Presentation on Transpiration and its types.pptx

Presentation on Transpiration and its types.pptx

1. Transpiration

2. The loss of excess water by diffusion through the stomata of leaves of a plant into the atmosphere is called transpiration. Although a small amount of water may be transpired through the other parts of the plant, 90% of the water diffuses out through the leaves. Transpiration …

3. TYPES OF TRANSPIRATION Stomatal transpiration Cuticular transpiration Lenticular transpiration Stomatal Transpiration Water vapour diffuses out through minute pore (stomata) present in soft aerial part of plant is known as Stomatal Transpiration. Of the total water loosed, near about 85 – 90% of water loosed by the stomatal transpiration.

4. Stomatal transpiration…. Osmotic diffusion of water in the leaf from xylem to intercellular spaces above the stomatal through the mesophyll cells. Opening and closing of stomata . Simple diffusion of water vapours from intercellular spaces to outer atmosphere through stomata.

5. Cuticular Transpiration Cuticle, the outermost waxy layer of the epidermal cells actually retards water loss through epidermal cells. Nevertheless, cuticle is permeable to water vapour to some level. Such transpiration through the cuticle is called Cuticular Transpiration.

6. Lenticular Transpiration In woody plants, where the bark tissues contain lenticels, transpiration occurs through them. This transpiration is known as Lenticular Transpiration.

7. Mechanism of stomatal Movement Stomata are the tiny pores present in the epidermal surface of leaves. The pores are guarded by two kidney-shaped cells known as guard cells. The inner wall of guard cell towards the stomata is thicker as compared to the outer walls. The opening and closing of stomata operate as a result of Turgidity changes in the guard cells. During daytime, guard cells photosynthesis due to which osmotic pressure increases. The guard cells absorb water from the neighboring cells. Guard cells become turgid. As a result, the outer thin walls of guard cells are pushed out and the inner thicker walls are pulled inwards resulting in stomata to open. During night or in a condition of water scarcity, guard cells are in a flaccid state and remain closed. Transpiration is the main driving force for the ascent of sap (rising of water in the tall trees through xylem vessels) which depends upon the following physical properties of water.

8. GUTTATION….

9. Significance of Transpiration Plants absorb solar energy far in excess of their requirement. Very little of this is used in photochemical reactions. The rest is mostly dissipated as thermal energy which is harmful to the cells. Easy availability and abundance of water in plant cells and the high specific heat make water the ideal material for the disposal of solar energy absorbed in excess by plants. Thus the transpiration plays a significant role in keeping the internal temperature of the plant cells uniform and constant. It is also supposed that transpiration has a role in the upward movement of water and also in absorption and translocation of mineral salts by means of the pull and suction force it develops. But there are no concrete evidence to prove this.

10. Ganong’s Potometer experiment to measure the rate of transpiration…. The water loss by the process of transpiration can be demonstrated by several types of glass apparatus, called Potometers. In most of the potometers, the rate of transpiration can be measured directly and expressed in gms per hour per sq. cm of leaf area. But these methods are not accurate because of the fact that the amount of water absorbed by the twig (which is measured by the apparatus) is not actually transpired at the same time. This is a glass apparatus fitted with a wooden stand. It is one of the most suitable potometers used for the demonstration or determination of the rate of transpiration. It consists of a narrow graduated horizon­tal limb which holds two vertical wide-mounted tubes — one of which is fitted with a rubber cork through which passes a leafy twig while the other acts as a reservoir of water which is fitted with a stopcock in the connecting tube to control water supply. The other ends of horizontal limbs bend at right angle and at the opposite side of the vertical wide mouthed tube.

11. Experiment to demonstrate Transpiration pull It is made up of glass tube having a side limb. The mouth of the side tube is fitted with a cork having a hole, through which the twig is inserted in the tube. Upper end of the straight tube is closed by a cork and in its lower end a cork with a capillary tube is fitted. Lower part of the capillary tube is placed in beaker containing water. A scale is fitted on the capillary tube.

12. Points to remember… Loss of water in the form of vapour from the aerial part of plants is called transpiration. Transpiration is of three kinds: 1.Stomatal 2.Cuticle 3.Lenticular Minute pores surrounded by two guard cells found on epidermis are called stomata. S tomata open and close according to changes in the turgor pressure of the guard cells. Transpiration helps to cool the leaf surface. Loss of water in the form of liquid is Guttation.

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