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Comprehending Transport and Tonicity Through Osmosis and Diffusion
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Transcript of Comprehending Transport and Tonicity Through Osmosis and Diffusion
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Comprehending Transport and Tonicity through Osmosis and Diffusion.
Burhan Riaz
BSC2010C
Section 13
Seat 34
02/24/2010
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INTRODUCTION:
Membrane transport occurs in all kingdoms of life from the very small amoeba to the complex
mammals (Campbell et al. 2008). There are two varieties of membrane transport(Campbell et
al. 2008). Passive transport occurs without the need for energy and allows molecules to travel
from high to low concentrations (Thomas et al. 2010). Diffusion, a type of passive transport,
allows lipid-soluble molecules to travel with their concentration gradient (Campbell et al. 2008).
Diffusion will occur at different rates from many variables including the weight of the molecule
that is being diffused, the distance between the membrane and the solution outside of the cell,
surface area of the cell, etc (Thomas et al. 2010). Osmosis is a specific kind of diffusion that
applies to water moving through a cell membrane from a high to low concentration gradient
(Campbell et al. 2008). Facilitated diffusion uses a transporter protein that requires no energy
to move water-soluble objects through the membrane (Thomas et al. 2010). Active transport
will require energy in order to move a molecule against its concentration gradient from a low to
high concentration gradient (Thomas et al. 2010). Unlike facilitated diffusion, a trans-membrane
protein that requires ATP is needed (Thomas et al. 2010). These transporters are selective and
will move an ion or molecule through the membrane if the energy requirement is met
(Campbell et al. 2008). Osmosis is important to the water treatment industry (Eslamifard 2009).
Through manipulating osmosis, water treatment facilities can collect clean water by creating
semi-permeable filter and then create a hypertonic “pond” which will move water from the
other side of the membrane filter to its side (Eslamifard 2009). . A similar concept applies to
perovskite (a type of mineral) membranes which can move oxygen ions when there is a lower
concentration and a higher concentration of oxygen ions (Wang and Yang 2005).
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Before we begin exploring the effect of osmosis on plant cells, we will need to know
how tonicity works. Tonicity is the osmotic pressure or ratio of two solutions divided by a semi-
permeable membrane (Campbell et al. 2008). There are three ways to define tonicity (Thomas
et al. 2010). Hypertonic solution is where the solute concentration is higher outside the cell
(Thomas et al. 2010). This implies there is more water within the cell. So naturally, water will
diffuse out of the cell to help equalize the lower concentration of water outside the cell
(Campbell et al. 2008). This can cause a cell to shrivel (Campbell et al. 2008). A hypotonic
solution implies that there is more solute within the cell than outside (Campbell et al. 2008).
Water will diffuse into the cell and cause it to swell up (Campbell et al. 2008). An isotonic
solution is where the concentration of solute is the same outside the cell and inside (Campbell
et al. 2008). Water will actually diffuse into and out of the cell at an equal rate (Campbell et al.
2008). The purpose of this experiment is to see the effect on tonicity of a potato at 4 different
concentrations of solute (Thomas et al. 2010). This can be accomplished by measuring the
weight of a potato cylinder before and after it has been submerged into the solution (Thomas et
al. 2010). The null hypothesis for this experiment would be if all the potato cylinders did not
change weight after being submerged in the solutions. The alternate hypothesis would be that
at least one of the potato cylinders changed weight after completing the procedures. My lab
partner and I hypothesized that there would be a change in weight after submerging the potato
cylinders in the sucrose solution due to the fact that water moves from a high concentration to
a low concentration (Thomas et al. 2010). By putting the cylinders in different molarities of
sucrose, the weight of the cylinders should change according to the workings of osmosis.
METHODS:
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My lab partner and I conducted this experiment on February 17, 2010, and followed the
instructions from “Laboratory Manual for Biology I, 16th Edition” (Thomas et al., 2010). We
began with obtaining a potato from the lab table. Using a cork borer, we cut out four potato
cylinders. To accurately compare the potato cylinders for weight change, we needed them to
be the same size. So, using a ruler, we cut the cylinders with a knife to 3 centimeters and made
sure there was no skin attached to them. We then put the cylinders into separate cups labeled
dH2O(distilled water), 0.25M sucrose, 0.50M sucrose, and 1.0M sucrose. We then took the 4
cups to a balance station to weigh the cores. We pressed the reset button to take account the
weight boat’s own weight. We then put the cylinders on the weight boat one-by-one and
recorded the results to the nearest 100th gram on the laboratory manual. The cylinders were
placed back into their cups and enough solution of dH2O or sucrose (according to the labels on
the cups) was poured into the cups. We did not measure the amount of solution that was
poured into the cups. Instead we made sure that the cylinders were submerged fully in their
solutions. We waited 1 hour and 15 minutes for the potatoes to soak in the solution. After
waiting, we carefully laid the cylinders onto a paper towel and dried the cylinders by rolling
them. We then brought the cylinders to the same balance station and weighed them each.
