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TRANSPORT in PLANTS. What must be transported in plants?  H 2 O & minerals  Sugars  Gas Exchange.

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Presentation on theme: "TRANSPORT in PLANTS. What must be transported in plants?  H 2 O & minerals  Sugars  Gas Exchange."— Presentation transcript:

1 TRANSPORT in PLANTS

2 What must be transported in plants?  H 2 O & minerals  Sugars  Gas Exchange

3 Transport of Water & Minerals  Occurs in the xylem  H 2 O is moved from root to leaves  Transpiration  loss of H 2 O from leaves (thru stomata) Processes  Evaporation  Cohesion  Adhesion  Negative Pressure

4 Transport of Sugar  Occurs in the phloem  Bulk Flow Calvin Cycle (Dark Rxns) in leaves loads sugar into the phloem Positive Pressure Movement Source (where sugar is made) to Sink (where sugar is stored/consumed)

5 Gas Exchange  Photosynthesis CO 2 in O 2 out Transport occurs through stomata  Surrounded by guard cells Control opening & closing of stomata  Respiration O 2 in CO 2 out Roots exchange gases w/ air spaces in the soil Why can over-watering kill a plant?

6 Transport in Plants  Three main physical forces that fuel transport in plants: Cellular  Gases from the environment into plant cells  H 2 O & minerals into root hairs Short-Distance Transport  Cell to cell  Moving sugar from leaves into phloem Long-Distance Transport  Moving substances through the xylem & phloem of a whole plant

7 Cellular Transport  Passive Diffusion down a concentration gradient Occurs faster w/ proteins  Carrier Proteins (facilitated diffusion)  Active Requires energy Proton Pump  Pumps H + out of a cell  Creates a proton gradient (stored energy)  Generates a membrane potential Used to transport many solutes

8 Cellular Transport –Active Transport

9 Cellular Transport -Water Potential  Combined effects of solute concentration & physical pressure  Moves from high H 2 O potential to a low H 2 O potential Inversely proportional to solute concentration  Adding solutes – Lowers water potential Directly proportional to pressure  Raising pressure- Raises water potential Negative pressure (tension) decreases water potential

10 Cellular Transport- Water Potential  H 2 O potential = pressure potential + solute potential A) adding solutes reduces H 2 O potential B & C) adding pressure, increases H 2 O potential D) negative pressure decreases H 2 O potential

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12 Short-Distance Transport  Movement from cell to cell by… Transmembrane  Crosses membranes & cell walls  Slow, but controlled  Called the apoplastic route Cytosol (cytoplasm)  Plasmodesmata junctions connect the cytosol of neighboring cells  Called the symplast route

13 Long-Distance Transport  Bulk Flow Movement of a fluid driven by pressure Xylem: tracheids & vessel elements  Negative pressure  Transpiration creates negative pressure by pulling xylem up from the roots Phloem: Sieve tubes  Positive pressure  Loading of sugar at the leaves generates a high positive pressure, which pushes phloem sap thru the sieve tubes

14 Four Basic Transport Functions 1) Water & Mineral Absorption of Roots 2) Transport of Xylem Sap 3) Control of Transpiration 4) Translocation of Phloem Sap

15 Water & Mineral Absorption  Root Hairs Increase surface area  Mineral Uptake by Root Hairs Dilute solution in the soil Active Transport Pumps  May concentrate solutes up to 100X in the root cells  Water Uptake by Root Hairs From high H 2 O potential to low H 2 O potential Creates root pressure

16 Water and Mineral Absorption – Root Structure DICOT ROOT MONOCOT ROOT

17 Water and Mineral Absorption – Water Transport in Roots Apoplastic or symplastic Until the endodermis Is reached!!

18 Water and Mineral Absorption – Control of Water & Minerals in the Root  Endodermis Surrounds the stele Selective passage of minerals Freely enters via the symplastic route Dead end via the apoplastic route  Casparian Strip Waxy material Allows for the preferential transport of certain minerals into the xylem

