Root pressure is more important at night, while during the day, when stomata are open, transpiration pull becomes the major driving force for the movement of water in the xylem.
When is root pressure more significant in water transport, and what becomes the primary driving force during the day?
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Root pressure is more significant in water transport during the night when transpiration is low. In the absence of significant transpirational pull, water accumulates in the roots due to active mineral uptake and osmotic processes, creating positive pressure. This facilitates a passive upward movement of water through the xylem. However, during the day, transpiration becomes the primary driving force in water transport. As sunlight triggers stomatal opening, water evaporates from leaves, creating a negative pressure that pulls water up from the roots, dominating over root pressure. This transpirational pull is the predominant force in daytime water movement within plants.