transport tissues in plants

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  • Created by: Em99
  • Created on: 27-04-16 21:20
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  • Transport tissues in plants
    • Xylem
      • cellulose microfibrils vertically in the stem increase the strength.
      • as the stem ages, increasing amounts of lignin are laid down in the walls
        • cells become impermeable to water
        • tissue becomes ore supportive + contents of the cell die
        • the living cells around the cambium are on the outside of the tree under the bark
      • end walls between cells break down so xylem forms hollow tubes running from roots to the tip of stems and leaves
      • water and minerals are transported from roots to leaves in the transpiration stream
      • water moves from xylem to surrounding cells through specialised pits in the walls
    • Phloem
      • phloem sieve tubes are made up of cells joined to make tubes that run from highest shoots to end of the roots
      • walls between cells become perforated to from specialised sieve plates
        • phloem contents flow through holes to these plates
      • phloem sieve tubes survive because they have companion cells
        • companion cells are very active linked to sieve tube elements by plasmodesmata
        • cell membranes od companion cells have infolding's to increase surface area which they can transport sucrose to the cell cytoplasm
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