Define an Osmotically Active Substance. Part of the series: Chemistry & Biology. An osmotically active substance is best understood by learning that osmosis is the movement of water from areas of high concentration to areas of low concentration. Find out how osmotically active substances cause osmosis to occur with help from a science teacher and field biologist in this free video on chemistry. Read more: http://www.ehow.com/video_4801934_define-osmotically-active-substance.html
