Plants continuously absorb water and approximately 98% of water is lost as water vapour during transpiration. Nearly 2% water retained in plants for various physiological activities. Transpiration is a necessary evil because it has both advantages and disadvantages. they are fallowing.
Advantages of Transpiration
Fallowing are the some advantages of transpiration.
- It controls the rate of absorption of water: Active transpiration favours passive absorption of water in plant. Transpiration develops the transpiration pull which favours ascent of sap and continuous absorption of water from the soil by the root system.
- It helps in absorption and translocation of mineral salts in plants: Earlier it was thought that more rapid rate of transpiration resulted in an increase of the rate of absorption of mineral salts through increased rate of absorption of water. Moreover the absorption of mineral requires are expenditure of metabolic energy. The absorbed minerals are translocated and distributed by transpiration process.
- Its role in regulation of temperature: Transpiration keeps the plant body and the environment cool. It prevents the heating of plant leaves during excessive day temperature.
- It maintains turgidity of the cells: Transpiration maintains an optimum turgidity of the cells, which is important for growing cells.
- It brings about opening and closing of stomata: Transpiration brings about the opening and closing of stomata and indirectly influence the process of photosynthesis and respiration.
Disadvantages of transpiration
- Nearly 98% of the total water absorbed by the plants is lost in the form of vapour, only 2% or less than that is actually used for growth and other metabolic activities.
- Transpiration often results in water deficit which causes injury to plants by desiccation.
- High rate of transpiration with low rate of water absorption may result in internal water deficit. If such conditions continue for sometime, permanent water deficit results. In severe cases the plants may dry up.
- Many xerophytes have to develop different structural modifications to reduce the rate of transpiration. Thick cuticle, multi layered epidermis, sunken stomata, reduction of leaves, modification of leaves into thorns are the modification. These are extra burden on the plants.
- Deciduous plants have to shed their leaves during autumn to check transpiration.
Even though there are certain disadvantages of transpiration Barnes has described the process as an unavoidable evil. The anatomical structure of the leaves, particularly stomata are required for gaseous exchange in photosynthesis and respiration, the loss of water vapour through them is only a side effect.