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Question
Assertion :Cohesion, adhesion and surface tension give high tensile strength to water. Reason: Capillarity is aided by small diameter of the tracheary elements.
Assertion :Cohesion, adhesion and surface tension give high tensile strength to water. Reason: Capillarity is aided by small diameter of the tracheary elements.
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Solution
The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
Transpiration pull or cohesion-tension theory is given by Dixon and
Jolly in 1894. It was further improved by Dixon in 1914. This
theory is based upon the cohesive and adhesive properties of water
molecules, which forms the unbroken continuous water column in the
xylem.
Water molecules are held together by strong cohesion force
which is due to hydrogen bonds amongst them. There is another force of
adhesion which holds water to the walls of xylem vessels. Water
molecules are attracted to one another more than the water molecules in
the gaseous state. It produces surface tension that accounts for high
capillarity through tracheids and vessels. Water column is present in
tracheary elements. There is a continuous column of water from roots
through the stem and into the leaves. These tracheary elements form this
continuous system through their unthickened areas. Since, a large
number of tracheary elements are present together, no breakage in the
continuity of water occurs even if there is a blockage of one or few of
them.So, the correct answer is 'Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion'.
Transpiration pull or cohesion-tension theory is given by Dixon and Jolly in 1894. It was further improved by Dixon in 1914. This theory is based upon the cohesive and adhesive properties of water molecules, which forms the unbroken continuous water column in the xylem.
Water molecules are held together by strong cohesion force
which is due to hydrogen bonds amongst them. There is another force of
adhesion which holds water to the walls of xylem vessels. Water
molecules are attracted to one another more than the water molecules in
the gaseous state. It produces surface tension that accounts for high
capillarity through tracheids and vessels. Water column is present in
tracheary elements. There is a continuous column of water from roots
through the stem and into the leaves. These tracheary elements form this
continuous system through their unthickened areas. Since, a large
number of tracheary elements are present together, no breakage in the
continuity of water occurs even if there is a blockage of one or few of
them.
So, the correct answer is 'Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion'.
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