Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. The molecules can be atomic, and go right through the selectively permiable/semiperiable membrane. Diffusion uses no cellular energy because it is a passive transport.

Movement of molecules is accomplished due to kinetic energy of the molecules.

Diffusion continues until the molecules are evenly distrubuted throughout the space - equilibrium. Molecules continue to move randomly during equilibrium.

Examples of molecules that move through the cell memebrane this way are: oxygen, nitrogen, water and carbon dioxide.

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"Diffusion." Psychology Wiki. Web. 17 Jan. 2011. http://psychology.wikia.com/wiki/Diffusion.

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"GRAPHICS." Indiana University. Web. 17 Jan. 2011. <http://www.indiana.edu/~phys215/lecture/lecnotes/diff.html>.