Question
The loss of water vapour from leaves (TRANSPIRATION) generates. __ a NEGATIVE pressure, which draws water through XYLEM from the roots, up to the leaves NO change in pressure but pulls water up from the roots [ANY of these] a POSITIVE pressure, which draws water from the roots through the XYLEM, to the leaves
Answer
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Niall
Master · Tutor for 5 years
Answer
a NEGATIVE pressure, which draws water through XYLEM from the roots, up to the leaves
Explanation
Transpiration in leaves or plants creates a negative pressure or tension (as if drawing or pulling) in xytem, the specialised tissue for conducting water and dissolved substances upward in the plant body. The cohesion of water molecules and their adhesion to the walls of xylem help in upward suction from root to leaves, this effect is roughly similar to how you drink a liquid using a straw. The water vapor loss(due to transpiration) reduces pressure at the top and water column in the plant is lifted upwards due to adhesion-cohesion. Notably it doesn't create positive pressure nor remains neutral, neither can just any situation work precisely or scientifically. It rather creates negative-pressure contrary- discharge model for maintaining water circulation, influenced by various biological and environmental factors.