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How do xylem and phloem transport materials through vascular plants?

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Diagram explaining ATP's role in powering cellular activities, with arrows showing ATP produced by mitochondria, chloroplasts, and glycolysis, and used for making biomolecules, transporting substances, and driving energy-requiring processes; includes a structural diagram of ATP with labeled adenine, ribose, and phosphate groups. — Physiology Adenosine triphosphate (ATP) is the power source of many biochemical reactions. It is produced in the cell structures and system listed at the left to energize the important life processes listed on the right. An abbreviated chemical formula of the structure of ATP is also shown. The two high-energy P―O―P bonds are responsible for its power.

In vascular plants, xylem and phloem serve as specialized tissues for long-distance transport, functioning similarly to a circulatory system.1

Xylem: Water and Mineral Transport

Xylem transports water and dissolved minerals upward from the roots to the rest of the plant. This process is primarily driven by transpiration, where water evaporates from the leaves, creating a negative pressure gradient that pulls water upward through the xylem vessels. This mechanism, known as the cohesion theory, relies on the cohesive strength of water molecules and their adhesion to the walls of the xylem. In some conditions, such as early spring, root pressure may also contribute to upward movement.23

Phloem: Nutrient Transport

Phloem transports products of photosynthesis—primarily sugars—from "source" areas (like leaves) to "sink" areas (such as roots, fruits, or growing tissues). Unlike the unidirectional flow of xylem, phloem transport is variable and under metabolic control. The most widely accepted explanation is the pressure-flow hypothesis, which suggests that sugars are actively loaded into sieve tubes at source regions, increasing osmotic pressure and causing the solution to flow toward sink regions where pressure is lower.4