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Chapter 30.5. How Do Organic Compounds Move Through Plants?. AP Biology Spring 2011. Conducting Tubes in Phloem. Phloem: living vascular tissue with organized arrays of conducting tubes, fibers, and parenchyma cells. Conducting Tubes in Phloem.

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chapter 30 5

Chapter 30.5

How Do Organic Compounds Move Through Plants?

AP Biology

Spring 2011

conducting tubes in phloem
Conducting Tubes in Phloem
  • Phloem: living vascular tissue with organized arrays of conducting tubes, fibers, and parenchyma cells
conducting tubes in phloem3
Conducting Tubes in Phloem
  • Sieve tube cells: alive at maturity and are interconnected side by side and end to end from the roots to the leaves
  • Companion cells: located next to sieve tubes and function to actively transport the products of photosynthesis into the sieve tubes
conducting tubes in phloem4
Conducting Tubes in Phloem
  • Carbohydrates are mainly stored as insoluble starch molecules that must be converted to more soluble carbohydrates
    • Such as sucrose before being transported throughout the plant
  • Translocation: transport of sucrose and other compounds through phloem
  • Movement of molecules through phloem is from sources to sinks
    • Source: mostly leaves
    • Sink: flowers and fruits
  • Observations of plant-sucking insects demonstrates that the sugary fluid in the phloem is under high pressure
  • Pressure flow theory: translocation depends on pressure gradients
    • Solutes are loaded by active transport into the phloem from a source (ex. Leaves)
    • Water enters by osmosis due to increase in solutes
    • Pressure builds in sieve tubes pushing the sucrose-laden fluid out of the source, into the stems, and on the sink (ex. Fruit)