9.2 phloem structure and func4onadamsbio.weebly.com/uploads/7/6/7/5/76752321/phloem_9.2.1.pdf ·...
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9.2PhloemStructureandFunc4on
Copyright Pearson Prentice Hall
9.2 U. 1 Translocation: Plants Transport organic compounds from
sources to sinks – Movement from Source to Sink
• A process of phloem transport moves sugars through a plant from a source to a sink.
• A source is any cell in which sugars are produced by photosynthesis.
• A sink is any cell where the sugars are used or stored (fruits, roots, seeds).
PlantSinksNotthattypeofsink!
9.2U.2Incompressibilityofwaterallowstransportalonghydrosta4cpressuregradients
• Hydrosta4cpressureisinliquids• Highconcentra4onsofsugarinthesievetubesleadstoanuptakeofwaterduetothecrea4onofalowconcentra4onofwaterinthesievetube
• Assugarisremovedatthestoragesite,theconcentra4ongradientshiGsandwaterexitsthetubebyosmosis
PHLOEMTissue• PhloemCellsarealive.• SieveTubeelements(cells)lacksnucleus&cytoplasm
• Sievetubeelementsareconnectedtoeachotherviasieveplates
• Sieveplateshaveholeswhichallowmovementofwateranddissolvedorganicmolecules
• CompanionCellshasnucleusanddensecytoplasm
• CompanioncellsareaKachedtosievetubeelementviaplasmodesmata
Sieveplate
9.2.U.3Ac4vetransportisusedtoloadorganicmoleculesintophloemsievetubesatthesource
9.2.U.4Highconcentra4onsofsolutesinthephloematthesourceleadtowateruptakebyosmosis
• Thesourceduringgrowingseasonistheleaf
• Glucosefromphotosynthesisisconvertedtosucrosefortransport
• CompanioncellusesATPtoac4velyloadsucroseintophloem,increasingconcentra4on
• Waterflowsfromxylemtophloembyosmosis
• Sapvolumeandpressureincreaseleadingtomassflow
• Organicmoleculesunloadedatsink,convertedtoinsolublestarchforstorage
• Waterreleasedandflowsbackintoxylembyosmosisandcyclecon4nues
9.2U.5Raisedhydrosta4cpressurecausesthecontentsofthephloemtoflowtowardsthesink
• 1.Transloca>onmovestheorganicmolecules(sugars,aminoacids)fromtheirsourcethroughphloemtothesink.Phloemvesselss4llhavecrosswallscalledsieveplatesthatcontainpores.
• 2.Companioncellsac4vely(ac4vetransport)loadsucroseintothephloem.
• 3.Waterfollowsthehighsoluteinthephloembyosmosis.Aposi4vepressurepoten4aldevelopsmovingthemassofphloemsapforward.
• 4.Companioncellsac4velyunload(ATPused)theorganicmolecules
• 5.Organicmoleculesarestored(sucroseasstarch,insoluble)atthesink.Waterisreleasedandrecycledinxylem.
Watchthebelowanima4onsontransloca4on
Clickonthelinksbelowtoaccessanima4ons:
• hKp://www.youtube.com/watch?v=-b6dvKgWBVY&feature=related
• hKp://www.youtube.com/watch?v=MxwI63rQubU&feature=related
• hKps://youtu.be/xGCnuXxbZGk
TransportinPlantsSummary• 1.Sourceproducesorganicmolecules• 2.Glucosefromphotosynthesisproduced
• 3.Glucoseconvertedtosucrosefortransport• 4.Companioncellac4velyloadsthesucrose• 5.Waterfollowsfromxylembyosmosis• 6.Sapvolumeandpressureincreasedtogive
Massflow
• 7.Unloadtheorganicmoleculesbythecompanioncell
• 8.Sucrosestoredastheinsolubleandunreac>vestarch
• 9.Waterthatisreleasedispickedupbythexylem
• 10.waterrecyclesaspartoftranspira4ontoresupplythesucroseloading