Give an example of water's cohesive nature playing a role in a biological process

Water molecules are continuously interacting with one another through hydrogen bonds. These hydrogen bonds are what hold water together. It is referred to as cohesion.

Cohesion plays a major role in water and dissolved nutrients having the ability to be transported up a tree, against gravity. Simply, the transport of water occurs when water on an upper leaf evaporates, it pulls the water below it and all water molecules down to the roots are gradually pulled up.