Chapter 36 Plant Transport I II Overview A Small Scale Transport B Medium Scale Transport C Large Scale Transport Plant Transport A Review 1 B Plasma membrane is semi permeable a lets some substances through and keeps others out b plasma membrane is a bilayer hydrophilic heads and hydrophobic tails c hydrophobic molecules can diffuse passive transport d hydrophilic molecules need transport proteins active transport Small Scale Transport 1 Active Transport pumping against the concentration gradient requires energy a Proton Pump Pumps H out of the cell Requires ATP goes against concentration gradient Creates potential energy Results in 1 Ch 36 b Co transport Passage of one solute coupled with passage of another 1 neutral solutes Sugars co transport with H ions Example H ions co transport with sucrose to move sugar into phloem 2 some ions anions Some ions co transport with H ions Example H ions co transport with NO3 to move NO3 into roots 2 Ch 36 c Ion channels Open and close in response to voltage and or chemical factors Open and close to let SPECIFIC ions through Example K ion channel in guard cells to release K ions when the stomata is closed 2 Passive Transport moving from a high concentration to low concentration with no energy expenditure Solute concentration and pressure will affect the uptake or loss of water a Water Potential Physical property that determines the direction in which water will flow Includes the effects of solute concentration and pressure If there are no barriers water moves high to low Water Potential Solute Potential Pressure Potential Note Units are in Mpa megapascal b Solute Potential Osmotic Potential It is the number of dissolved molecules Directly proportional to the molarity Solutes in plants tend to be mineral ions and sugars 3 Ch 36 c Pressure Potential How much physical pressure is on the solution d Artificial Model Figure 36 8 a right arm has solutes therefore making water potential lower thus resulting in water moving to the right b right arm now has pressure added to the solution which offsets the solute concentration thus resulting in no net movement of water c increased the positive pressure which increases the water potential thus the net movement of water is now to the lef d have a negative pressure on lef side thus pulls water toward the lef 4 Ch 36 e Facilitated Diffusion We are looking at the movement of water Movement of water across a membrane is slow Need aquaporin transport C Medium Scale Transport 1 2 Plant compartments that affect transport a apoplast everything outside of the plasma membrane Includes cell walls and extracellular spaces b symplast entire mass of cytosol Includes plasmodesmata and cytoplasmic channels Three Transport Routes a Transmembrane Route Out of one cell across cell wall and into another cell b Symplastic Route A continuous route through the cytosol c Apoplastic Route A continuous route through the cell walls and extracellular spaces 5 Ch 36 D Large Scale Transport 1 Due to Bulk Flow Movement of liquid in response to a pressure gradient Occurs from higher to lower pressure independent of the solute concentration 2 Occurs within the Xylem Specifically the tracheids and vessel elements Phloem Specifically in the sieve tube elements 6 Ch 36 III Coordination for Transport A Upward 1 Roots a Epidermis Water and minerals pass through the epidermis of roots Root tips and root hairs have a very permeable epidermis Active transport aids in the mineral accumulation b Endodermis Once water and minerals enter epidermis of roots must pass through endodermis Innermost layer of cells in root cortex Surrounds the vascular cylinder stele Serves as a last checkpoint for selective passage c Casparian strip Part of the endodermal wall Waxy made of suberin It is impervious doesn t let it pass to water and dissolved minerals Up until this point water and minerals have been traveling through cortex by symplast or apoplast routes 1 symplastic route Casparian strip allows water and minerals traveling via the symplastic route to pass through 2 apoplastic route Casparian strip blocks water and minerals traveling via the apoplastic route to pass through 7 Ch 36 2 Stems Water and dissolved minerals that made it past the Casparian strip and into the xylem must move upward through the plant against gravity a Transpiration Leaves sweat Lose water vapor which causes pressure Water lost by leaves is replaced by water brought up from roots b Xylem sap Dilute solution of water and dissolved minerals carried through the xylem vessels and xylem tracheids Bulk transport 8 Ch 36 c Counteracting gravity 1 pushing At night low transpiration Root cells still pumping minerals into vascular cylinder More solutes decreases water potential inside vascular cylinder Causes more water to flow into vascular cylinder from the root cortex which creates root pressure 2 pulling During day transportation is high High transpiration causes a pulling force 3 cohesion tension hypothesis Transpiration exerts a pull on xylem sap Puts the xylem sap under negative pressure or tension Cohesion of water molecules transmits the pull Ultimately it s solar powered Sun causes water to evaporate from leaf Which lowers water potential so more water comes up from the roots 3 Leaves Leaves have lots of surface but not much volume If photosynthesis increases water loss increases a Stomata Regulate transpiration rate Site of water loss Evidence of wilting seen in stomata first 9 Ch 36 b Evaporative cooling sweat Lowers the temperature of the leaf Protects enzymes involved in photosynthesis Do not want to damage because of high temperatures c Guard cells Positioned on either side of the stomata Changes shape open and closed 1 Role of water potential and potassium ions Shape depends on water potential Guard cells take up or release potassium ions Lots of water present Potassium ions go in Reduces water potential inside Water moves in Stomata opens Not much water present Potassium ions move out Increases water potential inside Water moves out and stomata closes 10 Ch 36 d Xerophytes Have modified leaves to reduce transpiration Stomata on lower leaf surface in a depression that shelters it from the wind B Downward 1 Translocation Transport of organic nutrients in the phloem of vascular plants 2 Phloem Sap Mostly sucrose Travels from leaves to stems and roots Sugar sink a net consumer or depository of sugar Can travel through both symplastic and apoplastic routes 11 Ch 36 3 Sieve Tube