Diffusion in membranes

Abstract

Nature is always in motion. As simple as it is, this statement is true in the sense that numerous phenomena in living systems are characterized by nonequilibrium. Our muscles are in constant need of energy provided by the metabolic pathway, the blood flows in our veins as long as the heart keeps going, and yet old cells are constantly being replaced by fresh ones as a typical life time of a cell is on the order of one day. The state of living beings can therefore only rarely be described by equilibrium. However, even if a true equilibrium were possible in living systems, we would find spontaneous thermal fluctuations to occur around the equilibrium state, again implying that the matter were moving in time.