Which term refers to the driving force behind ATP synthesis due to a higher concentration of protons outside the mitochondria's inner membrane?

The term that refers to the driving force behind ATP synthesis due to a higher concentration of protons outside the mitochondria's inner membrane is the proton gradient. This gradient arises when protons (H⁺ ions) are actively transported from the mitochondrial matrix into the intermembrane space during cellular respiration, creating a difference in concentration.

This difference in proton concentration creates potential energy, analogous to water stored behind a dam. As protons move back across the inner mitochondrial membrane through ATP synthase—a protein complex—they drive the conversion of adenosine diphosphate (ADP) and inorganic phosphate into adenosine triphosphate (ATP), the energy currency of the cell.

Understanding the role of the proton gradient is crucial in cellular respiration and energy production, highlighting how essential it is for ATP synthesis. The other terms, while related to biological processes, do not specifically describe this mechanism: cohesion pertains to the attraction between molecules of the same substance, solute refers to a substance dissolved in a solution, and enzyme denotes proteins that catalyze biochemical reactions, none of which are directly linked to the proton gradient's role in ATP synthesis.