Phloem and xylem are the two main transport vessels in plants. Explain how the structure of phloem vessels is adapted to carry out their function of transporting sugars around the plant.

Phloem is composed of living cells – the sieve‑tube elements are alive, unlike the dead xylem vessels. The sieve tubes are connected by sieve plates, allowing cytoplasm to flow between cells so that sugars can move as a continuous stream.

Companion cells are attached to each sieve‑tube element and provide the ATP needed for active loading of sugars into the sieve tubes at the source (leaves) and for unloading at the sink (roots, fruits, growing tissues).

Because the sieve tubes are living and continuous, sugars can be transported in both directions along the phloem, from source to sink, a process known as translocation.

Any sugars that are not immediately required are converted into starch in the sink tissues for storage.