Module 3 - Section 3 - Transport In Plants

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  • Transport In Plants
    • Xylem and Phloem
      • Xylem
        • Transports water and mineral ions in solution.
        • No end walls and no cytoplasm-So substances can flow uninterrupted.
        • Cell wall contains lignin-Supports cell wall, stopping them collapsing under high pressure.
        • Small pits in walls-Allows minerals in where there's no lignin
      • Phloem
        • Transports sugars in solution up and down plant.
        • Sieve tube elements-Living cells are joined end to end to for.
        • Lots of holes to allow solutes to pass.
        • Have no nucleus, little cytoplasm and few organelles, so rely on companion cell to survive.
          • Companion cell- Carry out living functions for sieve
    • Water entering the Plant
      • Osmosis- From high water potential to low water potential inside root hair cell.
      • Symplastic Pathway
        • Goes through living parts (cytoplasm) of cell. Connects cells through plasmodesmata. Via Osmosis
      • Apoplastic Pathway
        • Moves through non-living(cell wall) of cells.
          • Moves from high hydrostatic pressure to low hydrostatic pressure.
            • Water blocked going into Xylem due Casparian Strip. So needs to take Symplastic Pathway.
    • Transpiration
      • Water Movement Up Plant
      • Transpiration Stream-
        • Cohesion-molecules stick together so whole column of water flows.
          • Tension - Pulls more water into leaf when water transpires.
            • Adhesion-Attract to walls of vessel to help rise.
      • Result of Gas Exchange.
        • Plant needs to open stomata to allow in CO2 for photosynthesis but lets out water at the same time.
      • Factors Effecting Transpiration Rate
        • Wind
        • Humidity
        • Temperature
        • Light Intensity
      • Xerophatic Plants
        • Adapted to live in dry climates
        • Waxy layer on Epidermis, Spines instead of leafs, close stomata in hottest part of days, Sunken pits, Hairs on Epidermis, Roll Leaves
      • Hydrophytic Plants
        • Adapted to live in aquatic habitats
        • Air Spaces, Stomata only present on top of leaves, Flexible leaves and stems
    • Translocation
      • Movement of dissolved substances (assimilates) to where they're needed in the plant
      • Mass Flow Hypothesis
        • Source
          • Active transport used to load solutes(sucrose) into sieve tubes
            • Lowers water potential in sieve tubes, so enters via osmosis into phloem, creates high pressure in sieve tubes at the end source of plants.
        • Sink
          • At the end solutes are removed fro phloem to be used. Diffusion.
        • Flow
          • Pressure gradient from source end to sink end. Pushes solutes along sieve tube toward sink, where they'll be stored or used.
      • Active Loading
        • Used at the source to to move substances into companion cells from surrounding tissues, against conc gradient.
        • 1. Actively transport H+ ions into surrounding tissue.
          • 2. H+ binds to co-transport protein, and re enters cell via diffusion. sucrose also attaches to protein so moves sucrose into cell too.
            • 3.Sucrose is transported out of companion cell in same way

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