Unit 4

 Every living cell exists in a liquid environment.  One of the functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other.  Diffusion- The movement of molecules from an area where they are more concentrated to an area where they are less concentrated.

 In solutions particles constantly and randomly move.  Concentration- The concentration of a solute in a given volume of solution. M/V (Examples: 12g/3L, 4g/1L)  Diffusion moves particles from an area where they are more concentrated (4g/1L) to areas of less concentration (2g/1L).  Diffusion depends upon random particle movements.  Substances diffuse without using energy.  Diffusion uses the concentration gradient to move particles instead of using energy.  The concentration gradient is the differences in concentrations from one area to another.

 Osmosis- The diffusion of water (and dissolved substances) through a selectively permeable membrane.  Works like diffusion (moves from higher to lower concentration, without energy)  The selectively permeable membrane lets some things pass through it (water) and not others (sugar).  Osmosis continues until the concentration on both sides of the membrane is the same (no gradient).  When this happens the two solutions are said to be Isotonic.

 Hypertonic- High concentration of particles in solution.  Hypotonic- Low concentration of particles in solution.  Isotonic- When the concentration of particles in two solutions are the same (equal).  Osmotic Pressure- Produces net movement, this is created by the pressure on the hypertonic side of the membrane.

 The diffusion of (larger) substances with the aid of protein channels.  Happens at a faster pace then regular diffusion.  Hundreds of different protein channels have been found, each is specific to the substances they move.  Even though facilitated diffusion is fast and specific via protein channels, it still requires a concentration gradient and doesn’t use energy.

 The movement of materials against the concentration gradient  Requires Energy  Generally carried out by transport proteins called protein pumps, that are found in the membrane.  The movement of large molecules or clumps of material can be done using this process.

 Endocytosis - The process of taking material into the cell by means of inner folds, or pockets in the cell membrane.  Exocytosis - The release of large molecules or material, vacuole membrane fuses with the cell membrane forcing the material out.  Phagocytosis - Process in which an extension of the cytoplasm surrounds and engulfs a particle.  Pinocytosis - The process of forming fluid filled vacuoles along the membrane.