Project Report Index
Transpiration of Plants - Introduction : Land plants absorb large amount of water from the soil, small fraction of the water absorbed by the plants is really in the making of their body structure. Rest of it is lost from the aerial part’s of the plants in the form of water vapours.
“The loss of water in the form of vapours from the aerial parts of the plants is known as transpiration.”
All aerial parts (leaves, stems, flowers and fruits) of the plants transpire water. Rate of the transpiration is much higher during the day in comparison to night.
Mechanism of Transpiration : We have learnt that water rise up in the stem through xylem. Form xylem vessels of leaves water diffuses into mesophyll tissue making cells turgid. The walls of mesophyll cells remain saturated with water. From cell walls water is lost into intercellular spaces in the form of water vapor. Soon, the concentration of water vapour in the intercellular spaces are connected to atmosphere through stomata. The air surrounding the leaves thus becomes more humid, and water vapours from there diffuses into drier region of the atmosphere. The process of water loss involving evaporation from the cells walls into intercellular spaces and then diffusion of water vapor from intercellular spaces into the atmosphere through stomata, lenticels or cuticles goes on continuously.
Loss of water vapours from aerial of plants takes place through stomata, cuticle and lenticels.
Transpiration have three main types
Stomatal Transpiration : Loss of water vapour through microscopic pores (stomates) surrounding by specialized guard cell is called stomatal transpiration stomatal are distributed mostly on the leaves. However they are found on young greens, stems, flowers and fruits.
Culticular Transpiration : Some transpiration takes place by the direct evaporation of water from the outer walls of the epidermal cells. The epidermal cells are mostly cutinized and culticularized. This layer is impermeable to water. Water loss due to evaporation through cuticle is called cuticular transpiration.
Lenticular Transpiration : Water loss through the lenticels in woody stems and fruits is called lenticular transpiration.
Simple Poto Meter Method : A small rubber tubing taken and a graduated one ml. pipette is inserted into it. Both rubber tube and pipette is filled with water a tree branch is taken and recut while immersed in water this is done to exclude the entry of air into xylem vessel. The twig is now inserted into the other end of rubber tubing while its cut end is still immersed in water. As the leaves lose water due to transpiration, the water column is graduated pipette moves down. The fall in the level of water in the graduated pipette after a fixed period of time will give the rate of transpiration.
Factor Affecting on Transpiration
A) Internal Factor :
This reduce the rate of transpiration with an increase in the shoot-root ratio.
B) External Factor :
Significance of Transpiration
Leaf anatomy was designed to facilitate gaseous exchange for photosynthesis and respiration. Transpiration however becomes unavoidable. Under conditions of defect water supply, it becomes a serious problem. It thus appear that transpiration has been forced on the plants. Plants have to bear it even if they have to spent a lot of energy on it. Carties, therefore rightly called “Transpiration a necessary evil.”
1. Ascent of Sap : Transpiration exerts a tension pull on water column in xylem which is responsible for the ascent of sap.
2. Absorption of Water : Transpiration helps passive absorption of water.
3. Transport of Minerals : Transpiration assists translocation of mineral salts through xylem.
4. Cooling Effect : Transpiration create cooling in the plants.
1. Wilting Injury : Permanent wilting is not recovered and lead to death of plants.
2. Stunted Growth : Excessive rates of transpiration leads to stunted growth of plants.