Question

Explain why the evaporation of water from leaves lowers their temperature.

Short answer

The temperature of leaves decreases due to evaporation. It is due to alteration in kinetic energy of water molecules. The reduction in the average kinetic energy of the liquid from leaves lowers their temperature.

Step-by-step solution

Evaporation in plants

Evaporation is the event by which water from the substance is transformed into a gaseous state. In plants, evaporation is termed transpiration. It results in upward conduction of water through xylem vessels. Transpiration also results in the loss of water from plants through stomata.

Effect of evaporation in plants

In plants, evaporation of water from the leaves lowers their temperature. In leaves, water molecules move at different speeds. When they gain energy from the environment, they gain more kinetic energy and exit from leaves in the form of gas (called evaporation).

When molecules leave the liquid, average kinetic energy decreases. Thus, the temperature drops due to the reduction in the kinetic energy of molecules of the liquid.

Reason for lower temperature of plants due to evaporation

When water molecules of leaves gain energy from sunlight, their kinetic energy (motion) will also increase. Due to sufficient kinetic energy, molecules leave the liquid in the form of a gaseous state.

Molecules with the greatest kinetic energy leave the liquid and reduce the rest of the molecules in a liquid. As the temperature is directly proportional to average kinetic energy, the temperature decreases with a decrease in kinetic energy due to evaporation.