Xylem and phloem

Plants have tissues to transport water, nutrients and minerals.

Xylem transports water and mineral salts from the roots up to other parts of the plant, while phloem transports sucrose and amino acids between the leaves and other parts of the plant.

Cross-section of a plant root, showing a vascular bundle of xylem and phloem in the centre.Xylem and phloem in the centre of the plant root

This table explains what is transported by the xylem and phloem:

TissueWhat is movedProcess
XylemWater and mineralsTranspiration stream
PhloemSucrose and amino acidsTranslocation

Xylem

Mature xylem consists of elongated dead cells, arranged end to end to form continuous vessels (tubes).

Mature xylem vessels:

  • contain no cytoplasm
  • are impermeable to water
  • have tough walls containing a woody material called lignin

Phloem

Phloem consists of living cells arranged end to end. Unlike xylem, phloem vessels contain cytoplasm, and this goes through holes from one cell to the next.

Phloem transports sucrose and amino acids up and down the plant. This is called translocation. In general, this happens between where these substances are made (the sources) and where they are used or stored (the sinks).

This means, for example, that sucrose is transported:

  • from sources in the root to sinks in the leaves in spring time
  • from sources in the leaves to sinks in the root in the summer

Applied chemicals, such as pesticides, also move through the plant by translocation.