Water uptake and movement up the stem

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  • Created by: Steff06
  • Created on: 27-03-16 14:46
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  • Water uptake and movement up the stem
    • Water UPTAKE from the soil:
      • Minerals REDUCE the WATER POTENTIAL of the cell cytoplasm so water is taken up across the PLASMA MEMBRANE by OSMOSIS as the molecules move down the water potential GRADIENT.
      • The epidermis layer contains ROOT HAIR cells that INCREASE the SURFACE AREA of the root.Cells absorb minerals from the soil by ACTIVE TRANSPORT using ATP energy.
    • Movement across the ROOT:
      • ENDODERMIS is a layer of cells surrounding the xylem. Endodermis consists of special cells that have a WATERPROOF STRIP in some of their walls - CASPARIAN STRIP.
      • Casparian strip BLOCKS the APOPLAST pathway, forcing water into the SYMPLAST pathway.
      • Endodermis cells move minerals by ACTIVE TRANSPORT from the CORTEXinto the XYLEM. This DECREASES the water potential in the XYLEM so water moves from the cortex through the endodermal cells to the xylem by OSMOSIS.
      • This REDUCES the water potential in the cells just outside the endodermis. This creates a water potential GRADIENT across the whole cortex. Water is moved along the SYMPLAST pathway from the root hair cells across the CORTEX and into the XYLEM.
      • At the same time, water can move through the apoplast pathway across the CORTEX. This water moves into the cells to join the symplast pathway just before passing through the endodermis.

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