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

• The roots, stem 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