19 Water & Mineral Absorption & Mycorrhizae  Symbiotic relationship b/w fungi & plant Symbiotic fungi increase surface area for absorption of water & minerals Increases volume of soil reached by the plant Increases transport of water & minerals to host plant

20 Transport of Xylem Sap: Pulling  TRANSPIRATION-COHESION-TENSION MECHANISM  Transpirational Pull Drying air makes H 2 O evaporate from the stomata of the leaves  Cohesion b/w H 2 O molecules causes H 2 O to form a continuous column  Adhesion H 2 O molecules adhere to the side of the xylem  Tension As H 2 O evaporates from the leaves, it moves into roots by osmosis

21 Transport of Xylem Sap: Pushing  Root Pressure – pushes H 2 O up xylem Due to the flow of H 2 O from soil to root cells at night when transpiration is low Positive pressure pushes xylem sap into the shoot system  More H 2 O enters leaves than exits (is transpired) at night Guttation - H 2 O on morning leaves

22 Transport of Xylem Sap- Ascent of H 2 O in Xylem: Bulk Flow Due to three main mechanisms:  Transpirational Pull Adhesion & cohesion  Water potential High in soil  low in leaves  Root pressure Upward push of xylem sap Due to flow of H 2 O from soil to root cells

23 Control of Transpiration: Gas Exchange  Stomate Function Compromise b/w photosynthesis & transpiration  Amount of transpiration (H 2 O loss) must be balanced with the plant’s need for photosynthesis Leaf may transpire more than its weight in water every day! OPEN STOMATA CLOSED STOMATA

24 Control of Transpiration- Leaf Structure

25 Control of Transpiration - Photosynthesis vs. Transpiration  Open stomata allow for CO 2 needed for photosynthesis to enter  There is a trade-off….. Plant is losing water at a rapid rate  Regulation of the stomata allow a plant to balance CO 2 uptake with H 2 O loss What types of environmental conditions will increase transpiration?

26 Control of Transpiration – Stomatal Regulation  Microfibril Mechanism Guard cells attached at tips Microfibrils elongate & cause cells to arch open Microfibrils shorten & cause cells to close  Ion Mechanism Uptake of K + by guard cells during the day  H 2 O potential becomes more negative  H 2 O enters the guard cells by osmosis  Guard cells become turgid & buckle open Loss of K + by guard cells  H 2 O potential becomes more positive  H 2 O leaves the guard cells by osmosis  Guard cells become flaccid & close the stomata

27 Control of Transpiration- Stomatal Regulation

28 Control of Transpiration – Stomatal Regulation  Three cues that open stomata at sunrise: Light Trigger  Blue-light receptor in plasma membrane  Turns on proton pumps & takes up K + Depletion of CO 2 in air spaces  CO 2 used up at night by the Calvin Cycle Internal Clock (Circadian Rhythm)  Automatic 24-hour cycle

29 Control of Transpiration- Adaptations that Reduce Transpiration  Small, thick leaves Reduces surface area- to-volume ratio  Thick cuticle  Stomata on lower leaf side with depressions Depressions shelter the stomata from wind  May shed leaves during dry months  Fleshy stems for water storage  CAM metabolism Takes in CO 2 at night & can close stomata during the day

30 Translocation of Phloem Sap  Phloem Sap Water & sugar (mostly sucrose) Moved through sieve tube members  Porous cross walls that allow sap to move through  Travels in many directions From source to sink (where sugar is consumed/stored)  Source: leaf  Sink: roots, shoots, stems,& fruits

31 Translocation of Phloem Sap- Loading of Sugars  Flow through the symplast or apoplast in mesophyll cells into sieve-tube members  Active co-transport of sucrose with H + Proton pump

32 Translocation of Phloem Sap- Pressure Flow  Bulk Flow Movement Sugar loaded at the source  Reduces water potential Causes H 2 O to move into sieve-tube members Creates a hydrostatic pressure that pushes sap through the tube Sucrose is unloaded at the sink Water moves into xylem & is carried back up the plant

33 Phloem Transport

34 Pressure Flow and Translocation of Sugars


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