Final answer:
Hydrogen ions activate ATP synthase by moving from high to low concentration areas through a process called chemiosmosis, which allows ATP synthesis.
Step-by-step explanation:
Hydrogen ions activate the enzyme ATP synthase by moving from an area of high concentration to an area of low concentration during a process called chemiosmosis. This movement occurs in the mitochondria of eukaryotic cells, where hydrogen ions flow from the intermembrane space to the mitochondrial matrix, or in chloroplasts during photosynthesis, where the flow is from the thylakoid space to the stroma. These ions diffuse through the inner membrane through a specialized protein channel embedded within ATP synthase. As hydrogen ions pass through ATP synthase, their electrochemical potential energy is converted into mechanical energy, which ATP synthase harnesses to synthesize ATP from ADP and an inorganic phosphate (Pi), in a mechanism similar to a hydroelectric dam generating electricity.