Ap Biology Lab One: Osmosis And Diffusion

Title:

AP Biology Lab #1: Diffusion and Osmosis

Purpose: In this lab, we will be conducting an experiment where we will observe the acts of passive transport: diffusion and osmosis. The experiment will show how molecules in a solution are able to move from an area of high concentration to an area of low concentration. With this, it will also show us how hypertonic and hypotonic solutions exist, as well as how cells try to get back into an isotonic state. In doing so, this lab will allow us to learn why and how diffusion and osmosis happens in all living things. We will be testing the movement of solutes from their area of high concentration to the area of lower concentration that surrounds them. Hypothesis: Exercise A) I believe molecules of starch and glucose will enter the water in the beaker. Exercise B) I believe osmosis will occur and try to make each solution isotonic. Exercise C) I believe the water potential of the potato will be negative. Exercise D) I believe there is no hypothesis to give. Exercise E) I believe the salt will cause the cell to become hypertonic. Procedure: Exercise A) 1) Obtain a dialysis tubing that has been submerged in water. Tie off an end to form a bag. 2) Test the solution for a presence of glucose. 3) Place a starch solution into the bag. 4) Fill a beaker 2/3 full of water and add a solution to the water. Record the color change of the solution and amount of glucose present. 5) Immerse the bag into the beaker of solution. 6) Wait 30 minutes or until a distinct color change has taken place in both the bag and solution. 7) Test the liquid remaining in the beaker for any presence of glucose. Exercise B) 1) Obtain 6 strips of presoaked dialysis tubing. 2) Tie a knot in one end of each piece of tubing to form 6 bags. Fill them each up with different solutions. 3) Rinse and record weight of each bag. 4) Place each bag into a beaker to find the molarity of the solution in the dialysis bags. 5) Now fill each beaker with 2/3 of water or enough to completely submerge the bag. 6) After 30 minutes, remove bags from water and determine their mass. Exercise C) 1) Slice a potato into 4 discs without skin. 2) Pour assigned solution into a beaker. 3) Measure and record the mass of the 4 discs. 4) Put all 4 discs into the designated solution and let sit overnight. 5) Remove discs. Measure and record their total mass. 6) Calculate percentage change from initial to final and graph data.

Exercise D) 1) Complete the questions on the calculations of water potential from experiment. Exercise E) 1) Prepare a wet mount slide of an epidermis of an onion. Observe and record what you see. 2) Add a few drops of a salt solution across the slide. Sketch and describe the onion cell. 3) Remove the cover slip and flood the onion cell with water. Observe and describe what happened to the cell. Data: Exercise A) Table 1.1

Bag Beaker

Presence of Glucose in Water Through Dialysis Bag Initial Contents Solution Color Presence of Glucose Initial Final Initial Final 15% Glucose & 1% Murky Clear Dark Olive Yes Yes Starch Green H2O & IKI Dark OrangeAutumn No Yes bottom, Clear Orange Yellow-top

Exercise B) Table 1.2

Contents in Dialysis Bag 0.0 M Distilled Water 0.2 M Sucrose 0.4 M Sucrose 0.6 M Sucrose 0.8 M Sucrose 1.0 M Sucrose

Percent Change in Mass of Dialysis Bags –Group Data Initial Mass Final Mass Mass Difference Percent Change in Mass 21.1 grams 21.0 grams 0.1 grams -0.47% 21.3 grams 21.5 grams 24.0 grams 23.4 grams 23.5 grams

22.2 grams 23.4 grams 26.7 grams 25.7 grams 26.3 grams

0.9 grams 1.9 grams 2.7 grams 2.3 grams 2.8 grams

4.20% 8.40% 11.25% 9.83% 11.91%

Table 1.3

Content in Dialysis Bag 0.0 M Distilled Water 0.2 M Sucrose 0.4 M Sucrose 0.6 M Sucrose 0.8 M Sucrose 1.0 M Sucrose

Group 1

Percent Change in Mass of Dialysis Bags–Class Data Group Group Group Group Group Group Total 2 3 4 5 6 7

