PLANT PHYSIOLOGY
TRANSPORT IN PLANT
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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the pull of sugar up the plant due to increased pressure
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cation exchange
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the pull of water up a plant due to hydrogen bonding and transpiration
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the attraction of water to the sides of the xylem
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Detailed explanation-1: -According to the cohesion-tension theory, transpiration is the main driver of water movement in the xylem. It creates negative pressure (tension) equivalent to –2 MPa at the leaf surface. Water from the roots is ultimately pulled up by this tension.
Detailed explanation-2: -The cohesion-tension theory (C-T theory) by Boehm (1893) and Dixon and Joly (1894) postulates that the water ascent in trees is exclusively due to the transpirational pull from continuous water columns in the xylem conduit running from the roots to the leafs.
Detailed explanation-3: -The molecules of water show cohesion and molecules of water and vessel wall show adhesion. Because of cohesive and adhesive forces, water column does not break and is pulled upward by the force called as transpiration pull.
Detailed explanation-4: -The cohesion-tension hypothesis is an intermolecular attraction theory that explains how water flows upward (against gravity) through plants’ xylem. Transpiration pull is the principal method of water flow in plants, employing capillary action and the natural surface tension of water.
Detailed explanation-5: -The evaporation of water during transpiration creates a negative pressure in the leaves. This, in turn, creates a suctional pull. This suctional pull is referred to as the transpirational pull and helps water flow towards the stem from the roots and the roots absorb more water.