Osmosis and Diffusion Lab using Potato Cores
Instructions and Rubric
Audrey Farnsworth
Group 3:
Oliver, Dawson, Audrey, Brook
Introduction:
Water can move through protein channels in cell membrane/cell walls. The water will move due to
the water potential of the cells. If there is a greater concentration of solutes (chemicals) inside the
cell than outside the cell and the chemicals can not move, then water will respond by moving into
the cell. This process involves water gradients called water potentials. If one area has a great deal
of water, it has a high water potential. If an area has a great deal of dissolved material (less water)
it has a low water potential. Water will attempt to move down it gradient, that is, from high to low
water potential. You job is to observe this using potato cores that are placed into various solutions
of sugar water. The sugar is too big to easily move through the cell membrane/cell wall. So,
depending on the water potential of the cells vs. the solution water will move in or out. This lab
lets you observe this and determine the concentration of solutes in the potato cells.
Hypothesis
If there is a greater density within the solution, then potatoes will float. If the there is a low density
within the cup of solution than the potatoes should sink.
Variable identified:
Independent
- Time
- How much water
- How much the solution is
Dependent
- How big of a change occurs in the potato’s
- If they sink or float
- If they get bigger or smaller
Control variable
- The control in this experiment is the one with only purified water in the cup, no sugar. This way
we can see what changes and what doesn’t, within the experiment.
Materials:
 You will be working in groups of 4 if at all possible to share the work load (2 buddy groups)
 Potato cores (4 per condition)
 Sucrose solutions (.2, .4, .6, .8, 1.0 )
 Distilled water
 Electronic balance
 Plastic weighing tray
 Plastic cups (6)
 Graduated cylinder (50 ml)
 Scalpel
 Marking tape

Blue tweezers
Observations:
Water: sank
0.1: floated
0.2: sank
0.4: in the middle
0.6: floated
0.8: floated
Procedures:
1) Using marking tape, label 6 cups with the following solution types (.2, .4, .6, .8, 1.0 and Di water)
2) Place approximately 50 ml of the various solutions, each cup receiving a separate solution.
Suggestion, measure the di water with the graduated cylinder, and fill the other cups to the same
level
3) Obtain 24 potato cores and cut them to equal sizes (about 2.5 cm). All the cores you use must be
the same length. Divide your 24 cores into 6 groups and gently blot them dry with a paper towel
4) Using the electronic balance and plastic weighing tray mass (weigh) each group of potato cores
and record the data in a table that is labeled with a detailed title and which provides the error
measurement of the electronic scale. MAKE SURE TO TARE THE TRAY. The table should record
the type of solution in the cup and the mass of the potatoes in the cup.
5) Place the potato core sets in their appropriate cup and place in Mr. Boyer’s back prep room in
the fume hood that is labeled with your block (3B or 4B).
24 hours later (app) you will need to come and measure the mass of your potato cores. To do this
you must pore off the fluid in the cup and use the plastic blue tweezers remove the cores, blot them
dry just as you did in the set up phase and final measure them using a plastic weighing tray. MAKE
SURE TO TARE THE TRAY. Record your potato group mass on your data chart.
Finally dump your potato cores in the trash and wash and dry your equipment (cups, tweezers and
return them to their stations
Calculations. For each setup (all 6) you will need to calculate a percent mass change. To do this
you will use the following formula (final mass-initial mass)/initial mass x 100. You will need to
record this data in your data table as well. Make sure to keep track of the positive and negative
changes if they occur
Data chart
1st day
PREWATER
Group 1 (Water): 1.9 g
Group 2 (1.0 molar): 2.5 g
Group 3 (0.2 molar): 2.5 g
Group 4 (0.4 molar): 2.5 g
Group 5 (0.6 molar): 2.2 g
Group 6 (0.8 molar): 2.3 g
2nd day
AFTER Water:
Group 1 (water): 2.8 g
Group 2 (1.0): 1.6 g
Group 3 (0.4): 2.2 g
Group 4 (0.2): 2.7 g
Group 5 (0.6): 2.0 g
Group 6 (0.8): 1.8 g
Conclusion:
After all the procedures and observing, the potato cores sunk at different rates, the water (control)
sank at the very beginning, and stayed there. The other started out floating or sinking, then
changed positions overnight. Therefore depending on the density of the solute changes and decides
if the potato cores floats or sink.
Refection/ evaluation:
Reflection back on this lab, I can see many good things and bad things that our group did. The good
things are that we worked well together, with communication during the lab, and getting all the
work done that needed done. The bad things or the errors is that we split of after the day of the lab,
so I think that our data and reports are all going to be really different.