Advantages of Transpiration:
(i) Ascent of sap: Ascent of sap mostly occurs due to pull exerted by transpiration of water.
(ii) Removal of excess water : It has been held that plants absorb far more amount of water than is actually required by them. Transpiration, therefore, removes the excess of water.
(iii) Cooling effect : Radiant heat falling on the plants increases their temperature which may be dangerous to the plants. Transpiration, by evaporating water, lowers down their temperature.
(iv) Mechanical tissue : The development of mechanical tissues which is essential for providing rigidity and strength to the plants, is favoured by the increase in transpiration.
(v) Increasing Concentration of Mineral Salts : The sap absorbed from the soil contains low concentration of mineral salts. The loss of water through transpiration increases the concentration of mineral salts in the plant.
Disadvantages of Transpiration :
(i) Wilting : Wilting or loss of turgidity is quite common during noon due to transpiration being higher than the rate of water absorption. Wilting reduces photosynthesis and other metabolic activities.
(ii) Reduced Growth : Transpiration reduces availability of water inside the plant. Water deficit decreases the growth and hence the plant gives a stunted appearance.
(iii) Abscissic Acid : Water stress produces abscisic acid. Abscissic acid prevents several plant processes and promotes abscission of leaves, flowers and fruits.
(iv) Wastage of Energy : Since 98-99% of absorbed water is lost through transpiration, the energy used in absorption and conduction of water goes waste.
(v) Modification : In order to reduce transpiration during critical periods, the plants produce several types of modification like thick cuticle, hair, prickles, spines, thons, sunken stomata, phylloclades, cladodes, etc.
