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