Water Potential (4)

The extensive hydrogen bonding in water gives a new property known as cohesion, the mutual attraction between molecules. A related property, called adhesion, is the attraction of water to a solid phase, such as cell wall. The water molecules are highly cohesive. One consequence of cohesion is that water has exceptionally high surface tension, which is the energy required to increase the surface area of a gas-liquid interface. Surface tension and adhesion at the evaporative surfaces in leaves generate the physical forces that pull water through the plant’s vascular system. Cohesion, adhesion and surface tension give rise to a phenomenon known as capillarity. These combined properties of water help to explain why water rises in capillary tubes and are exceptionally important in maintaining the continuity of water columns in plants.