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| Summary |
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| Cell is the structural and functional unit of the organism. Water is the principal constituent of plants and is essential for the maintenance of life, growth and development. Plants absorb water from the soil through their roots, transport it to other parts of the plant through the xylem and lose it into the atmosphere by transpiration. Hence, there is a soil - plant - atmosphere continuum of water. Various physical phenomena such as diffusion, osmosis, turgor and cohesion-tension play a role in the absorption of water from the soil and its transport within the plants. The upward movement of water in plants is mainly through the forces of cohesion between water molecules and adhesion between the water and the walls of the xylem cells. |
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| The bulk of water absorbed by the plants is lost from leaves into the atmosphere as vapour by the process called transpiration. Since stomata are the openings through which water is lost from plants, transpiration is mainly controlled by stomatal movements. The opening and closing of stomata depend on changes in the turgor of guard cells. Turgidity of guard cells is regulated by K+ fluxes between them and the surrounding epidermal cells. |
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| Transpiration is also influenced by environmental factors such as light, temperature, availability of soil water and atmospheric humidity. Transpiration facilitates the movement of water and minerals, absorbed by roots, to other aerial parts of the plant. The water requirement of crops principally determines their cultivation in various agro climatic zones. Plants growing in areas of severe water scarcity have various adaptations to minimise water loss. |
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