Diffusion Diffusion – net movement of molecules from high [ ] to low [ ] [ ] = concentration Goal of diffusion: equilibrium Equilibrium – even distribution Diffusion Passive Transport Facilitated diffusion – transport proteins in the membrane provide pathways for molecules to pass Ex: ions, polar molecules Osmosis Osmosis – passive transport of water across a selectively permeable membrane May cause shape and size of cells to change Osmosis Hypertonic solution: solution outside cell has a higher concentration of solute Osmosis Hypotonic solution: solution outside cell has lower solute [ ] Water flows into cell Hypo; flow Cell will swell/grow May eventually burst Osmosis Isotonic solution: solutions with equal concentrations of solute Osmosis Water balance is important Hypertonic and hypotonic solutions will cause damage to cells Why can’t a freshwater fish live in the ocean? Challenge Question What type of solution is present when a plant wilts? What type of solution should be provided to a wilting plant to help it become rigid again? energy Large Molecule Transport Endocytosis – moves materials into a cell Endo = into Uses a vesicle, or membrane-bound transport sac Requires energy