Proton motive force (PMF) is the energy generated by the movement of protons (H⁺ ions) across a membrane, creating a gradient. This gradient results in a difference in both concentration and electrical charge, which can be harnessed by cells to perform work, such as synthesizing adenosine triphosphate (ATP) through ATP synthase. In cellular respiration and photosynthesis, PMF plays a crucial role. In mitochondria, for example, electrons move through the electron transport chain, pumping protons into the intermembrane space. This process establishes the PMF, which drives protons back into the matrix, ultimately producing ATP, the energy currency of the cell.