-Because water potential is high in soil and roots but low in leaves and the atmosphere,
there is a water potential gradient between roots and shoots.
-For water to move UP the plant, the water moves DOWN the gradient. When it does so, it
replaces water lost to transpiration.
What Factors Affect Water Potential
-Isotonic: Solute in cell= solutes outside of cell
-Hypotonic: solutes in the cell >solutes outside the cell… water flows in cell
-Hypertonic: solutes in the cell<solutes outside the cell… water flows out of cell
-The concentration of the solution is important, because when solutions are separated by a
selectively permeable membrane, such as the plasma membrane of a cell, water passes
through the membrane from regions of low solute concentration to regions of high solute
-This movement of water across membranes, in response to differences in water potential is
-The tendency for water to move in response to differences in solute concentrations is called
solute potential or osmotic potential.
-The solute potential of a solution is defined by its solute concentration relative to pure
water. If water contains a high concentration of solutes, then is has a low solute potential
compared with pure water.
-When an animal cell is placed in a hypotonic solution and water enters the cell via osmosis,
the volume of the cell increases until it bursts.
-This does not happen to a plant cells however… if a plant cell swells in response to
incoming water, its plasma membrane pushes against the relatively rigid cell wall. The cell
wall resists ex[ansion of the cell volume by pushing back. The Force exerted by the wall is
called Wall pressure.
-As water moves into the cell, the pressure inside (Turgor pressure) increases until
wall pressure is induced.
-Cells that are firm and that experience wall pressure are said to be turgid.
-Pressure potential: a term used for all physical pressures on water.