Upload
jessica-bae
View
1.255
Download
0
Embed Size (px)
Citation preview
Abstract
A close scrutiny over the membranes suggests two crucial forces, diffusion and
osmosis, to reach a state of dynamic equilibrium. Diffusion represents the molecules’
natural proclivity to travel down its concentration gradient. A type of diffusion of water
molecules is called osmosis. The three experiments examined the molecules’ movements
through a selectively permeable membrane, depending on the variation of molarity of the
solution. Using IKI and starch and glucose solution, the first experiment inspected the
plausibility of IKI and glucose molecules to diffuse across a dialysis bag, a selectively
permeable membrane., The following experiment observed the percent change in mass of
the dialysis bags, which contained a solution of unknown sucrose molarity, in respect to
the different molarity of an equilibrium point, where the concentration of molecules
between the two solutions was equal. Similarly, the final experiment utilized potato cores
and different sucrose molarity solutions to find the equivalent point, 0.305M. Each
experiment ascertained the principle of diffusion and osmosis through molecules gradient
movement depending molarity of the solution. The coloration of the dialysis bag and
glucose and test strip proved that relative size of the molecules that could pass through
cell membranes. Due to the molecules’ tendency to move from higher concentration to
lower concentration, the mass of potato cylinders increased before the equivalent point,
0.35M, was reached; however, once the molarity achieved at 0.4M, the mass decreased,
losing its water to the surroundings.
1. Introduction
Diffusion and osmosis are important for all living organisms. Also, people apply
osmosis and diffusion to their lives like making Kim chi in Korea and sometimes use the
properties of diffusion to make better perfumes.
Diffusion is the movement of particles from higher concentration to lower
concentration. Once diffusion occurs, the higher concentration of a certain area will
decrease, and the lower concentration near the higher concentration area will increase1.
Then, as time goes on, the concentration will be in equilibrium. The driving force of
diffusion and osmosis is constantly moving particles of substances. In addition, diffusion
and osmosis is related to the entropy, which is a measure of randomness, or disorder. The
second law of thermodynamics applies to diffusion and osmosis because it states that all
energy transformation increases the entropy of universe6. For example, in the dorm, when
somebody makes popcorn and after few minutes, the smell of popcorn diffuses from
microwave to the whole hallway and even in the rooms.
Osmosis is one kind of diffusion, but it is little bit different because osmosis is the
diffusion of water. Osmosis is movement of water molecules through a semi-permeable
membrane from higher water potential to lower water potential. The water potential
represents the measure of free energy of water6, in other words, it represents how much
water can move. Osmosis works from lower solute concentration to higher solute
concentration. Also, Osmosis is passive, which means no energy input is required. Three
conditions of osmosis can exist: hypotonic solution, isotonic solution, and hypertonic
solution. Hypotonic solution is same as fresh water. Isotonic solution has equal
concentration, and there’s no net flow of water. Hypertonic solution is higher
concentration solution. In Korea, people apply osmosis when they make Kim chi. So,
Koreans put cabbage in salty water, and the water comes out from the cabbage. Osmosis,
then, makes cabbage shrivels and increases the concentration of Kim chi flavor by letting
out the water from cabbage.
Diffusion and osmosis is a crucial factor for all the living organisms. Diffusion
and osmosis are ways of eating for unicellular organisms such as amoeba. The substances
needed for amoeba diffuse through its membrane. For another example, in the human
body, lipids are diffusing through phospholipid bilayer, which is selectively permeable
and allows certain substances to go through the membrane. It enables organisms to let
waste out of cell and permits nutrition in to the cell needed by using concentration
gradient. However, since plasma membrane forms a selective barrier between the inside
of the cell and outside of the cell to prevent necessary nutrition going out or harmful toxic
going into the cell, not all substances can go through the plasma membrane. Osmosis in
plants is a vital action because it makes plants alive, but sometimes it also can kills
plants. Plants absorb water by using osmosis. However, if soil has higher concentration of
fertilizer than that of plants, the plants will give water out of the cell and shrivels. Thus,
Plants in hypertonic soil is very harmful.
