Q1.  Why is transpiration called a necessary evil?

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.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 a necessary evil.