observing osmosis through molarity
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Observation of diffusion and Osmosis in Different Solution Concentrations
Andoni Colmenares
BSC2010C
Section 23
Seat 20
02/24/2010
INTRODUCTION
The cells within the human body are like miniature cities, bustling with energy and
processing many differing substances into new ones in order to sustain balance and life itself
(Campbell et al. 2008). One of the most fundamental processes vital for cell survival is the
ability to move molecules from an area of high concentration to an area of low concentration
(Campbell et al. 2008). In the process known as diffusion, molecules move with the
concentration gradient in response to the tonicity around the cell (Campbell et al. 2008). The
important cellular process of osmosis allows cells to absorb or release water when there is a
change in the concentration of the solute or the solvent within or around the cell (Campbell et al.
2008). Without these important cellular characteristics many fundamental life sustaining
processes, such as breathing, would not be possible (Campbell et al. 2008). Also the amount of a
specific substance in the body can often are a life or death factor. The calculation of the different
levels of substances diffused in a cell is highly important for patient assessment and
consequently patient care (Caon, 2). Yearly new substances are being synthesized and it is
important to learn about their effects on this necessary life sustaining process (Xibao 2010). To
more thoroughly understand the process of osmosis and diffusion, further information must be
covered.
When a liquid is completely mixed with two substances it is called a solution (Campbell
et al. 2008). A Solvent is the substance doing the dissolving and a solute is the substance being
dissolved (Campbell et al. 2008). In an aqueous solution water is said to be the solvent
(Campbell et al. 2008). Substances naturally move within a cell from areas of high to low
concentration (Campbell et al. 2008). There is said to be a concentration gradient when there is a
difference between solvent and solute and movement between the concentrations (Campbell et
al. 2008). This movement of substances occurs through membranes, within the cell, which
separate the two different concentrations (Campbell et al. 2008). The plasma membrane of cells
allows selective admittance or no admittance of substances in and out of the cell (Campbell et al.
2008).
According to Campbell et al. (2008) Cells contain semi permeable and or impermeable
membranes. In an impermeable membrane substances are not able to travel through the
membrane to the other side (Campbell et al. 2008). Semi permeable membranes are selective but
they permit some things to go through them (Campbell et al. 2008). In a semi permeable
membrane substances are moved through the membrane by either active transport or passive
transport (Campbell et al. 2008). Active transport requires energy because it uses transmembrane
proteins, proteins moving through membranes, called transporters to move against their
concentration gradient (Thomas et al. 2010). On the other hand, passive transport moves
substances from an area of more to less concentration (Thomas et al. 2010). No energy is
required during passive transport because substances flow with the gradient (Thomas et al.
2010). Diffusion is a type of passive transport which is influenced by the solute concentration
within the cell and the solute concentration of the cell's surroundings (Thomas et al. 2010).
Osmosis is a form of diffusion which describes water molecules moving through a semi-
permeable membrane from higher to lower concentration (Thomas et al. 2010). The ability of a
cell to perform osmosis, that is to gain or lose water, is influenced by tonicity (Campbell et al.
2008). Tonicity is the how the solution around the cell affects the absorption or evacuation of
water into or out of the cell (Campbell et al. 2008). Through the process of osmosis water can
make a cell isotonic, hypertonic or hypotonic (Campbell et al. 2008) According to Campbell et
al. (2008) If the amount of solute inside and outside the cell is equal and there is no net change of
water the cell and solution are considered to be isotonic. If there happens to be more solute
outside the cell, the selectively permeable membrane will allow water to leave the cell (Campbell
et al. 2008). In this case the cell is considered hypertonic; diffusion actually causes the cell to
shrivel up (Campbell et al. 2008). In a hypotonic solution the tonicity accounts for the cell's
expansion as well (Campbell et al. 2008). There is more water rushing into the cell because there
is a higher concentration of solute in the cell (Campbell et al. 2008).
The selectively, permeable membrane is essential to living cells because it allows
necessary substances to enter and it impedes unnecessary ones (Campbell et al. 2008). The lipid
bi-layer allows sugars, such as glucose, to pass through it which in turn provide energy for the
cell (Campbell et al. 2008). If the membrane did not allow the glucose to enter, it would not be
converted into expendable energy for the cell to use (Campbell et al. 2008).
Now diffusion is vital to plants and animals cells because substances have a tendency to
move from areas of higher to lower concentration (Campbell et al. 2008). According to Campbell
et al. (2008) without diffusion the semi-permeable membrane would not have any way to move
substances through it. The cell's energy making process would not be able to even start
(Campbell et al. 2008). If a cell does not have a permeable membrane substances would not be
able to pass through and the cell would die (Campbell et al. 2008). If tonicity was not a factor
cell's would not be able to rely on the energy less process of diffusion and osmosis which deliver
nutrients to the cell and drive energy making processes (Campbell et al. 2008). Therefore the
permeability of a membrane and the tonicity of the solution, which fuels passive transport and
diffusion, are significantly important to a cell's well being (Campbell et al. 2008).