2. Materials
Balance
250mL beaker
Cork borer
Dialysis tubing
Distilled water
15% glucose and 1% starch solution
Graduated cylinder
Lugol’s (Iodine Potassium) solution
Solution of unknown sucrose molarity
Pipet
Potato
Six plastic cups
Stirring rod
Sucrose
Test strip
3. Methods
Exercise A)
An approximately 30cm long and 2.5cm wide piece of dialysis tubing that had
been submerged in water was obtained. One end of the tubing was tied to form a
bag. The other end was rubbed together in order to separate the edges.
A 15mL of the 15% glucose and 1% starch solution was placed in the bag. The
other end of the bag tied off, leaving sufficient space for the expansion of the
contents in the bag. The color of the solution was recorded.
A 250mL beaker was filled with distilled water. Approximately 4mL of Lugol’s
(Iodine Potassium) solution was added to the distilled water. The color of the
solution was recorded.
The bag was immersed into the beaker of solution.
The setup was left for 30minutes or until a distinct color change in the bag or in
the beaker was displayed. The final colors of the solution in the bag and of the
solution in the beaker were recorded.
The liquid in the beaker was tested for the presence of glucose and the result was
recorded.
Exercise B)
Six 30cm strips of presoaked dialysis tubing were obtained.
A solution of unknown sucrose molarity, which was prepared by the instructor,
was poured into the six dialysis bags. Most of the air was removed from each bag
by drawing the dialysis bag between two fingers. Sufficient space, about one-third
to one-half of the piece of tubing, was left for the expansion of the contents in the
bag.
After each of the six dialysis tubing bags were dried, their initial mass was
measured and recorded.
150mL of each of the following solutions: distilled water, 0.2M sucrose, 0.4M
sucrose, 0.6M sucrose, 0.8M sucrose and 1.0M sucrose were prepared in the
separate 250mL beakers. Each beaker was labeled accordingly to indicate the
molarity of the solution.
Each bag was completely submerged into the beakers, which were filled with
different molarity of solution.
The setup was left for 30 minutes.
At the end of 30minutes, the bags were removed from the beaker.
Six bags were carefully blotted and their mass was determined. The final mass of
the bags were recorded.
Exercise C)
150mL of each of the following solutions: distilled water, 0.2M sucrose, 0.4M
sucrose, 0.6M sucrose, 0.8M sucrose and 1.0M sucrose were prepared in the
separate 250mL beakers. Each beaker was labeled accordingly to indicate the
molarity of the solution.
A cork borer was used to cut six pairs of four potato cylinders. Any potato skin
was peeled. Four potato cylinders were needed for each beaker.
Each set of four potato cylinders was separately weighed on the balance and their
mass was recorded.
Each set of potato cylinders was put into their respective beaker, which contained
different molarity of solution.
The beaker was covered with plastic wrap to prevent evaporation.
The setup was left for overnight.
The potatoes were taken out from the beaker and gently blotted on a paper towel.
Each pair of four potatoes’ mass was measured on the balance. Their mass was
recorded.
4. DataPresence of Glucose in Solution Through Dialysis Tubing
InitialContents
Solution Color Presence of GlucoseInitial Final Initial Final
Bag 15% glucose & 1% starch
Milky; foggy
Blue black Yes Yes
Beaker H2O & IKI Amber Amber No Yes
The data above, which recorded the color transformation of the solution in
dialysis tubing and presence of glucose in the beaker, justified the movement of both
glucose molecules and IKI molecules.
