transport through the roots

• water travels through the roots via the root cortex into the xylem by 2 pathways:

  • Symplast pathway
  • Apoplast pathway
• the apoplastic pathway is where water passes between cells without entering them (through intercellular spaces).
• the symplast pathway is where water moves from cell to cell, passing through plasmodesmata.
• the symplast pathway - goes through living parts of the cells ( the cytoplasm )

  the cytoplasm of neighboring cells connect via the plasmodesmata (small channels in cell walls) and water moves via osmosis
• symplast pathway

  
• the apoplast path - goes through the non living parts of the cells (cell walls). The walls are very absorbent and water can simply diffuse through them aswell as passing through spaces between them

  • water can carry solutes and move from areas of high hydrostatic pressure to areas of low i.e along a pressure gradient which is an example of mass flow
• when water in the apoplast pathway gets to the endodermis cells in the root, its path is blocked by a waxy strip called the casparian strip.

  water now has to take the symplast pathway which is useful because it means water has to go through the cell surface membrane which are able to control what enters and leaves the cell.

  then it moves into xylem
• casparian strip


  a waxy strip in the cell walls preventing water going via the apoplast pathway once it gets to the endodermis cells in theroot
• the apoplast pathway

  
• both pathways are used but the main one is the apoplast pathway because it provides the least resistance
• Symplast pathway


  The movement of water and solutes through the cytoplasm of living plant cells, often via the plasmodesmata.
• Cytoplasm


  The gel-like substance found inside a cell, excluding the nucleus, where many of the cell's organelles are located.
• Plasmodesmata


  Small channels that connect the cytoplasm of neighboring cells, allowing for the movement of water and solutes between cells.
• Osmosis


  The process by which water moves across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.