chain
c. charge separation
d. primary photo-event
From Google:
Chemiosmosis is the movement of ions across a semipermeable membrane, down their electrochemical gradient. An example of this would be the generation of adenosine triphosphate (ATP) by the movement of hydrogen ions (H+) across a membrane during cellular respiration or photosynthesis.