Question

Explain why transpiration in higher plants is considered a necessary evil.

Answer 1

Hint: The process of water movement through a plant and its evaporation from aerial parts of the plant, such as leaves, stems, and flowers is called transpiration. Water is essential for plants but only a minor amount of water taken up by the roots is utilized for growth and metabolism.

Complete answer:
Transpiration occurs through the stomatal pores and can be considered as an essential "cost" related to the opening of the stomata to permit the diffusion of carbon dioxide gas from the air for photosynthesis.

The disadvantages of transpiration in higher plants include:
- Transpiration reduces the amount of water availability in plants and thus, it causes decreased nutrient availability to the plant which in turn results in slow growth or stunted growth.
- Loss of turgidity is seen in higher plants during the noon as the rate of transpiration exceeds the rate of absorption. Under water-stress, plants release abscisic acid which in turn leads to detrimental effects on plants, like falling of leaves, fruits, etc. It also reduces the yield of the plant by 50 per cent as the water-stress condition decreases the meristematic activity in plants.
- There is a wastage of a lot of energy in absorbing and lifting the more content of water than required. Shedding and wilting of leaves are present due to transpiration. The growth of seeds and fruits is limited due to the reduction in waste content in the plant.
- Even genetically offspring include the bad characteristics that include resistance from the disease. Therefore, transpiration is considered a necessary evil.

Note: Transpiration also helps to cool plants, changes the osmotic pressure of cells and allows mass movement of mineral nutrients and water from roots to shoots. Two chief factors that influence the amount of water flow from the soil to the roots: the hydraulic conductivity of the soil and the magnitude of the pressure gradient through the soil.