Mass Transport in plants

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  • Created by: emma
  • Created on: 06-03-14 19:40
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  • Mass Transport in plants
    • Roots
      • root pressure
        • Active transport of ion by the endodermis
          • Ions move into the xylem which lowers water potential in the xylem
            • Water enters xylem by osmosis
      • Have extensions to increase the surface area
        • actively transport ions into cytoplasm to lower water potential
          • water can enter cytoplasm via osmosis
      • Water can flow the symplastic way (through cytoplasm)
        • Or apoplastic way (through cell wall)
          • Casparian strip prevents water movement in cell wall of endodermis and is forced into the cytoplasm
    • Xylem
      • Hollow tubes (dead)
        • contain lignin which is waterproof
          • Pits enables water to move between vessels in case of a blockage
      • Transpiration is evaporation of water through stomata
        • Lowers water potential of mesophyll cells in leaf
          • Water moves out of xylem via osmosis
            • water moving out of xylem creates negative pressure in xylem vessel
      • Water forms a continuous column in narrow xylem vessel
        • water molecules stick together (cohesion)
          • Water molecules are attracted to walls of xylem
    • Rate  of transpiration
      • Light
        • Stomata open in light and close in dark
          • ROT higher in light
      • Temperature
        • Increased temperature increases ROT
          • Rate of diffusion increase as molecules have more energy
      • Humidity
        • Air spaces in leaf saturated
          • Air out of leaf much less water vapour
            • Large concentration gradient so increased rate of diffusion
      • Air movement
        • Moves water vapour away from stomata
          • Increases water potential gradient between inside and outside of leaf
            • More diffusion so increase ROT
    • Potometer
      • Leaf shoot cut under water
      • Potometer filled with water
      • Leafy shoot fitted to potometer under water
      • Potometer sealed with jelly
      • An air bubble is introduced into tube
      • As transpiration occurs water moves through the capillary
  • water can enter cytoplasm via osmosis

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