This lecture covers the principles of diffusion in liquids, including Fick's law and the diffusion coefficient. It also discusses mixing in laminar flow conditions, the H-filter for filtration, and the nutrition of bacteria in relation to diffusion. Additionally, it explores the diffusion layer in microelectrodes, the response time of microelectrodes, liquid chromatography, and optimal flow speed for plug flow. The scaling of liquid chromatography and shear-driven liquid chromatography are also addressed, providing insights into the dynamics of microfluidics.