Question

How do cohesion and adhesion help plants transport water?

Answer 1

Hint: The cohesion and adhesion forces present between the water molecules helps in the transportation of water in the plants. The surface tension present between the water molecules helps in their movement.

Complete answer:
The tendency of the liquid or fluid surfaces to shrink into a minimum surface area and resist the external forces is called the Surface tension of that liquid. Surface tension is the property of the surface of the liquid. It arises due to an imbalance of the intermolecular forces from all directions- in a bulk medium. The attraction between the water molecules at the liquid surface is not balanced, and a net force is present in a particular direction.

The property of attraction between the molecules of the same kind is called cohesion, and the forces present between them are called the cohesive forces. Whereas, the property of attraction between the molecules of two different kinds is called adhesion, and the forces present between them are called adhesive forces. The cohesive forces present between the water molecules keeps them together and provides stability to them. The adhesive forces help the water molecules to stick to other surfaces like glasses, leaves, or any other plant surfaces. The water molecules stick to these surfaces and thus do not runoff. These two forces together aid in the process of surface tension by maintaining a balance between the water molecules and outside surfaces and the environment.
Water has a high degree of surface tension amongst its molecules- due to the presence of hydrogen bonding in them. The surface tension of water impacts living things and has major applications in the living world.

The phenomenon of surface tension and the cohesive and adhesive forces present between the water molecules helps in the transportation of water in the plants. The surface tension between the water molecules on the surface of the plant and the water molecules below them creates a pull on the water column. This pull is responsible for the transport of water from the roots to their leaves. The adhesive forces stick the water droplets on the surface of leaves and prevent them from evaporating into the atmosphere. The movement of water molecules in the plant body is due to the adhesive forces between the water molecules and surfaces of the root and stems. The cohesive forces present between the water molecules hold them together and ease up their transportation.

Note: The process of movement of water in the plants and its evaporation through the surface of leaves is called transpiration. The transpirational pull is caused due to the evaporation of water from the leaves and helps in the upward movements of water in the plants.