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Recap - StarterRecap - StarterState 3 differences between
xylem and phloem structures
State the differences between the symplast and apoplast pathways
Define transpiration and state where does this occurs
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Starter – Challenge!Starter – Challenge!X-word on keywords on plant
transport learnt last lesson
8 min
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Last Lesson....Last Lesson....
Movement of water in plant cells
Movement of water through the plant
Movement of assimilates (sugars and other chemicals made by the plant cell) by translocation
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Explain how Explain how translocation happens happens
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TaskTaskDescribe how
sucrose moves along the phloem from source to sink using the following keywords:
mass flow water potentialosmosis hydrostatic
pressure
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Exam ObjectivesExam Objectives
Describe, with the aid of diagrams, the mechanism of transport in phloem involving active loading at the source and removal at the sink, and the evidence for and against this mechanism (HSW1, 7a).
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The evidence for translocationThe evidence for translocation
How we know phloem used for movement of sucrose:-
Use of radioactively labelled carbon dioxide (which will be used in photosynthesis), the labelled carbon soon appears in the phloem
Ringing tree to remove phloem results in sugars collecting above the ring
Aphid feeding on plant stem, mouthparts are taking food from the phloem
How we know energy from ATP needed for translocation:-
Companion cells have many mitochondriaUse of poison to prevent synthesis of ATPThe rate of flow of sugars is so high that energy
must be needed to drive the flow, rather than diffusion
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Evidence for translocationEvidence for translocation
How we know it is Source / sink mechanism:-pH of companion cells is higher than that of
the surrounding cellsElectrical potential difference across
membrane of companion cellsHigher sucrose concentration in the source
than in the sinkEvidence against this mechanismNot all the solutes in the phloem sap move at
the same rateSucrose is moved to all parts at the same rate,
rather than going more quickly to areas with alow concentration
The role of sieve plates is unclear
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Homework CheckHomework CheckComplete plant transport booklet
pages 5, 6, 7
Try some practice exam Qs
Revise for Mock exams for Monday and Thursday next week on all of F211 – Use Moodle to do practice exam Qs and revision activities