Passive Transport

Passive Transport

1. DIFFUSION

   • small nonpolar molecules move through the hydrophobic region of the phospholipid bilayer
     • CO2
     • O2
     • H20
       • OSMOSIS
       • Slow
       • small amounts of H2O only
     • glycerol
     • ethanol
     • N2
   • uses kinetic energy of molecules
   • only effective over very small distances
   • moves molecules to reach an equilibrium
     • At equilibrium movement of molecules occurs but there is no net change

2. FACILITATED DIFFUSION

   • Requires a transmembrane protein that spans the phospholipid bilayer
     • CHANNEL PROTEINS
       • Aquaporins
         • Rapid movement of H2O
       • Ion channels
         • charged ions
           • Chlorine Cl-
           • Sodium Na+
           • Potassium K+
           • Calcium Ca2+
           • Hydrogen Ion H+
       • forms hydrophilic pore
     • CARRIER PROTEIN
       • Glucose transport into the cell
         • Uses Symport with Na+ and glucose
       • binds to a specific molecule
       • undergo a change in conformation
   • polar molecules
   • ions, amino acids, nucleoside, carbohydrates

3. does not require ATP

4. moves molecules along a concentration gradient from areas of high concentration to areas of low concetration

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