Exercise number 4 ABC
Exercise 4: Staining Introduction to Diffusion and Osmosis Khanh Mong Biology Lab 100B – 100B – Summer Summer 2012 Dr. Veno July 31, 2012
Purpose The general purpose of Exercise 4 is to fully understand the relationship between molecular size/charge and the rate of diffusion across a semi-permeable membrane; or in other words, demonstrate diffusion across a semi-permeable membrane. The next purpose is to measure the effects of various concentrations of solute in the process of osmosis. Then, we learned to distinguish between hypotonic, isotonic, and hypertonic environments. Lastly, we examine the effects of osmosis on plant cells. The purpose of exercise 4A is to test the permeability of the tubing to glucose, starch, and iodine potassium iodide. We used two tests in this experiment, including the I 2KI test for presence of starch and the Benedict’s test for reducing sugar. A hypothesis was created that the smaller molecules, such as glucose and water will diffuse through the dialysis bag’s membrane causing it to expand, due to the concentration gradient. We would test this hypothesis by filling the bag with a solution consisting of water, glucose and starch, tie it off and weigh it. In exercise 4B, the purpose is to test the osmotic behavior in cells. We tested the osmotic behavior by placing the cells in a hypertonic solution or a hypotonic solution. Based on the observation of the cells’ behavior in each different condition, we could differentiate the two types of water. I came up with the hypothesis that Solution B is hypertonic and Solution A is hypotonic. Follow the hypothesis, Solution B has the greater osmolarity compare to solution A Exercise 4C is about estimating the osmolarity of plant cells. For plants, the amount of water in their cells is important for the ongoing functions and daily vital activities. The amount of water in a plant cell must be maintained. The molarities affect both the cell’s weight and the cell’s volume. If the plant cell is immersed in a hypotonic solution, the weight and volume will
2
increase at intervals at which the cell takes in the water. If a plant cell is submerged in a hypertonic solution, the weight and volume will decrease as water exits.
Materials and Methods 4A: Diffusion of Molecules through a Selectively Permeable Membrane
In this experiment, we define the permeability of assigned chemical substances using dialysis tubing, which is an artificial semi permeable membrane. We took dry dialysis tubing and soaked in the water for a few minutes. One end of the tube we tide with rubber string. In the tube we added 4 pipettesful of 30 % glucose solution and then added 4 pipettesful of starch solution. We tide the opening of the tube with rubber string to make sure solution would not spill. In the mean time, we prepared a 500 ml beaker with 300 ml of water with several drops of I 2KI solution until the water become yellow-amber color. We placed the bag in the solution and left it there for 30 minutes. After 30 minutes, we closely observed the changes in both solutions. To be able to determine the presence of glucose molecules we performed Benedict’s test. In order to perform this test, we needed 3 test tubes. In the first test tube we took a sample of 2 pipettesful from the dialysis bag. In the second test tube, we took a sample of 2 pipettesful from the beaker. In the third sample, we filled it with water. In each test tube we added 1 drop of Benedict’s reagent and heated the test tubes in the hot water bath for about 3 minutes. We recorded our observations. 4B: Osmotic Behavior in Cells
The materials for exercise 4B are: 2 compound microscopes labeled A and B, 1 slide of Elodea in salt solution, and 1 slide of Elodea in distilled water. In this exercise, we investigated the osmotic behavior of a plant cells placed in different molar solutions. We took a small sample
3
of the Elodea in distilled water solution and placed on the slide with the drop of water. We covered it with watch glass and observe the cells under the microscope. On the second slide we took a sample of Elodea in a NaCl (hypertonic) solution. We placed the watch glass and observe the cells under the microscope. 4C: Estimating the Osmolarity of Plant Cells
The materials needed for this exercise include: one large potato tuber, 250 ml beakers or cups, wax marking pencil, forceps, paper towels, metric ruler, aluminum foil, sucrose solutions, razor blade, cork borer, deionized (DI) water, balance, petri dish and a calculator. The process was quite simple, potato cores were made by cutting through a fresh potato with a cork borer. The slices were made similarly in length and then sliced lengthwise. Then we weighed the slices, and placed them in a beaker containing a sucrose solution. The concentrations of sucrose were 0, 0.2, 0.4, 0.6 and 0.8 molar. After a while, the cores were re-weighed and the percent change in the mass was recorded.
Results Table 1, Exercise 4A: Diffusion of Molecules Recorded
Solution
Original
Original
Final
Color After
Source
Contents
Color
Color
Benedict’s Test
Bag
Sucrose and
Milky
Purple
Yellow
Clear
Yellow
Orange
Starch Beaker
H2O and I2KI
4
Water
Clear
Clear
Clear
Clear
Table 1 above shows how the color of the sources changed from original to final, and after the Benedict Test. The color change after each process suggested the significance of the tests upon the sources. Drawing of Elodea cells
Solution A
Solution B
Based on the predictions and observations, solution B is hypertonic, while solution A is hypotonic. Because of the specific character of hypertonic, solution B has the greatest osmolarity.
