The Process of Osmosis in Potato Cells
Tracey Zhang 3B
Research Question:
Will the placing of potato cores in greater concentrations of sucrose create a
smaller net flow of water into the cell?
Introduction:
Osmosis, the natural tendency for water to disperse and reach equilibrium, plays
a huge role in cellular processes. By placing a cell in liquid with a lower
concentration of solutes than the cell, the surrounding water will naturally flow
into the cell, providing it with this necessity. Likewise, if the cell is placed in
liquid with a higher concentration of solutes than the cell, the water will flow
from the cell out into the surrounding. Water can easily flow through the cell
membrane/cell wall through protein channels. However, the materials, such as
sucrose, are too large to enter through and thus remain outside. When the
solution has a high concentration of solutes than the cell, it is hypertonic to the
cell. On the other hand, if the solution has a lower concentration of solutes than
the cell, it is hypotonic to the cell. If the solutes have reached equilibrium, then
both solutions are isotonic. Unfortunately, this can also prove fatal to the cell. If
the concentration of water is hypertonic to the cell, then too much water may
flow out, killing the cell through water deprivation. Similarly, if too much water
flows into a cell from a hypotonic solution, the cell can explode.
Hypothesis:
If a potato core is placed in a greater concentration of sucrose, then it will have a
smaller net flow of water into the cell than a potato core placed into a smaller
concentration of sucrose because the greater concentration of sucrose contains
less water.
Variable(s):
Independent variable: the concentration of sucrose
Dependent variable: the percent change of the mass of potato cores
Experimental group: 0.0 sucrose concentration; 0.2 sucrose concentration; 0.4
sucrose concentration; 0.6 sucrose concentration; 0.8 sucrose concentration; and
1.0 sucrose concentration
Control group: none
Controls: the temperature of the sucrose concentrations, the amount of
concentration used, the length of the potato cores, and the type of potato used
Materials:
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Potato cores (4 per condition)
Sucrose solutions (.2, .4, .6, .8, and 1.0)
Distilled water (.0)
Electronic balance
Plastic weighing tray
Plastic cups (6)
Graduated cylinder (50 ml)
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Scalpel
Marking tape
Blue tweezers
Procedure:
1. Using marking tape, label 6 cups with the following solution types (.0, .2,
.4, .6, .8, and 1.0 water)
2. Place approximately 50 ml of the various solutions into a cup, with each
cup receiving a separate solution.
3. Obtain 24 potato cores and cut them to equal sizes (about 3.5 cm). All the
cores you use must be the same length
4. Divide your 24 cores into 6 groups and gently blot them dry with a paper
towel.
5. 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.
6. Place each group of 4 potato cores into one of the six cups.
7. After 24 hours, pour the fluid out of the cups.
8. Use plastic blue tweezers to remove the cores and blot them dry.
9. Place the potato cores on the scale and measure the mass (tare out the
plastic tray).
10. Finally dump your potato cores in the trash and wash and dry your
equipment.
11. Calculate the negative/positive percent change in mass for each set of
potato cores using the formula (final mass/initial mass x 100).
Data Chart:
Percent Change of the Mass of Potato Cores in Different Sucrose Concentrations
Group 5:
The Concentration at which the Sucrose Solution is Isotonic to the Potato Core
Graph:
The sucrose solution is isotonic to the potato core at a concentration of 0.22.
Discussion:
The data shown above seems to reveal a trend between the sucrose
concentration and the change in mass of the potato core. At a concentration of
0.00, there is a positive percent change of 6.7%, meaning that water is flowing
into the cell. This is also true at a sucrose concentration of 0.20, with a positive
percent change of 6.3%. The flow of water into the cell indicates that the sucrose
concentration is hypotonic to the cell, causing the water to desire equilibrium by
flowing into the cell. The sucrose concentration at 0.00 is more hypotonic than
the sucrose concentration at 0.20 as evidenced by a higher flow of water into the
cell at 0.00 than 0.20 by 0.4%.
At a sucrose concentration of 0.40, a negative percent change occurs at -6.3%.
This shows that the mass of the potato core is now decreasing, meaning that
water is flowing out of the core into the solution. The flow of water out of the
cell indicates that the sucrose concentration is now hypertonic to the cell. This
decrease in mass grows at a sucrose concentration of 0.60 to -22%. At a
concentration of 0.80, the percent change increases to -29%. This means that
even more water is flowing out of the cell into the surroundings, decreasing the
mass by a greater number. Finally at 1.00, the flow of water out of the cell is the
greatest at a mass change of -42%.
Based on the data, a correlation between the sucrose concentration and the
change in mass of the potato core is evidenced. As the sugar concentration
increases, the flow of water decreases until at a concentration 0.22 (based on the
line of best fit), in which the sucrose concentration is isotonic to the potato core.
This means that at this point, water has reached equilibrium, with the net flow of
water being 0 (water is still flowing in both directions, but it essentially remains
the same on both sides). The flow of water out of the potato core at sucrose
concentrations less than 0.22 shows that they are hypotonic to the potato cores.
At sucrose concentrations greater than 0.22, the flow of water goes the opposite
direction out of the cell into the surrounding solution. This indicates that a
sucrose concentration greater than 0.22 is hypertonic to the potato cores. Thus,
it can be concluded that greater concentrations of sucrose create a smaller net
flow of water into the cell.
This is constant with the scientific principles of osmosis. A solution that is
hypertonic to another solution means that water from the other solution will
flow into the first. If the first solution is hypotonic to the second solution, then
water will flow from the first into the second. Thus, if the concentration of
sucrose increases and the potato cores remain constant, then the flow of water
into the potato core would logically decrease. This is made evident by the
experiment, which showed a decrease in the net flow of water into the cell as the
concentration of sucrose increased.
The data is also consistent with the findings of other groups. When compared to
Group 5’s data, the largest difference in data is only 3.3% at a sucrose
concentration of 0.00. This does not seem to be a significant difference; though it
may simply be attributed to the different times the two groups measured the
mass. Group 5’s line of best fit also crossed the x-axis at 0.24, meaning that a
sucrose concentration of 0.24 is isotonic to the potato cores. This is again very
similar to the number our group got, which is 0.22. With Groups 1, 2, and 4, the
concentration at which the solution is isotonic to the potato core is also very
similar. The largest difference is between my group’s data (3) and Group 1’s
data at a difference of 0.53. This is a huge variation because it means that
sucrose concentrations at 0.40 and 0.60 in Group 1’s data were hypotonic, while
in our data, it was hypertonic. Group 1 may have accidentally used the wrong
sucrose concentrations because the data is an outlier from the others. The other
four groups have similar numbers for when the sucrose concentration is isotonic
to the potato cores.
Conclusion/Evaluation:
The results of the experiment support my hypothesis because it showed that a
greater concentration of liquids creates a smaller net flow of water into the cell.
The majority of this lab went according to plan, with no major problems
occurring. An aspect that may have skewed the data was simply eyeing the
amount of solution in the cup as 50 mL after the first cup was measured. This
created a scientific inaccuracy, though it did make the lab go a lot quicker in the
short time span given. Our group also worked very efficiently and diligently,
especially when making sure all the potato cores were cut the same length. If I
could do the lab over again, I would accurately measure the concentrations of
sucrose to 50 mL for every single cup. An extension of this lab that I would be
interested in doing would be using different types of potatoes and comparing
their concentration of solutes.