∞ generated and posted on 2016.01.19 ∞
Movement of substances from high to low concentrations via random motion.
Simple diffusion, a.k.a., or , gives rise to substance movement down concentration gradients. This includes movement across lipid bilayers via diffusion directly across the lipid component (i.e., the membrane interior).
Contrast facilitated diffusion as well as various forms of active transport across membranes.