9.2
Transport in the Phloem of plants
Essential Idea: Transport in the phloem of plants.
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Nature of Science: Developments in scientific research follow improvements in apparatus: experimental methods for measuring phloem transport rates using aphid stylets and radioactively labelled carbon dioxed were only possible when radioisotopes became available.
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UNDERSTANDINGS:
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Plants transport organic compounds from sources to sinks.
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Incompressibility of water allows transport along hydrostatic pressure gradients.
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Active transport is used to load organic compounds into phloem sieve tubes at the source.
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High concentrations of solutes in the phloem at the source lead to water uptake by osmosis.
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Raised hydrostatic pressure causes the contents of the phloem to flow towards sinks.​
APPLICATIONS & SKILLS
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Application: Structure-function relationships of phloem sieve tubes.
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Skill: Identification of xylem and phloem in microscope images of stem and root.
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Skill: Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively labeled carbon dioxide.
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RESOURCES
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VIDEO: Phloem function (phloem sieve tubes and translocation)
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VIDEO: Plant Transport - Xylem and Phloem (transpiration)