What physiological mechanism drives the continuous upward ascent of sap through tall forest trees from roots to canopy foliage?
Answer and explanation
Correct answer: C. transpiration pull combined with cohesion and adhesion of water molecules
- Step 1: Water evaporates from stomata during transpiration, creating negative tension (transpiration pull) in leaf mesophyll. Step 2. Due to hydrogen bonding, water molecules exhibit strong cohesion to each other and adhesion to xylem walls. Step 3. This maintains an unbroken water column lifted to great heights. Answer: transpiration pull combined with cohesion and adhesion of water molecules. Why not the others: Capillarity alone can only lift water a few centimeters; root pressure is insufficient for tall trees; barometric pressure does not drive ascent.
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