The lab experiment involves osmotic diffusion through a semi-permeable membrane.
There are four different controlled variables involved. Each variable contains a potato piece and
a greater or lesser concentration of glucose in each solution. Each variable has different
tonicities. After the experiment the weights of the potatoes may differ according to the flow of
osmosis. Through passive transport water will move from levels of higher to lower
concentration. The null hypothesis states that the differences in glucose concentration will
neither affect the weight nor the size of the potatoes. The alternate hypothesis states that the
potatoes weight and size will change according to the differences in glucose concentration.
METHODS
All methods of this lab report were taken from Biology 1 (Thomas et al. 2010)
To begin the experiment my partner and I acquired a potato and proceeded to bore four
holes into the potato using a cork borer. We then cleaned the skin of each potato and used a
metric ruler to measure each piece. We cut each potato cylinder into lengths of three centimeters
each. Then my partner and I placed each potato slice into separate cups and labeled the cups:
dH20, 0.25M, 0.50M and 1.0M. Afterward we went to the balance station and used the weight
boat to make sure the balance was at zero. The weight boat is a plastic piece that we place on the
scale to make it balanced at zero. My partner and I removed each potato piece from each cup,
then individually placed and weighed the potato cylinders on the weight boat. We wrote down
the values after each weigh in. Then we wrote down the weights on a table in the row labeled
weight before and under the column which corresponded to each cup. Following this, my partner
and I poured 20 to 25 ml of dH20 or sucrose solution into each relevant cup. Thereafter, we let
the potatoes soak for one hour and fifteen minutes. Ensuing this, my partner and I dried off any
excess solution from the potatoes by slowly drying them on a paper towel. Then we removed
each potato from each cup and weighed the cylinders on the same weighing scale as we did
before we added the solutions. We recorded the weights on the row labeled weight after and
under each respective column. Afterward we found the difference of the before and after
weights. We found the difference by subtracting the before weight, of each cup, from the after
weight of each cup. Then we used the percent change formula to get the percent change of the
two values. The percent change formula states final value minus initial value divided by initial
value multiplied by a factor of one hundred.
RESULTS
After my partner and I conducted the experiment we found that there was a visual size
and calculated weight increase among the potatoes. The cup labeled dH2O had a before weight of
0.94g and an after weight of 1.07g. This was the heaviest potato and it certainly appeared to have
increased in size. There was a 0.13g difference between the before and after weight of this
potato. The calculated percent change was 13.8%. The next potato labeled 0.25M had an initial
weight of 0.97g and an after weight of 1.01g. The difference between the before and after weight
was 0.04g. The calculated percent change was 4.1%. The potato in the cup labeled 0.50M had an
initial weight of 1.0g and an after weight of 0.9g. The difference between the before and after
weight was -0.09g. The calculated percent change was -9% for this potato. The potato in the final
cup labeled 1.0M had a before weight of 0.94g and an after weight of 0.78g. This potato
noticeably shrank in size. The difference between before and after weight was -.016g. The
percent change calculated was -17%.
0M (dH2O) .25M .5M 1M5 3.88 -10.89 -14.29
25.3 0 -29.1 -2115.625 12.63 2.94 -6.2518.09 12.5 7.53 -8.255.94 -3.81 -10.5 -17.914.3 10.8 6.82 -4.175.05 -1.05 -7.84 -18.75-2.7 -2.7 -13.4 -21.87.45 1.04 -6.38 -18.485.2 1.05 -4.06 -19.78.2 1 -5 -167.8 -1.06 -7.87 -19.57
23.17 9.57 5.56 -2.3311.1 0.95 -5.05 -13.4-8.47 -11.1 -25 -25.7-0.925 -9.615 -12.121 -19.3879.09 0 -11.54 -25.2416.87 15.07 2.78 -22.55.1 1.02 -11.46 -18.183 -3 -9 -14
2.13 -2.88 -10.58 -243 -1.2 -4.7 -13
8.1 2.7 -4.6 -16.55.2 -2 -11.2 -20.2
Average
8.025833333
1.408125
-7.2775
4
-16.691
5Sta. Dev.
7.843049078
6.572027
8.756984
6.308652
Table 1: Class average and standard deviation of percent changes
0.00 0.25 0.50 1.00
-20
-15
-10
-5
0
5
10Pe
rcen
t Cha
nge
Solution Molarities
Figure 1: Average percent changes with standard deviation
DISCUSSION
The null hypothesis of this experiment stated that the differences in glucose concentration
will neither affect the size nor weight of the potatoes. The alternate hypothesis stated that the
weight and size of the potatoes will change according to the differences in glucose concentration.
