BRAINCAKECohesion-Tension Theory
The cohesion-tension theory explains how water moves up the xylem from the roots to the leaves, even in tall trees.
Water molecules are polar: the oxygen atom carries a slight negative charge and the hydrogen atoms a slight positive charge. Neighbouring water molecules are therefore attracted to each other by hydrogen bonds. This attraction between water molecules is called cohesion.
The theory works as follows:
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Key terms in this lesson
- water potential
- A measure of the tendency of water molecules to move out of a solution; water moves from a higher to a lower (more negative) water potential.
More in Transport in Plants
- Root Hair Cells
- Symplast Pathway
- Apoplast Pathway
- Transpiration
- Adhesion and Capillarity
- Modelling Transpiration
- Measuring the Rate of Water Uptake
- Factors Affecting Transpiration
All 21 lessons in Transport in Plants · All Edexcel AS-level Biology topics