Cohesion

Definition

Cohesion is the property of water molecules that allows them to stick to each other due to hydrogen bonding. This unique characteristic plays a critical role in various biological processes, including the transport of water in plants and the maintenance of cell structure. Cohesion helps create surface tension, allowing small organisms to walk on water and enabling water to rise through plant capillaries against gravity.

5 Must Know Facts For Your Next Test

1. Cohesion is responsible for the high surface tension of water, allowing small insects to walk on its surface without sinking.
2. In plants, cohesion contributes to the upward movement of water through xylem vessels during transpiration.
3. Cohesion allows water to form droplets, which is crucial for processes like pollination and seed dispersal.
4. The phenomenon of capillary action, which helps draw water up from the roots to the leaves, relies on both cohesion and adhesion.
5. Cohesion also plays a role in regulating temperature in organisms since water has a high heat capacity due to its cohesive properties.

Review Questions

• How does cohesion contribute to the transport of water in plants?
  • Cohesion helps facilitate the transport of water in plants by allowing water molecules to stick together as they move through xylem vessels. When water evaporates from the leaves during transpiration, it creates a negative pressure that pulls more water upward from the roots. This continuous column of water is maintained because of cohesive forces between water molecules, which prevents them from breaking apart as they travel against gravity.
• Discuss how cohesion interacts with adhesion in biological systems.
  • Cohesion and adhesion work together in biological systems to enable processes such as capillary action. While cohesion allows water molecules to stick to each other, adhesion enables them to cling to other surfaces, such as the walls of plant xylem vessels. This combination allows water to move upward through narrow tubes against gravity, essential for transporting nutrients and maintaining hydration in plants. The balance between these two forces is crucial for many physiological processes.
• Evaluate the importance of cohesion in maintaining homeostasis within living organisms.
  • Cohesion is vital for maintaining homeostasis in living organisms by regulating temperature and facilitating nutrient transport. The high heat capacity of water due to cohesion helps stabilize internal temperatures within cells and tissues, preventing drastic fluctuations that could harm biological functions. Additionally, the cohesive properties allow efficient movement of water and dissolved substances within organisms, ensuring that essential nutrients reach all parts effectively. Thus, cohesion plays a key role in sustaining life by supporting the physical and chemical processes necessary for homeostasis.

Related terms

adhesion:

The tendency of water molecules to stick to other substances, which is important for processes like capillary action.

hydrogen bond: A weak bond formed between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom, crucial for the properties of water.

surface tension: The elastic-like force existing at the surface of a liquid that makes it behave like a stretched membrane, influenced by cohesion.