Xylem & Phloem (Cambridge International IGCSE Biology)

The Xylem & Phloem

Spec point — 8.1.1 · State the functions of xylem and phloem: (a) xylem – transport of water and mineral ions, and support (b) phloem – transport of sucrose and amino acids Identify in diagrams and images the position of xylem and phloem as seen in sections of roots, stems and leaves of non-woody dicotyledonous plants

The xylem & phloem

What is the function of the xylem and phloem

• Plants contain two types of transport vessel:

  • Xylem vessels (pronounced: zi-lem) transport water and minerals roots to the stem and leaves
  • Phloem vessels (pronounced: flow-em) transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem

• These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles

Transport tissue in a dicotyledonous plant

Exam Hint 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

Spec point — 8.1.1 · Relate the structure of xylem vessels to their function, limited to: (a) thick walls with lignin (details of lignification are not required) (b) no cell contents (c) cells joined end to end with no cross walls to form a long continuous tube

Adaptations of xylem vessels: Extended

• 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

Xylem cells lose their top and bottom walls to form a continuous tube through which water moves through from the roots to the leaves