Diffusion and Osmosis in Potato cores and Dialysis bag PDF

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Diffusion and Osmosis in Potato cores and Dialysis bag.The diffusion of free water across a selectively permeable membrane is called osmosis. In this process water molecules move from an area of higher concentration to an area of lower concentration.The osmolarity of solutions can be hypotonic, isot...

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Diffusion and Osmosis in Potato cores and Dialysis bag By: Group 1 Introduction Cells consist of membranes that select and allow certain molecules or solutes through selectively permeable membranes. Those membranes are known as Plasma membranes. They allow certain molecules to pass in and out of the cell via active or passive transportation .Molecules have thermal energy due to their constant motion which results in the directional movement of particles of any substance from higher concentration to lower concentration. This movement of molecules is called diffusion. For diffusion to happen the molecules have to pass through membrane pores. (Urry et al., 2020). Diffusion is a process of passive transport which does not require any energy. In this process substance from an area of higher concentration transports to an area of lower concentration to achieve dynamic equilibrium (Urry et al., 2020). As mentioned in figure 1 below both solute and solvent particles move in this process. For example, When we add a drop of pink dye in a glass of water, the dye moves from an area of higher concentration to an area of lower concentration until it reaches the concentration equilibrium. The diffusion of free water across a selectively permeable membrane is called osmosis. In this process water molecules move from an area of higher concentration to an area of lower concentration.The osmolarity of solutions can be hypotonic, isotonic or hypertonic (Urry et al., 2020). When the solute concentration of extracellular fluid is lower than the solute concentration of fluid inside the cell then water enters into the cell. This also means that the extracellular fluid has a higher concentration of water in the solution than does the cell. In this situation, water will follow its concentration gradient and enter the cell. The extracellular environment in this situation is considered to be hypotonic (Urry et al., 2020). When the solute concentration of extracellular fluid is higher than the solute concentration of fluid inside the cell . This also means that the extracellular fluid has a lower concentration of water in the solution than does the cell. In this situation, water will follow its concentration gradient and move out of the cell. The extracellular environment in this situation is considered to be hypertonic . When the solute concentration of extracellular fluid is equal to the solute concentration of fluid inside the cell then there is no net movement of water in or out of the cell . This extracellular environment in this situation is considered to be isotonic(Urry et al., 2020).

(Helmenstine & Helmenstine, 2021) Figure 1 : Diffusion and Osmosis

In the first part of this project, we determined the osmolarity of potatoes by using different solutions of sucrose concentrations. As in osmosis, water moves from an area of higher contraction to the lower concentration . We put the small pieces of peeled potatoes in different concentrations of sucrose solution and weigh the potatoes before and after 3 hours of experiment to determine whether the potato pieces gained or lost mass. We hypothesized potatoes shrink and their mass decreases as they lose water in strong sucrose solutions because of osmosis. Alternatively, Potato expands and their mass increases as water enters inside cells in diluted sucrose solutions because of osmosis. In the second part of this project we performed an experiment that involved diffusion across a semipermeable membrane. We used a porous dialysis tubing for passive transportation of glucose molecule which mimic the semi permeability of cell membrane.A mixture of glucose solution with starch was placed inside the dialysis tubing and the dialysis tubing was placed in a large container with the mixture of water and Iodine and ample time was allowed for the diffusion process to occur for the glucose or starch molecules to diffuse through the dialysis bag . We hypothesized small glucose molecules will be able to pass through semi permeable dialysis tubing membranes while larger molecules of starch will not .

Materials and Methods Part 1 of Diffusion & Osmosis in Potato cores and Dialysis bag To begin the first part of lab #3 ( Diffusion and Osmosis) the molar solutions must be made. Six small cups were labeled as: 0 M, 0.2 M, 0.4 M, 0.6 M, 0.8M and 1M this was to indicate the different sucrose molar concentrations. Each cup was placed on the scale and the scale was tared, sucrose was added to each individual cup respective to the amount labeled on the cup. After the sucrose was added to each cup, 15mL of water was added to each cup. A spoon was used to mix the solution completely. After the molar solutions were made, a potato was peeled and sliced into 12 slices. The potatoes were split into 6 groups, each containing 2 slices of the peeled potato, the initial mass was recorded for the 6 groups of potatoes. After recording the initial masses of the potato slices, each of the two slices were placed into their respective small cup with sucrose solutions. The cups were left for three hours at room temperature to allow the potatoes to absorb the sucrose. After the three hours were over, the slices of potatoes were removed from the cups and blotted using napkins to ensure that excess water was removed. The final mass was recorded of all of the potato slices, two at a time. The following formula was used to determine the percent change:

Final mass - Initial mass Initial mass100 Part 2 of Diffusion & Osmosis in Potato cores and Dialysis bag For the second part of lab #3 (Diffusion and Osmosis), a large plastic container was filled ¾ of the way with water. Iodine solution was added until the color was a dark yellow amber or brown color. A dialysis tube submerged in the iodine solution for 30 seconds to absorb the solution. After the dialysis tube was removed, a rubber band was tied to one end of the tube and the opposite end of the tube was left open to add in 1 tablespoon of the glucose starch solution. Another rubber band was added to prevent any leakage. The initial weight was recorded on tables 4 & 5. The container containing the dialysis bag was swirled gently every 30 minutes for a total of 2 hours. After the bag was incubated for 2 hours, the final weight and color of the bag was recorded. The percent change was calculated using the same formula as used in the first part of this lab. For this part, we used glucose strips and two small cups. We labeled the two small cups as: “Bag” and “Container.” Then we added 1 teaspoon of the content inside of the dialysis bag into the cup labeled “bag”. After this we added 1 teaspoon of the content from the large container into the cup labeled “container”. We then placed a glucose detection strip in each cup. After two seconds, we held the strip horizontally and waited 15 seconds while holding the strip still. Results Osmolarity in potato cores: Once the mass difference was calculated, we could then move onto the % change in mass. To calculate the % change in mass, it is the final mass-initial mass/initial mass *100. Table 1: Potato cores incubated in different concentrations of sucrose to determine osmolarity Initial Mass (g)

