Abstract
Osmosis is an important phenomenon for several plant and animal life functions. Like any other small molecule, water moves from one side of membrane to the other by diffusion. The diffusion of water across a selectively permeable membrane however is given a special name, osmosis. To understand osmosis, the designed experiment has been conducted as discussed in this laboratory report. This experiment begins with a dialysis tubing which is selectively permeable and is filled with water and sugar syrup. This tubing is then submerged in beaker with water and syrup. The experiment is conducted with three tubing and beakers with varied combination of water and sugar syrup. In the established system, water moves from a region of high water concentration to a region of low water concentration that is from water to sugar syrup. The concentration differences across the membrane drive the water across a selectively permeable membrane which is dialysis tubing in this experiment. Whenever two fluids with different concentrations of solute are separated by a selectively permeable membrane, water will flow one to the other, moving down the concentration gradient. The greater the difference in water concentration, the greater the osmotic pressure, and the more quickly the water moves. In humans and other multi-cellular organisms, osmosis helps regulate the concentration of fluid surrounding the cell, keeping it at the same concentration as that of the cell’s cytoplasm. In such cases, the extracellular fluid is said to be isotonic. This experiment demonstrates possible three situations; hypertonic, isotonic and hypotonic.
Introduction
Osmosis is the movement of water molecules through a selectively permeable membrane corresponding to the water potential gradient (Cath et al. 2006). The movement of water occurs across the selectively permeable membrane from an area of high water potential (low solute concentration) to the area of low water potential (high solute concentration). Osmosis releases energy and can be made to work, but it is a passive process, like diffusion. The movement of water by osmosis is processed by solute concentration (Yaroshchuk 2010). If the solution surrounding the cell is of lower concentration in comparison to the concentration of cell, the solution is referred to as hypotonic. When a solution is hypotonic, the water diffuses into the cell through the process of osmosis leading to swelling of cell. When the solution surrounding the cell is of higher concentration in comparison to the cell; the water from the cell moves out resulting in shrinking of cell. Such solution is called hypertonic solution and the water diffuses out of the cell by osmosis leading to shrinkage of cell. If the concentration of the cell and the surrounding solution is equal, it is referred to as isotonic, no movement of water occurs into the cell or into the solution.
The purpose of this experiment is to investigate the relationship between solute concentration and the movement of water through a semi-permeable membrane by the process of osmosis. Through this experiment, we study the process of osmosis by creating three model cells using dialysis tubing. The first model cell will contain water and syrup (sugar solution) submerged into beaker of water, second model cell will contain water and syrup submerged into water and syrup beaker. The last model cell will contain water and submerged into water and syrup beaker. From this experiment we expect that the water from the dialysis tubing will move towards the more concentrated solution of sugar.
Materials
In this experiment the apparatus used was three dialysis tubing each 10 cm in length and three 250 ml beakers and syringe from home lab kit and scissors, water, thread, sugar, metric ruler and a balance supplied by the experimenter.
Procedure
Experiment was started with using three 250 ml beakers which were labelled as 1, 2 and 3. In beaker # 1, water was filled up to about 250 ml and the other two beakers #2 and #3 were prepared by adding 35 teaspoons of sugar in 250 ml of water for both. Three segments of dialysis tubing each 10 cm in length were cut off and submersed in the beakers with water. Once the segments started to unfold, one end of each segment was folded back on itself to about 1cm and was tied tightly with string. The other end of each segment was rubbed with the finger to open the free end. Once the free end was open, two of the dialysis tubing was filled with sugar solution and all the air was squeezed out. Then we folded over the free ends and tied it tightly with a string. The two dialysis tubing was then rinsed gently with water to remove any sugar solution spilled during filling. The third dialysis tube was filled with water and then tied with a string on the free end. The first dialysis tube that was filled with sugar solution was marked as tube #1 and the last two dialysis tubes with sugar solution was marked as tube #2 and #3. Thereafter, the tube #1 with sugar solution was placed in beaker #1 with water, tube #2 in beaker #2 and tube #3 was placed in beaker #3. After placing all the tubes into the beaker, we made sure that each tube was completely submerged into the solution. Then, we observed each model cells after one, two and three hours and recorded the results.
