Diffusion/Osmosis

1A
Introduction: Diffusion is the constant movement of solutions from high concentration to low concentration. Selectively permeable membranes can manipulate diffusion by allowing certain solutions through and not allow others.

Purpose: The purpose of this experiment is to observe how a selectively permeable membrane effects the rate of diffusion of different sized molecules.

Methods: first, we tested a 15% glucose/1% starch solution for the presence of glucose and then filled a dialysis bag with the solution.

From that we recorded the color. Then we filled up a beaker with distilled water and put 4ml of lugols solution in it, we then recorded that color. Then we took the dialysis bag, submerged it in the water, and waited for 30 minutes.

We then recorded the colors of the bag and the water after the time, we also tested for glucose and recorded the data.

Data:

Discussion: When we tested for glucose at the end, it was present in the dialysis bag, but not present in the water surrounding the bag. The glucose seemed unable to pass through the dialysis bag. However, the color of the glucose solution in the dialysis bag was different from the start. The original color of the dialysis bag's solution was clear, and the original color of the water with the lugols solution was orange. At the end of the experiment, the color of the solution in the dialysis bag was dark purple, and the water surrounding it was still orange. This shows that the lugols solution diffused into the dialysis bag to make a different color. The dialysis bag proved to have a selectively permeable membrane by slowing lugols solution in, while keeping the glucose in.

Conclusion: this experiment showed us an example of selectively permeable membranes. The membrane allowed lugols solution to diffuse in and out, but did not allow glucose to diffuse out.

1B
Purpose: the purpose of this lab was to observe osmosis of water molecules interacting with different molarities of sucrose. We did this by looking at the flow of water in or out of a semipermeable membrane.

Introduction: Osmosis is the diffusion of water across a membrane. The water will travel from a lower concentration of solute to a high concentration. Animal cells are always trying to maintain an isotonic state (equal concentrations of solute and solvent in and out of the cell). Osmosis moves water across the membrane to equal out the concentration of solvent. 

Methods: We started with six different dialysis bags. We added differing molarities of sucrose into each of the bags.

We weighed and recorded the initial mass of each bag. We then submerged the bags into cups that was filled with water. We then let the bags sit in the cups for half an hour. Once time was up we took the bags out of the cups and measured the final weight. We then compared the initial mass to the final and came up with a percent difference. We chose to use a percent difference rather than a mass difference due to the fact that the amount of solution in each bag was not uniform. Since the initial masses were all different percent difference is a more accurate measurement when comparing the data.

Data

( our group data)

	DISTLLED WATER	0.2 M	0.4M	0.6M	0.8M	1.0M
Group 1	0.45	2.38	5	5.86	6.06	7.93
Group 2	5.15	8.47	8.54	10.43	9.76	17.44
Group 3	0	4.33	8.61	14.41	12	10.05
Group 4	2.17	1.73	3.14	6.9	7.2	11.54
Group 5	0.8	6.8	3.6	6.9	5.4	8.3
Group 6	0.89	2.5	3.1	5.3	6	7.4
Group 7	11.4	9.8	10.7	12.3	13.7	13.4
Group 8	2.7	3	4.9	6.2	4.3	6.1
Group 9	0.63	2.14	4.85	8.19	8.6	2.17

Group 10	1.1	4.95	10.57	16.07	19.09	16.87
CLASS AVG:	2.01	4.61	6.3	7.88	9.21	9.69

(Class data)

Graphs and Charts: 

(Class graph)

Discussion: Our results for the most part were what we expected. Osmosis makes water
travel from high concentration from low concentration of solute to high. In this experiment the bags had a lower concentration water than their environment (except for our control). This means that we expected water to rush into the bags in order to reach an isotonic state. What we witnessed was very similar to what we expected. After we weighed each bag we saw that most of the bags increased in weight by a considerable amount. This meant that water was entering the bag, thus adding weight. We saw that the higher the molarities the greater the percentage weight increased. This means that the higher molarity bags allowed more water in. This makes sense since more water is needed to even out the concentrations. We did see a few inaccuracies in our experiment. Our control group was distilled water. For out control group we saw an increase of .625%. In theory this number should be 0% due to the fact that the bags contents are the same as the solution that it is put in, however this can be accounted for by the fact that we used distilled water in the dialysis bags, but sink water for the cup. The difference between the two can make a difference in the data. Our biggest outlier can be seen with our 1M bag. This bag should have the highest percent change due to the fact that it had the highest molarity. Instead we had a negative mass percentage. This means that the bag actually lost water. We do not have an absolute reason as to why this occurred. Our best speculation that such an unusual measurement would take place is that there could have been a hole in the bag. This would allow water to rush out of the bag at a faster rate than it entered in. If this were the case water it would make sense as to why the bag lost weight.

