Question

fter thoroughly reviewing the physical process of capillary action and surface tension and viscosity, write a thoughtful, complete, but concise response to the following: Explain how capillary action is used to transport water and nutrients in trees. Explain how surface tension and viscosity are used to transport water and nutrients in trees.

Answer 1

Capillary action is defined as the movement of water within the spaes of a porous material due to the forces of adhesion, cohesion, and surface tension. 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.

The cohesion of water molecules to each other relative to the much less polar N₂ and O₂ of air or other surfaces leads to the property called surface tension. This property is responsible for the beading-up of water on leaf epidermal waxes. The drop rounds up because of its cohesiveness and the lack of adhesion to the non-polar wax allows the drop to roll off of the leaf and to drip off, onto the soil below the leaf. This of course provides the water for the root to take up nutrients, and to cool that leaf ultimately by evaporative cooling.