Passive transport(downhill transport) Active transport (uphill transport) Electrochemical potential Eloctrochemical polential High gradient of the substrate Low High gradient of the s边strate Passive diffusion ©.Symport Secondary active transport ○Antiport Facilitated diffusion ATP Primary active transport ADP Figure 2-4.Classification of membrane transport mechanisms.Light blue circles depict the substrate.Size of the circles is proportional to the concentration of the substrate.Arrows show the direction of flux.Black squares represent the ion that supplies the driving force for transport(size is proportional to the concentration of the ion).Dark blue ovals depict transport proteins. 人凤只生公版松