Xylem and Phloem

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  • Plant Vessels
    • Xylem
      • Made from dead cells
      • Coated in lignin
        • Stops the xylem from collapsing
        • Forms patterns
          • Annular (rings)
          • Reticulate (network of broken rings)
        • Incomplete lignification results in pores in the walls known as pits or bordered pits
          • The pores help the water to leave from one vessel and pass onto the next one
      • No end walls
      • No cell contents
      • No nucleus or cytoplasam
      • Transports water and minerals
    • Phloem
      • Transports sucrose
      • Companion cells
        • Dense cytoplasam
        • Large nucleus
        • Mitochondria
        • Plasmodesmata link the companion cells to the sieve tube
      • Sieve tube element
        • Thin layer of cytoplasam
        • No nucleus
        • Line up end to end to form a tube
    • A source- releases sucrose into the pholem
    • A sink- takes sucrose from the pholem
    • How sucrose gets into the pholem
      • An active process
      • 1. H+ ions are pumped out of the companion cells by the use of ATP
        • 2. The H+ ions diffuse back into the companion cells with sucrose attached
          • 3. The sucrose molecules diffuse into the  sieve tube element through the plasmodesmata
    • Movement of sucrose along the pholem
      • 1. Sucrose is actively loaded into the sieve tube element. This results in the reduction of the water potential
        • 2. Water moves into the sieve tube element by osmosis. This increases the hydrostatic pressure
          • 3. The water moves down the sieve tube element to a lower hydrostatic pressure at the sink
            • 4. Sucrose leaves the phloem by diffusion or active transport. This increases the water potential
              • 5. Water moves out of the sieve tube element by osmosis. The hydrostatic pressure goes down
  • 1. Sucrose is actively loaded into the sieve tube element. This results in the reduction of the water potential
    • 2. Water moves into the sieve tube element by osmosis. This increases the hydrostatic pressure
      • 3. The water moves down the sieve tube element to a lower hydrostatic pressure at the sink
        • 4. Sucrose leaves the phloem by diffusion or active transport. This increases the water potential
          • 5. Water moves out of the sieve tube element by osmosis. The hydrostatic pressure goes down

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