Membrane Diffusion & Osmosis

Fick's Law — Particle diffusion across semipermeable membrane

Controls

J = −D·∇C (Fick's first law)
Particles cross membrane only at channel positions.
Osmotic pressure: net flow down gradient.
Goldman equation: V_m = (RT/F)·ln(Σ Pk·[X]out / Σ Pk·[X]in)