Diffusion expends no energy of its own. What does a concentration gradient itself represent?

1. Diffusion expends no energy, since nothing has to be spent to let molecules spread out. 2. Concentration gradients are themselves a form of potential energy. 3. That potential energy is dissipated as the gradient is eliminated, which is why diffusion runs on its own. 4. ATP is a molecule the cell makes and spends, not something a gradient stores in the membrane. 5. Kinetic energy belongs to the moving molecules, not to the difference in their concentrations. 6. A gradient of an uncharged solute carries no electrical charge, so the last option confuses two different gradients. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 5 "Structure and Function of Plasma Membranes", section 5.2 Passive Transport_