OSMOSIS
    Osmosis is the process by which water molecules diffuse across a membrane from an area of greater concentration to an area of lesser concentration.  The direction in which the water molecules move are related to it's environment.  A solution can either have a hypotonic environment or a hypertonic environment.  Hypotonic environment is an environment in which the concentration is lower inside the solution than in the environment outside the solution.  Therefore water will move into the cell until equilibrium is established.  Hypertonic environment is one in which the concentration of the solute molecules outside the cell is higher than the inside.  In this situation water will diffuse out of the cell until equilbrium is met.  A solution can also be isotonic to it's environment, this means water will diffuse in and out of the cell at equal rates.

CARRIER TRANSPORT
    There are two types of carrier transport, facilitated diffusion and active transport.  The proteins located in the cell membrane that aid in the transport of molecules across the membrane are called carrier molecules.  These proteins are also known as permeases.  Usually a carrier molecule is specialized for just one type of molecule movement.
    Facilitated diffusion is a passive form of transport, that is it moves the molecule without expending energy.  This is often used to speed up diffusion for large molecules such as glucose.
    A common form of active transport is the sodium-potassium pump.  This is a chemical mechanism that moves sodium ions (Na+) out of the cell and forces potassium ions (K+) in.   This kind of transport is against the concentration gradient so it uses energy.

GATED CHANNELS
    A gated channel is another form of passive transport.  This occurs when proteins form a passageway across the lipid membrane.  A gated channel by definition is a protein-controlled passage that permits the cell membrane to be permeable as needed.  Some of these passageways are permanently open for molecules that cannot diffuse through the membrane by any other means.  Other gated channels only form due to a change or signal of the environment.

ENDOCYTOSIS AND EXOCYTOSIS
    Endocytosis is the process by which cells take in substances that are too large to enter the cell through any kind of transport.  The material is enclosed by a portion of the cell, which folds into itself and forms a pouch. The pouch then pinches off from the cell membrane and enters the cytoplasm.  The contents are then digested by cellular enzymes.  Exocytosis is the process by which large particles leave the cell.  After the Golgi apparatus has produced a vesicle it fuses with the cell membrane and dumps it's contents outside the cell.