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Transport of Solute in Solvent through Osmosis Essay

Objective:

The objective is to simulate passive transport: diffusion of solutes and osmosis of water through a semipermeable membrane (dialysis tubing). The experiment will show how molecules in solution move from areas of higher concentration to areas of lower concentration in the attempt to reach homeostasis in different circumstances.

Introduction:

The main purpose of this lab was to observe diffusion and osmosis. This is demonstrated using dialysis tubing and a combination of monosaccharaides, disaccharides, water (H20), and sodium chlorine (NaCl), also known as table salt. We then calculated the percent change of mass over a period of time. Due to kinetic energy, cells tend to bump into one another; this is the result of the process called diffusion. Diffusion is the movement of molecules from a place of higher concentration to a place of lower concentration. In this lab, diffusion causes a physical change of our cells (mass). Osmosis is a type of diffusion that involves water. Osmosis occurs when water moves through a semi-permeable membrane. The water moves from a place of higher water concentration to a place of lower water concentration. Water potential measures free energy of water in any solution. A solution is a liquid mixture of two or more components. This mixture consists of a minor component (the solute) which is consistently distributed within a major component (the solvent). Water potential consists of 2 parts: osmotic potential and pressure potential. Osmotic potential pertains to the water molecules that move from a hypotonic solution to a hypertonic solution (changing the concentration gradient), while pressure potential pertains to the exertion of pressure the cell is under. The pressure is caused by the height of water exposed to the atmosphere above the artificial cell. The concentration gradient is generally the difference in concentration of a dissolved substance in a solution. This occurs between a region of high density and lower density. Water potential of distilled water in atmospheric pressure is 0, because the osmotic and pressure potentials are 0. For example, in plant cells, osmotic potential is lowered because more of its solute is being dissolved in the cytoplasm. When placed in pure water, the cells of the plant are hypertonic. This means the plant cells have more osmotic concentration. The water potential within the beaker is higher making it hypotonic, meaning it has a lower osmotic pressure. Therefore the water will move into the cell because water moves from hypotonic environments to hypertonic environments. This results in a swelling cell. On the contrary, if solute is added to the beaker, the water potential in the cell will be greater, resulting in a hypotonic cell. Therefore water will move out of the cell, causing it to shrivel. This is relative to this lab. However, not all solutions are like this. Solutions that have reached the state of equilibrium are isotonic. This means that both solute and solvent have the same osmotic pressure. The rates of the reaction are determined by the molecular size of the particles. If the particles or smaller, they diffuse through the semi-permeable membrane much faster than particles larger than the semi-permeable membrane. This is because the smaller particles have less of a resistance to pass through the selectively permeable membrane. If the particle is larger it is going to take a much longer time for the particle to push its way through the membrane.

Materials:

Dialysis tubing
Scissors
Small funnel
Graduated cylinder
Paper towel
Digital scale
400mL beaker
250mL beaker
1 mL pipette
Test tube
Hot plate
Weigh boats
Pipette
Pipetter

Methods:

1) Obtain ten 40 centimeter strips of dialysis tubing and soaked them in water. This will moisten the dialysis tubing to a rubbery texture that is easier to maneuver and work with. Tie off one end of the tubing 2cm from the end to form a bag. Finally to open the other end of the bag, we rubbed the closed, untied end between our fingers until the edges separated.

2) Measure 25mL of the applicable solution needed for the dialysis cell. This should be done with a 25mL graduated cylinder. Measuring with a 25mL graduated cylinder insures that no errors be made. To properly measure 25mL, the graduated cylinder should be placed on a flat surface and you should be at eye level with its measurements. A full 25mL is measured at the bottom of the meniscus. Once the solution has been measured, using a small funnel, pour the solution into the dialysis bag by inserting the tip of the funnel into the open end. Finally make a note of what the cell is containing; it is very easy to get them mixed up. A source of error that is unwanted.

3) Tie the open end of the dialysis bag 2cm from the end of the bag.

