Question

Traspiration is called a necessary evil. justify the statement.

Answer 1

because it is necessary for plant to evaporate extra water from the plant

Answer 2

The stomata are primarily meant for absorption of CO2but these also help in exchange of gases, but at the same time water vapors also escape through stomata. Thus transpiration is described as necessary evil because it is an inevitable process but potentially harmful. Loss of water can lead to wilting, serious desiccation, and often death of a plant, if there is shortage of water. There is good evidence that even mild water stress results in reduced growth rate, and reduction in yield.


However, transpiration is beneficial to the plants in several ways.


1) Mineral Absorption: Minerals absorbed in water are absorbed into the roots; move up through the plant in the transpiration stream.


2) Optimum Turgidity: In some plants if transpiration is not allowed to occur, plants become very turgid, do not grow well and there is shortage of water in their cells.


3) Energy Exchange: When water is evaporated from the exposed surface of cells of leaves, it exerts a cooling effect on plant.


4) Effect on Growth and Development:Transpiration is a necessary factor in the normal growth of some plants e.g. pear, sunflower.


5) Absorption of Water: Water is conducted or transported in upward direction in most tall plants due to transpiration.

6) Exchange of Gases: Wet surface of leaf cells allow gaseous exchange.
What is Transpiration?
The evaporation of water from the surface of leaf cells in actively growing plants is calledTranspiration. Thus more water enters the plant from the soil. The water enters the plant in the form of liquid but when it is on the surface of the leaves, it converts into gaseous form due to evaporation. The cohesive properties of water (hydrogen bonding between adjacent water molecules) allow the column of water to be ‘pulled’ up through the plants as water molecules are evaporating at the leaf surface. This process has been termed the Cohesion Theory of Sap Ascent in plants.