Phloem and translocation

Plants transport dissolved sugars from their leaves to other parts of the plant. There, the sugars can be used immediately or stored for later use. This movement of food molecules through the plant is called translocation.

Translocation takes place in phloem, which forms tubes running through the plant. Each tube consists of elongated living cells arranged end to end. Their end walls have pores, allowing cell sap containing dissolved sugars to pass from one cell to the next along the tube.

Xylem

Xylem is plant tissue that carries water and dissolved mineral ions from the roots, through the stem, to the leaves. Its vessels also help support the plant.

Xylem vessel structure

Xylem vessels are hollow tubes formed from dead cells. The end walls of the cells have broken down, leaving a continuous pathway through which water can move.

The vessel walls are strengthened with lignin. This helps prevent the vessels from collapsing as water is pulled through them and also provides support for the plant.

Water movement in xylem

Water travels upwards through the xylem in the transpiration stream. As water is lost from the leaves, it helps pull a continuous column of water up through the vessels from the roots. Dissolved mineral ions are carried with the water.