Transpiration, Magnitude of transpiration, Types of transpiration Structure of Stomata ,Significance of transpiration.

Transpiration, Magnitude of transpiration, Types of transpiration Structure of stomata, Significance of transpiration.


Excess amount of water in the plant body is present in the plant body. This help to increase the rate of transpiration. In most plant species a large quantity of water absorbed form the soil, is lost into the atmosphere. The loss is mainly in the from of invisible vapours, although sometimes liquid water can also escape out. The loss of water in the form vapours is called transpiration. While the loss of water in liquid form is called guttation. Transpirations a vital physiological phenomenon. The mechanism of throwing of excess amount of water outside the plant is known as transpiration. It is regulated by the activity of guard cells. Several types of pressures are involved in transpiration. The surface area of transpiration is regulated by guard cells. Transpiration occurs only in the living cells. Transpiration process occurs in order to prevent the dryness of surface area. It maintains suitable temperatures in the plant body. It plays important rote in opening and closing of stomata, helps in ascent of sap. & absorption of water and minerals by roots.

Root system absorbs a large quantity of water from the soil. Out of total water only 2% is utilized for various of plants. Remaining about 98% of water is lost to the atmosphere through aerial part. The loss of water from aerial parts of plants in the form of vapors is termed as transpiration. The loss of water from aerial parts of plants in the form of vapors is termed as transpiration.

In some shade loving plants like ferns water is lost in liquid form through hydathodes. This is called guttation.

                         Magnitude of Transpiration

The quantitative importance of transpiration has been indicated by variety of studies over the years. E.C. Miller (1938) reported that a single Maize plant might transpire as much as 200 liters of water over its lifetime. The quantity of water lost is different from plant to plant and also from plant part. There are number of factors governing the loss of water. They are light, temperatures, humidity, and atmospheric pressure. It also differs due to the structural peculiarities. The sunflower plant looses about 56 kg of water within 4.5 months. At the same period Crotalaria juncea lost 27 kg of water in its life cycle of 4.5 months. These data of loss of water, physiological importance of transpiration in the life of plants. Thus during transpiration water is lost in the form of water vapour or it is evaporated. Thus, there is always surplus water in plants. This surplus water is lost from the aerial surface of plants in the form of vapours. This is called as transpiration


                         Type of Transpiration

Most of the transpiration take place from leaves which is known as foliar transpiration. Water is also lost from stems, flowers, fruits, etc. Transpiration may takes place through cuticle, lenticels or stomata and based on these transpiration is of three types:

a)  Cuticular transpiration

The epidermal layer of leaves and herbaceous stems is covered by cuticle. When water is lost through cuticle, it is called cuticular transpiration. Cuticle is waxy coating or layer present on the epidermis of leaves and herbaceous stems. Cuticle is mainly to prevent loss of water from plants, but transpiration takes place through cracks in it. It is nearly 5-10% of total water loss by simple diffusion.

b)  Lenticular transpiration

Lenticels are fine pores present on the older parts of plants. They are present in the bark of old stems. There is loss of water through lenticels. Such transpiration is called as lenticular transpiration. About 0.5% of water lost through the lenticels. It is quite negligible.

                                            c)   Stomatal transpiration

Loss of water through stomata is called stomatal transpiration. Stomata are the minute pores or openings present in the epidermis of leaves. About 80-90% of water is loss by stomatal transpiration. Leaves are the main transpiring organs. Stomatal transpiration occurs during day  time when stomata are open Stomatal transpiration is lowest when  stomata are fully closed and it is rapid when stomata are fully opened.

                             Structure of Stomata

Stomata are the minute openings or pores. Which are present in the epidermis of leaf. Each stoma consists of an elliptical pore i.e. stomatal aperture and surrounded by two specialized cells called as guard cells. Each guard cell is kidney shaped in dicots or dumb-bell shaped in monocots. Each guard cell contains a nucleus, chloroplasts and central vacuole filled with cell sap. The inner wall of guard cells is thicker and non elastic, while outer wall is thin and elastic and it can be stretched. Guard calls are surrounded by subsidiary cells or accessory cells. Usually stomata occur on both surface but mostly confirmed to lower surface of leaf. In aquatic plants, stomata represent to upper surface only. The size of stomata varies from plant to plant. The number of stomata in leaves also varies for ex. In Maize stomatal number is 52 on the upper surface and 68 on lower surface per square centimeter. In sunflower stomata are 58 on upper surface while 156 stomata on lower surface per square centimeter. An individual stoma of Maize, a representative species is approximately 4 mm wide by 26 mm long. 


                         Advantages of transpiration

                        1)     Transpiration removes excess water from plants

                        2)      It helps in water absorption by suction pressure.

                        3)      Transpiration helps in the circulation of water in plant body.

                        4)      It helps in ascent of sap and distribution of mineral salts in plants.

                        5)     It keeps the plants cool and thus prevents drying/desiccation of plant.

                        6)     It improves the quality of fruits.





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