The xylem and Phloem

• What is the purpose of xylem?

  To transport water and minerals, also to provide structural support.
• Describe the structure of the xylem?

  Xylem are long cylinders made of dead tissue with open ends allowing them to form a continuous collumn. Xylem vessels also contain pits which enable water to move sideways between the

  vessels
• How is the xylem thickened?

  They are thickened with a tough substance called lignin, which is deposited in spiral patterns to enable the plant to remain flexibl
• In the xylem, what direction can water flow in?

  Only upwards.
• Describe the structure of phloem vessels?

  Phloem vessels are tubes made of living cells

  Phloem vessels consist of siee tube elements and companion cells

  Sieve tube elements form a tube to transport to transport sugars in the dissolbed form of sap
• How are sieve tube elements and companion cells in phloem linked?

  The cytoplasm of sieve tube elements and companion cells is linked through structures known as plasmodesmata which are gaps between cell walls which allow communication and flow of substances such as minerals between the cells
• What are companion cells involved in?

  Companion cells are involved in ATP production for active processes such as loading sucrose into sieve tubes
• Xylem vessels

  • Very long, tube like structures formed by cells
  • Connected end to end
  • No end walls in cells, allowing uninterrupted tube for water to pass up easily
  • Cells are dead, containing no cytoplasm
• Xylem vessel cell walls

  • Thickened with lignin, providing support and preventing collapse
  • Lignin deposited in spirals or rings, allowing flexibility and preventing breaking
• Pits

  Allow water and mineral ions to move through the vessels where there is no lignin
• What cells are in phloem tissue?


  Phloem fibres, parenchyma, sieve tube elements, and companion cells