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प्रश्न
Discuss the factors responsible for ascent of xylem sap in plants
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उत्तर १
Xylem sap ascends mainly due to forces generating in the foliage of plants as a result of active transpiration. Thus, the factors which enhance the rate of transpiration are also the factors responsible for ascent of xylem sap in plants.
Various factors responsible for ascent of xylem sap in plants are as follows:
(i) Capillarity: There is limited rise of water in narrow tubes or capillaries due to forces of cohesion amongst molecules of water and their property of adhesion to other substance.
(ii)Root pressure: It is positive pressure that pushes sap from below due to active absorption by root
(iii)Transpiration pull: Transpiration in aerial parts brings the xylem sap under negative pressure or tension due to continuous withdrawal of water by them. Water column does not break due to its high tensile strength related to high force of cohesion and adhesion.
उत्तर २
Transpirational pull is responsible for the ascent of water in the xylem. This ascent of water is dependent on the following physical factors:
Cohesion – Mutual attraction between water molecules
Surface tension – Responsible for the greater attraction between water molecules in liquid phase than in gaseous phase
Adhesion – Attraction of water molecules to polar surfaces
Capillarity –Ability of water to rise in thin tubes
These physical properties of water allow it to move against gravity in the xylem.
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संबंधित प्रश्न
Differentiate between Transpiration and Evaporation
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What are stomata?
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Name the phenomenon being demonstrated.
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Given alongside is the diagram of an experimental set-up to demonstrate a certain phenomenon in plants.
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An apparatus as shown below was set up to investigate a physiological process in plants. The setup was kept in sunlight for two hours. Droplets of water were then seen inside the bell jar. Answer the questions that follow:
Suggest a suitable control for this experiment.
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Complete the following by choosing the proper option.
Stomata : Transpiration :: Hydathode : ____________.
Boojho wanted to test the presence of starch in leaves. He performed the following steps.
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He did not get the expected result. Which step did he miss? Explain.
Analogy:
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