1. Moving water, minerals and sugars Jorge Melo

2. Introduction Plants use photosynthesis to convert light energy to chemical energy Simple organic substances, such as CO2, H2O and ions are used in their raw form to produce glucose and other carbohydrates. 3. Introduction How does the plants obtain H2O and CO2? Does the plants have a circulatory system like us? 4. Introduction American sequoias (giant redwood) Height of 60 meters How these trees lift water? 5. Objectives Explain the need for transport systems in multicellular plants Describe the distribution of xylem and phloem tissue in roots, stems and leaves Explain the absorption process in roots Describe transport mechanisms 6. Plants have two separate transport tissues Xylem tissue: Water and ions travel upwardsRootsStemsLeavesFlowersFruits Phloem tissue: Sucrose and other assimilates travel upwardsand downwards Movement of water in the xylem and phloem is by mass flow.Everything travels in the same direction within each of columnof xylem or phloem Note that neither plant transport system carries O2 or CO2 7. Xylem and Phloem 2 distinct transport systems In both the walls of the tubes are further thickened by the addition of: Cellulose (organic compound polysaccharide) Lignin (woody material) 8. Water transport in 3 parts Transpiration (or evapo-transpiration) is thetransport of water and minerals from roots to leaves.It involves three basic steps: 1- Absorption at the roots. 2 - Capillary action in the xylem vessels. 3 - Evaporation at the leaf. 9. Roots Root hair Single-celled extensions of some cells Very thin (200-250 m) A single root can have thousands Increases the surface area Absorbs water by osmosis 10. Roots Osmosis Movement of H2O molecules from an area of high concentration to an area of lower concentration lower solute concentration in the soil Higher solute concentration in the root High water potential in soil Low water potential in roots 11. Two different routs Apoplast pathway: When H2O soaks through the cell walls and then seepsacross the root from cell wall to cell wall and throughthe spaces between cells Symplast pathway: When H2O enters the cell walls and moves from cell to cell by osmosis Or through strands of cytoplasm that makes direct connection between adjacent cells- plasmodesmata 12. When water reaches the stele the apoplast pathway isblocked. Endodermis cells (stele) have suberin (waterproof) 13. Casparian strip: belt ofwaxy material, allows onlyminerals in the symplast topass into the vascularcylinder throughthe plasma membrane ofendodermal cells. Cells in the vascularcylinder transport waterand minerals throughoutthe plant. 14. Task 1 15. Xylem Long narrow cells Xylem elements Start as living cells (nucleus, cell wall) Then differentiated into specialised structures and died No living material Just empty shells 16. Protoxylem: The first one toXylem be developed behind rootand shoot tips. Lignin added Primary xylem in rings and spirals to formannular vessels (rings). Metaxylem: more mature and walls are fully lignin. Secondary thickening Secondary XylemThe seasonal growth of the xylem shows up as annual rings. The ring from the previous year transports little water but is useful for support. 17. Primary xylem Protoxylem Metaxylem 18. Root cross section 19. Stem 20. Leaf 21. Leaf cross section 22. Task 2 23. Palisade and spongy mesophyll cells have verylarge internal surface for gas exchange.As the carbon dioxide concentration in the air isso low (0.04%), the surfaces are large so thatenough can be absorbed for photosynthesis. 24. The air inside leaves is always fully saturated withwater vapour.Usually, the air outside is less saturated than thisand so a concentration gradient for water vapourexists between the air spaces and the outside.Water vapour therefore diffuses down thishumidity gradient.The pathway with the least resistance isthrough the stomata. It is open during theday to allow CO2 in and water out. In mostplants it is closed at night. 25. How does the water goes up? 26. Transpiration drives themovement of water in plants The loss of water from leaves by transpiration causes water to travel upwards through the plant by mass flow. The mechanism is called cohesion-tension and it works as follows: 27. Cohesion-tension theory Water loss caused by transpiration Causes a pulling force Negative pressure produced Transpiration pull 28. Cohesion-tension theory2 important factors of the water: Cohesion: H2O molecules tend to stick together by hydrogen bonding Adhesion: H2O molecules tend to stick to the inside of the xylem 29. Cohesion-tension theory Root Absorption through osmosis Endodermal cells actively secrete mineral salts Why? To keep the water potential in the xylem lower Causing water to be drawn through the endodermis pulling of water caused by cortex cells producepositive hydrostatic pressure inside the xylem , forcingwater upwards Root pressure 30. Cohesion-tension theory Capillarity Third force Water tends to rise inside narrow tubes by capillaryaction Capillarity relies upon the tendency of watermolecules to stick to walls of xylem vessels byadhesion. This force may be