4) Rinse the dialysis cell thoroughly under water to guarantee any foreign substance that may have touched the dialysis cell is rinsed off and gently blot the dialysis cell with paper towel. The dialysis cells must be completely dry so when the cell is being weighed, the digital scale will not be weighing water weight on the cell as well. Using a weigh boat, measure the cells mass. The weigh boat is used for the purpose to avoid cross contamination between the cell and scale. To insure that the cell is the only thing being weighed, place the weigh boat on the scale and press clear. This will set the scale to 0 with the weigh boat still on it. Place the cell on the weigh boat and record the total weight of the cell. Your data should be weighed in grams (g). Before submerging your cell in its beaker with solution correlated on Table #1, the dialysis cell must be weighed. This will give us an idea of what the cell begins at and in what way diffusion and osmosis affects the dialysis cell. The cell must be weighed every 30 minutes in a time period of 90 minutes. The dialysis cell should be weighed four times.

5) Submerge each prepared dialysis cell in a 400mL beaker with 150 mL’s solution correlating to Table #1. These solutions must be measured using a 100 mL graduated cylinder. Measuring with a 100mL graduated cylinder ensures that no errors be made. To properly measure 100mL, the graduated cylinder should be placed on a flat surface and you should be at eye level with its measurements. A full 100mL is measured at the bottom of the meniscus. Because 150mL of the solution is needed, two separate measurements must be made. An entire measurement from the 100mL graduated cylinder and a half should be measured. Record the time the dialysis cell is submerged in the solution; this will insure an accurate timing at which the dialysis cell must be weighed. Label each dialysis cell and solution filled beaker. This will provide knowledge as to which solution is contained in each beaker and avoid any error from being made.

6) In 30 minute intervals for 90 minutes, the cells must be removed from each beaker and blotted try with clean paper towel to be weighed. Record each measurement every time the cell is being weighed. Do not rinse the cell under water again; this may compromise the cell and solution within the beaker.

7) At the conclusive part of the cell (last time weighing the cell) remove the cell from the solution filled beaker, and blot it dry. Proceed to using scissors to cut the cell, and pour the remaining content into a 250mL beaker. Label each beaker as to which it is containing.

8) Using 3 clean test tubes perform a chloride (Cl-) test, a glucose test and a sucrose/lactose test. Obtain 2mL of each solution from each beaker. This is done using a pipette and pipette. Place the tip of the pipette in the solution of the beaker, and the pipetter is placed at the other end of the pipette. The pippetter sucks the solution into the pipette, this is a better method then using ones mouth to suck up the solution because it is more accurate and safer. Using a hot plate and a beaker filled with water, place each finished test tube into the beaker. The water contained in the beaker must be boiling before each test tube is placed within it. Using this method, the solutions reaction will occur at a much faster rate. This applies to each test. In the (Cl-) test, 2 drops silver nitrate(AgNo3) are added to each 2mL solution that has been measured and placed into a test tube from the obtained material from the cell. This test measures for the salt content in the solution. In the glucose test, Benedict’s test is performed using a 1:1 ratio of Benedict’s test to solution. These tests for the glucose in each solution. Finally the sucrose/lactose test uses the same content as the glucose test. Benedict’s test is performed using a 1:1 ratio of Benedict’s test to solution. This test measures for reducing sugars. The indicator for each test is color. When there is a color change to the solution that means the test has tested positive.

9) At the end of the lab, all observations should have been recorded in your notebook.

Results:

The data shows (Graph #1 and Graph #2) that in each case, the dialysis bag slight increases or decreases in mass over a period of 90 minutes. The increase or decrease in mass of the dialysis cell is solely based upon the concentration gradient within the dialysis cell and its environment as to which it is placed in. In each graph, it displays which dialysis cells have increased or decreased in mass. For each cell that has increased in mass, (A1, B1, C1, D1, E1, and F1), diffusion and osmosis has occurred into the cell. As a result the cell has swollen because water has moved into the cell. Dialysis cells that have decreased in mass, (A2, B2, C2, D2, E2, and F2), have had the opposite reaction occur. Diffusion and osmosis has moved water out of the cell, causing a decrease in mass. This is due to the dialysis cell containing a hypotonic solution as its environment at which it was submerged is hypertonic. This then causes the cell to shrink in mass. Due to the different data shown in Graph #1 and Graph #2, we know that the cells and environments contained different concentration gradients because not all data is the same. This means that no dialysis cells or environments have reached equilibrium and have become isotonic.

