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Diffusion, osmosis, and functional significance of biological membranes
Diffusion is the process in which substances move from an area of higher concentration to an area of lower concentration. If a semipermeable membrane is involved in this movement then this process is known as Osmosis. Semipermeable membrane is any biological membrane in the body that is selectively permeable. These membranes protect the cell from external environment. These are also involved in the movement of molecules in and out of the cell. This movement of molecules result in the differences in concentration until an equilibrium is established. In this research, we have done experiments on Elodea cells to know the process of osmosis and diffusion, and the concept of tonicity. We have used different materials such as dyes, dialysis tubes, and gelatin for our experiments. Our results are according to the already established research outcomes, i.e. water moves from higher concentration to lower concentration and this movement increases with temperature.
Diffusion is the process in which substances move from an area of higher concentration to an area of lower concentration (Nair, and Peate n.p.). Diffusion is a commonly found process in biological systems, but it is very slow in nature on a macroscopic scale. On the other hand, osmosis is the process of diffusion of molecules through a semipermeable membrane (biological membrane) from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal (Perry, Morton, and Perry 90).
Temperature and concentration are among the most important factors in these processes. If temperature is increased, the amount of energy for diffusion is also increased resulting in faster movement of particles, thereby increasing the rate of diffusion. Similarly, in case of concentration difference, molecules move from an area of higher concentration to an area of lower concentration in order to maintain equilibrium and relieve the pressure on the system such as solute and solvent system.
Biological membrane is a separating membrane that works as a selectively permeable barrier in living beings. Cellular membranes are among the most important biological membrane of the body found in almost every living being. The cellular membrane structure was first introduced by Garth L Nicolson and S Jonathan Singer in 1972 as a fluid mosaic model (Morange 3). This means that they are made up of phospholipid bilayer having integral and peripheral proteins, glycolipids, and cholesterol. These are basically used to separate the important chemicals as well as structures of cells from the surrounding environment having harmful chemicals and structures. Biological membranes are also important in regulating the movement of important molecules and ions, in and out of the cell, i.e. selective permeability (Perry, Morton, and Perry 89).
Tonicity refers to the comparison of solute concentrations of two solutions. The solution with lower concentration is known as hypotonic solution, whereas the solution with higher concentration is known as hypertonic solution. Solutions having the same concentration are known as isotonic. Tonicity can be explained with the help of experiments on the leaf of Elodea plant. If the Elodea cells are hypotonic, water molecules move into the cells making them turgid, and if the Elodea cells are hypertonic, water molecules move out of the cell making the cell plasmolyzed, which is the pulling away of cytoplasm of the cell away from the cell wall. In case of isotonic nature, the net movement of water in and out of the cell would be same.
In order to work on the rates of diffusion, three dyes can be used. These are potassium dichromate having the molecular weight of 294, Janus green dye having the molecular weight of 511, and aniline blue dye having the molecular weight of 738. Dialysis bag or tubing is also used for the experiment. This bag is made up of thin cellulose sheet having many tiny pores allowing the smaller molecules to move through it, but prohibiting the larger molecules from passing.
Materials and Method
Different materials such as dyes, dialysis tubes, and gelatin are used. There were different parts for this experiment. Experiment 3.1 dealt with the rate of diffusion of solutes. Experiment 3.2 dealt with osmosis. Experiment 3.3 dealt with selective permeability of membranes. Experiment 3.4 dealt with plasmolysis in plant cells. Experiment 3.5 dealt with the determination of concentrations of solutes in cells.
In the Experiment 3.1, diffusion of molecules has been demonstrated depending on the size of molecules and the temperature of the system. Approximately, a milliliter of potassium dichromate was placed in two test tubes. Similar amount of Janus green was placed in two other tubes, and the similar amount of aniline blue was placed in the last two test tubes. Each test tube had 5% of gelatin. Three of the test tubes having different dyes were placed in the refrigerator at 5˚C, and three test tubes with different dyes were placed in the room temperature. After sometime, the rate and distance of diffusion at different temperatures were determined.
In Experiment 3.2, osmosis was demonstrated. In this experiment, there were four dialysis bags. First bag was filled with deionized water and labeled as tube one. Second bag was filled with 10ml of 15% sucrose solution and labeled as tube two. Third bag was filled with 10ml of 30% sucrose solution and labeled as tube three. And the fourth bag was filled with 10ml of deionized water and labeled as tube four. Excess air was removed and the bags were folded. 200ml of deionized water was then added in three plastic cups, which are labeled as one to three, and 30% sucrose solution was added to the fourth plastic cup, labeled as four. Above mentioned bags were then placed in the corresponding cups. Weight of each bag was determined after every 15 minutes for an hour. All weights were then recorded.
Experiment 3.3 was done to test the permeability of specific molecules and ions such as starch, sulfate ion, chloride ion, and albumin. There was a dialysis bag for this experiment. Approximately, 25ml of 1% soluble starch was added in 1% sodium sulfate in the bag. The bag was placed in 100 ml of 1% albumin in 1% sodium chloride. After about 75 minutes, 20 ml of the solution was taken from the cup in which the bag was placed and evenly distributed in four test tubes. Similarly, 20ml of the solution from the bag was distributed in four other test tubes. In order to test the presence of starch, several drops of iodine were added to both types of test tubes. Turning of solution to bluish black color shows the presence of starch. In order to test the presence of sulfate ion, some drops of 2% barium sulfate were added to both types of test tubes. White precipitate of barium sulfate appear in the presence of sulfate ion. In order to test the presence of chloride ions, few drops of silver nitrate were added to both types of test tubes. In this case, milky white precipitates were formed. In order to test the presence of proteins, several drops of Biuret reagent were added to the last two tubes. Appearance of violet color showed the presence of proteins. All changes were observed and recorded.
Experiment 3.4 dealt with plasmolysis in Elodea plant cells. Two young leaves were taken from an Elodea plant. One leaf was placed on a wet mount utilizing deionized water as a base, while the other leaf was put on a wet mount utilizing 20% NaCl solution as a base. Coverslips were placed on both of the slides, which were then viewed under a microscope. Conditions of the leaves and actual cells were then examined in the lab.
Experiment 3.5 dealt with solute concentration in potato tuber cells. Different molar concentrations of the starch were placed in different beakers. A potato was peeled and cubed. These cubes were then weighed, and placed into different beakers for a specific time. Cubes were then removed from the beaker, and weighed again. The weights were then recorded to conclude the experiment.
Diffusion and osmosis are among the most important processes of nature that are helpful in the movement of water from one area to another. This change in concentration in the body can have some influence, whether positive or negative, on the cells. Our experiments have concluded that molecules and ions move from one concentration to the other, and larger molecules may show problem in the movement. Temperature and concentration can also have important effects on the diffusion and osmosis. Experiments on Elodea cells have shown that water molecules having solute move into the cells and make them turgid, if these cells are hypotonic. Whereas, Elodea cells show plasmolysis, if they are hypertonic as water molecules move out of the cell. Our results are according to the already established research outcomes.
Morange, Michel. "What History Tells Us Xxx. The Emergence of the Fluid Mosaic Model of Membranes." Journal of biosciences 38.1 (2013): 3-7. Print.
Nair, M., and I. Peate. Fundamentals of Applied Pathophysiology: An Essential Guide for Nursing and Healthcare Students. Wiley, 2013. Print.
Perry, J., D. Morton, and J.B. Perry. Laboratory Manual for Non-Majors Biology. Cengage Learning, 2012. Print.
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