Lecture Notes: Adhesion of Water to Polar or Charged Surfaces

Adhesion Overview

• Definition: Adhesion is the attraction between water molecules' polar ends and polar surfaces.
• Mechanism:
  • Water molecules form hydrogen bonds with each other.
  • Bonds occur with polar materials like membranes, containers, spiderwebs, cellulose fibers in xylem vessels, and other hydrophilic materials.

Impacts of Adhesion on Organisms

Meniscus Formation

• Aqueous Solutions: Adhesive forces between polar water molecules and glass surfaces cause meniscus formation in test tubes.
• Nonpolar Liquids: Do not form a meniscus (e.g., mercury).

Water Droplets

• On Polar Surfaces: Water forms beads on surfaces like pine needles or plant leaves due to adhesion, preventing them from falling off.

Capillary Action

• Definition: Water is drawn through narrow tubes or porous solids, such as xylem vessels, soil, paper, cellulose fibers.
• Mechanism:
  • Adhesion helps water move from underground sources through soil channels to plant roots.
  • Aids in moving water above the water table into plant roots.

Special Case: Resurrection Plants

• Example: Rose of Jericho (Selaginella lepidophylla)
  • Capillary action enables rapid rehydration through desiccated cell walls.

Plant Tissue Moisture

• Cell Walls: Made of polar/hydrophilic cellulose fibers that act like wicks.
  • Keeps plant cells moist by continuously drawing water from xylem vessels.

Seasonal Adaptation

• Xylem Refilling: Adhesion helps refill air-filled xylem vessels, crucial in spring post-winter to prevent frost damage.

Cohesion vs. Adhesion

• Cohesion:
  • Caused by hydrogen bonds between water molecules.
  • Each water molecule bonds with four others, forming a strong tetrahedral arrangement.
  • Cohesion makes water stick together, differentiating it from adhesion.

Conclusion

• Adhesion and cohesion both play critical roles in water's interaction with the environment and are fundamental to processes in plants and other organisms.