The sodium-potassium pump in cell membranes is powered directly by:

1. Sodium is concentrated outside cells and potassium inside cells, against their natural diffusion gradients. 2. Maintaining a gradient against diffusion requires active transport, which consumes energy. 3. The sodium-potassium pump uses energy supplied by ATP. 4. Therefore ATP, not passive forces, powers the pump. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 26 "Fluid, Electrolyte, and Acid-Base Balance", p.1251 §Body Fluids and Fluid Compartments_