Water Movement Through Plants

Uptake by root hairs, apoplastic pathway, symplastic pathway, water into xylem, water up stem in xylem, movement across leaf, movement out of stomata, transpiration

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  • Created by: Megan
  • Created on: 27-04-14 17:04

Uptake by root hairs

  • Root hairs are long and thin - provides a large surface area and thin diffusion pathway for water
    • 1. - Soil around the roots has a very high water potential
    • 2. - Root hair cells contain sugars, mineral ions, etc so have a lower water potential
    • 3. - Water moves by osmosis, down the water potential gradient
    • 4. - Moves up the cells of the root cortex after absorption by the apoplastic or symplastic pathways
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Apoplastic Pathway

  • Water moves between cell membrane and cell wall
  • Water has cohesive properties, so more water drags more water down the water potential gradient, along cell walls of the root cortex
  • Water reaches the impermeable Casparian ***** just before xylem, and is forced back into the cytoplasm.
  • Then travels by the symplastic pathway
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Symplastic Pathway

  • Moves across the cytoplasm of cells in the root cortex
  • Passes from cell to cell across plasmodesmata which creates a continous cytoplasm
  • Water entering the root hair cell raises the water potential so it's above the first cell in the cortex
  • Water moves down the water potential gradient, along the symplastic pathway
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Water into Xylem

  • Active transport of mineral ions into xylem by carrier proteins
  • Creates a lower water potential in the xylem than in the root cortex
  • Water moves down the water potential gradient into the xylem
  • Root pressure is created - contributing to water moving up plants
  •  Root pressure
    • Pressure increases with rise in temperature
    • Metabolic inhibitors cease root pressure
    • Decrease in abailability of oxygen reduces root pressure
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Water up the Stem

Cohesion Tension Theory

  • Water evaporates from leaves in transpiration
  • Water molecules form hydrogen bonds and stick together - cohesion
  • They form a continuous column up the xylem
  • Water evaporates from mesophyll cells so more water is drawn up
  • Creates a transpiration stream
  • Puts xylem under tension
  • Creates negative pressure within the xylem - pulls more water into leaf


  • Adhesion to the sides of the xylem prevents backflow

Diameter Change

  • Day time - transpiration stream at greatest, more negative pressure so diameter shrinks
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  • Photosynthesis only occurs in light
  • Stomata are open to release CO2 so transpiration occurs


  • Affects water potential gradient outside of the stomata


  • Rise in temperature increases kinestic energy so increases evaporation
  • Rise in temperature decreaes humidity, increases water potential gradient

Air Movement

  • Water vapour accumulates around stomata
  • Wind disperses water vapour
  • Maintains water potential gradient
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