Xylem and phloem

?
  • Created by: Amy.L.J
  • Created on: 27-09-18 14:28

Xylem

Phloem

  • contains: vessels, tracheids, parenchyma and fibres
  • vessels- dead hollow cells with a wide lumen. they have thick lignified walls to prevent cells from collapsing and provides water proofing.
  • side walls may have pits to allow lateral movement of water
  • vessels are main conducting cells in angisperms-large leaf surface area means transpiration losses, hence water demand is high- large vessels large amounts of water can be carried.
  • Tracheids- dead hollow cells with narrow lumens than vessels. Tracheids are connected vertically to eachother via bordered pits. Narrower lumens encourages capillarity. Have tapering ends which dovetail together and various patterns of lignified thickening- provides mechanical strength.
  • Parenchyma- thin celluose walls with living contents-contribute to support via turgidity.
  • Fibres- similar to fibres in sclerenchyma
  • Contains: sieve tub elements, companion cells, parenchyma, fibres
  • sieve tube elements- living tubular cells, linked end to end by sieve plates, allows for bidirectional flow of solutes. Cytoplasm thin and peripheral with few organelles, no nucleus so flow unimpeded.
  • cellulose cell walls-allows exchange of substances.
  • each sieve tube element is directly connected via plasmodesmata to its own companion cell. The companion cell controls the movement of solutes in the sieve tube element. Plasmodesmata allow exchange of solutes between sieve tube element and companion cells.
  • Companion cell- dense cytoplasm. Has nucleus and abundant other organelles e.g ribosomes, mitochondria and golgi body- Nucleus controls activities of sieve tube elements. Ribosomes allow production of enzymes and carriers. Mitochondria produce ATP for active transport in the sieve tube element.
  • Provide support through turgidity.
  • Fibres- provide support and some protection for delicate sieve tube elements

Transport

Transport

  • carries water and some minerals
  • carries solutes such as sucrose

Comments

No comments have yet been made