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

Xylem

 

  • 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

     

 

 

Phloem

 

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

     

 

 

Vascular-tissue-in-a-dicotyledonous-plant

 

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.

转载自savemyexam

 

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