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[A]: The water molecules are held togeth...

[A]: The water molecules are held together from cells of leaf to root because of cohesive force.
[R]: Water does not ascend in ttJ_e tissue due to_ transpiration pull.

A

If both A and R are true and R is the correct explanation of A

B

If both A and R are true but R is not the correct explanation of A

C

If A is true and R is false

D

If both A and R are false

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To analyze the assertion and reasoning provided in the question, we will break it down step by step. ### Step 1: Understanding the Assertion The assertion states that "The water molecules are held together from cells of the leaf to root because of cohesive force." **Explanation:** Cohesion refers to the attraction between molecules of the same substance. In the case of water, cohesive forces are due to hydrogen bonding between water molecules. This property allows water to form a continuous column from the roots to the leaves of the plant. ### Step 2: Understanding the Reasoning The reasoning states that "Water does not ascend in the tissue due to transpiration pull." **Explanation:** This statement is incorrect. Transpiration pull is actually a key mechanism that helps water ascend through the xylem tissue of plants. When water evaporates from the stomata in the leaves, it creates a negative pressure (suction) that pulls water upward from the roots through the xylem vessels. ### Step 3: Evaluating the Assertion and Reasoning Now, we need to evaluate the truthfulness of both the assertion and the reasoning. - The assertion is **true** because cohesive forces do hold water molecules together, allowing them to move from the roots to the leaves. - The reasoning is **false** because transpiration pull is responsible for the upward movement of water in plants. ### Step 4: Conclusion Based on the evaluation: - The assertion (A) is true. - The reasoning (R) is false. Thus, the correct answer is that A is true and R is false. ### Final Answer: C: A is true and R is false. ---
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The force of interaction between the molecules of same substance is called cohesive force hile force of interaction between molecules of different substances is called adhesive force . Both the forces are attracive and have a range of about 10 A . If we consider a molecule . A well inside a liquid we find that it is equally attracted by the surrounding molecules in all the dirctions ( with a sphere of radius 10 Å ) and so it does not experience any resultant force . On or near the surface of a liquid , the molecules do not exist on the free side and so a molecule ( say B ) experiences a resultant force vertically downwards into the liquid . For this reason , the molecules of the surface have a tendency to go into the liquid . Thus , the surface tends to contract and gives rise to surface tension . As surface molecules like B experience a net downward force of cohension and have tendency to go down , so in increasing the area of the surface more molecules are to be shifted to the surface from inside . Thus , more mechnical work will have to be done against the net downward force of cohension . This work is stored by the molecules in the surfaces as potential energy called free surface energy . Furthermore , molcules like P , in contact with the liquid will stick to the solid surface , i.e will meet it if the force of adhesion A is greater than net force of cohension C . The liquid will not the solid surface if C gt A Also , molecules like Q at the surface in contact with the solid will experience a net force of cohension C_(R) . If adhesion A is greater then cohension C_(R) , the resultant force will be F . As the liquid can't support tangential force , F must be perpendicular to the surface of the liquid . So , the menisus will be concave and the angle of contact will be acute ( gt 90^(@)) . However , if adhesion is lesser than cohension , the resultant force F will be directed into the liquid and so the menisus ( which is perpendicular to F as liquid support tangential force ) will be convex and the angle of contact will be obtuse ( gt 90^(@)) The free suface energy , stored in the surface is because of work done

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The force of interaction between the molecules of same substance is called cohesive force hile force of interaction between molecules of different substances is called adhesive force . Both the forces are attracive and have a range of about 10 A . If we consider a molecule . A well inside a liquid we find that it is equally attracted by the surrounding molecules in all the directions ( with a sphere of radius 10 Å ) and so it does not experience any resultant force . On or near the surface of a liquid , the molecules do not exist on the free side and so a molecule ( say B ) experiences a resultant force vertically downwards into the liquid . For this reason , the molecules of the surface have a tendency to go into the liquid . Thus , the surface tends to contract and gives rise to surface tension . As surface molecules like B experience a net downward force of cohension and have tendency to go down , so in increasing the area of the surface more molecules are to be shifted to the surface from inside . Thus , more mechnical work will have to be done against the net downward force of cohension . This work is stored by the molecules in the surfaces as potential energy called free surface energy . Furthermore , molcules like P , in contact with the liquid will stick to the solid surface , i.e will meet it if the force of adhesion A is greater than net force of cohension C . The liquid will not the solid surface if C gt A Also , molecules like Q at the surface in contact with the solid will experience a net force of cohension C_(R) . If adhesion A is greater then cohension C_(R) , the resultant force will be F . As the liquid can't support tangential force , F must be perpendicular to the surface of the liquid . So , the menisus will be concave and the angle of contact will be acute ( gt 90^(@)) . However , if adhesion is lesser than cohension , the resultant force F will be directed into the liquid and so the menisus ( which is perpendicular to F as liquid support tangential force ) will be convex and the angle of contact will be obtuse ( gt 90^(@)) A liquid particle B , which is present in the vicinity particle A can exert a force on A if the distance of B from A is

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TRUEMEN BIOLOGY ENGLISH-Plant Physiology -ASSERTION AND REASON
  1. [A]: The driving force for passive absorption is non metabolic in orig...

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  2. [A]: The movement of ions from endodermis to xylem elements is an acti...

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  3. [A]: The water molecules are held together from cells of leaf to root ...

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  4. [A]: Passive absorption of a substance oc- curs from its lower to high...

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  5. [A]: Xylem transports sap from root to shoot. [R]: Phloem transloca...

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  6. [A]: Maximum transpiration occurs in meso- phytes than xerophytes. ...

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  7. Assertion : Thick cuticle is mostly present in disease resistant pla...

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  8. Assertion. Submerged plants get carbon dioxide in the form of carbona...

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  9. [A]: Phloem is the main conducting tissue. [R]: Phloem does the· fu...

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  10. [A]: Antitranspirants are used to retard tran- spiration. [R]: AbA ...

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  11. [A]: Rate of transpiration is high in low wind velocity. [R]: Wind r...

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  12. [A]: The rate of transpiration is indirectly pro- portional to RH. [...

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  13. [A]: High pH in guard cells activate phosphorylase to convert starch i...

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  14. [A]: Daily periodicity of stomata! movement is not the characteristic ...

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  15. [A]: In Nepenthes, lamina is modified to capture insects to get nitrog...

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  16. [A]: The downward· movement of minerals through soil is effected by qu...

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  17. [A]: Auxins are found in large amounts in the apical Meristem of shoot...

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  18. [A]: In C4 plants, CO2 fixation occurs at three sites. [R]: CO2 is f...

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  19. [A]: Oxidation of H2O takes place during pho- tosynthesis. [R]: Ph...

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  20. [A]: The rate of photosynthesis is determined in terms of the rate of ...

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