Discussion:

The purpose of this lab was to observe the physical mechanisms of osmosis and diffusion. Diffusion is the movement of particles. The particles move from areas of higher concentration to an area of lower concentration. The diffusion of water moves into or out of a selectively permeable membrane, this process is called osmosis. Because of the selectively permeable membrane, nothing but water and other very small particles are able to diffuse. The dialysis tubing is similar to the function of the cell membrane. As a result the dialysis cell loses water and also gains because of osmosis due to the transport of water. This occurs when the dialysis cell is placed in an environment in which water concentration is greater than that of the cell. The dialysis cell gains water when placed in and environment in which the concentration is lower. This concept describes how molar concentration (the number of moles in a solute per liter of solution) affects diffusion. The perception of solutions diffusing has been observed in different situations. Diffusion always moves from a high concentration to a low concentration, this is affected by molar concentration. As the molecular mass decreases, more solution is diffused. This hypothesis was made due to the knowledge of molecules diffusing down a concentration gradient. As a result, the mass of the dialysis tubes have increased, as the molarity of a solution increases, the percent of change in mass will increase as well. This affect occurred in cells (A1, B1, C1, D1, E1, F1). As the molarity of a solution decreased in other dialysis tubes, the mass of the dialysis tubes have decreased and percent change in mass has decreased as well. The amount of increase and decrease of diffusion is based on the molecule size. This occurred in cells (A2, B2, C2, D2, E2, F2). As molecular size increases, the rate of diffusion decreases. This is because it has a greater resistance going through the medium of the membrane. When molecular size decreases, then rate of diffusion increases because the molecule has less of a resistance to go through the dialysis cells semi-membrane.

Acknowledgments:

I would like to thank Ms. Huggins for preparing each of the solutions for the class as well as the class for preparing portions of the lab as a group effort. Without having any group effort within the class, the lab would have taken more time then what would have been given. I would also like to thank the class for contributing in providing portions of the lab data, without this data we would have not been able to properly provide right information need for the lab.

References:
Campbell, N.A., and Reece, J.B. 2002. Biology, 8th ed. Benjamin Cummings. Pp. 131-134 for osmosis. Molecular Cell Biology, 4th edition, Harvey Lodish, Arnold Berk, S Lawrence Zipursky, Paul Matsudaira, David Baltimore, and James Darnell. New York: W. H. Freeman; 2000. Chapter 2. Separate from Biology in the Laboratory 3e, Doris R. Helms, Carl W Helms, Robert J.
Kosinski, John C. Cummings; W.H. Freeman, Dec 15, 1997

Data:

Table #1: Experimental protocol to follow for tests of osmosis and diffusion.

Summary:
This table shows us what solution is contained within the dialysis cell or its environment contained in a beaker. This chart also tells us what test has to be conducted upon the beaker and the cell solution after the 30 minute intervals made in a period of 90 minutes. When the cell has finished diffusing after a period of 90 minutes, then these tests can be conducted.

Solution in beaker
Solution in cell
Test solution in beaker for*…
Test solution in cell for*…
A1
H2O
NaCl
Cl-
Cl-
A2
NaCl
H2O
Cl-
Cl-
B1
H2O
glucose
glucose
glucose
B2
glucose
H2O
glucose
glucose
C1
H2O
sucrose/lactose
lactose
lactose
C2
sucrose/lactose
H2O
lactose
lactose
D1
NaCl
glucose
glucose
Cl-
D2
glucose
NaCl
Cl-
glucose
E1
NaCl
sucrose/lactose
lactose
Cl-
E2
sucrose/lactose
NaCl
Cl-
lactose
F1
glucose
sucrose/lactose
none
none
F2
sucrose/lactose
glucose
none
none

Table #3: Example showing molecular mass of particles

Summary:
This table is to shows the molecular mass of the particles used in the lab. This will help understand why some solutions diffuse faster than others. When a particle is bigger, it takes a longer time for it to diffuse through the membrane because it has to push itself through the membrane rather than slide through the membrane as a small particle would.