Class Average

0.47%

0.75%

2.0%

2.48%

1.0%

2.89%

2.7%

12.29%

1.756%

4.20%

3.80%

5.0%

6.11%

5.1%

4.26%

5.8%

34.27%

4.896%

8.40%

8.00%

8.0%

8.60%

10.6% 7.30%

9.9%

60.80%

8.686%

11.25% 12.30% 10.0% 13.70% 17.7% 9.80% 9.83%

10.6% 85.35%

12.193%

16.99% 20.0% 11.01% 17.6% 11.30% 14.9% 101.63% 14.519%

11.91% 18.10% 22.0% 16.20% 18.1% 16.74% 20.0% 123.05% 17.579%

Graph 1.1

Exercise C) Table 1.4

Contents in Beaker

Initial Mass

0.0 M 6.3 Distilled Water grams 0.2 M Sucrose 6.3 grams 0.4 M Sucrose 6.3 grams 0.6 M Sucrose 6.3 grams 0.8 M Sucrose 6.3 grams 1.0 M Sucrose 6.3 grams

Final Mass 8.0 grams 6.0 grams 5.5 grams 5.3 grams 4.9 grams 5.5 grams

Potato Core Results–Group Data Mass Percent Class Average Percent Difference Change in Change in Mass Mass 1.7 grams 26.98% 22.16%

Temperature 21.5°C

0.3 grams

-4.76%

-1.10%

21.5°C

0.8 grams

-12.70%

-13.24%

21.5°C

1.5 grams

-15.87%

-18.33%

21.5°C

1.5 grams

-32.44%

-26.23%

21.5°C

0.7 grams

-11.29%

-20.77%

21.5°C

Table 1.5

Contents in Beaker 0.0 M Distilled Water 0.2 M Sucrose 0.4 M Sucrose 0.6 M Sucrose 0.8 M Sucrose 1.0 M Sucrose

26.98%

Group 2 28.0%

Potato Core Results–Class Data Group Group 4 Group Group 3 5 6 17.5% 17.0% 23.4% 20.9%

-4.76%

3.4%

-1.6%

2.0%

4.6%

-12.70%

-17.0%

-22.2%

-16.7%

-15.87%

-25.0%

-25.4%

-32.44%

-27.0%

-11.29%

-21.0%

Group 1

Graph 1.2

Group 7

Total

21.10%

154.95%

Class Average 22.16%

-25.0%

13.70%

-7.66%

-1.10%

-15.1%

-17.1%

8.20%

-92.74%

-13.24%

-26.0%

-21.5%

-15.8%

1.34%

-128.3%

-18.33%

-29.7%

-31.0%

-22.2%

-26.5%

-23.70%

-183.6%

-26.23%

-22.2%

-25.0%

-21.5%

-26.9%

-17.40%

-145.37%

-20.77%

Exercise D) Percent Change in Mass 20% 10% -3% -17% -25% -30%

Sucrose Molarity Distilled Water 0.2M 0.4M 0.6M 0.8M 1.0M

Graph 1.3

Analysis: Exercise A) 1) Glucose is leaving the bag and the IKI is entering the bag. The change in the color of the bag proves IKI is entering the bag and after testing the beaker, we found there to be glucose, which proves that glucose was leaving the bag and entering the beaker of H2O and IKI. 2) In the results, the IKI moved from the beaker to the bag. This caused the change in the color of the bag. The IKI moved into the bag to make the concentrations outside the bag equal to inside the bag. The glucose solution moved out of the bag. The glucose moved to make the solute concentration inside and outside the bag equal. 3) If the initial and final percent concentration of glucose and IKI for the bag and the beaker were given, they would show the differences and prove the movement of these substances to reach equilibrium. 4) Water molecules, IKI molecules, Glucose molecules, and Membrane Pores. Starch molecules are too large to enter or exit through the holes of the dialysis tubing. 5) If the experiment started with glucose and IKI inside the bag with H2O and starch in the beaker, the glucose and IKI would move out of the bag to make the concentrations equal,

