Transport in Plants

  • Substances transported in plants
    • Water and nutrients: absorbed by the roots and transported through the xylem
    • Carbohydrates: moved from the site of production to the site of storage, through the phloem. Also moved from the site of storage to areas of new growth.
    • Hormones: Moved from where they are produced to the tissues they act on through the phloem.
  • Xylem transport
    • Pressure differential created by transpiration and osmosis moves water throughout the plant
  • Water potential
    • Represented by Ѱw
    • Is made up of two components:
    • Physical Forces: Gravity and/or pressure on the cell wall (turgor pressure)⍦p
    • Concentration: of solutes in the solutions on either side of the plasma membrane. ⍦s​
    • ⍦w = ⍦p + ⍦s​
  • Transport Routes
    • Apoplastic: Moves through the cell walls and the spaces in-between cells
    • Symplastic: Moves through the cytoplasm of cells which are connected through the plasmodesmata meaning they do not have to cross membranes
    • Transmembrane: Moves through membranes between cells and within cells
  • When water enters the endoderm is is directed by the waterproof Casparian strip, forcing it to use the symplatstic route
  • Ions in soil are moved using active transport from the ground into the roots.
  • After they enter the vascular stele they are transported using bulk flow.
  • In the xylem positive root pressure and negative pressure caused by transpiration moves water through the xylem
  • The stomata is opened and closed by the turgor pressure in the guard cells
    • When cells are turgid the stomata is open, and when the cells are flaccid it is closed
  • C4 and CAM plants have adapted to reduce water loss in warm climates by taking in CO2 at night and storing it to be sued the following day.
  • Phloem Transport:
    • Sap (carbohydrates and hormones) move using translocation which is driven by differences in turgor pressure (pressure-flow hypothesis)
    • Flow is from source to sink
    • Phloem loading: is an active process where proton pumps in the companion cause carbs from the source to enter the sieve tubes.
    • The difference in water potential from phloem loading causes water to be absorbed from the xylem and carbs to be moved by bulk transport.
    • Phloem unloading: An active process where water moves via osmosis back to the xylem causing carbs to move into the sink
  • 35-45 mc
  • 3-5 sa
  • 2-3 questions per slide show