5
Table 2, Exercise 4C: Estimating Plant Cells Molarity Approximate time in solutions: 1.5 Sucrose Molarity
0.00
0.10
0.20
0.30
0.40
0.50
0.60
1.10
1.20
1.10
1.10
1.10
1.20
1.10
1.20
1.20
1.10
1.10
1.10
1.20
1.10
-0.10
0.00
0.00
0.00
-0.10
-0.30
-0.30
-8.33
0.00
0.00
0.00
-9.09
-25.00
-27.27
Final weight (g) Initial weight (g) Weight change (g) % change in weight
6
Graph of Percentage Change in Weight
Y = Change in Weight (%) 0.00 1
2
3
4
5
6
7
-5.00
-10.00
-15.00
Series2
-20.00
-25.00
-30.00
X = Sucrose Molarity (%) Based on the results of table 2, I had successfully developed a graph demonstrating the relationship of percentage change and amount of sucrose molarity. As we can see, as the sucrose molarity increases, the percentage change in weight decreases.
Analysis of Results Sample Calculations Final weight (g)
1.10
1.20
1.10
1.10
1.10
1.20
1.10
Initial weight (g)
1.20
1.20
1.10
1.10
1.10
1.20
1.10
-0.10
0.00
0.00
0.00
-0.10
-0.30
-0.30
Weight change (g)
7
Weight Change Final weight (g)
1.10
1.20
1.10
1.10
1.10
1.20
1.10
Initial weight (g)
minus 1.2
1.20
1.10
1.10
1.10
1.20
1.10
Weight change (g)
equal -0.1
0.00
0.00
0.00
-0.10
-0.30
-0.30
Percent change in weight Final weight (g)
1.10
1.20
1.10
1.10
1.10
1.20
1.10
Initial weight (g)
1.20
1.20
1.10
1.10
1.10
1.20
1.10
-0.10
0.00
0.00
0.00
-0.10
-0.30
-0.30
-8.33
0.00
0.00
0.00
-9.09
-25.00
-27.27
Weight change (g) % change in weight
Weight change = (-0.10 g/Initial weight 1.20 g)*100 = -8.33%
Discussion and Interpretation of Results Addresses Discussion questions for part 4A
Significance of final colors of Benedict test The final colors are different with the colors after the Benedict’s tests. Did results support hypothesis – explain why or why not The results support the hypothesis that there had to be chemical reactions that caused all the changes. Explanation of results The color purple existed because of the presence of starch. Yellow amber suggested that there was no starch. The solution turned orange because of a reducing sugar was present.
8
Predict size of I2KI molecules relative to glucose & starch The size of I2KI molecules were approximately the same size or smaller than glucose molecules, and definitely smaller than starch molecules. Explanation of what happens if experiments starts with glucose & I 2KI in bag and starch in beaker The final color of the beaker would be purple, while the final color of the bag would be amber yellow. The starch cannot get through the tube while I 2KI can, so I2KI will enter the beaker and turn beaker solution purple. Finally, the presence of sugar will turn both solution to orange. Addresses Discussion questions for part 4B
Proper identification of which solution is hypertonic Based on the predictions and observations, solution B is hypertonic Proper identification of which solution is hypotonic Solution A is hypotonic. Explains which solution has greatest osmolarity Because of the specific character of hypertonic, solution B has the greatest osmolarity. Explains whether pond water is isotonic, hypertonic, or hypotonic to Elodea cells Pond water is hypotonic to Elodea cells because pond water is the natural home of Elodea. Usually, water flow from the surrounding medium into the Elodia. Because water flowed into the cell, pond water must be hypotonic. Addresses Discussion questions for part 4C
What sucrose concentration does the curve cross the zero line on graph Normally, at about 0.3M Sucrose, the vurve cross the zero change line on the graph.
9
Explains how data can be used to determine osmolarity of potato tuber tissue The graph shows the amount of sucrose in the potato tuber tissue at default, and how the weight changes as we increase the concentration of sucrose in the solution that the potato tuber tissue is contained in. Estimates osmolarity of potato tuber Approximately, the osmolarity of the potato tuber tissue is about 0.3M Background info and explanation of osmosis Molecules undergo constant motion, which enables them to move from one region to another. The motion of a molecule in solution is constantly affected by collisions with other molecules, which results in random motion. Diffusion, which is important to living systems, occurs in response to molecular motion and to a concentration gradient, that is, molecules moving from areas of high concentration to areas of low concentration until equilibrium are reached. During osmosis, the diffusion of water molecules down a concentration gradient occurs across a semi-permeable membrane. A semi – permeable membrane is a membrane which allows some materials to pass through while rejecting others. This is true of the plasma membrane surrounding all living cells. (O'Loughlin) Conclusions and sources of error Basically, the test is supposed to prove the hypothesis. However, our group failed on our experiment. The possible errors we made was to dry the potato slices too fast. Plus, we definitely think that we did not have enough time for the solution to have a fair effect on the potato slices.
10
Works Cited
FONTANA, D.. "Diffusion and Osmosis." Geoegia state university. New Republic, 2012. Web. 31 Jul 2012. .
McQueen, Nancy, Amelia Russo-Neustadt, and Sandra Sharp. Introduction to Cell Biology and Genetics. 2. LA: CSULA, 2012. Print.
Narguizian, Paul. Principles of Biology. Nature Education, 2012. 0. .
O'Loughlin, M.. "Animation: How osmosis works." . McGraw-Hill Higher Education, 2006. Web. 31 Jul 2012. .
11
