AP Bio Lab 1 Water Potential

Water Potential
 The combined effect of:
 Solute concentration
 Pressure
…are incorporated into a single measurement
called water potential
 Water moves from the area of HIGH water
potential  to the area of LOW water potential
when moving across a membrane
*H20 moves from areas of high
pressure to areas of low pressure*
Solute Potential
 Pure water has a solute potential of zero. Solute potential
is NEVER positive.
 Adding more solute is a negative experience; the solute
potential always becomes negative or more negative
Sample Problem
 The molar concentration of a sugar solution in an open
beaker has been determined to be 0.3M. Calculate the
solute potential at 27 degrees. Round your answer to the
nearest hundredth.
 If the sugar solution was placed inside of dialysis tubing
and put in a beaker of pure water (Ψ=1) what would
happen? Why?
Pressure Potential
 Is the sum of all pressure on water
 Get b/c of 2 things:
 Turgor pressure- force created by the cell membrane
pushing against the cell wall (must have water inside to
push cell wall out)
 You CAN’T know this unless given so assume that the
pressure potential is zero unless otherwise told
Lab Set Up
 Changes to procedure:
 Part B, bags are 15cm long NOT 30cm
 Part B, add 10ml of each sucrose solution to each bag
 You don’t know the molarities they are labeled (A-F). You
must determine which solution goes to which molarity
based on your collected data.
 Put all dialysis bags and string in the same beaker for the
weekend and cover!
 No cork borer for potato cylinders so cut 4 relatively
equally sized cubes for each solution  REMOVE ALL
SKIN (set up scales first before getting so you can mass
and drop in the solutions immediately).
 Label all beakers that are using/will use