Question

Transpiration is a necessary evil . Explain

Answer 1

The loss of excees water in the form of vapor from the aerial parts of the plant is known as transpiration. Transpiration is essential for the movement of water and minerals from the root to the healthy parts of the plant. But excess transpiration may result in drying up of the leaves or wilting and loss of soil water. Hence it is termed as a necessary evil.

Answer 2

Transpiration is the process by which plant lose water through the stomata. 
It is considered as an evil because excessive loss of water tend to hamper with the photosynthetic process of plants by closing the stomatas.