Channel proteins transport water and certain ions down either a concentration gradient, in the case of water, or an electric potential gradient in the case of certain ions, from an area of higher concentration to lower concentration. While water molecules can directly cross the membrane by passive diffusion, as mentioned above, their transport can be enhanced by channel proteins called aquaporins.

Flash animation of Transport of Substances Across a Membrane by Channel Proteins.swf by Gary E. Kaiser, Ph.D.
Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus
This work is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work at http://faculty.ccbcmd.edu/~gkaiser/index.html.

Last updated: Feb., 2018
Please send comments and inquiries to Dr. Gary Kaiser