Cohesion

Definition

Cohesion is the property of water molecules that allows them to stick to one another due to hydrogen bonding. This characteristic plays a vital role in creating surface tension and is crucial for various biological processes, such as water transport in plants and the behavior of liquid water in general. Cohesion not only affects how water behaves as a liquid but also influences its interactions with other substances, making it a fundamental concept in understanding both molecular interactions and the properties of water that are essential for life.

5 Must Know Facts For Your Next Test

1. Cohesion leads to high surface tension in water, allowing small objects, like insects, to rest on the surface without sinking.
2. The strength of cohesion in water is due to the presence of hydrogen bonds, which are relatively strong compared to other types of intermolecular forces.
3. Cohesion is essential for the process of transpiration in plants, where water moves up through the xylem due to cohesive forces between water molecules.
4. The cohesive properties of water contribute to its unique density characteristics, such as ice being less dense than liquid water, allowing it to float.
5. Cohesion also plays a critical role in the formation of water droplets, as molecules pull together to minimize surface area.

Review Questions

• How does cohesion contribute to the movement of water in plants?
  • Cohesion allows water molecules to stick together, which is crucial for the process known as transpiration. As water evaporates from the leaves, it creates a negative pressure that pulls more water upward from the roots through the xylem. This continuous column of water relies on cohesive forces, allowing plants to efficiently transport nutrients and maintain hydration.
• Compare and contrast cohesion and adhesion and explain their significance in biological systems.
  • Cohesion is the attraction between like molecules, while adhesion is the attraction between unlike molecules. Both properties are significant in biological systems because they influence how water interacts with plant cells and other surfaces. For example, adhesion helps water move against gravity when it clings to cell walls during capillary action, while cohesion contributes to surface tension, which supports small organisms on water surfaces.
• Evaluate how the cohesive properties of water affect ecological systems and biodiversity.
  • The cohesive properties of water play a pivotal role in shaping ecological systems by influencing various processes such as nutrient transport and habitat formation. For instance, high surface tension enables certain aquatic insects and organisms to thrive on the surface of ponds and lakes, contributing to biodiversity. Additionally, the ability of plants to efficiently transport water through cohesion not only supports their growth but also affects local ecosystems by regulating moisture levels and influencing species distribution.

Related terms

Hydrogen Bonding: A type of weak chemical bond that forms when a hydrogen atom covalently bonded to an electronegative atom experiences attraction to another electronegative atom.

Adhesion:

The tendency of water molecules to cling to other substances, which works in conjunction with cohesion to influence water's behavior in various environments.

Surface Tension:

The elastic tendency of a fluid surface that makes it acquire the least surface area possible, largely due to cohesive forces among liquid molecules.