important in the upward movementof water in small plants but no relevance in large trees 31. How does the water goes up? Transpiration pull (negativepressure) Root pressure (positive pressure) Capillarity (small plants)2 important factors of the water: Cohesion: H2O molecules tend tostick together Adhesion: H2O molecules tend tostick to the inside of the xylem 32. Transpiration Spongy mesophyll cells are not tightly packed Air spaces are direct contact with the air outside theleaf, through small pores called stomata If air outside the leaf contains less H2O vapour theninside There is a H2O potentialgradient from the airspaces inside the leaf tothe outside 33. Task 3 34. Moving water, minerals and sugars Jorge Melo 35. How does the water goes up? Transpiration pull (negativepressure) Root pressure (positive pressure) Capillarity (small plants)2 important factors of the water: Cohesion: H2O molecules tend tostick together Adhesion: H2O molecules tend tostick to the inside of the xylem 36. Objectives List factors that affects rate transpiration Describe xerophyte properties List the series of events that leads to translocation 37. Potometer Measures the water absorption Estimate the rate of transpiration Air/water tight Water transpired Water entering to xylem 38. Factors affecting rate of transpirationLight intensity: Affects the opening and closing of the stomata ROT Indirect effect 39. Factors affecting rate of transpirationHumidity: Humid atmosphere Contains a lot of H2Omolecules Reduction of the waterpotential gradient betweenthe air spaces and atmosphere ROT decreases Low humidity increases ROT 40. Factors affecting rate of transpirationTemperature: Temperature kinetic energy Rate of diffusion throughthe stomata pores Air is able to hold morewater molecules at highertemperatures ROT 41. Factors affecting rate of transpirationWind speed: Still air makes the H2Omolecules to accumulatearound the stomata pores(leaves) Reduces the H2Opotential gradient andslows the ROT Wind disperse H2Omoleculesgradient in H2Opotential ROT 42. Xerophytes Vs Mesophytes 43. xerophytes A plant adapted to live in dry conditions They have a range of adaptations to reduce the loss of water vapour by transpiration. 44. xerophytes Leaves Small to reduce the surface area Thick to reduce surface area: volumes ratio 45. xerophytes Sunken Stomata 46. xerophytes Stomata Set deep inside the leaf so that they are at the base of a depression full of water vapour Some plants open their stomata at night to store and absorb CO2 47. xerophyte Thick waxy cuticles reduce water loss through the epidermis 48. Xerophytes Rolling up of leaves Lower surface faces inside and traps humid air next to the stomata Varies with conditions 49. Xerophytes Leaf hairs Trap damp air Reduces air movement Cut down transpiration 50. Task 1 51. Transport in the Phloem Most photosynthesis occurs in the leaves. The reactions take place in the chloroplasts. The compounds that the plant makes arecalled assimilates. Many of these are exported form the leavesto the rest of the plant in the phloem. 52. Sources and Sinks The transport of these assimilates is calledtranslocation. This literally means from place to place. Assimilates are loaded in the phloem in the leaves, they are often called sources. They are transported to other parts of the plant, suchas roots, stems, flowers, fruits and seeds. These arecalled sinks. 53. Movement in the Phloem in an activetransport The transport of theseassimilates is calledtranslocation Sucrose and otherassimilates travelthroughout a plant inphloem sieve tubes. These are made fromcells called sieveelements. 54. Sieve tube Made of sieveelements Living cells No nucleous Ribosomes or tonoplast Diameter 10 15 um End walls: sieve plates Large pores 55. Alongside sieve tubesare companion cells.Mesophyll cells in theleaf are close to veinscontaining sieve tubes.Sucrose travels tothe phloemcompanion cells intwo ways. 56. From cell to cell throughthe plasmodesmata.Along cell walls in themesophyll.Carrier proteins in thecell surface membranesof companion cellsactively pump sucroseinto the cytoplasm.From here it passesthrough plasmodesmatainto a sieve element. 57. The accumulation of sucroseand other solutes, such asamino acids, in sieveelements lowers the waterpotential so that waterdiffuses in by osmosis fromadjacent cells and form thexylem.This creates pressure inthe sieve elementscausing the liquid(phloem sap) to flow outof the leaf. 58. Phloem sieve elements areadapted for transport as ithas: End walls that have sievepores allowing sap toflow freely. Little cytoplasm toimpede the flow of sap. Plasmodesmata to allowassimilates to flow infrom companion cells. 59. Sieve elements differform xylem vesselsbecause they are alive.They have somecytoplasm withorganelles.They are notlignified, as they donot need towithstand the sameforces as exist in thexylem. 60. Sucrose is unloaded atsinks.This is taken up by thecells and is respired orstored s starch.This reduces theconcentration ofphloem sap and lowersthe pressure, so helpingto maintain a pressuregradient form source tosink so the sap keepsflowing in the phloem. 61. Task