9.2 water transport in multicellular plants

    Cards (17)

    • what does turgor pressure provide
      provides a hydrostatic skeleton to support the stems and leaves
    • turgor also drives cell expansion how is this useful
      it is the force that enables plant roots to force their way through tarmac and concrete
    • how does the loss of water by evaporation help plants
      keeps plants cool
    • where is water taken into the plant
      root hair cells
    • how are root hairs adapted as exchange surfaces
      • microscopic size means they can penetrate easily between soil particles
      • millions of microscopic hairs with large SA:VOL ratio
      • each hair has a thin surface layer so diffusion and osmosis can happen quickly
      • concentration of solutes in the cytoplasm of root hair cell maintains a water potential gradient between the water in the soil and the cell
    • why does soil water have a very high water potential
      because it has very low concentration of dissolved minerals
    • how does water move into the root hair cell by osmosis
      because water in the soil had a high water potential where as inside the root hair cell theres a low water potential so water moves into the cells as water moves from an area of high water potential to an area of low water potential
    • which two pathways does water move from roots to xylem
      • symplast pathway
      • apoplast pathway
    • how does water move through the symplast route
      • water moves continuously through the cytoplasm of adjacent cells through the plasmodesmata
      • root hair cell has a higher water potential than the next cell along so water moves into the next cell by osmosis and this continues until the xylem is reached
    • how does water move through the apoplast route
      • water moves through the cellulose cell walls (fibres with water filled spaces)
      • as water moves into the xylem more water is pulled through continuously due to the cohesive forces between water molecules
      • the continuous flow of water and the cohesive forces creates tension which means there a continuous flow of water through the cell wall
    • what is the endodermis
      layer of cells surrounding the vascular tissue (xylem and phloem) of the roots
    • what is the casparian strip
      band of waxy material called suberin that runs around each of the endodermal cells forming a waterproof layer
    • when and why does the apoplast pathway stop and join the sympoplast pathway
      • both pathways travel across the roots until it reaches the endodermis
      • here the apoplast pathway joins the sympoplast pathway due to the effect of the casparian strip
      • water must pass selectively permeable cell surface membranes so this excludes any potentially toxic solutes in the soil water from reaching living tissues as membranes have no carrier proteins to admit them
    • how does water move into the xylem
      • the solute concentration in the cytoplasm of the endodermal cells is relatively dilute compared to the cells in the xylem
      • also endodermal cells move mineral ions into the xylem by active transport
      • so the water potential is much lower in xylem than in the endodermal cells
      • as a result water moves by osmosis from endodermal cells into the xylem
    • what happens once inside the vascular bundle
      water returns the apoplast pathway to enter the xylem and move up the plant
    • what results in root pressure
      active pumping of minerals into the xylem to produce the movement of water
    • what does root pressure do
      gives water a push up the xylem but under most circumstances it is not a major factor