Which process explains how water is pulled up the xylem in a tall tree?
Answer and explanation
Correct answer: A. Cohesion between water molecules and tension from transpiration pulling the water column
- Step 1: Water evaporates from leaf mesophyll cells and diffuses out through the stomata.
- Step 2: The tension pulls on the continuous water column, which holds together through cohesion, so water rises in the xylem.
Answer
Cohesion between water molecules and tension from transpiration pulling the water column.
Why not the others: Root pressure alone pushes water up from the root hairs: root pressure is too weak to lift water to the top of tall trees. Active transport pumps water up through the xylem vessels: xylem vessels are dead and water movement is passive. Phloem sap pushes water up as it flows by mass flow: phloem moves sugars, not water, up the stem.
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