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Chapter 36: Transport in Plants

Chapter 36: Transport in Plants. Leaves  roots may be 100m apart. Plants. How do plants move materials from one organ to the other ?. Question ?. Levels of Plant Transport. 1. Cellular 2. Short Distance 3. Long Distance. A) Cellular Transport

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Chapter 36: Transport in Plants

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  1. Chapter 36: Transport in Plants

  2. Leaves  roots may be 100m apart. Plants

  3. How do plants move materials from one organ to the other ? Question ?

  4. Levels of Plant Transport 1. Cellular 2. Short Distance 3. Long Distance

  5. A) Cellular Transport The transport of solutes and water across cell membranes. Types of transport: Passive Transport Diffusion and Osmosis. Requires no cellular energy. Materials diffuse down concentration gradients. Problem: very slow Mechanisms Transport Proteins Ex: Carrier Proteins Selective Channels Potassium Channel Found in most plant cell membranes. Allow K+ but not Na+ to pass. Often “gated” to respond to environmental stimuli. B. Active Transport C. Water Transport 3 Levels of Plant Transport

  6. 2. Active Transport • Requires cell energy. • Moves solutes against a concentration gradient. • Ex: Proton Pump (another example of Chemiosmosis) • Uses ATP to move H+ out of cells. • H+ creates a membrane potential. • H+ allows cotransport. • Membrane Potentials • Allow cations to moved into the cell. • Ex: Ca+2, Mg+2 • Cotransport • Couples H+ with anions to move both into cell. • Ex: NO3-

  7. Summary

  8. 3. Water Transport • Osmosis - water moves from high concentration to low concentration. • Water Potential • The potential energy of water to move from one location to another. • Abbreviated as y • Has two components: • Pressure potential: yr • Solute potential: yp y = yr + yp

  9. Problem • Cell wall creates a pressure in the cells. • Water potential must account for this pressure. • Pressure counteracts the tendency for water to move intoplant cells.

  10. Bulk Flow • The movement of water between two locations due to pressure. • Much faster than osmosis. • Tension (negative pressure). • May cause bulk flow against the diffusion gradient.

  11. Tension • Is a very important force to "pull" water from one location to another. • Plant Vacuoles • Create Turgor Pressure against the cell wall. • Affect water potential by controlling water concentrations inside cells.

  12. Tonoplast • Name for the vacuole membrane. • Has proton pumps. • Comment – genetic modification of these pumps gives plants salt tolerance.

  13. Proton Pumps • Drives solutes inside the vacuole. • Lowers water potential (yp)inside the vacuole. • Result • Water moves into the vacuole. • Vacuole swells. • Turgor pressure increases.

  14. Turgor Pressure • Important for non-woody plant support. • Wilting: • Loss of turgor pressure. • Loss of water from cells.

  15. Turgid Flaccid

  16. Aquaporins • Water specific facilitated diffusion transport channels. • Help water move more rapidly through lipid bilayers. • Short Distance Transport 1. Transmembrane route 2. Symplast route 3. Apoplast route

  17. Materials cross from cell to cell by crossing each cell's membranes and cell walls. 1. Transmembrane

  18. The continuum of cytoplasm by plasmodesmata bridges between cells. 2. Symplast

  19. Extracellular pathway around and between cell walls. 3. Apoplast

  20. Point • Movement of materials can take place by all 3 routes.

  21. Long Distance Transport • Problem: diffusion is too slow for long distances. • Answer: tension and bulk flow methods.

  22. Absorb water. Take up minerals. Start - Roots

  23. Main site of absorption. Comment - older roots have cork and are not very permeable to water. Root Hairs

  24. Very spongy. Apoplast route very common. Problem Can't control uptake of materials if the apoplast route is used. Root Cortex

  25. Endodermis with its Casparian Strip. Solution

  26. Casparian Strip • Waxy layer of suberin. • Creates a barrier between the cortex and the stele. • Forces materials from apoplast into endodermis symplast. • Result • Plant can now control movement of materials into the stele.

  27. Casparian Strip Endodermis

  28. Mycorrhizae • Symbiotic association of fungi with roots of plants. • Help with water and mineral absorption (replaces root hairs in some plants). • May also prevent toxins from entering the plant.

  29. Mycorrhizae

  30. Xylem Sap • Solution of water and minerals loaded into the xylem by the endodermis. • Endodermis - also prevents back flow of water and minerals out of the stele.

  31. Xylem Sap Transport Methods 1. Root Pressure 2. Transpiration (Ts) • Root Pressure • Root cells load minerals into xylem. • Water potential (yp) is lowered. • Water flows into xylem. • Result • Volume of water in xylem increases • Xylem sap is pushed up the xylem tissues creating root pressure.

  32. Root Pressure: limited way to move xylem sap. Most apparent at night. Excess water may leave plant through Guttation. Comments

  33. Transpiration (Ts) • Evaporation of water from aerial plant parts. • Major force to pull xylem sap up tall trees.

  34. TCTM Theory • Transpiration • Cohesion • Tension • Mechanism

  35. How does TCTM work? • Water evaporates from leaves, especially from the cell walls of the spongy mesophyll. • Reason: water potential of the air is usually much less than that of the cells.

  36. As water evaporates: • Cohesion: water molecules sticking together by H bonds. • Adhesion: water molecules sticking to other materials (cell walls etc.). • Result • The loss of water from the leaves creates “tension” or negative pressure between the air and the water in the plant.

  37. Tension causes: • Xylem sap to move to replace the water lost from the mesophyll cells.

  38. Xylem Sap • Is “pulled” by the resulting tension all the way down the plant to the roots and soil.

  39. Summary • Xylem sap moves along a continual chain of water potential from: air leaf stem roots soil

  40. Comments • Tension is a negative pressure which causes a decreased in the size of xylem cells. • Xylem cells would collapse without secondary cell walls.

  41. 1. Environmental 2. Plant Structures Factors that Affect Transpiration Rate Multiple Layer Epidermis Stomatal Crypt

  42. Environmental Factors 1. Humidity 2. Temperature 3. Light 4. Soil Water Content 5. Wind

  43. Plant Structure Factors 1. Cuticle 2. Stomate Number 3. Hairs

  44. Stomates • Openings in the epidermis that allow water and gas exchange. • Controlled by Guard Cells. • Control rate of Ts and Ps.

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