Osmosis in Potato Lab
Purpose: The purpose of this experiment is to measure the effect of osmosis on
potato tissue
Background Information: Notes on cell transport, cell membrane and types of
solutions – hypertonic, hypotonic, isoto nic
Materials:
-6 petri dishes
-Potato and cork borer
-Dissecting razor/scalpel
-NaCl Solutions of: 1.0%, 2.0%,
3.0%, 4.0%, 5.0%
-Ruler
-Marking Pencil
-Distilled H20
Procedure: Work at a team and divide the work between each other!
1. Obtain 6 Petri dishes and label them with the six different concentrations.
2. Add enough of each of the solutions so that it nearly fills each of the petri
dishes.
3. Using the cork borer, obtain seven cylinders of potatoes. Push the borer
through the length of the potato, twisting it back and forth. You MUST have
seven complete, undamaged cylinders at least 5 cm long.
4. Using the razor blade or scalpel, cut the cylinders so that they are all 5 cm
long, removing any peel from the ends.
5. Record the exact length of each of the seven cylinders and which solution
they will be placed into. NOTE- one cylinder will act as a control
6. At the same time, place the potato cylinders into the petri dishes, cover them
and leave them undisturbed for at least 25 minutes. Note the time they were
put into the dishes.
7. Take a picture of the potatoes in the dishes- everyone must have a picture.
8. While waiting, start setting up your table in Excel. Title (not the lab title)
independent variable first column, then the dependent and a final column for
observations on rigidity. For Dependent variable- it will be initial length, final
length, and change in length (don’t forget units). The symbol for ‘change’ is Δ
found in symbols under the music symbols.
9. After 25 minutes or set time, remove the potatoes and immediately start
measuring and recording length- use teamwork here! Also record the rigidity
of the cylinder. Don’t forget the control.
10. Calculate the Δ in length and indicate an increase of length with a + sign and a
decrease of length with a – sign.
11. Once you are sure you are gone, the potatoes go in the garbage, the Petri
dishes should be washed and dried, the razor/scalpel should also be washed
and dried, and all equipment must be returned.
12. Make a line graph of your data.
13. Answer the following questions
Pictures
Before:
After:
Data Table:
Potatoes
Initial Length Final Length
 in length (%)
Rigidity
Original Potato
5 cm
5 cm
1.00 %
Potato in 0%
Salt Solution
Potato in 1%
Salt Solution
Potato in 2%
Salt Solution
Potato in 3%
Salt Solution
Potato in 4%
Salt Solution
Potato in 5%
Salt Solution
5 cm
5.3 cm
1.06%
5 cm
5.1 cm
1.02%
5 cm
5 cm
1.00%
5 cm
4.9 cm
0.98%
5 cm
4.9 cm
0.98%
5 cm
4.9 cm
0.98%
Firm and
smooth
Harder and
bumpy
Not as soft
and bumpy
Soft and
bumpy
Soft and
bumpy
Soft and
bumpy
Soft and
bumpy
Graph:
Questions:
1. From your observations, is there any evidence to suggest that water has
entered the potato cells? Explain.
From my observations, there is evidence to suggest that water has entered
the potato cells because the potato cells expanded when water entered
making the cylinder of potato become larger.
2. What is the slope line of your graph showing, what is the trend?
My graph is showing a negative slope line, this shows that the higher the
concentration of salt in the water, the smaller the potato becomes.
3. When the slope line crosses the zero point, what does this mean?
When the slope line crosses the zero point, it means that the potato shrinks
in size.
4. From your data, how can you determine the water concentration of the
potato? Explain.
From my data, I can determine the water concentration of the potato by
looking at the Δ in length. If the potato stayed the same size, the water
concentration was the same in and outside the potato. If the potato
expanded, the water concentration was lower in the potato than outside the
potato. If the potato shrunk, the water concentration was higher in the potato
than outside the potato.
5. Which would provide more reliable data, the class average or your own
group’s data? Explain.
The class average is more reliable then your own group’s data because by
taking the average you eliminate possible errors in calculations and the
experiment, and allows for better data.
6. When food is pickled, as much water as possible must be removed from the
cells. How would you do that?
To make food pickled, to remove as much water as possible from the cells,
you must add a lot of salt to the liquid so that water must leach out of the
cells to balance the amount of salt in the water.
Evaluation:
During the osmosis lab, there could have been many aspects that could have been
improved to make the lab more accurate. First, if the class had placed the potato in
the salt solution for the same amount of time, then the class average would have
been more accurate. Next, if the class used the same size borer, the results would
have been more accurate. Thirdly, the experiment could have been improved if the
potatoes were left in the salt solution for a longer amount of time, because clearer
results would have shown up. Lastly, the osmosis lab could have been more accurate
if the students had worn gloves while boring the potato because the salt content on
the student’s hands could have contaminated the potato and salt solution.