changing the color of the solution within the beaker, the starch, however, could not move into the bag because its molecules are too big to pass through the semi-permeable membrane of the dialysis tubing. Exercise B) 1) The molarity of the sucrose in the bag determines the amount of water that either moves into or out of the bag, which in turn, changes the mass. For example, when the bag contained a 0.2M solution, water entered the bag to make the concentrations inside and outside of the bag more equal. As this happened, the mass rose by 0.9 grams, a 4.2 percent increase. 2) If each of the bags were placed into a 0.4M solution instead of distilled water, the masses of the bags would have changed in different ways. The mass of the bags filled with distilled water and 0.2M sucrose would have gone down because water would have left the bag. The mass of the 0.4M bag would have stayed the same because the concentrations are now equal. The masses of the 0.6M, 0.8M, and 1.0M bags would have increased because water would have moved into the bag to equalize the concentrations. 3) The percent change in mass was calculated to show how much the mass increased due to the addition of water, which was trying to equal the concentrations in both the bags and the cups. 4) Initial Mass Final Mass Mass Percent Change in Mass Differences 20.0 grams 18.0 grams 2.0 grams 18 – 20 = 2 ; 2 / 20 = 0.10 ; 0.10x100=10% change in mass 5) The sucrose solution in the beaker would have been hypotonic to the distilled water in the bag. Exercise C) 10: Molar Concentration of Sucrose:  Group: 0.17M  Class: 0.19M Exercise D) Water Potential from Experimental Data:  Group: -1(0.17 mole / liter)(0.0831 liter bar / mole °K)(295°K) = -4.1675 bars  Class: -1(0.19 mole / liter)(0.0831 liter bar / mole °K)(295°K) = -4.6578 bars 1) The water potential of the potato core after dehydrating will decrease because the water within the potato would evaporate and therefore lower the water potential. 2) The solute concentration of the plant cell is hypertonic because the solute concentration is higher than the water concentration. Because of this, water will diffuse into the cell to reach dynamic equilibrium. 3) The pressure potential of the system is equal to 0. 4) The water potential is greater in the dialysis bag. 5) Water will diffuse out of the bag since the water potential is higher in the bag and water moves from areas of higher water potential to areas of lower water potential. 7) b: Molar Concentration of Solutes in the Zucchini: 0.35 mole / liter

8) a) Solute Potential = -1(0.35 mole / liter)(0.0831 liter bar / mole °K)(295°K) = -8.5801 bars b) Water Potential = 0 + -8.5801 = -8.5801 bars 9) Adding solute to a solution increases solute potential because the solute concentration increases. 10) a) Distilled Water will have a higher concentration of water molecules. b) Distilled Water will have a higher water potential. c) The red blood cells would increase in size because water is moving from the area of higher water potential (the distilled water) to the area of lower water potential (the red blood cells) until equilibrium is reached. Exercise E) Procedure: 1) The cells look like normal plant cells.

2) The cells shrunk (shriveled up) with no other changes.

3) The cells increased back to their normal size.

Analysis of Results: 1) Plasmolysis is the lose of water and turgor pressure within a plant cell. 2) The onion cells should plasmolyze because the area surrounding them had a lower water potential thus water should have moved out of the cells.

3) Grasses that live on the sides of roads that have been salted in the winter tend to die because the water is drained from their cells as the water moves out of the grass cells and into the hypertonic NaCl area around it. Conclusion: In this lab, we observed passive transport, both diffusion and osmosis, but more osmosis than anything else. I was wrong for my hypothesis in Exercise A. Starch molecules cannot diffuse out of the bag and into the water surrounding it because I learned that they were far too big to exit though the semi-permeable dialysis tubing. My hypothesis for Exercise B was right on target. We witnessed how the bags got heavier after 30 minutes, indicating water diffused into the bag to try and make them isotonic with their surrounding environment. In Exercise C, I was right once again: the water potential for the potato was negative; indicating water movement towards the potatoes was high. Since there was no hypothesis to state for Exercise D, I was right in my hypothesis for Exercise E. The onion sample, once with salt added to it, showed how the cells became hypertonic and shriveled up, but as soon as water hit them, they grew right back up and became turgid once again. After looking at our data and the class data, I believe we had made a couple of mistakes. First, we had a negative percent change in mass when it was a dialysis bag of water submerged in a cup of water, meaning there should have been no percent change in mass, especially not a negative change. This means water left the bag and none entered it. I think this could only have had happened if the cup had a small drop of sucrose or any other substance before we poured water into it, but nonetheless, a human error. Our next and biggest mess-up was when we did not weigh our potatoes initial mass before we put them in their assigned solutions. This caused us mass confusion and also bad results, as we had to take the initial weight of the potatoes from another group. Had we not have had these errors, I believe we would have received some spot on results.