Percent Change in Mass of Dialysis Bags
Contents in Dialysis Bag
Initial Mass Final Mass Mass Difference
Percent Change in
Massa) 0.0M Distilled Water
7.29g 7.91g 0.62g 8.50%
b) 0.2M Sucrose
17.47g 17.56g 0.09g 0.52%
c) 0.4M Sucrose
10.22g 9.99g -0.23g -2.25%
d) 0.6M Sucrose
13.33g 12.44g -0.89g -6.68%
e) 0.8M Sucrose
13.48g 12.46g -1.02g -7.57%
f) 1.0M Sucrose
14.55g 12.85g -1.7g -11.68%
By comparing the initial and final mass of the six dialysis tubing, which were
submerged into the different solutions, the following data explicitly demonstrated the
variation in mass of the dialysis tubing.
Percent Change in Mass of Potato Cylinders
Contents in Beaker
Initial Mass Final Mass
Mass Difference
Percent Change in Mass
a) 0.0M Distilled Water
13.29g 16.19g 2.90g 21.82%
b) 0.2M Sucrose
13.50g 14.15g 0.65g 4.96%
c) 0.4M Sucrose
13.10g 11.60g -1.50g -11.45%
d) 0.6M Sucrose
13.28g 10.85g -2.43g -18.30%
e) 0.8M Sucrose
13.04g 9.41g -3.63g -27.84%
f) 1.0M Sucrose
12.57g 8.85g -3.72g -29.59%
The data above illustrated the change in mass of the potato cylinders depending on the
molarity of the solutions.
5.Result
The molarity, M, was calculated by drawing the best fit line, and setting y value
as 0. The sucrose solution and dialysis bag was in equilibrium in 0.31. The concentration
of mysterious solution was about 0.31M. So, molarity less than 0.31M showed an
example of hypotonic, and molarity higher than 0.31M showed and example of
hypertonic.
Potato core’s molarity, M, was examined by setting the y value as 0. Its molarity
was 0.35. Osmosis worked in the solution with potatoes. In lower concentration solution
than 0.35M, the water molecules went into potato cores, which told that solution was
hypotonic. However, in higher concentration than 0.35M, the water molecules went out
of potato cores, which showed that solution was hypertonic.
6. Conclusion
The difference of the solutions’ concentrations promoted two movements of
molecules between the solution in the beaker and that of the dialysis bag. In the first
experiment, the apparent color change of solution, from opaque white to amber, in the
dialysis tubing demonstrated that Iodine Potassium Iodide (IKI) had entered into the bag.
Conversely, the test strip proved the presence of glucose in the beaker, indicating that
glucose had left the bag.
The color transformation and the test strip confirmed that the molecules of
glucose and IKI were small enough to pass through the selectively permeable membrane.
The glucose and IKI molecules moved to equalize the concentration of each molecule
between the two solutions. IKI molecules presented in the beaker, which contained higher
concentration of IKI, moved into the dialysis tubing that had lower concentration of IKI
molecules. Similarly, glucose molecules moved from the higher concentration, dialysis
tubing, to the lower concentration, beaker, making the solute concentration of the two
solutions equal. Since the starch molecules were too large to pass the permeable
membrane, the color of the beaker remained as brown instead of turning into blue, stating
no reaction between the starch and the IKI. Based on the observation, the smallest size
ranked from IKI molecules, water molecules, glucose molecules, membrane pores, and
starch molecules.
Though the first experiment did not include any quantitative values, by recording
the initial and final percent change in mass of the solution presented in the dialysis
tubing, diffusion of water into the dialysis bag could be verified. Since the mass of
glucose was negligible, the variation of mass in the dialysis tubing indicated the
movements of the water molecules.
Hypothetically, if the experiment started with a glucose and IKI solution inside
the bag and only starch and water outside, the results could be predicted based on the
principles of diffusion and osmosis. Since the size of the molecules were small enough to
pass through the membrane pores, glucose molecules and IKI molecules would move out
of the dialysis tubing into the beaker. Correspondingly the water molecules, which were
smaller than the membrane pores, would move into the dialysis tubing from the baker. On
the contrary, the starch molecules would remain in the beaker because of their too large
molecules’ size to pass through the membrane pores.
