Abstract
In this practical study, the impact of solute concentration on osmosis was investigated. Sucrose was the solute of choice for the experiment. Visking tubing was used to reflect a partially permeable membrane in which sucrose penetrated to create an osmotic condition similar to that of the cell. The selective permeability of the tubing was used to investigate the net transfer of water molecules across the concentration gradient. The experiment was conducted using a concentration of 30% sucrose and a series of dilutions performed to create solutions of lesser concentrations. The observation was made of the impact of various concentrations of solutions on the osmotic potential and conclusions drawn to that effect.
Introduction
Diffusion is the transfer of particles from an area of high concentration to one with low concentration while osmosis is a special type of diffusion with a membrane that is semi-permeable to allow for the movement of solvent molecules. An example to demonstrate the process of diffusion is when a teacher puts on strong cologne and enters a class where no student has put on any perfume (Shewmon, 2016). When the teacher is at the door, the students closest to the door will fast get the smell of the cologne and later, with time the particles of the cologne will travel through the class to reach the furthest student from the door.
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In another example, potassium permanganate is mostly used to demonstrate the process of osmosis. In a beaker full of water, some potassium permanganate is placed at the center of the beaker with water through the use of a straw, and then the straw is lifted out. The color of potassium permanganate is seen to spread through the beaker of water, and after some time, the whole beaker has changed color to purple (Frank-Kamenetskii, 2015). These two processes are extremely significant to living things as they assist in different processes such as digested food from the intestine diffusing to the bloodstream, the movement of waste like urea and carbon dioxide into the bloodstream from the cell body.
Osmosis is essential to organisms as it maintains a balance between the internal and external environments, mostly in the kidneys of animals and assists the roots of plants in the absorption of water from the soil. In this practical lesson, the impact of sucrose concentration on osmosis was investigated with dialysis tubing acting as a semi-permeable membrane (Odom, Barrow & Romine, 2017). An osmotic setting comparable to that of the body cell was replicated with the use of sucrose. From a solution of 30% sucrose concentration, a series of dilutions was performed to create more diluted solutions and the impact of the various solutions on the osmotic potential observed.
Materials and Methods
The dialysis tubing was dissected into four, 15 cm long strips and then the soaked in water to make them open easily by rubbing between the fingers. Using rubber bands that were yellow, one end was secured and with an allowance of 1-2 inches of the tubing left below the band. A seal was then created above the rubber band by use of a knot tied tightly to prevent the spillage of the solution (Odom, Barrow & Romine, 2017). Water was then used to test for leakage on the dialysis tubing, and with the conviction that no solution could leak through, the procedure was repeated using the three remaining tubing and rubber bands of red, blue, and green color used for securing the ends.
To create a 30% sucrose solution of 200mL, 60g of sucrose powder was added to 160 mL of warm water then mixed thoroughly by shaking the stock solution. Graduated cylinders were then used to measure liquids to create sucrose solutions that were 15%, 30%, and 3% in concentration. To attain the solutions, 5mL of the stock solution and 5mL of water was used for the 15%, 10mL of stock solution and no water for the 30%, and 2mL of the stock solution and 18mL of water for the 3% solution (Odom, Barrow & Romine, 2017). Also, 150 mL of the stock sucrose solution that remained was labeled "30% Sucrose" in a beaker. Similarly, the remainder of the stock solution was used in serial dilution to mix an extra 200mL of 3% solution that was placed in a beaker and marked “3% Sucrose.”
In the visking tubing that had the yellow rubber band, 10mL of the 30% of a solution containing sucrose was measured and subsequently added to the tubing before it was sealed with a rubber band of a matching color. A similar process was repeated, where after 10mL of the 15% of the sucrose solution was measured and added to the red colored rubber band tubing. The tubing was then secured with a matching band color. Again, 10mL of the 3% solution of sucrose was measured and placed in the visking tubing secured with blue bandings and the opening of the tubing sealed with a band of the same color (Odom, Barrow & Romine, 2017). The same was performed with the remaining dialysis tubing fastened with a green rubber band to one end. After measuring 10mL of the 3% solution of sucrose, it was placed and fastened with a matching green color rubber band.
After verification of the volume of the solutions, their initial volumes were recorded in a tabular form then the tubing with blue, yellow, and red rubber bands was placed in the beaker labeled "3% Sucrose." The tubing that was secured with the green bands was dipped in the beaker that was marked “30% Sucrose.” Null and alternative hypotheses were then formulated. The null hypothesis stated; water will flow in the visking tubing the alternative hypothesis stated that water would not flow in the tubing (Odom, Barrow & Romine, 2017). The scientific reasoning behind the hypothesis formulation is based on the knowledge that during osmosis, solvent molecules through a partially permeable membrane will flow from a solution of high solvent concentration to that of a low dilution.
The visking tubing was allowed to settle in the beaker solutions for one hour before the top was cut open and the contents placed in a graduated cylinder for measurement. The results were recorded, and the net displacement computed, as indicated in table 1 below. While measuring the final volume of each of the visking tubing, care was taken to ensure that the cylinder was completely rinsed and dried before the addition of the contents of separate tubing (Odom, Barrow & Romine, 2017). The cleaning was done to eliminate errors in the results by ensuring that there was no contamination of the cylinder that might lead to flawed outcomes.
Results
To get the net displacement, the final volume was deducted from the initial volume of each of the solutions and the results tabulated, as shown in the table below. For the yellow-banded visking tubing 30% sucrose solution, the net displacement found was 13 less ten, which are the same as 3. The positive sign in front of the answer indicates an increase in the net solution. The same process was repeated for the dialysis tubing secured with a red band, and the net displacement was a positive one (Shaffer et al., 2015). Again the positive sign was used as an indication of positive displacement, while the blue banded tubing had a zero value meaning no displacement took place. Therefore, the solution that was used at the beginning of the experiment was completely used up at the end of the experiment.
