Scientific model
Particles move by random thermal motion. Passive transport has net movement down a concentration gradient. Channels increase permeability for selected particles. Pumps use ATP to move particles against a gradient.
Particle count and molecular size are visual scales. Concentrations, transport rates and ATP use are educational approximations based on the simulated particle population.
Applications and misconceptions
Membrane transport supports nerve signals, kidney function, digestion, cell volume control and medicine delivery. Equilibrium does not mean molecules stop moving; it means movement in both directions is balanced.