Definition

• Adhesion is the clinging of one substance to another through intermolecular forces. You see adhesion in action whenever you use glue on a project or a hook-and-loop fastener on a shoe, or observe an ant scaling a wall. In terms of water properties, adhesion is the bonding of a water molecule to another substance. This is similar to cohesion, which is the bonding of water molecules to each other. Water's adhesive property arises from the attraction of its slightly positive hydrogen to other slightly negative molecules.
  
  

How It Works

• Both adhesion and cohesion in water are made possible by positively charged hydrogen molecules bonding to negatively charged molecules. (In the case of cohesion, the hydrogen bonds to oxygen of another water molecule.) Hydrogen bonds are special in that they can break and reform with great frequency. This constant rearranging of hydrogen bonds allows a substantial percentage of all the molecules in a given sample to bond to each other (cohesion) or to another substance (adhesion), or both. This collection of hydrogen bonds allows for the tight binding of the substances and makes the molecules cling together.
  
  

Capillary Action

• Capillary action is the ability of a liquid to flow against gravity in a narrow space. An example of this is when you place a straw into a glass of water. The water seems to "climb" up the straw before you even place your mouth on the straw. The water has created hydrogen bonds with the surface of the straw, causing the water and straw to adhere. As the hydrogen bonds keep interchanging with the straw's surface, the water molecules interchange positions and some begin to ascend the straw.
  
  

In Plants

• Adhesion and capillary action are necessary to the survival of most organisms. The most common example is of water transport in plants. The water molecules adhere to the cellulose molecules in the walls of the xylem, the tissue that conducts water and nutrients in vascular plants. As water molecules are removed by transpiration in the leaves, the next water molecule moves upward to take its place, pulling the stream of molecules continuously along the stem/trunk and nourishing the plant.