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| Points to Remember |
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 Cell is the structural and functional unit of life. |
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The direction in which water flows from one cell to another cell depends on the water potential. |
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Two factors which affect the water potential are the amount of solutes and the external pressure. |
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Due to endosmosis protoplasm expands and exerts pressure on elastic cell wall - Turgor pressure. |
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In the smaller pores of the soil, water is held against the force of gravity by capillary forces is called capillary water. |
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Movement of water from the soil into root hairs and from there to the cells of the xylem with lower water potential results in root pressure which pushes the water up in the xylem vessels. |
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When root pressure is high and transpiration is low, plants may lose small quantities of liquid water in the form of drops from the margins of tips of leaves. This process is called guttation. |
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The adhesion of water molecules to the xylem vessels and cohesion of water molecules, both by hydrogen bonds, together help to form thin, unbroken columns of water in the capillaries of xylem vessel elements. |
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When the transpiration pull is exerted, a negative pressure or tension is generated in the xylem. |
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About 98% water absorbed by land plants evaporates from aerial plants parts and diffuses into atmosphere. |
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The opening and closing of stomata is controlled by the size and shape of guard cells resulting from the change in their turgor pressure. |
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The stomata open when guard cells take up K+ ions from the surrounding cells. |
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The uptake of K+ ions is balanced by one of the factors as: |
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| a) uptake of Cl- |
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| b) Transportation of H+ ions released from organic acids |
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| c) by the negative charges of organic acids when they lose H+ ions (hydrogen ions). |
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Wilting occurs when loss of water by transpiration exceeds the rate of water uptake by roots. |
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Transpiration is influenced by environmental factors like light, temperature, wind, atmospheric humidity and availability of soil water. |
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Cultivation of agro-climatic zones is determined by water requirement of crops. |
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| The scope of the chapter in real life applications: |
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Turgidity plays an important role in plants. So wilting can be remedied by watering. |
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Anti-transpirant spray reduces the rate of transpiration. |
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| The use of anti-transpirants is still under study and in an experimental stage due to certain limitations in their application on plants. |
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