Structure of phloem

• Phloem - The tissue that transports biological molecules in plants
• Structure of phloem:

  • No nucleus or organelles, just a thin layer of cytoplasm around the edge of the cell
  • This maximises space for mass flow
• Structure of phloem:

  • Phloem is made up of sieve tube elements - long thin structures arranged end to end
• Structure of phloem:

  • Each sieve tube is supported by a companion cell
  • This has the organelles including a nucleus and many mitochondria to produce ATP and help sieve tubes carry out living functions
• Structure of phloem:

  • Phloem is made up of sieve tube elements
  • There are end walls between cells but these contain holes to let solutes pass through - this is why they are known sieve plates
• Phloem tissue contain two key cells:

  • Sieve tube elements
  • Companion cells
• Phloem tissue: Sieve tube elements

  • Living cells
  • Contain no nucleus
  • Contain few organelles
• Phloem tissue: Companion cells

  • Provide ATP required for active transport of organic substances