Biology / Unit 11 Bio 2543 short lesson, about 20 seconds
Cohesion-Tension Theory of Sap Ascent
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The idea
Cohesion-tension theory explains sap ascent: leaf evaporation creates tension pulling water upward through the xylem, held continuous by cohesion and adhesion to vessel walls.
In practice
A redwood pulls water nearly 116 meters upward on this tension alone, no pump organ expending energy on the lift.
Where people slip
This lift needs an unbroken water column — an air bubble, an embolism, can block the flow.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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