The Cell Membrane A. Fluid-Mosaic Model – a semi- permeable membrane composed of a phospholipid bilayer with embedded proteins

1. Phospholipid bilayer

II. Molecules move constantly, randomly and away from each other A II. Molecules move constantly, randomly and away from each other A. Speed depends on temperature and size of molecules

B. Concentration gradient – difference in concentration of a type of B. Concentration gradient – difference in concentration of a type of molecule in two adjacent areas C. Equilibrium – molecules evenly dispersed (no concentration gradient)

Passive Transport – does NOT require energy A. Diffusion – net movement of molecules from an area of high concentration to an area of low concentration 1. Down/along the concentration gradient until equilibrium is reached http://www.youtube.com/watch?v=H7QsDs8ZRMI

Osmosis – the diffusion of water across a semi-permeable membrane. 1. If membrane is not permeable to solute, water will move to try to even out the concentration of the solute on either side of the membrane

Facilitated Diffusion 1. Most molecules cannot pass through lipid bilayer by diffusion (too big, polar) 2. Use membrane proteins

Active Transport Requires energy – move molecules from low concentration to high concentration (against concentration gradient) Requires membrane proteins

Endocytosis and Exocytosis A. Transport groups of molecules B. Also requires energy Exocytosis