Edexcel IGCSE Biology 复习笔记 2.8.2 Transport Systems in Flowering Plants

Edexcel IGCSE Biology 复习笔记 2.8.2 Transport Systems in Flowering Plants



  • The rootsstem and leaves form a plant organ system for the transport of substances around the plant
  • Plants also possess two specialist transport vessels called the xylem and phloem
  • The xylem and phloem are arranged throughout the root, stem and leaves in groups called vascular bundles



Structure and function of the xylem

  • Xylem vessels transport water and minerals (pronounced: zi-lem) from the roots to the stem and leaves
  • The xylem has some key structural features
    • It is composed of dead cells which form hollow tubes
    • Xylem cells are strengthened by lignin and so are adapted for the transport of water in the transpiration stream






Structure and function of the phloem

  • 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)
    • This means that movement can be in any direction around the plant


  • The phloem has structural features different to the xylem
    • The cells are living cells and are not hollow
    • Substances move from cell to cell through pores in the end walls of each cell






The position of the xylem and phloem in the stem compared to the root



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.