TYPES OF CELLULAR TRANSPORT

• The spread of  particles through random motion from regions of higher concentration to regions of lower concentration.
• The concept of diffusion is tied to that of mass transfer driven by a concentration gradient, but diffusion can still occur when there is no concentration gradient.

OSMOSIS:
the movement of water through a semipermeable membrane.

•  Osmosis does not create energy, it does release kinetic energy and can be made to do work, but is a passive process, like diffusion. Net movement of solvent is from the less-concentrated (hypotonic) to the more-concentrated (hypertonic) solution, which tends to reduce the difference in concentrations.
• Osmosis is of great importance in biological processes where the solvent is water. The transport of water and other molecules across biological membranes is essential to many processes in living organisms. The energy which drives the process is usually discussed in terms of osmotic pressure.

FACILITATED DIFFUSION :
the diffusion of a substance  across  membrane. It is "facilitated" because a transport protein in the membrane enhances the transport of the substance across the membrane.

Facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane integral proteins.
The facilitated diffusion may occur either across biological membranes or through aqueous compartments of an organism.
The transport proteins responsible for this function are referred to as facilitative transporters or uniporters, examples of which include the ubiquitous glucose transporters (GLUT family), a variety of amino acid transporters, facilitative urea transporters.

Facilitated transporters mediate the transport of membrane-impermeant solutes down a concentration gradient across biological membranes. Facilitated diffusion is a form of passive transport and, therefore, the direction of transport is always down a concentration gradient.

Active Transport:
When cells must move materials in an opposite direction - against a concentration gradient. It requires Energy in the form of ATP.
Proteins or Pumps are found in the cell membrane transport molecules across the membrane

Active transport is used to: 
1. Generate charge gradients. For example in the mitochondrion, hydrogen ion pumps pump hydrogen ions into the intermembrane space of the organelle as part of making ATP. 
2. Concentrate ions, minerals and nutrients inside the cell that are in low concentration outside. 
3. Keep unwanted ions or other molecules out of the cell that are able to diffuse through the cell membrane. 
In all these cases the key is that active transport uses energy to send substances against the direction they would travel by simple diffusion: that is from a region of low concentration to a region of high concentration.