During the day, when stomata are open and transpiration rates are high, the primary driving force for water movement in the xylem is transpiration pull. This process relies on the cohesive and adhesive properties of water molecules to create tension, pulling water upward from the roots.
What is the primary driving force for water movement in the xylem during the day?
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The primary driving force for water movement in the xylem during the day is transpiration. Transpiration is the process by which water vapor escapes from the stomata of leaves into the atmosphere. As water molecules evaporate from the leaf surfaces, a negative pressure, known as tension or suction, is created in the leaf, pulling water up through the xylem vessels. This negative pressure, combined with cohesive forces between water molecules and adhesive forces between water and xylem cell walls, facilitates the ascent of water from the roots to the leaves. Transpiration is a key factor in the upward movement of water in plants.