Color of Rubber Band |
Sucrose Conc. (%) |
Initial Vol. (mL) |
Final Vol. (mL) |
Net Displacement (mL) |
|
Blue |
3 |
10 |
0 |
0 |
|
Yellow |
30 |
10 |
13 |
+3 |
|
Green |
3 |
10 |
6 |
-4 |
|
Red |
15 |
10 |
11 |
+1 |
Table 1: Permeability of tubing against the concentration of sucrose
The visking tubing tied with the green band of rubber was used as the control experiment. A control experiment is an investigation conducted scientifically but with the experimental group(s) and the control group maintained under the same variables except for the aspect under investigation. The purpose of the control is to establish or determine the impact of the aspect being studied (Shaffer et al., 2015). Thus, the net displacement of the solution in the control group was established to be negative four. The negative sign was an indicator of negative displacement or decrease in the volume of the solution.
Discussion
As explained earlier, osmosis involves the transfer of water particles from a solution of high concentration to low via a partially permeable membrane. In this investigation, the tubing with the yellow and red colored bands of rubber was placed in a hypotonic solution. There are three types of solutions in this topic, hypertonic, hypotonic, and isotonic (Shaffer et al., 2015). A hypertonic solution is one that is highly concentrated in solutes, and our case would be the solutions placed in the yellow and the red-banded dialysis tubing. Also, the "30% Sucrose" used in the study happens to be a hypertonic solution.
On the other hand, a hypotonic solution is one that has a low gradient of the solute molecules, and in this experiment, would be the green banded tubing. An isotonic solution is described as one that has an equal concentration to that of the surrounding medium. Thus, the dialysis tubing with blue rubber bands falls in this category. Therefore, the solution in which the yellow and red tubing were placed had a high concentration of solvent molecules in comparison to their concentrations (Shaffer et al., 2015). Therefore, the movement of the solvent molecules was from the "3% Sucrose" to each of the two tubings using the visking tubing as the semi-permeable membrane.
The increment witnessed in the yellow, and red bags supports the null hypothesis, which stated that water would move into the tubing. Therefore, the experiment demonstrated osmosis as the permeability of the dialysis tubing was founded on the differences in the concentration of the tubing against the concentration of the liquid in the beaker they were placed (Shaffer et al., 2015). For the blue banded tubing identified as isotonic, was placed in a solution of equal concentration and thus, no observable change was made. Since the gradient in the two solutions was the same, there were no movements of solvent molecules. Hence, osmosis failed to take place, and thus, we fail to accept the null hypothesis and accept the alternative hypothesis.
Since osmosis failed to take place, it would be expected that the concentration in the final volume would be equal to the initial volume. Thus, the changes of the volume can allude to the process of diffusion, which has the capability of taking place in both liquids and gases, unlike osmosis, which can only take place in liquids. There is also the possibility of an error causing the changes in the volume of the liquid (Shaffer et al., 2015). The most probable error that could have taken place is the leakage of the solution as the process of diffusion just like osmosis, takes place in the presence of a concentration gradient which in this case was missing.
As for the dialysis tubing secured with green rubber bands and was placed in a "30% Sucrose" which had more solute concentration, the results indicated that there was a negative displacement of 4mL. These outcomes fail to agree with the null hypothesis; hence, the alternative hypothesis is accepted. As much as the control experiment did not gain liquid but still osmosis was demonstrated as the permeability of the visking tubing allowed the water molecules which are smaller than the solvent molecules to pass through in the opposite direction (Shaffer et al., 2015). The flow of the solvent particles was from the green banded tubing to the solution in the beaker and was caused by the differences in the concentration of the sucrose solution. The gradient in the concentration led to the smallest particles moving from the region of high solvent concentration to the "30% Sucrose" which had fewer solvent molecules.
The objective of the investigation was achieved as all the experiments except one demonstrated the impact of the concentration of sucrose on osmosis. This fact was evident in the red and yellow banded visking tubing, even though the bag with the green rubber band demonstrated the same in the opposite direction. Due to the errors experienced in the experiment as witnessed in the blue dialysis tubing, future experiments will have the tubing secured more tightly to prevent leakages as they could lead to wrong conclusions (Shaffer et al., 2015). There will also be double checking to verify that the bags are not leaking as doing the verification once could lead to similar results as witnessed in this experiment.
These experiments are important as osmosis is the only mechanism that permits the transportation of water molecules in and out of the cells in living things. Since water carries dissolved food substances and oxygen; osmosis can be said to be relevant in the transportation of water, food, and oxygen (Shaffer et al., 2015). This transportation is made possible by the movement of the water particles from a hypotonic to the hypertonic solution, and since the body of the organisms is hypertonic in nature, water plus food and oxygen in it move into the body cells while the waste is eliminated in the same way.
References
Frank-Kamenetskii, D. A. (2015). Diffusion and heat exchange in chemical kinetics (Vol. 2171). New Jersey: Princeton University Press.
Odom, A. L., Barrow, L. H., & Romine, W. L. (2017). Teaching Osmosis to Biology Students. The American Biology Teacher, 79(6), 473-479.
Shaffer, D. L., Werber, J. R., Jaramillo, H., Lin, S., & Elimelech, M. (2015). Forward osmosis: where are we now?. Desalination, 356, 271-284.
Shewmon, P. (Ed.). (2016). Diffusion in solids. Basel: Springer.
