plant stems

• 2 functions of the xylem

  • transport dissolved minerals and water around plant
  • provides structural support
• xylem- lignified cell wall

  withstand pressure of water+impermeable to water
• xylem- no end plates


  allows mass flow of water and solutes as cohesive and ahesive forces not prevented
• xylem- long, hollow tubes

  formed by dead cells so dont contain cytoplasm or organelles which would slow down speed of water
• xylem- pits in walls


  small regions in walls not lignified, allows lateral movement of water/minerals between xylem vessels
• function of phloem tissue

  transport organic compounds from sources eg leaves to sinks eg roots, occurs up and down plant via translocation
• structure of phloem 


  made of different cell types- sieve tube elements and companion cells - also contain living cells
• sieve tube elements


  line up end to end forming continuous tubes

  • has cellulose cells walls which strengthen phloem and help to withstand pressure
  • no nucleous, vacuole or ribosomes= allows max space for translocation
  • thin cytoplasm= reduces friction to facillitate movement
• companion cells 


  role= loading and unloading sugars into sieve tube elements

  • contain nucleus and organelles
  • transport proteins in membrane- allow movement in and out of sieve tube element
  • lots of mitochondria to provide ATP for transport
  • plasmodesmata- thin region of cell wall= links to sieve tube elements
• scelerenchyma fibres

  • provide support and no transport
  • bundles of dead cells
  • long,hollow tubes no end walls
  • lignified cells wall but no pits
  • more cellulose in wall