Osmosis

Phenomenon that occurs across a barrier—for example, a cell membrane that is water-permeable but does not allow the passage of other and larger molecules, such as salts, amino acids, or sugars. The resultant imbalance is adjusted by having some of the water seep over to the side of the larger molecules. This osmotic effect corresponds to a form of pressure (osmotic pressure) that is created across the membrane. Osmosis is an essential element of a plant’s ability to draw water out of the earth into its roots and up through the trunks and stems.