Results
Model cell #3 was the only tube that demonstrated drastic volume decrease. Initially, the model cells #3 was round shaped and cell shrunk after three hours (see Fig.1). Model cell #1 had a volume increase and change of shape from a round to swell shape in comparison to the other two cells (see Fig. 2). While model cell #2, showed no sign of change in shape and volume it stayed as it was in the beginning of the experiment.
Discussion
The process of osmosis is well demonstrated through the experiment. Two dialysis tubing demonstrated changes in volume and shape. These two dialysis tubing had different concentrations of surrounding solutions with respect to the cell concentration. This experiment supported the hypothesis that the water moves from more concentrated solution to low concentrated solution in semi-permeable membranes (Hamann 1993).
In model cell #1, the water diffused into the cell through osmosis which caused the cell to swell. The water moved from the low concentration sugar solution in the beaker to high concentration solution inside cell. The cell was submerged in hypotonic condition, therefore resulted in swelling of cell.
Model cell #2 showed no sign of water movement through osmosis because the sugar concentration inside the cell was equal to outside the cell and this condition is referred to as isotonic.
Model cell #3 displayed water movement by osmosis outside the cell because the sugar concentration outside the cell was more in comparison to inside. Therefore, this led the cell to shrink and this type of condition is hypertonic.
The process of osmosis is important to ensure movement of fluids in the body (Lord 1999). This experiment has shown that the osmosis process involves the movement of water from high concentration gradient to low concentration. Cells in low solution concentration absorb water and swells in size whereas high concentration surrounding solution causes the outward movement of water, thereby squeezing the cell. To achieve no movement of water between cell and its surrounding solution, the cell and solution surrounding the cell should be of same concentration.
The experiment was conducted to demonstrate the process of osmosis with regard to the impact of concentration of the solution on the inward/outward movement of water from the cell. The hypothesis of the experiment was to ascertain the movement into and out of the dialysis tubing filled with water and/or sugar syrup in the surrounding solution of water and/or sugar syrup. The hypothesis was confirmed as the dialysis tubing in hypertonic solution got shrunk and dialysis tubing in hypotonic solution swelled whereas the dialysis tubing in isotonic solution remained same. The process of osmosis is significant for the biochemical processes occurring in plants and animals and accurate knowledge of hypertonic and hypotonic solution on cells indicates that for cell to remain in equilibrium, the surrounding media should be isotonic to the cell to inhibit any movement across the down gradient. The experiment can also be extended further to ascertain reverse osmosis which involves forcing of water out of the cell. Also, while repeating the experiment, I would like to use color ink of blue or red in the dialysis tubing to make the results more visible that is when the water will move out of dialysis tubing in hypertonic solution, the surrounding solution will get coloured and in hypotonic solution, the solution in dialysis tubing will get diluted with color getting faded whereas in isotonic solution, there remain a complete isolation between the coloured dialysis tubing and colorless surrounding solution.
Literature Cited
Cath TY, Childress AE, Elimelech M. 2006. Forward Osmosis: Principles, applications and recent developments. Journal of Membrane Science. 281(1-2): 70-87.
Hamann CH, Theile V, Koter S. 1993. Transport properties of cation-exchange membranes in aqueous and methanolic solutions. Diffusion and Osmosis. Journal of Membrane Science. 78(1-2): 147-153
Lord RCC. 1999. Osmosis, Osmometry, and Osmoregulation. Postgraduate Medical Journal. 75: 67-73.
Yaroshchuk A. 2010. Influence of osmosis on the diffusion from concentrated solutions through composite/asymmetric membranes: Theoretical analysis. Journal of Membrane Science. 355(1-2): 98-103.
