Question

“Transpiration is a necessary evil .” Explain.

Answer 1

Hint: Transpiration is defined as the loss of water in the form of water vapors from the aerial parts of a plant including leaves and stem. A very high amount of water is lost by transpiration.

Complete answer: The process of transpiration occurs through different ways.
These are –
1. Cuticular transpiration: A wax-like covering on the epidermis of leaves and stems is a cuticle. The main constituent of the cuticle is cutin. This is present to preserve transpiration but soma water is transpired in the form of water vapors. By this method, about 5-10% of total transpiration occurs.
2. Stomatal transpiration: Stomata are specialized structures that are mainly kidney-shaped and are responsible for gaseous exchange between plants and the environment. Water is lost in vapor form through the stomata. About 90% of the total transpiration is done by this method.
3. Lenticular transpiration: Some openings are present in the bark of roots and stems are called lenticels. These are mainly present in plants of marshy areas. These also allow gaseous exchange. Loss of water through lenticels accounts for about 5-10% of the total transpiration.
It is beneficial for plants by regulating the temperature of plant tissues and is also harmful as it exerts pressure on the plant for water absorption. Thus, it is a necessary evil.
Additional information:
There are some factors that affect transpiration. These include temperature, humidity, light, transpiring area (leaf area), leaf orientation, diseases, etc.

Note: Transpiration regulates the amount of water in plants. Transpiration is different from the simple evaporation process because transpiration is affected by certain internal conditions of plants and is a comparatively slower process than evaporation.