Surface Tension

Definition

Surface tension is the property of a liquid's surface that allows it to resist an external force due to the cohesive nature of its molecules. This phenomenon occurs because molecules at the surface experience an imbalance of intermolecular forces, resulting in a tight 'film' that can support small objects or droplets. The significance of surface tension in biological contexts includes its role in processes such as nutrient absorption and the behavior of cells in water.

5 Must Know Facts For Your Next Test

1. Surface tension is measured in force per unit length, commonly expressed in dynes per centimeter (dyne/cm).
2. In water, surface tension is notably high due to strong hydrogen bonding between water molecules.
3. Surface tension is crucial for the formation of droplets, allowing them to maintain a spherical shape.
4. Biological systems rely on surface tension for processes such as the movement of water through plant xylem and the stability of alveoli in the lungs.
5. Surfactants are substances that reduce surface tension and are often used in detergents and soaps to enhance cleaning by breaking down barriers between water and oils.

Review Questions

• How does surface tension affect the movement of water in plants?
  • Surface tension plays a key role in the movement of water within plants, particularly through structures called xylem vessels. The cohesive properties of water molecules allow them to stick together, creating a continuous column that can resist breaking. This cohesion, combined with surface tension, helps facilitate the upward movement of water from roots to leaves, enabling essential processes like photosynthesis and nutrient transport.
• Compare and contrast the effects of cohesion and adhesion on surface tension.
  • Cohesion refers to the attraction between similar molecules, which contributes to surface tension by creating a tight 'film' on the liquid's surface. In contrast, adhesion is the attraction between different types of molecules and can influence how liquids interact with surfaces. Together, these forces determine how liquids behave at interfaces; while cohesion promotes the integrity of the liquid's surface, adhesion can lead to phenomena such as capillary action, where liquid can rise against gravity in narrow spaces.
• Evaluate the significance of surfactants in biological systems regarding surface tension.
  • Surfactants play an essential role in managing surface tension in biological systems. By reducing surface tension, surfactants ensure that alveoli in the lungs remain open during gas exchange, preventing them from collapsing. Additionally, surfactants are critical in various cellular processes where they aid in transporting nutrients and waste products by modifying the interactions between fluids and cell membranes. Their ability to lower surface tension is vital for maintaining homeostasis and supporting life processes.

Related terms

Cohesion:

The attraction between molecules of the same substance, which contributes to surface tension by causing liquid molecules to stick together.

Adhesion: The attraction between molecules of different substances, which plays a role in how liquids interact with surfaces, affecting things like capillary action.

Capillary Action:

The ability of a liquid to flow in narrow spaces without the assistance of external forces, largely influenced by surface tension and adhesion.