Why Is Transpiration Also Known As A 'Necessary Evil'?

The loss of water in the form of vapors from aerial parts of the plant is called transpiration. Transpiration is said to be a necessary evil because it is an inevitable, but potentially harmful, consequence of the existence of wet cell surfaces form which evaporation occurs. Loss of water from the plant results wilting, serious desiccation and often death of a plant if a condition of drought is experienced. There is strong evidence that even mild water stress results in reduced growth rate and in crops to economic losses through reduction of yield.

Despite its apparent inevitability, transpiration is also of great significance for the plant.
Water is conducted in most tall plants due to transpiration pull.

Minerals dissolved in water are distributed throughout plant body by transpiration stream.
Evaporation of water from the exposed surface of cells of leaves has cooling effect on plant. Wet surface of leaf cells allow gaseous exchange.Transpiration affects indirectly the processes of respiration and photosynthesis.

The loss of excess water in the form of water vapour through evaporation from the surface of the internal tissues of the aerial parts of plants especially leaves, is known as Transpiration.

Since water is one of the most important compounds needed for various important life processes, a loss of water by transpiration is obviously harmful. This harmful effect becomes dangerous when excessive transpiration leads to the wilting of the plants. To reduce the loss of water, several practices are commonly employed by the farmers and the gardeners. One of them is to remove the weeds from the vicinity of the crop plants. These weeds transpire a lot of water and also utilize soil minerals, thus depleting the soil of its two important constituents, the water and the mineral salts.

If it is not done, the crop plants would only be stunted. To minimize the transpiration during the summer months, the green houses are whitewashed to cut down the light intensity and the temperature. Interior of the green houses is sprayed with water to saturate the atmosphere with humidity and thus decrease the transpiration. In propagation of plants by cutting or in trans-plantation of seedlings, some of the leaves are removed to reduce the transpiration and thus avoid wilting. Besides wilting, other harmful effects of excessive transpiration include inhibition of protein synthesis and breakdown of proteins and retardation of metabolic processes like photosynthesis. This is the reason why Transpiration is often called as necessary evil.

why transpiration necessary evil