Transport in flowering plants (self created)

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Transport in flowering plants (self created)

  1. 1. LESSON OBJECTIVES  To learn about the structure and functions of the xylem  To learn the mechanisms by which water is transported from the roots to the leaves (and other plant parts) in flowering plants  To know the definition of transpiration and the factors that affect the rate of transpiration
  2. 2. VASCULAR BUNDLES  Tissues that are responsible for the transport of materials in plants  Present in all parts of a plant including the roots, stem and leaves  Consist of xylem and phloem Xylem: Transport of water and dissolved mineral salts Phloem: Transport of food substances
  3. 3. VASCULAR BUNDLES IN A DICOTYLEDONOUS ROOT
  4. 4. VASCULAR BUNDLES IN A DICOTYLEDONOUS STEM
  5. 5. VASCULAR BUNDLES IN A DICOTYLEDONOUS LEAF
  6. 6. XYLEM - STRUCTURE  Long, hollow, dead tubes forming continuous columns from roots to leaves  No cytoplasm in the lumen  Walls are strengthened by deposits of lignin  Pits present in xylem walls – enable transport of water between xylem vessels  Two xylem cell types: tracheids and vessel elements
  7. 7. Tracheid Vessel element
  8. 8. XYLEM - FUNCTIONS  Conducts water and dissolved mineral salts from roots to stems and leaves  Provides mechanical support within the plant
  9. 9. MECHANISMS OF WATER TRANSPORT IN PLANTS  Root pressure  Capillary action  Transpiration pull
  10. 10. ROOT PRESSURE  Force that helps to drive water upward into the xylem  Mainly generated by osmotic pressure in the cells of the roots, which is in turn caused by active transport of mineral ions into the root cells  Usually occurs when transpiration rate is low—at a low transpiration rate, the dissolved mineral ions accumulate in the root xylem and lower the water potential  Water then moves from the root hair cells into the xylem, through the cortical cells and the endodermis, by osmosis
  11. 11. CAPILLARY ACTION  A phenomenon where liquid spontaneously rises in a narrow space such as a thin tube  Since xylem vessels in plants are very narrow tubes, capillary action helps in moving water up the vessels  The forces of cohesion (attractive forces between water molecules) and adhesion (attractive forces between water molecules and the xylem walls) help to move water upward in the xylem  Plays an important part in upward movement of water in small plants
  12. 12. TRANSPIRATION  Definition: The loss of water vapour from the aerial parts of a plant, especially through the stomata of the leaves  Water continuously moves out of the mesophyll cells to form a thin film of moisture over their surfaces  From the wet cell walls, water evaporates into the intracellular spaces, and from there diffuses through the stomata to the surrounding air
  13. 13. TRANSPIRATION  As water evaporates from the mesophyll cells, the cell sap becomes more concentrated  Water from cells deeper inside the leaf thus move into the mesophyll cells by osmosis  These cells in turn remove water from the xylem vessels. As they do that, the whole column of water moves up the vessels from the roots to the leavesTRANSPIRATION PULL
  14. 14. TRANSPIRATION PULL  The suction force due to transpiration which pulls water up the xylem vessels  The main force that drives the transport of water and dissolved mineral salts up tall trees  The stream of water up the plant/tree is known as the transpiration stream
  15. 15. FACTORS AFFECTING THE RATE OF TRANSPIRATION  Light  Temperature  Wind  Humidity To be investigated in online activity
  16. 16. SUMMARY  The xylem is responsible for the transport of water and dissolved mineral salts in flowering plants  Root pressure, capillary action and transpiration pull are the three mechanisms of water transport in flowering plants  Transpiration pull is the main mechanism of water transport in tall trees
  17. 17. Before we end, let’s view this animation to remind us of what we have learnt today 

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