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How does xylem transport water and minerals through a plant?
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Plant
Grandidier's baobas (Adansonia grandidieri) in Madagascar.
Xylem is a specialized vascular tissue in plants that functions as a system of tiny, rigid tubes to transport water and dissolved minerals from the roots to the rest of the plant, while also providing structural support.12
The Mechanism of Transport
Water movement through the xylem occurs passively along a gradient of decreasing pressure. The primary driver of this process is transpiration pull, described by the cohesion hypothesis.34
- Transpiration: As water evaporates from the leaves, it creates a negative pressure (tension) that pulls the water column upward through the plant.543
- Cohesion and Adhesion: Water molecules are held together by cohesion, allowing them to form a continuous, unbroken column. Simultaneously, adhesion between water molecules and the walls of the xylem vessels helps support the column against gravity.543
- Root Pressure: In some conditions, such as when transpiration is low, root pressure generated by osmotic uptake of water in the roots can help push fluids upward, though this is generally insufficient to move water to the tops of tall trees.53
This mass flow of water ensures that essential mineral nutrients are efficiently distributed from the soil to all above-ground plant parts.32