Water transport in multicellular plants

• What does turgor pressure provide

  A hydrostatic skeleton to support the stems and leaves
• What is turgor pressure

  The pressure exerted by the cell surface membrane against the cell wall in a plant
• What is the turgor pressure of a leaf cell

  1.5 MPa
• What does turgor pressure allow roots to do


  Force their way through concrete and tarmac
• What are root hair cells in the plant used for

  They are the exchange surface where water is taken into the plant
• What are the adaptions of a root hair cell

  * microscopic size means it can easily penetrate between soil particles

  * the microscopic size have a large SA:V ratio

  * each hair has a think surface layer so diffusion and osmosis can take place easily

  * concentration of solutes in cytoplasm of root hair cell maintains the water potential gradient between the soil and cells
• How does water move into the root hair cell from the soil

  Soil water has a low concentration of dissolved minerals so it has a very high water potential. The cytoplasm of the root hair cells contains many solvents so had a lower water potential so water moves into the root hair cell by osmosis
• What is the symplast pathway 


  The continuous cytoplasm of a plant cell that is connected by plasmodesmata. The root hair cell has a higher water potential than the next cell so water will move into it by osmosis
• What is the apoplast pathway 


  This is the movement of water through the cell walls. As water moves into the xylem more water is pulled through due to cohesion
• water move into the xylem

  1. water moves across root in 2 pathways until it reaching endodermis
  2. The endodermis is particulary noticeable in the roots because of the effects of the casparan strip.
  3. At this point water in apoplast pathway can go no further and passes through a selectively permeable membrane to join the symplast pathway. 
  4. the solute concentration is higher in the xylem than the endodermal cells and the endodermal cells continues to pump more minerals ions into the xylem
  5. means the the endodermis has a high water potential so pumps water into the xylem, back into apoplast
• What does the active pumping of minerals to move water into the xylem cause

  Root pressure
• What is root pressure

  It gives the water a push up the xylem but in most cases it is not a major factor in the movement of water
• What is the casparian strip


  Band of waxy material called Suberin that runs around each of the endodermal cells forming a waterproof layer
• What is the endodermis

  The layer of cells surrounding the vascular tissue
• What is the evidence for the role of active transport in root pressure

  * some poisons such as cyanide affect the mitochondria and prevent the production of ATP. If cyanide is applied to root cells there is no energy and root pressure disappears

  * root pressure increases when temp increases and falls in low temps suggesting chemical reaction is involved

  * if levels of oxygen or respiratory substrates falls root pressure falls