●① lipid soluble diffusion( simple diffusion) o The nonionized molecules are usually lipid soluble and can diffuse across the cell membrane 2 Filtration through pores o Hydrophilic lipid-insoluble substances can cross membranes through water-filled pores ●③ Passive facilitated diffusion o This flows the concentration gradient but dose not obey simple diffusion lows. It is believed to involve a carrier mechanism⚫ ① lipid soluble diffusion (simple diffusion) ⚫ The nonionized molecules are usually lipid soluble and can diffuse across the cell membrane. ⚫ ② Filtration through pores ⚫ Hydrophilic lipid-insoluble substances can cross membranes through water-filled pores. ⚫ ③ Passive facilitated diffusion ⚫ This flows the concentration gradient but dose not obey simple diffusion lows. It is believed to involve a carrier mechanism