Movement of Water through Plants

Movement of Water through Roots

• Root hair cell absorbs water via osmosis since it has a lower water potential than the surrounding soil
• The water then moves through the cortex in one of two pathways
  • Symplastic Pathway
    • water travels through the cytoplasm via osmosis, as water moves into the cytoplasm of one cell, it increases the water potential of that cell so water moves down a water potential gradient via osmosis to the cytoplasm of the next cell through a fine strand of cytoplasm linking adjacent cells (Plasmodesma)
  • Apoplastic Pathway
    • Water travels through the cell wall
    • tension because of the cohesive nature of water draws water molecules through spaces in the cell wall
    • when water from the apoplastic pathway reaches the endothelium, it is forced into the cytoplasm by a waterproof ***** called "the casparian *****"
• At the endothelium, mineral ions enter the xylem via active transport from the endothelial cells
• This decreases the water potential of the Xylem, so water moves into the Xylem via Osmosis 

Up the Stem

• Water evaporates via the stomata when they are open (controlled by guard cells)
• Cohesion Tension Theory
  • Water molecules form hydrogen bonds with adjacent water molecuels 
  • In this way they form an unbroken pathway 
  • because of this tension, when water has left the stomata, more water is drawn up through the mesophyll to replace it
  • this tension also pulls water moleucles up the stem
• root pressure also aids in moving water up the stem, root pressure is caused by the active transport of mineral ions into the xylem, causing water to move into the xylem at the root.