Transport in Plants — BIOLOGY STD 11 Science — Question

1. Cohesion: Mutual attraction between water molecules is called cohesion.
2. Adhesion: Attraction of water molecules to polar surfaces is called adhesion.
3. Surface Tension: Water molecules are attracted to each other in the liquid phase more than to water in the gas phase. This gives a liquid an ability to acquire the least possible area and explains the spherical shape of raindrops.

These properties give water high tensile strength, i.e., an ability to resist a pulling force, and high capillarity, i.e., the ability to rise in thin tubes. In plants capillarity is aided by the small diameter of the tracheary elements- the tracheids and vessel elements.