Explain how the structure of the xylem and phloem vessels are each adapted to carry out their functions in the transport system of a plant.

Xylem vessels are formed from dead cells that have been hollowed out, so the cells contain no living material. The end walls of adjacent cells are removed, giving a continuous tube that allows water to move freely. The cell walls are thick, lignified and impermeable to water, which prevents loss of water from the vessel and gives the structure strength.
Phloem vessels consist of living sieve‑tube elements. The sieve plates between cells are perforated, so the cytoplasm is continuous and sugars can move between cells. Companion cells, which are also living, supply ATP from respiration to power the active loading of sugars into the sieve tubes.