How do trees move water from roots to leaves without a pump?
Quick Answer
Trees pull water upward mainly through evaporation from leaves, which creates tension in the xylem. Cohesion between water molecules helps keep the water column unbroken over long distances.
The Full Story
Most trees move water by the cohesion-tension mechanism. As water evaporates from tiny pores in leaves called stomata, it creates negative pressure that pulls more water upward through xylem vessels and tracheids. Cohesion between water molecules and adhesion to the walls of xylem help maintain a continuous column of water from roots to canopy. This system can move water to heights of more than 100 meters in the tallest trees, such as coast redwoods.
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