Advanced Placement (AP) Biology Practice Exam

Which phenomenon describes the way water molecules stick to each other?

1. Cohesion

2. Adhesion

3. Hydrophilicity

4. Solvation

The correct answer is: Cohesion

Cohesion refers to the intermolecular forces that hold water molecules together due to hydrogen bonding. This property allows water molecules to be attracted to one another, resulting in phenomena such as surface tension, where the surface of the water behaves like a stretched elastic membrane. This molecule-to-molecule attraction is significant in various biological processes, including the transport of water in plants during transpiration and the formation of water droplets. Understanding cohesion is particularly important in studying water's unique properties, such as its high boiling and melting points compared to other similar substances, which directly impact life on Earth. The strong cohesive forces also contribute to the formation of structures like water beads, emphasizing the role of cohesion in influencing the behavior of water in different environments.