The second experiment tested the relationship between the change in mass and the
molarity of sucrose within the dialysis bags. According to the result, the graph
demonstrated that as molarity of solution in the beakers increased, the change in mass
decreased. Knowing the molarity of the unknown solution, 0.31M, the mass of each bag
in this experiment could be predicted when all the bags were placed in a 0.4M sucrose
solution. Since the environment contained higher concentration of solutes, the water
molecules transferred from the potato cylinders to the environment, losing their weight.
Throughout the experiments, the percent change in mass was used rather than the
change in mass due to the different initial and final mass of the six bags. Change in mass
did not measure the amount of change proportional to the solutions. The change in mass
could be same despite the amount of actual difference made between the bags. The
percent change in mass, in fact, calculated the exact mass difference regardless of the
bags’ initial and final mass. The sucrose solution in the beaker would have been
hypertonic to the distilled water in the bag because the concentration of sucrose solution
was higher.
A dialysis bag was filled with distilled water and then placed in a sucrose
solution. The bag’s initial mass in 20g and its final mass was 18g. Then the percent
change of mass could be calculated as following:
Percent change of mass = [(final mass) – (initial mass)]/ initial mass x 100 = [18g (final mass) – 20g (initial mass)]/ 20g (initial mass) x 100 = 10%
Utilizing the concepts of osmosis and diffusion, the lab could be designed to
measure the speed of osmosis. For example, if the solution with dialysis bag was heated
up, the speed could be different. For another instance, if the seaweeds went into the
mysterious sucrose solution, osmosis might not occur because seaweeds came from salty
water.
In the second experiment, percent change in mass and molarity demonstrated that
osmosis worked. Percent change in mass was calculated by using balance, and molarity
was measured in the best fit line equation, which was same as figuring out x-intercept.
The molarity of mysterious sucrose solution was 0.31M. At this molarity condition, it
was isotonic, which meant the amount of flow of water between two solutions was equal.
In the third experiment, potato core’s molarity was calculated in the same way as in the
second experiment. Potato cores had 0.35M, and sucrose solutions below 0.35M were
hypotonic, upper than 0.35M were hypertonic, and sucrose solutions with 0.35M were
isotonic solution, or in equilibrium.
In order to obtain the solution with different molarities, a calculation had to be
done to measure the amount of sucrose needed for 150mL of distilled water. Using the
molarity equation, moles of solute / L of solvent, mass of sucrose could be calculated.
The molecular mass of the sucrose, 342g, was multiplied by 0.15mL to calculate the
amount of sucrose needed to make a 1.0M of sucrose solution. Then, to make 0.2M,
0.4M, 0.6M, and 0.8M, each molarity could be multiplied to 51.3, result of the previous
calculation. Through this calculation, the mass of sucrose needed to make each solution
with different molarities could be calculated.
Though the lab did not include any vagaries that would influence the result, there
were few possible errors. In the first experiment, the dialysis tubing could have leaked or
broke, transforming the solution in the beaker into a dark blue due to the reaction
between starch and IKI. The second experiments, which incorporated six different
molarities of solutions, could not have contained an exact amount of sucrose dissolved.
The different molarity would cause the dialysis tubing to gain or to lose its weight. In the
last experiment, a piece of potato skin might have been left unpeeled, causing erroneous
results. The potato cylinders might not have been perfectly dried when their mass was
weighed, causing additional weight of water to be included.
7. Bibliography
1.http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation
how osmosis works.html
Animation of Osmosis, McGrawhill.com
2.Biology 8th Edition by Campbell, Reece, Urry, Cain, Wasserman, Minorsky, Jackson
3.http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html
Diffusion and Osmosis by Carl R. Nave, Physical Science Information Gateway,
4.http://biology.arizona.edu/sciconn/lessons/mccandless/ Diffusion, Osmosis, and Cell
Membranes, An Integrated Science Instructional Unit by John R. MacCandless. Jr
5.http://www.blobs.org/science/article.php?article=20, Diffusion and Osmosis by Tim
Shepard MBBS Bsc
6.Power Point “Osmosis and Diffusion” by Mary Poarch