Using the “before” and “after” weight we found the difference and % change. We found the
difference by subtracting the “before” weight from the after “weight”. Then we divided the
difference by the “before” and multiplied the number by 100 to find the percent difference. We
used Microsoft Excel to calculate the averages and standard deviations of the entire class’
percent changes. Finally we noted any physical changes in the potato cylinders.
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RESULTS:
The potato cylinders appeared to have changed in physical appearance after completing
the procedures. They looked smaller in length and width. They also changed in weight. The
cylinder in dH2O was the only one to gain weight. It started off with 1.15 grams and weighed
1.19 grams (3.48% changes) by the end of the experiment. The 0.25M cylinder weighed 1.04
grams and decreased to 0.97 grams (-6.73% change). The 0.50M cylinder weighed 1.11 grams
and decreased to 0.92 grams (-17.12% change). The 1.0M cylinder weighed 1.15 grams and
decreased to 0.85 grams (-26.1% change). We then combined our results with the rest of the
class.
0.0M (dH2O) 0.25M (grams)
0.5M (grams) 1.0M (grams)
-9.9 8.8 -26.7 -22.414.4 3.2 0 -16.7-4.55 -13.04 -9.35 -36.210.039 -0.039 -0.01 -0.19
13.265 5.263 0 -12.63211.34 0 -22.22 -16.38.11 -0.93 -14.56 -29.253.9 -3.9 -10.3 -19-3.5 -5.8 -11.9 -22.7
0 -10.5 -17.2 -30.715 18 0 -7
5.05 5.32 -3.16 -21.72.66 -1.1 -9.1 -2219.8 5.4 -7.3 -23.73.92 -6.67 -15.69 -26.216.4 0 -14.3 -27.5
12.33 -1.22 -6.49 -18.5213.265 5.263 0 -12.632
10.7 2.1 -16.1 -26.88 1 -12 -27
6.25 -0.93 -12.15 -26.473.48 -6.73 -17.12 -26.112 3.09 -9 -19
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0.97 -2.06 -12 -24.24Average 6.372041667 0.188208333 -10.27708333 -21.4564167
Std. Dev. 7.095403935 6.481563895 7.290645274 7.888965766
Table 1: Collection of percent changes from all classmates including averages and standard
deviations.
0.0M 0.25M 0.5M 1.0M
-24
-22-20
-18-16
-14-12
-10-8-6
-4-2
02
468 6.37204166666667
0.188208333333334
-10.2770833333333
-21.4564166666667
Perc
ent C
hang
e
Solution Molarity
Figure 1: Averages of percent changes including standard error bars.
DISCUSSION:
Despite having a large standard deviation, it is safe to believe that the null hypothesis no
longer applies. There is more evidence pointing towards the alternate hypothesis which states
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that the percent changes will differ in at least 1 out of the 4 solutions. In fact, every solution
shows that the average percent change has either increased or decreased according to figure 1.
The dH2O solution shows a 6.37% increase in average weight. This implies that this solution was
hypotonic and water moved inside the potato cylinder through osmosis. The 0.25M sucrose
solution shows a minor .188% increase. This may imply that the solute concentration was
almost the same within the potato and outside. Nevertheless the potato absorbed some water
from the water. The cylinder in the 0.5M sucrose solution decreased by -10.28%, indicating that
the solution was hypertonic. This means there was more water in the cylinder than the solution
which had more solute. Therefore, water moved outside the potato through osmosis. Following
this trend, the 1.0M sucrose solution decreased the weight of the potato cylinder by -21.46%.
From our results, we can assume that for water to move outside the potato through osmosis, it
requires the molarity of a sucrose solution to be between 0.25 and 0.5.
There was most likely some kind of human error involved in our class’ attempt to record
the percent changes of the potato cylinders. Looking at table 1, there are some instances where
there is 0% change in weight. This would make sense in the .25M solution because the average
percent change is very small. However the 0% changes are recorded in the 0.5M solution
category. I believe that someone may have made a mistake while measuring the before and
after weights or made a mistake calculating the percent difference. Osmosis has long been used
by water treatment facilities (Eslamifard 2009). Using what we learned from our experiment we
may be able to replicate a scenario where we can extradite hazardous materials while creating
drinkable water.
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Works Cited
Campbell, N. Reese, M. Wasserman, L. Cain, , J. Urry, , S. Minorsky, P. Jackson, R. 2008. .
Biology 8th edition. Pearson Publishing. San Francisco
Haihui Wang, Weishen Yang. “Oxygen Diffusion through Perovskite Membranes" Diffusion .
Fundamentals 1 (2005) 1.1 - 1.17
Madaeni Eslamifard. “Recycle unit wastewater treatment in petrochemical complex using .
reverse osmosis process.” Journal of Hazardous Materials. 2009 Sep 2: Vol. 174 (1-3), .
pp. 404-9.
Thomas, P. Walters, L. Boyers, B. Yeargain, M. 2010. Laboratory Manual for Biology 1, 16th .
edition.