Diffusion and Osmosis are key biological processes. The tendency of molecules to move from areas of more molecular concentration to areas of less, is called diffusion. The tendency is seen in experiments of liquid, gas, and solid diffusion, until equilibrium is attained. An animated simulation explains what is happening at the molecular level. Osmosis experiments involve single and multi-cellular animals and their semi-permeable membranes. The charge and size of molecules is critical for allowing only the desired molecules to pass through semi-permeable membranes. Plants depend on their environment for the proper amount of water diffusing into their cells in order to maintain a viable internal pressure called turgor. As long as the concentration of solutes (organic and inorganic compounds) remains greater inside a cell than outside, water diffuses into a cell through its membrane to equalize the internal and external concentrations, and the cell retains turgor. When the reverse happens, water flows out of the cell, and the plant wilts.

Originally released by Benchmark Media, 2000. Streaming video file encoded with permission for digital streaming by Infobase on April 30, 2015.

Diffusion (5:13); --Rate of Diffusion and Molecular Mass (5:30); -- Osmosis in Animal Cells (5:15).