BY2 - Transport In Plants

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  • BY2 - Transport In Plants
    • Structure & Distribution of Vascular Tissue
      • Vascular bundle consists of to main tissues.
        • Xylem
          • Arranged centrally in the roots.
            • Anchors plant into the soil.
          • Transports water and minerals.
          • Made up of vessels and tracheids.
            • Vessels form continuous tubes.
              • Their walls are made of lignin.
                • Waterproof
                • Strenthens plant.
                • Prevents the plants from collapsing under suction or tension.
              • Mature xylem vessels are dead and have no cytoplasm.
                • This is advantageous because there is nothing blocking the flow of water and minerals.
            • Tracheids have tapered ends.
              • This is so they can 'fit' together.
              • Pits allow the transfer of water between cells.
        • Phloem
    • Root Structure
      • Epidermis
        • Single layer of cells with long extensions called root hairs.
        • Hairs provide a large surface area so more water can be absorbed.
      • Endodermis
        • Singular layer of cells that surround the vascular bundle.
        • Cells contain suberin which is waterproof.
        • Waterproof layer is the Casparian Strip.
      • Pericycle
        • Contains meristematic cells for growth.
      • Vascular Bundle
        • Contains xylem and phloem cells.
    • Water & Mineral Transport (roots)
      • Water enters the plant via the root hair cells.
        • This occurs via osmosis.
          • Water moves from a high water potential to a lower water potential.
      • Water can cross the root by one of these three pathways:
        • Apoplast Pathway
          • Water moves through the cell walls.
            • Apoplast pathway stops at the endodermis because of the Casparian Strip.
              • This seals the cell walls (it is waterproof).
              • At this point water must cross the cell membranes via osmosis.
                • Water then travels via the symplast pathway.
                  • Some of the uptake of water goes into the xylem.
                    • Water is now in the cell
                      • Nucleus has control over the cell content.
        • Symplast Pathway
        • Vacuolar Pathway
          • Water moves through the vacuoles of cells.
          • Via osmosis
          • Water crosses the cell wall cytoplasm of each cell.
    • Movement of Water from Roots to Leaves
      • 1. Water moves in by osmosis, either by the apoplast, symplast or vacuolar pathways to the xylem.
        • 2. Water moves up the xylem by a 'pulling' effect called the transpiration stream.
          • Cohesive forces between molecules and adhesive forces between the water molecules and the xylem.
          • 3. Water evaporates through the stomata so that more water molecules are pulled up to replace those that have been lost.
            • 4. High hydrostatic pressure and high root pressure is caused by water entering the roots.
              • 5. Lower hydrostatic pressure as water is being lost.
                • 6. Capillarity - Water rising up narrow tubes.
      • The main force that pulls water up is transpiration.
        • Water travels in the xylem, up through the stem and to the leaves where most of it evaporates as water vapour into the atmosphere.
          • This creates a 'pull' - more water is puled up the stem.
        • Cohesion
          • Strong attraction water molecules exert on one another.
          • This attraction pulls up other water molecules.
          • Adhesive Forces
            • Attraction or adhesion between the water molecules and the xylem wall, which is hydrophilic.
          • Cohesive and adhesive forces combine - COHESION-TENSION THEORY.
        • Capillarity
          • Another force that contributes to the water moving up narrow tubes.
        • Root Pressure
          • (High hydrostatic pressure) A build up a high water potential in the roots compared to the low water potential in the leaves.
  • Vascular bundle is arranged on the periphery of the stem.
    • Gives the flexible support to the plant and resistance to bending.
    • Vascular bundle consists of to main tissues.
      • Xylem
        • Arranged centrally in the roots.
          • Anchors plant into the soil.
        • Transports water and minerals.
        • Made up of vessels and tracheids.
          • Vessels form continuous tubes.
            • Their walls are made of lignin.
              • Waterproof
              • Strenthens plant.
              • Prevents the plants from collapsing under suction or tension.
            • Mature xylem vessels are dead and have no cytoplasm.
              • This is advantageous because there is nothing blocking the flow of water and minerals.
          • Tracheids have tapered ends.
            • This is so they can 'fit' together.
            • Pits allow the transfer of water between cells.
      • Phloem
  • Vascular bundle is in the midrib of the leaves.
    • Gives flexibility and strength.
  • Cortex
    • Thick layer of packing cells (parenchyma)
    • Root Structure
      • Epidermis
        • Single layer of cells with long extensions called root hairs.
        • Hairs provide a large surface area so more water can be absorbed.
      • Endodermis
        • Singular layer of cells that surround the vascular bundle.
        • Cells contain suberin which is waterproof.
        • Waterproof layer is the Casparian Strip.
      • Pericycle
        • Contains meristematic cells for growth.
      • Vascular Bundle
        • Contains xylem and phloem cells.
  • Water travels through the cytoplasm.
    • Via osmosis
      • Down a water potential gradient.
        • Via the plasmaodesmata.
    • Symplast Pathway

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