Transpiration is regarded as a ‘necessary evil’ because it has both advantages and disadvantages.
Advantages:
1. lncreases rate of water absorption and mineral absorption.
2. lncrease the rate of transport within the plant body.
3. Reduces leaf temperature resulting in a cooling effect.
4. Water is circulated within the plant body and thereby maintains cell turgidity.
5. Promotes the development of mechanical tissues.
Disadvantages:
1. lf transpiration exceeds rate of absorption it results in death due to wilting.
2. In rapid transpiration, turgor is lost and general metabolism is affected.
3. It unnecessarily uses energy and creates, water shortage which causes death by desiccation.
Unavoidable:
As long as Stomata are open the process continues
