No Barrier: Substances “spread out” High concentration to low concentration e.g.: Red dye placed in glass of water Passive Diffusion
Substances diffuse High concentration to low concentration Pores in membrane must be large “ Down the concentration gradient” Dynamic equilibrium, equal rates in both directions Passive Diffusion Biological membrane:
Facilitated Diffusion <ul><li>Carrier proteins: </li></ul><ul><li>Bind specific molecule & change shape </li></ul><ul><li>Pass molecule through middle of protein </li></ul>
Passive Diffusion: Osmosis <ul><li>Osmosis - diffusion of a water through a semi-permeable membrane </li></ul><ul><li>Moves down concentration gradient </li></ul>e.g. Two sugar solutions of different concentrations separated by porous membrane which lets water through but not sugar What will happen?
Passive Diffusion: Terms & Osmosis More concentrated to less concentrated Until concentration same on both sides: isotonic
Passive Diffusion: Osmosis &Terms Concentration of solute less: solution is hypotonic . Concentration of solute greater: solution is hypertonic .
Passive Diffusion: Osmosis: Outcomes to Living Cells (Animal) Animal cells No cell walls Isotonic environment: Influx of water equals the efflux of water No change in cell shape
Passive Diffusion: Osmosis: Outcomes to Living Cells (Animal) Hypertonic solution: Water leaves cell Shriveled, or crenate Hypotonic solution: Water enters cell Bursts, or lyses
Passive Transport and Facilitated Diffusion Passive transport & facilitated diffusion do NOT require ATP
Active Transport DOES require the input of Transport proteins AGAINST concentration gradient outside cell inside cell ATP
Lipid solubility Most important factor Hydrophobic molecules Passively diffuse Hydrocarbons, carbon dioxide, & oxygen
Molecular Size and Polarity Larger molecules, less permeable Lower kinetic energy Small pore sizes in the membrane Polar molecules hydrophilic, less permeable Very small, polar uncharged (water) molecules can diffuse Molecular Size Polarity - +
Charge Charged molecules hydrophilic, less permeable Surrounded by coat of water (hydration shell), increases the size