Phloem

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  • Phloem
    • Function
      • Transport sugars from one part of the plant to another, up or down the stem
    • Phloem Components
      • Sieve Tube Elements
        • Contain little cytoplasm and no nucleus
        • Lined up end-to-end to form a tube where sugars can be transported
          • Typically sucrose
            • Sucrose is dissolved in water to form sap
          • Unlike xylem, this tube contains cross-walls at intervals
            • These cross walls are perforated by pores to allow the sap to flow
              • Hence cross walls are called sieve plates and tubes are called sieve tubes
                • Sieve tubes have thin walls and are normally 5 or 6 sided
      • Companion Cells
        • In between sieve tubes with large nucleus' and dense cytoplasm
        • Have numerous mitochondria to produce ATP in active transport
          • Active transport used to load sucrose into sieve tubes
        • Cytoplasm and sieve tube elements are linked through many plasmodesmata (gaps in cell walls allowing communication and flow of substances between cells)

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