ATP synthase is the enzyme that

• A. Enzyme that splits water
• B. Enzyme that creates ATP
• C. Carrier that shuttles electrons
• D. Protein that transports protons without making ATP

Answer: (B)

The main idea is that ATP synthase uses a proton gradient to drive the production of ATP. Protons flowing down their gradient through the enzyme’s Fo portion cause a rotor to turn. That rotation induces conformational changes in the F1 catalytic sites, enabling ADP and inorganic phosphate to be joined into ATP. This is how cells harvest energy from gradients created by cellular respiration or photosynthesis.

So, ATP synthase is the enzyme that creates ATP. It’s not the enzyme that splits water, not a carrier that shuttles electrons, and not merely a proton transporter without making ATP (although it does conduct protons, its essential role under normal conditions is ATP synthesis).