Final answer:
In chemiosmosis, the energy-requiring process is the synthesis of ATP, facilitated by the flow of hydrogen ions through ATP synthase, powered by an electrochemical gradient.
Step-by-step explanation:
The process in chemiosmosis that requires energy is the synthesis of ATP. This occurs when hydrogen ions (H+ ions) flow through a protein complex known as the ATP synthase complex. ATP synthase serves a dual function as it acts as a channel protein aiding the flow of H+ ions across the membrane and also as an enzyme catalyzing the formation of ATP from ADP and inorganic phosphate.
This is driven by the electrochemical gradient established by the proton pump of the electron transport chain (ETC), which uses the free energy from redox reactions to concentrate H+ ions on one side of the membrane. The potential energy from this gradient then powers ATP synthase to synthesize ATP, as the H+ ions diffuse back across the membrane into the matrix.