Final answer:
ATP synthase acts as a channel protein, aiding the flow of protons and enabling chemiosmosis. It also functions as an enzyme, catalyzing the formation of ATP from ADP and Pi.
Step-by-step explanation:
When ATP synthase pumps H+ across a membrane against the electrochemical proton gradient, it acts as a channel protein helping the hydrogen ions across the membrane. This flow of protons through ATP synthase is known as chemiosmosis. Additionally, ATP synthase also acts as an enzyme, catalyzing the formation of ATP from ADP and inorganic phosphate (Pi).