After reviewing the results yielded I accept the alternate hypothesis and I reject the null
hypothesis because there were apparent weight and size differences among the potatoes in
varying glucose concentrations. The results of the experiment showed a steady decrease in the
size and weight of the potatoes as the concentration of the glucose in the solution increased. The
first potato, that was placed in a solution with no glucose, grew the largest and weighed the
heaviest after conducting the experiment. The cells in this potato, containing a water solution,
absorbed the most water thereby raising the weight of the potato significantly. The 13.8%
calculated percent change occurred because of the tonicity of the potato's solution. There was
much more water in the potato cells' solution then in the potato cells themselves. There was also
a greater amount of glucose in the potato than there was outside in the solution. Through osmosis
the water diffused through the potato cells' semi permeable membrane from an area of higher to
lower concentration. The second potato, placed in the solution labeled 0.25M, also increased in
weight and size. Although there was glucose in this potato's environment, the amount of glucose
in the potato was still greater than the concentration of glucose outside in the container. Because
the solute was still greater within the cells than in the cell's solution, water rushed into the potato
through osmosis thereby increasing the after weight and visual size of the potato. The potato,
placed in the cup of solution labeled 0.50M, had a lower final weight than initial weight. The
difference between the before and after weight was -0.09g. The potato placed in this solution
released more water than it gained. The potato and its solution are considered hypertonic. The
cells in this potato lost water because the concentration of glucose was higher in the solution that
the potato was placed in. Water evacuated the cells of the potato, due to the tonicity, resulting in
a decreased weight and size of the potato. The potato placed in the solution labeled 1.0M
weighed the least after the experiment and had the highest, most negative, percent change. This
potato had a -17% percent change which resulted in decreased potato size and weight. The
increased concentration of glucose, or solute, in the solution and the lesser amount of solute
within the potato cells caused the potato cells to lose water. The cells actually shrank as osmosis
carried water through the semi-permeable membrane out of the cells and into the solution which
the potato was placed in.
When the solute inside the cell is higher than the solute in the cell's environment, water
will naturally diffuse from higher to lower concentration (Campbell et al. 2008). The first two
potatoes, placed in solutions of only water and 0.25M glucose, both gained water and
consequently increased in after weight. These two potatoes are considered to be hypotonic. The
water diffused into the potato's cells which swelled them. On the other hand the other potatoes,
placed in cups labeled 0.50M and 1.0M, had a lower after weight than before weight. The solute
in the potatoes' solution was more concentrated so water diffused out of the potato cells. These
potatoes are considered to be hypertonic because osmosis caused water movement out of the cell
and into the solution (Campbell et al. 2008). Through passive diffusion water moved in and out
of these potato cells from higher to lower concentration depending on the concentration of solute
in the potato and solution (Campbell et al. 2008).
After the results of this project I will conduct another experiment involving different
substances than glucose. I will conduct a similar experiment to this one except I will use four
different solutions in different concentrations instead of differing concentrations of the same
solution. I will use solutions mixed with substances of only water, salt, and several different
sugars. The goal of this project will be to observe the effects of the four substances and many
concentrations of those substances and observe the impermeability of those substances. The
purpose of this project will be to gain a better understanding of the effects of different substances
on osmosis. As new substances are synthesized, such as gold nano-particles, it is important to
know how the diffusion of water is affected by the solutes that are in it (Xibao et al. 2010). The
results of this experiment are significant because the ability of water to diffuse through a
membrane, due to the concentration of solute in the aqueous solution, affects how our body's
cells conduct osmosis when certain solutes are present (Caon 2010). In the medical field it is
important to know the concentration of certain solutes because this affects patients when there is
a increase or decrease in the concentration of that substance (Caon 2010). At the hospital, nurses
regularly check the concentration of certain substances in the patient's body in order to make sure
that the patient is stable (Caon 2010). Therefore further exploration on this topic is important to
both people in the medical field and their patients alike.
Works Cited
Campbell, N. Reese, J. Urry, L. Cain, M. Wasserman, S. Minorsky, P. Jackson, R. 2008. Biology
. 8th edition. Pearson Publishing. San Francisco, Ca. 536 pages.
Caon, Martin. 2010. "Osmoles, osmolality and osmotic pressure: Clarifying the puzzle of .
solution concentration." Contemporary Nurse: A Journal for the Australian Nursing . .
Profession .29.1 (2008): 92-99.
Thomas, P. Walters, L. Boyers, B. Yeargain, M. 2010. Laboratory Manual for Biology 1, 16th .
edition.
Xibao G, Hongyin Y, Jiang Y, Ning L, Jinghe Y. 2010. Protein Enhanced Near-Infrared .
Fluorescence of AuNPs and Its Application for Protein Determination. Analytical Letters
. [serial online]. April 2010;43(4):701-710.