What is it?

Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration.

external image c8.7x11.diffusion.jpg external image 46667745.CRW_055401.jpg

Why is it needed by the cell?

Molecules move from an area from where there is a high concentration to an area where there is a low concentration. This occurs until equilibrium is reach. After equilibrium is reached, molecules still move randomly.

What types of molecules move through the membrane this way?

Molecules that are able to diffuse through the cell membrane include water molecules, oxygen, carbon dioxide, and other uncharged molecules.

Factors that determine the speed of diffusion:
  • Steepness of the concentration gradient
  • temperature
  • size of the molecule
  • charge of the molecule

Visual Aids

How diffusion works video

amimation of diffusion


"Dye in Water." Charles Jones photos at pbase.com. Web. 11 Oct 2010. http://www.pbase.com/charlesj68/image/46667745
"Diffusion." Unit 4 - Correia Life Science. Web. 11 Oct 2010. http://www.bio.miami.edu/~cmallery/150/memb/c8.7x11.diffusion.jpg