Xylem and phloem
Two pipes in a plant
- A tall tree lifts water from its roots to leaves many metres up.
- It uses two transport tissues that run through roots, stems and leaves.
- They lie side by side in vascular bundles.
Practice
Xylem carries:
Xylem carries water and mineral ions up from the roots (and gives support); phloem carries sucrose and amino acids.
Practice
Phloem carries:
Phloem carries sucrose and amino acids to wherever they are needed.
Xylem and phloem
| Tissue | Carries | Direction |
|---|---|---|
| xylem | water + mineral ions | up from roots (also gives support) |
| phloem | sucrose + amino acids | to wherever they are needed |
Practice
Xylem vessels carry water well because they are:
Xylem cells are dead and empty (water flows freely) with thick lignin walls that also support the plant.
Practice
Lignin in xylem walls also helps support the plant.
Lignin strengthens the xylem walls, which also gives the plant support.
Xylem structure (Supplement)
- Xylem is made of long tubes called vessels, well suited to carrying water:
- thick walls strengthened with lignin — also supports the plant,
- the cells are dead and empty, so water flows freely,
- joined end to end with no cross-walls — one long continuous pipe.
You've got it
Key idea
- xylem = water + mineral ions, upward, + support; phloem = sucrose + amino acids
- xylem vessels are dead, empty tubes with lignin-strengthened walls
- the two tissues run together in vascular bundles