Translocation in the phloem involves active energy expenditure, primarily through the use of ATP, to move materials such as sucrose. In contrast, water transport in the xylem is largely driven by passive physical forces such as cohesion and tension.
How is translocation in the phloem different from water transport in the xylem?
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Translocation in the phloem and water transport in the xylem represent distinct processes in plant vascular tissues. Phloem translocation involves the bidirectional movement of organic nutrients, mainly sugars, from source to sink tissues, driven by a pressure flow mechanism. The flow occurs through sieve tubes and relies on osmotic pressure gradients. In contrast, xylem transports water and dissolved minerals unidirectionally from roots to leaves through capillary action, cohesion, and adhesion forces. The driving force in xylem is transpiration, the evaporation of water from leaf surfaces, creating a negative pressure that pulls water upward. The two processes complement each other, supporting overall plant growth and function.