Fick's law gives the rate of transpo in case of

Fick's law is used to calculate the rate of simple diffusionSimple diffusion means that kinetic movement of molecules or ions occurs through a membrane opening or through intermolecular spaces without any interaction with carrier proteins in the membrane. The rate of diffusion is determined by the amount of substance available, the velocity of kinetic motion, and the number and sizes of openings in the membrane through which the molecules or ions can move.Ref: Guyton; 13th edition; Chapter 4; Transpo of Substances Through Cell Membranes