transport in plants

  • Created by: aryan26
  • Created on: 10-04-19 17:46
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  • transport in plants
    • xylem tissue
      • transports water and mineral ions in solution
      • also functions for support
      • in a root, the xylem is in the centre surrounded by phloem to provide support for the root
      • in the stems xylem and phloem are near the outside to reduce bending
      • in a leaf the xylem and phloem make up a network of veins
      • adaptations
        • 1: they are very long tube like structures formed from vessel elements joined end to end
        • 2: there are no end walls so its an uninterrupted tube
        • 3: the cells are dead so they contain no cytoplasm
          • 4:walls are thickened with lignin which supports them stopping them from collapsing inwards
            • deposited in a spiral or rings
        • 5: as a cell gets older the amount of lignin increases
        • 6:water and ions move in and out through small pits where there is no lignin
    • phloem
      • transports solutes mainly sugars like sucrose
      • arranged in tubes used for transport
      • tissue contains phloem fibres, phloem parenchyma, sieve tube elements and companion cells
        • sieve tube elements
          • living cells that form the tube for transporting solutes through the plant
          • joined end to end to form sieve tubes
          • end walls contain holes to let solutes pass
          • have no nucleus, thin layer of cytoplasm and few organelles
          • cytoplasm in adjacent cells is connected through the holes in sieve plates
        • companion cells
          • sieve tube elements can't survive alone
            • there's a companion cell for every sieve tube element
          • carry out living functions for themselves and the sieve cells
    • water transport
      • water enters through root hair cells and passes through the root cortex to the xylem
        • water is drawn into the roots via osmosis
      • symplast pathway
        • goes through living parts of the cell- the cytoplasm
        • cytoplasms of neighbouring cells connect via plasmodesmata (small channels in the cell wall)
        • water moves in this pathway via osmosis
      • apoplast pathway
        • goes through non-living parts- the cell walls
        • the walls are very absorbent so water can diffuse through
        • the water can carry solutes and move from high hydrostatic pressure to low hydrostatic pressure.
          • this is an example of mass flow
        • most used as it provides the least resistance

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