Name of Solution
Formula for Solution
Moelcular Mass of Solution (g)
Water
H2O
18g/ mol
Sodium Chloride
NaCl
58.5g/ mol
Glucose
C6H12O6
180g/ mol
Sucrose/ Lactose
C12H22O11
684g/ mol
Lactose
C12H22O11
342g/ mol

Table #2: Weight produced over time by different cells submerged in different solutions

Summary:
This table displays an increase or decrease in mass of the dialysis cell in 30 minute intervals over a period of 90 minutes. This helps us to understand the concentration gradients of the cell or environment of the cell due to its reaction. The cells that increases in size, we now know that the cell was hypertonic placed in a hypotonic solution because in order to reach equilibrium the amount of particles within the cell must be the same. Because they have not reached equilibrium this results in the movement of molecules moving from a hypotonic solution to a hypertonic solution through a selectively permeable membrane (dialysis tubing), this is called osmosis. In order for the particles to move across the membrane diffusion must occur for the movement from high osmotic concentration to lower osmotic concentration to occur. The cells that decrease in mass are hypotonic place in a hypertonic solution. We know that because osmosis and diffusion has occurred, allowing the solution and particles to move out of the cell into the cells environment. Once the cell is finished being weighed in 30 minute intervals over a period of 90 minutes, a silver nitrate (AgNO3) test (test for salts present in the solution), glucose test a sucrose/ lactose test (tests for reducing sugars) are conducted. The column in green represents whether the solutions tested positive or negative for the substances.

Change in Mass (g)
Time (min)
A1
A2
B1
B2
C1
C2
D1
D2
E1
E2
F1
F2
0
26.42
25.99
27.69
26.65
28.65
26.32
27.36
26.74
28.78
26.75
27.80
27.96
30
27.24
25.41
31.84
21.71
34.89
21.32
30.38
23.41
34.33
20.00
29.85
25.91
60
27.33
24.94
33.80
19.44
40.21
18.37
31.33
21.55
38.21
16.83
31.42
24.00
90
27.12
24.70
34.95
18.83
44.15
15.93
33.47
20.18
41.23
14.50
33.42
21.87

Test
(+/-)
positive +
positive +
positive +
positive +
positive +
positive +
positive +
positive +
positive +
positive +
positive +
positive +

Graph #1: Change in mass over 90 minutes in 30 minute intervals. Cells A to C.

Summary:
This graph visually shows us which dialysis cells gained or lost mass due to it concentration difference between the inside of the dialysis cell and its environment in which it was submerged in. Due to some cells having gained or lost more than other cells, some of the differences were much greater or lower than others. These means diffusion would have occurred faster or slower do to the solutions molecular size. When a particle is bigger, it takes a longer time for it to diffuse through the membrane because it has to push itself through the membrane rather than slide through the membrane as a small particle would.

Graph #2: Change in mass over 90 minutes in 30 minute intervals. Cells D to F.

Summary:
This graph visually shows us which dialysis cells gained or lost mass due to it concentration difference between the inside of the dialysis cell and its environment in which it was submerged in. Due to some cells having gained or lost more than other cells, this tells us that some of the concentration differences were much greater or lower than other. These means diffusion would have occurred faster or slower do to the solutions molecular size. When a particle is bigger, it takes a longer time for it to diffuse through the membrane because it has to push itself through the membrane rather than slide through the membrane as a small particle would.

Sources of Error:
Forgetting to rinse our dialysis bags with water before weighing our cell will cause cross contamination to occur thus changing the composition of the solution that the cell has been submerged in as well as affecting the rate of diffusion and osmosis due to the dialysis tubing pores having already been compromised.


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