How Water Passes Up The Stem
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How Water Passes Up The Stem

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How Water Passes Up The Stem How Water Passes Up The Stem Presentation Transcript

  • How water passes up the stem Movement of water and mineral ions through the xylem
  • How water passes up the stem
    • The tallest trees are over 60m high and may need as much as 250 dm 3 of water an hour to be transported upwards.
  • How water passes up the stem
    • In leaves
    • Water evaporates from spongy mesophyll cells so the air spaces become saturated with water.
  • How water passes up the stem
    • The air outside the stoma is not saturated so water diffuses out from an area of high water potential to region of lower water potential.
  • How water passes up the stem
    • As water evaporates from mesophyll walls more is drawn into cells to replace it.
    • Water can pass from the xylem to the leaf cells by both the apoplast and symplast pathway.
  • Water
  • Water Water is drawn up the xylem
  • Water Water is drawn up the xylem cytoplasm
  • Water Water is drawn up the xylem cytoplasm cell wall
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space Apoplast pathway (cell wall)
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space Apoplast pathway (cell wall)
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space Apoplast pathway (cell wall)
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space Apoplast pathway (cell wall)
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space Apoplast pathway (cell wall) Symplast pathway (cytoplasm)
  • Water Water is drawn up the xylem cytoplasm cell wall plasmodesmata stoma vacuole epidermal cell xylem vessel air space Apoplast pathway (cell wall) Symplast pathway (cytoplasm) Evaporation of water vapour
  • How water passes up the stem
    • Cohesion-tension theory
    • As water is removed from xylem more water molecules are ‘pulled up’ to replace them – this pulling force is known as transpiration pull (a bit like sucking on a straw).
  • How water passes up the stem
    • This mass flow of water relies upon two properties of water.
    • cohesion – water molecules tend to stick together
    • adhesion – the molecules also stick to the inside of the xylem vessels.
  • How water passes up the stem
    • Drawing up a column of water through the xylem in this way is called the cohesion-tension theory .
  • How water passes up the stem
    • It requires a large force to break such a water column – the xylem vessels would collapse under such tension if they were not thickened
    • The cohesion-tension theory is considered the main way water reaches the leaves from the roots.
  • How water passes up the stem
    • Root pressure also contributes to flow of water up the plant – the roots push water into the xylem and help to push up the water column.
    • (Evidence: if you cut a plants stem at soil level water will continue to come out of the cut stem for some time)
  • How water passes up the stem
    • Capillarity is a third force contributing to the movement of water. Water will move up narrow tubes by capillary action as water molecules will stick to the walls of the xylem vessels.
    • This force is important in small plants but of little significance in large trees.