chapter 30.5
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CHAPTER 30.5How Do Organic Compounds Move Through Plants?
AP BiologySpring 2011
CONDUCTING TUBES IN PHLOEM
Phloem: living vascular tissue with organized arrays of conducting tubes, fibers, and parenchyma cells
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 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
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
TRANSLOCATION
Observations of plant-sucking insects demonstrates that the sugary fluid in the phloem is under high pressure
TRANSLOCATION
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)
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