Effects of Osmosis in Potatoes Lab
Laurie Okamoto
Hypothesis:
The isotonic solution of the potato will be 1.0 as the potato is not pure water. It contains
much starch amongst other chemicals and compounds; therefore, it is reasonable to
hypothesize that the potato core will be isotonic at 1.0.
Also, based on previous research as to what solution is isotonic to the potato cores, the
concentration of glucose is most likely in the vaccinates of 0.8 -1.0 in regards to its
concentration.
Variables:
Independent: The concentration of glucose in the water. It is independent because the
amount of glucose will either make the solution hypotonic, isotonic, or hypertonic.
Dependent: The change in the mass of the potato core. It is dependent because the
amount of water in the potato will not change unless placed into a solution of sugar and
water (when left alone and not including evaporation).
Variables to Control:
Amount of water in the glass - the amount of water in the cup will change the amount of
water the potato absorbs or is taken as there will be more or less sugar and water
outside of the potato.
Concentration of Glucose – if the concentration of glucose is not carefully measured, it
will change the amount of water that is taken or absorbed into the potato. The more
sugar, the more hypertonic the solution will become changing the results of the lab.
Temperature of Water – the temperature of the water can affect the rate at which the
molecules are passed through the cell membrane of the potato, as molecules will move
at a higher rate when heated.
Procedure:
Take 12 pieces
of potato cores
of equal length
(at least 2.5cm)
and blot dry.
(cores were
3cm long)
(Note that in this image, the single potato at the top is against the cm side of the ruler.)
Using an electric balance and weighing boats (as in the right-most image), record the
weight of each.
Effects of Osmosis in Potatoes Lab
(In the image above, the cups are lined up from
the lowest concentration to the highest.)
Pour out approximately 50
mL of each concentration of the glucose and
water solution (distilled,
0.2, 0.4, 0.6, 0.8, 1.0) into
the labeled cups. Take a
picture of the potatoes
and record the data in a
table. After 24 hours
remove the potatoes with
tweezers, blot, and record
weight of potatoes.
Calculate the change in
weight of the potatoes
and add to table.
In the image in the upper left corner, the potatoes are lined up from the lowest [sugar] to
the highest as they are being blotted in the brown paper towel. (Note that the potatoes’
concentrations were recorded on the paper to avoid confusion.)
The images above display the potatoes after 24 hours. In the left most image, the
potatoes are lined up from the lowest [glucose] to the highest [glucose]; likewise, the
potatoes in the vertical image are lined up in the same fashion from bottom to top.
Effects of Osmosis in Potatoes Lab
The following is a table of the changes in mass of the potato cores after a period of 24
hours.
Change in Mass of Potatoes in Different Sugar Concentrations
(M) of water and
Change in Mass
glucose solution Initial Mass g
Final Mass g
Change in Mass g % rounded to
(ID)
(±0.01)
(±0.01)
(±0.01)
nearest 0.01
0.0
3.57
3.83
0.26
7.28
0.2
3.50
3.88
0.38
10.86
0.4
3.60
3.72
0.12
3.33
0.6
3.58
3.43
-0.15
-3.91
0.8
3.52
2.92
-0.60
-17.04
1.0
3.58
2.88
-0.70
-19.55
Change in Mass = Final Mass - Initial Mass
Change in Mass % = (Final Mass - Initial Mass)/Initial Mass * 100
Graph of Change in Mass of Potatoes
Note that in the graph above and the following graph that the data for the solution of 0.8
sugar has been noted as the outlier of the data based upon its distance from the trend
line.
Graph of Change in Mass of Potatoes in (%)
Effects of Osmosis in Potatoes Lab
(Note that the percentages have been rounded to the nearest hundredth.)
Reason for Outliers:
In both of the graphs, the outlier of data is the potato that was submerged in a solution
of 0.8 sugar. It is most likely that there was an error in either recording or reading the
data as it does not follow the trend line of the graph.
Analysis of Graphs:
Please note that in the graph above and in the following graph, the slopes are negative
because as the concentration of sugar increases, the mass of the potato decreases
because the the water is being drawn from the potato in an effort to balance the (M)
level in the water so that it is even with the potato. As the sugar (M) decreases, more
the mass of the potato increases because it will absorb more water. If an object is
submerged in water, its mass will change in an effort to become isotonic with its
surrounding solution.
Observations:
Samples with a lower concentration of sugar weighed more than those left in a solution
with a higher concentration of sugar.
The higher the concentration of glucose, the more flexible the cores become. Also, the
higher the concentration of sugar, the more yellow in color the cores appear to be. The
potato core in the 10% sugar solution became very soggy, it was limp and able to bend
in half without snapping; it was very spongy and soft to the touch.
The potatoes with a higher concentration of distilled water in their container were much
more rigid and lost a substantial amount of color. When broken, they almost sounded
Effects of Osmosis in Potatoes Lab
as though they were snapping. After they were snapped, the water seemed to seep out
of the area where the potato was broken.
The potatoes with a M of .2 seemed to be the most rigid of all the samples. This piece
of data seems to be out of order as logically, the most rigid of the samples would be the
cores suspended in the distilled water. It is likely that there was a mistake when the
solutions were poured into the cups.
Conclusion:
An isotonic solution for the potatoes is a solution where the change is close to zero, in
this case, the solution isotonic to the potatoes is in-between 0.4 and 0.6 (M). The
potatoes with the least amount of change were the cores soaked in solution of 0.4 sugar
as the change in mass was 0.12 grams.