Direction for: In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as
Assertion: In angiosperms, the conduction of water is more efficient because their xylem has vessels. Reason: Conduction of water by vessel elements is an active process with energy supplied by xylem parenchyma rich in mitochondriaA) If both assertion and reason are true and the reason is the correct explanation of the assertion.
B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
C) If assertion is true statement but reason is false.
D) If both assertion and reason are false.
Correct Answer: C
Solution :
Xylem is plants principal water-conducting tissue, forming a continuous system that runs throughout the plant body. Within this system water (and the minerals dissolved in the water) passes from the roots up through the shoot in an unbroken stream. When water reaches the leaves, much of it passes into the air as water vapour, mainly through the stomata. The two principal types of conducting elements in the xylem are tracheids and vessel elements, both of which have thick secondary walls, are elongated and have no living protoplast at maturity. In conducting elements composed of tracheids, water flows from tracheid to tracheid through openings called pits in the secondary walls. In contrast, vessel elements have not only pits but also definite openings or perforations, in their end walls by which they are linked together and through which water flows. A linked row of vessel elements forms a vessel. Conduction of water through these elements does not use active energy thus, it is a passive process. Primitive angiosperms have only tracheids,, but the majority of living angiosperms have vessels. Vessels conduct water much more efficiently than do strands of tracheids. In addition to conducting cells, xylem likewise includes fibers and parenchyma cells.
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