Yes, xylem is the plant tissue through which water moves as a result of transpiration.
Transpiration, the process of water movement through a plant and its evaporation from aerial parts, such as leaves, is intimately linked to the function of xylem. In fact, transpiration is the primary driving force behind the ascent of water in the xylem.
How Transpiration Affects Xylem: The Cohesion-Tension Theory
The most widely accepted explanation for how water moves up the xylem is the cohesion-tension theory. Here's a breakdown:
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Transpiration Creates Tension: As water evaporates from the leaves through the stomata (tiny pores), it creates a negative pressure or tension in the leaf cells. This is because the water potential in the air surrounding the leaf is typically lower than inside the leaf, encouraging evaporation.
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Tension Pulls Water Upward: This tension then pulls water from the xylem vessels in the leaf.
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Cohesion and Adhesion Facilitate Water Movement: Water molecules are cohesive (they stick to each other) due to hydrogen bonds. This cohesion allows the tension to be transmitted down the column of water in the xylem, all the way from the roots to the leaves. Adhesion (water sticking to the xylem walls) also helps counteract the force of gravity.
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Water is Drawn Up from the Roots: The tension ultimately draws water from the soil into the roots, through the root cells, and into the xylem, replacing the water lost through transpiration.
In essence, transpiration acts like a pump, pulling water upwards through the xylem. Without transpiration, water transport in the xylem would be significantly reduced or even non-existent.
