The Xylem & Phloem
- Plants contain two types of transport vessel:
- Xylem vessels – transport water and minerals (pronounced: zi-lem) from the roots to the stem and leaves
- Phloem vessels – transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem (pronounced: flow-em)
- These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles
Vascular tissue in a dicotyledonous plant
Exam Tip
If you are asked to identify the xylem or phloem in a diagram showing a cross-section of a root, stem or leaf just remember that xylem is always on the inside and phloem is always on the outside.
Adaptations of Xylem Vessels: Extended
Xylem cells lose their top and bottom walls to form a continuous tube through which water moves through from the roots to the leaves
- Function: transport tissue for water and dissolved mineral ions
- Adaptations:
- Cells joined end to end with no cross walls to form a long continuous tube
- Cells are essentially dead, without cell contents, to allow free passage of water
- Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant
