Transport in plants
Xylem moves water from roots to the leaves, and phloem moves food from the leaves to the rest of the plant. During transpiration water evaporates from the leaves and draws water from the roots.
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.
This table explains what is transported by the xylem and phloem:
| Tissue | What is moved | Process |
|---|---|---|
| Xylem | Water and minerals | Transpiration stream |
| Phloem | Sucrose and amino acids | Translocation |
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.