Adhesion in biology refers to the ability of a structure or substance to stick to another of not the same kind, such as a cell binding to a substrate. Adhesion is the attraction of molecules of one kind for molecules of a different kind, and it can be quite strong for water, especially with other molecules bearing positive or negative charges. Adhesion is a surface phenomenon that is the outcome of attractive forces that bind together dissimilar or different molecules. In biology, adhesive forces can hold two surfaces together, and in cell biology, adhesion is the binding of two or more cells together or the binding of a cell to a surface through cell adhesion molecules (CAM) . Adhesion is important in many water-based processes in biology, including the movement of water to the tops of trees and the drainage of tears from tear ducts in the corners of your eyes.