Explain why plants need both xylem and phloem vessels, and describe how each vessel is adapted for its function.

Plants need both xylem and phloem because they transport different materials: xylem carries water and dissolved minerals from the roots to the rest of the plant, which is essential for photosynthesis and other cellular reactions, while phloem distributes sugars and other organic nutrients produced in the leaves to all parts of the plant.

Xylem is specialised for water transport. It is composed of long, hollow, dead cells (tracheids and vessel elements) whose end walls are removed, creating a continuous, rigid tube. The cell walls are impermeable to water, so the water remains inside the vessel and is not lost through the walls.

Phloem is specialised for sugar transport. It consists of living cells, mainly sieve‑tube elements and companion cells. The companion cells supply ATP and other energy to power the active loading and unloading of sugars into the sieve tubes, allowing sugars to move up and down the plant in translocation.