2 What must be transported in plants? H2O & mineralsSugarsGas Exchange
3 Transport of Water & Minerals Occurs in the xylemH2O is moved from root to leavesTranspiration loss of H2O from leaves (thru stomata)ProcessesEvaporationCohesionAdhesionNegative Pressure
4 Transport of Sugar Occurs in the phloem Bulk Flow Calvin Cycle (Dark Rxns) in leaves loads sugar into the phloemPositive Pressure MovementSource (where sugar is made) to Sink (where sugar is stored/consumed)
5 Gas Exchange Photosynthesis Respiration CO2 in O2 out Transport occurs through stomataSurrounded by guard cellsControl opening & closing of stomataRespirationO2 inCO2 outRoots exchange gases w/ air spaces in the soilWhy can over-watering kill a plant?
6 Transport in PlantsThree main physical forces that fuel transport in plants:CellularGases from the environment into plant cellsH2O & minerals into root hairsShort-Distance TransportCell to cellMoving sugar from leaves into phloemLong-Distance TransportMoving substances through the xylem & phloem of a whole plant
7 Cellular Transport Passive Active Diffusion down a concentration gradientOccurs faster w/ proteinsCarrier Proteins (facilitated diffusion)ActiveRequires energyProton PumpPumps H+ out of a cellCreates a proton gradient (stored energy)Generates a membrane potentialUsed to transport many solutes
9 Cellular Transport -Water Potential Combined effects of solute concentration & physical pressureMoves from high H2O potential to a low H2O potentialInversely proportional to solute concentrationAdding solutes – Lowers water potentialDirectly proportional to pressureRaising pressure- Raises water potentialNegative pressure (tension) decreases water potential
12 Short-Distance Transport Movement from cell to cell by…TransmembraneCrosses membranes & cell wallsSlow, but controlledCalled the apoplastic routeCytosol (cytoplasm)Plasmodesmata junctions connect the cytosol of neighboring cellsCalled the symplast route
13 Long-Distance Transport Bulk FlowMovement of a fluid driven by pressureXylem: tracheids & vessel elementsNegative pressureTranspiration creates negative pressure by pulling xylem up from the rootsPhloem: Sieve tubesPositive pressureLoading of sugar at the leaves generates a high positive pressure, which pushes phloem sap thru the sieve tubes
14 Four Basic Transport Functions Water & Mineral Absorption of RootsTransport of Xylem SapControl of TranspirationTranslocation of Phloem Sap
15 Water & Mineral Absorption Root HairsIncrease surface areaMineral Uptake by Root HairsDilute solution in the soilActive Transport PumpsMay concentrate solutes up to 100X in the root cellsWater Uptake by Root HairsFrom high H2O potential to low H2O potentialCreates root pressure
16 Water and Mineral Absorption – Root Structure MONOCOT ROOTDICOT ROOT
17 Water and Mineral Absorption – Water Transport in Roots Apoplastic orsymplasticUntil theendodermisIs reached!!
18 Water and Mineral Absorption – Control of Water & Minerals in the Root EndodermisSurrounds the steleSelective passage of mineralsFreely enters via the symplastic routeDead end via the apoplastic routeCasparian StripWaxy materialAllows for the preferential transport of certain minerals into the xylem
19 Water & Mineral Absorption & Mycorrhizae Symbiotic relationship b/w fungi & plantSymbiotic fungi increase surface area for absorption of water & mineralsIncreases volume of soil reached by the plantIncreases transport of water & minerals to host plant
20 Transport of Xylem Sap: Pulling TRANSPIRATION-COHESION-TENSION MECHANISMTranspirational PullDrying air makes H2O evaporate from the stomata of the leavesCohesionb/w H2O moleculescauses H2O to form a continuous columnAdhesionH2O molecules adhere to the side of the xylemTensionAs H2O evaporates from the leaves, it moves into roots by osmosis
21 Transport of Xylem Sap: Pushing Root Pressure – pushes H2O up xylemDue to the flow of H2O from soil to root cells at night when transpiration is lowPositive pressure pushes xylem sap into the shoot systemMore H2O enters leaves than exits (is transpired) at nightGuttation - H2O on morning leaves
22 Transport of Xylem Sap- Ascent of H2O in Xylem: Bulk Flow Due to three mainmechanisms:Transpirational PullAdhesion & cohesionWater potentialHigh in soil low in leavesRoot pressureUpward push of xylem sapDue to flow of H2 O from soil to root cells
23 Control of Transpiration: Gas Exchange Stomate FunctionCompromise b/w photosynthesis & transpirationAmount of transpiration (H2O loss) must be balanced with the plant’s need for photosynthesisLeaf may transpire more than its weight in water every day!OPENSTOMATACLOSEDSTOMATA
25 Control of Transpiration - Photosynthesis vs. Transpiration Open stomata allow for CO2 needed for photosynthesis to enterThere is a trade-off…..Plant is losing water at a rapid rateRegulation of the stomata allow a plant to balance CO2 uptake with H2O lossWhat types of environmentalconditions will increase transpiration?
26 Control of Transpiration – Stomatal Regulation Microfibril MechanismGuard cells attached at tipsMicrofibrils elongate & cause cells to arch openMicrofibrils shorten & cause cells to closeIon MechanismUptake of K+ by guard cells during the dayH2O potential becomes more negativeH2O enters the guard cells by osmosisGuard cells become turgid & buckle openLoss of K+ by guard cellsH2O potential becomes more positiveH2O leaves the guard cells by osmosisGuard cells become flaccid & close the stomata
28 Control of Transpiration – Stomatal Regulation Three cues that open stomata at sunrise:Light TriggerBlue-light receptor in plasma membraneTurns on proton pumps & takes up K+Depletion of CO2 in air spacesCO2 used up at night by the Calvin CycleInternal Clock (Circadian Rhythm)Automatic 24-hour cycle
29 Control of Transpiration- Adaptations that Reduce Transpiration Small, thick leavesReduces surface area-to-volume ratioThick cuticleStomata on lower leaf side with depressionsDepressions shelter the stomata from windMay shed leaves during dry monthsFleshy stems for water storageCAM metabolismTakes in CO2 at night & can close stomata during the day
30 Translocation of Phloem Sap Water & sugar (mostly sucrose)Moved through sieve tube membersPorous cross walls that allow sap to move throughTravels in many directionsFrom source to sink (where sugar is consumed/stored)Source: leafSink: roots, shoots, stems,& fruits
31 Translocation of Phloem Sap- Loading of Sugars Flow through the symplast or apoplast in mesophyll cells into sieve-tube membersActive co-transport of sucrose with H+Proton pump
32 Translocation of Phloem Sap- Pressure Flow Bulk Flow MovementSugar loaded at the sourceReduces water potentialCauses H2O to move into sieve-tube membersCreates a hydrostatic pressure that pushes sap through the tubeSucrose is unloaded at the sinkWater moves into xylem & is carried back up the plant
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