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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
Transpiration is defined as:
Under what conditions do plant transpire more quickly?
The set up shown alongside was kept in sunlight for an hour. It was observed that drops of water appeared on the inside of the polyethylene bag.
- Name the process which is being demonstrated.
- Why was the pot and its soil left uncovered by the polythene bag?
- Why was the pot left in the sunlight?
- Suppose the pot in this experiment was placed inside a dark room instead of placing it in sunlight for some time. What difference will be noticed?
State whether the following statement is true or false. Rewrite the false statement correctly.
Transpiration is the loss of water from the roots of the plant.
How does transpiration help the roots absorb water and minerals from the soil?
Differentiate between osmosis and transpiration.
How does transpiration help in the uptake of water from the soil?
Distinguish between the following :
Cuticular transpiration and lenticular transpiration
Given alongside is the diagram of an experimental set-up to demonstrate a certain phenomenon in plants.
What is the purpose of the spring balance in the set-up?
What are stomata? What governs the opening and closing of stomata?
Describe an experiment to prove that transpiration occurs more from the undersurface of dorsiventral leaves.
Mention, if the following statement is True or False. If false rewrite the wrong statement in its correct form:
Moist cobalt chloride paper is blue in colour.
Complete the following by choosing the proper option.
Stomata : Transpiration :: Hydathode : ____________.
Which one is not related to transpiration?
Plants show temporary and permanent wilting. Differentiate between the two. Do any of them indicate the water status of the soil?
Define the term Vital capacity.
Which of the following is an external factor affecting the rate of transpiration?