F inal Mass (g)

Mass Difference (Final Initial)

% Change in Mass

0.0 M

1.24g

1.42g

.18g

14.5%

0.2 M

1.85g

1.76g

-.09g

-4.9%

Sucrose Concentration (Molar,M)

0.4 M

1.48g

1.38g

-.1g

-6.8%

0.6 M

.98g

.74g

-.24g

-24.5%

0.8 M

1.03g

.68g

-.35g

-34%

1M

.96g

.55g

-.41g

-42.7%

In Figure 1, we took the data from Table 1, and applied it to an excel graph. It is clear that the line on the graph is decreasing as the solute concentration increases. Once three hours went by , only one of the potato cores appeared to have an increase from the initial mass, while the others appeared to have an increase. The potato core with the increase had 0 Molarity of sucrose concentration which interprets that the osmolarity of the potato cores is 14.5%.

Figure 1:

Table 2: Weight of the dialysis bag containing starch solution before and after incubation in container containing iodine solution Initial Mass (g)

Final Mass (g)

Mass Difference (Final-Initial)

% Change in Mass

Dialysis bag

12.55g

14.83g

2.28g

18.15%

After 120 minutes of incubation, the following results are in the table shown below. Table 3: Results of dialysis bag after being incubated in iodine solution Dialysis Bag

Large Container

Observation (change in color)

white

Dark Amber

Interpretation

Black

Light Amber

Presence of starch (YES/NO)

YES

NO

Once the 120 minutes was up, the dialysis bag appeared to be Dark purple/black color. The solution in the container that the dialysis was placed in, also appeared to have become a different color. It began as a dark amber solution and seemed to have resulted in a light amber solution. Discussion Osmolarity of Potato: The results of this experiment supported the hypothesis. Water can pass through the cell membrane of the potato cell therefore osmosis will occur and water will move from the area of higher concentration to the area of lower concentration. The potato slice will gain mass with a low extracellular concentration of sucrose and lose mass with a high extracellular concentration of sucrose. It was expected that the solution would be isotonic with a low concentration of sucrose. By graphing the results of the experiment, it could be seen where the osmolarity of the potato is isotonic in relation to the sucrose solution at approximately 0.15M. With sucrose concentration between 0.0M and 0.15M the potato was hypotonic and the potato slice gained mass. With sucrose concentration above 0.15M the potato was hypertonic and the potato cells lost mass. As sucrose levels increased the potato's mass decreased. Referencing a website that performed the same experiment I found that they had very similar results. It was surprising to see that they had a different hypothesis stating “If you put a potato in 50ml of different sucrose and water solutions, then the potato’s mass in every beaker will decrease because it is in a hypertonic solution”(Hoiseth, 2014). Diffusion across a semi-permeable membrane: For this experiment it was hypothesized that iodine would enter the dialysis bag but glucose and starch would not leave the dialysis bag. It was concluded that iodine and glucose passed through the membrane of the dialysis bag but starch did not. The solution inside the bag turned a dark blue color meaning that iodine had entered the bag and reacted with the starch. The iodine solution outside the bag did not change to a dark color meaning that starch did not leave the dialysis bag. Glucose was tested using a glucose strip in the iodine solution and this test was positive meaning that glucose had diffused

through the dialysis bag into the iodine solution. In this case the results supported the hypothesis. There were no weaknesses found with this experiment since the results were either positive or negative. Referencing a website that shows this same experiment I found that they had similar results concluding that “The dialysis bag was permeable to glucose and iodine but not to starch” (Anderson, 2019).

Reference

Author: William Anderson (Schoolworkhelper Editorial Tea https://schoolworkhelper.net/Tutor and Freelance Writer. Science Teacher and Lover of Essays. Article last reviewed: 2020 | St. Rosemary Institution © 2010-2021 | Creative Commons 4.0; Author: Tutor and Freelance Writer. Science Teacher and Lover of Essays. Article last reviewed: 2020 | St. Rosemary Institution © 2010-2021 | Creative Commons 4.0. Selective Permeability of Dialysis Tubing Lab: Explained. https://schoolworkhelper.net/selective-permeability-of-dialysis-tubing-lab-explained/ (accessed Apr 28, 2021). Helmenstine, A.; Helmenstine, A. Osmosis vs Diffusion - Definition and Examples. https://sciencenotes.org/osmosis-vs-diffusion-definition-and-examples/ (accessed Apr 15, 2021). Hoiseth, S. Potato and Sucrose Experiment. https://prezi.com/wu1-gsalusz8/potato-and-sucroseexperiment/#:~:text=Because%20of%20there%20was%20no,reached%20equilibrium%2C%20making %20it%20hypertonic.&text=So%20because%20of%20osmosis%20the,equilibrium%20with%20the %20sucrose%20concentration. (accessed Apr 28, 2021). Urry, L. A.; Cain, M. L.; Wasserman, S. A.; Minorsky, P. V.; Orr, R. B. Campbell biology in focus, 3rd ed.; Pearson: Hoboken, NJ, 2020....