Conclusion: Our experiment meant to test the process of osmosis. We saw in our data that the concentration of solute has a direct correlation to the rate at which water passes through a semipermeable membrane. The higher the concentration the faster water moves.

1C
Purpose: The purpose of this experiment was to test the molarity of sucrose in potatoes. The experiment tested the effects of diffusion using an organic substance. We used the same idea of osmosis as we did in experiment 1B

Introduction: Potatoes are made out of all organic substances. Potatoes are made out of plant cells which means that they are primarily made out of starch and cellulose. Each potatoes piece contains a certain amount of sucrose in it.

Methods: We cut and measured twenty four pieces of potato.

We took an initial measure of four pieces at a time and then we put those four pieces into a cup each filled with water that had differing molarities of sucrose. We covered the cups with saran wrap then we let the cups sit overnight. The next day we uncovered the the cups and we weighed the potato pieces in the respective groups of four. 

Data:   

 class data)

(Our experiment was group 9)

Graphs and charts:

(class avg graph)

Discussion: The osmosis of water volumized the potatoes and added mass into them. The sucrose. Water potential is higher outside the cell than inside the cell then water will move from high to low. We wanted to know how much sucrose is in a potato. The graph shows the net change in weight of the potato in relation to the sucrose solution it was placed in. A potato with no change in weight would be at zero in the chart meaning it was placed in a solution of equilibrium. To fail safe our data we also used the entire class' experiments to avoid anomalies. The molarity of sucrose in a potato is approximately 2.28 M. This means if it was placed in a 2.28 M solution of sucrose then there would be no net change in the weight of the potato.

Conclusion: The potato has a sucrose concentration of approximately 2.28M as demonstrated by the class average graph.

Reference:  http://en.m.wikipedia.org/wiki/Molarity,   http://www.biologycorner.com/worksheets/labreport.html

1D

Purpose: The purpose for this part of the lab of the lab was to find the solute potential of the sucrose solution

Introduction: To find the solute potential, we used the equation Ys=-iCRT. The R is conastant because the solution was held in an open system. For temperature, we assumed a room temperature of 27 degrees celcius. And for molar concentration we found the solution to have a zero at 1.65 moles. Our ionization constant was 1.0, as sucrose doesn't dissolve in water. 

Methods: In order to find the molar concentration of the solution, we graphed out the molarity of the solutions as x and the percent increase in mass as y. When we drew the graph, the function crossed zero at about x=1.65. We already knew what R was, since the system was open. We knew what the ionization constant was, so the only thing left to find was the temperature. Since it had to be in kelvin, we added 27 degrees celcius to 273 degrees kelvin to get 300 degrees kelvin. We then plugged these value into the equation, 

                   Ys=-(1)(1.65)(1.0)(300)

                   Ys= -41.135

Discussion: Our results were normal and expected. We expected the solute potential to be negative, because anything other than pure water is negative. We also expected a high solute potential due to the molarity and the high temperature. 

Conclusion: After we plugged everything in, we found the solute potential to be -41.135

1E

Purpose:  the purpose of this experiment is to see the use of plasma lysis in plant cells.

Method:  you can see plasmolysis happen underneath the microscope.  Add salt water with the cell and you can see the water exit the cell.

Discussion:  plasmolysis is the exit of water from a plant cell.  Plasmolysis occurs when a plant cell is placed in a hypertonic solution.  The solution causes water exit the cell through diffusion.  This causes the cell to shrink and the cell with die due to lack of water.