Investigating Osmolarity of Plant Cells.
Materials:
Sucrose
Potato
Plastic cups
Electric balance
Cork bore
Scalpel
Water
Centimeter rulers
Aluminum foil
Forceps
Method:
Prepare a solution of sucrose that has a molarity of 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6.
The formula of sucrose is C12H22O11. Atomic mass of C is 12, H is 1 and O is 16.
Label each plastic cup with your group name and the molarity of solution in the cup. In
the cup pour 100 ml of the solution.
With a cork bore, make multiple bores in a potato. If you plan correctly you should be
able to go through the fat side of the potato from top to bottom. Twist the corer as you
push toward the table. Use the smaller borer to push the core out. Using the scalpel trim
off the skin and cut each to 2cm in length. The scalpel is sharp so use extreme caution.
Mass 3 potatoes bores, together, and record the mass in the chart below. Place the three
bores in the 0.0 molar cup. Make any notes of the initial size, appearance and if the bore
floats or sinks in the solution. Take a picture of the potato bores. Make note of the
balance number and use the same balance both days
Balance number______________
Repeat for each cup 0.1-0.6. BE SURE to re-zero the balance with the weighing boat
before you add the next set of three cores.
Cover each cup with a piece of aluminum foil to prevent evaporation. What would
evaporation do to the molarity of the solution in the cup?
Place the cups on the cart. (or where the instructed to place them.)
After 24 hours re-mass all the cores. Record the masses on the chart below. Take the
cores out of the solution using the forceps.
Note any changes in length and texture of the cores in each cup.
% change in mass = Change in mass x 100
initial mass
The Change in mass can be a negative value or a positive value.
Osmolarity 0.0
0.1
0.2
0.3
0.4
0.5
0.6
Final mass
Initial
mass
Change in
mass
% change
in mass
Change in
length
Construct a graph of change % change in mass and the osmolarity.
On the Y axis place the % change in mass. Place a 0 (zero) on the middle line of the Y
axis. Above the 0 line is a positive change and below the 0 line is a negative change.
The X axis is osmolarity. Graph the points and draw a smooth line.
At what point does the osmolarity line cross the zero line?_______________
This is the osmolarity of the potato core. At this point there is equal concentration of
solutes on either side of the membrane and therefore no mass change.