Summary
Water molecules stick together and to xylem walls, so evaporation tension pulls a continuous water column up.
In depth
Water evaporates from mesophyll cell walls, creating negative pressure (tension) pulling the water column. Hydrogen bonding gives cohesion; adhesion to xylem walls helps. Can lift water over 100 m in tall trees. Cavitation (air bubbles) can break columns.
Pulling on a water column without breaking it is possible because of strong hydrogen bonding and the narrow xylem diameter. The theory is supported by measurements of negative pressure with pressure bombs and by trunk diameter shrinking by day.
Remember: the driving force is evaporation from leaves, powered by the sun.
Frequently asked questions
What is Cohesion-Tension Theory?
Water molecules stick together and to xylem walls, so evaporation tension pulls a continuous water column up.
Which area of biology covers Cohesion-Tension Theory, and how advanced is it?
Cohesion-Tension Theory is one of the 56 topics in Plant Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Xylem, Transpiration, Translocation.
Can you give an example of Cohesion-Tension Theory?
Redwoods are over 110 m tall.
What should I learn before Cohesion-Tension Theory?
Work through the Beginner topics in Plant Biology first, such as Plant Kingdom, Photosynthesis, Chlorophyll, then return to Cohesion-Tension Theory. Intermediate topics assume the Beginner vocabulary.
What topics are related to Cohesion-Tension Theory?
The closest topics to Cohesion-Tension Theory are Xylem, Transpiration, Translocation, Leaves. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Cohesion-Tension Theory?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Cohesion-Tension Theory. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Cohesion-Tension Theory different from Xylem?
Cohesion-Tension Theory: Water molecules stick together and to xylem walls, so evaporation tension pulls a continuous water column up. Xylem: Vascular tissue made of dead cells that carries water and minerals upward from roots. Read both side by side and note what each one explains.
How should I study Cohesion-Tension Theory step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Xylem and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.