Transport in plants - xylem and phloem

• Xylem


  Vessels responsible for transporting water and mineral ions primarily from the roots to the stem and leaves
• Phloem


  Vessels that transport dissolved substances like sucrose and amino acids from the leaves to the rest of the plant
• Movement of substances in plants

  1. From one part of the plant to another

  2. Takes place in xylem and phloem vessels
• Xylem vessels


  • Have very strong walls to provide support for the plant
• Phloem vessels


  • Cells have perforations in their end walls that allow substances to pass from cell to cell
• Vascular bundles


  Groups of xylem and phloem vessels
• Arrangement of vascular bundles

  1. In roots

  2. In stems

  3. In leaves
• Roots don't have a conventional epidermis but do have root hairs for water uptake
• In the stem, the space between the vascular bundles and the epidermis is called the cortex, and the central tissue is called pith
• In leaves, the xylem is found at the top towards the upper surface, and the phloem is always at the bottom
• Xylem vessels bring water and minerals to the leaf cells, while the sieve tubes carry away the sugars and amino acids produced
• The presence of xylem in the veins gives the leaf structure and helps to support the softer tissues of the leaf blade
• Structure of xylem vessels

  • Comprised of a series of long hollow cells with no cytoplasm or organelles
  • No end walls, forming a continuous tube
  • Walls thickened with lignin, making them strong and impermeable
  • Also contain long lignified cells called fibers that provide additional support