---
title: "Cohesion-Tension and Water Movement in the Xylem"
description: "Evaporation from leaf cell walls creates tension that pulls water through the xylem. Hydrogen bonding gives the water column cohesion. Stomatal closure reduces transpiration-driven flow, while gas bub"
canonical: https://lightmysky.com/learn/science/cohesion-tension-and-water-movement-in-the-xylem-mt_9_TORolYIl
source: https://lightmysky.com/learn/science/cohesion-tension-and-water-movement-in-the-xylem-mt_9_TORolYIl.md
retrieved: 2026-11-12
---

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# Cohesion-Tension and Water Movement in the Xylem

Evaporation from leaf cell walls creates tension that pulls water through the xylem. Hydrogen bonding gives the water column cohesion. Stomatal closure reduces transpiration-driven flow, while gas bubbles can interrupt individual columns.

Subject: Science · Area: Organisms & Life Processes · Ages 17 to 18
Page: https://lightmysky.com/learn/science/cohesion-tension-and-water-movement-in-the-xylem-mt_9_TORolYIl

## Ready when they can

- Explains where the pulling force comes from and where in the plant it acts.
- Links cohesion in the column back to hydrogen bonding between water molecules.
- Uses the theory to predict what happens to the flow when the stomata close.

## Lesson: How leaves pull water skywards

Water evaporates from wet mesophyll cell walls into leaf air spaces. Water vapour then diffuses mainly through stomata. As water is lost, tension develops in the remaining water films. Tension means pressure below atmospheric pressure. It pulls replacement water from the leaf xylem and is transmitted down connected water columns. The main pull for transpiration-driven flow begins in the leaves.

Hydrogen bonds between neighbouring water molecules produce cohesion, helping transmit tension through a continuous column. Adhesion is attraction between water and xylem walls; it helps support water against gravity. Neither guarantees continuity. Gas bubbles can interrupt a column. This blockage, an embolism, reduces flow through the affected vessel, while other water-filled vessels may still conduct.

*(drawing: This is a causal sequence, not a drawing of xylem anatomy.)*

Closing stomata reduces water vapour loss. Transpiration-driven tension generally weakens and xylem flow slows. Closure does not instantly remove all tension or stop every route of water loss. Some water can escape through the cuticle or incompletely closed stomata, and stored water can continue moving within the plant.

With open stomata and ample soil water, warmer, drier, windier air usually raises transpiration. At steady water balance, root uptake rises to replace that loss. The rates need not match immediately because stored water can supply the leaves. In drought, stomatal closure or limited soil water may prevent higher uptake despite hot weather.

Mature xylem vessels are dead, hollow conducting tubes with no living cytoplasm. Pressure differences drive water through their open passage, or lumen; the vessels do not need to make ATP for this flow. Root pressure can push water upward in some conditions, but cannot account for ascent to the tops of tall trees by itself. Transpiration provides the main pull.

**Recap.** Leaf evaporation creates tension. Cohesion transmits the pull through connected water columns. Stomatal closure reduces flow; bubbles can interrupt individual vessels.

*Lesson, questions and flashcards written for this dataset. OpenStax sections on leaves and transport of water and solutes in plants were consulted for biological facts.*

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Transpiration and Transport in Plants](https://lightmysky.com/learn/science/transpiration-and-transport-in-plants-mt_AqN0vL8QRu)

## Optional connections

- [Water and Hydrogen Bonding in Living Systems](https://lightmysky.com/learn/science/water-and-hydrogen-bonding-in-living-systems-mt_79dzlo6fD5)
- [Water Potential and Osmosis Quantified](https://lightmysky.com/learn/science/water-potential-and-osmosis-quantified-mt_dFBz-cE6W0)

## Opens up

- [Translocation and the Mass Flow Hypothesis](https://lightmysky.com/learn/science/translocation-and-the-mass-flow-hypothesis-mt_WZ8id0kou4)