Osmosis is the random diffusion of solvent water molecule from an area of low solute concentration to areas where the solute concentration is high through a semi permeable membrane so as to equalize the concentration of the solute on both sides (Kylstra, Longmuir, and Grace 289). It is a biological process essential to both flora and fauna that results into various physiological effects, for this experiment water and a mixture of syrup and water will be used to demonstrate the process. A laboratory report hence illustrates what the students involved, understood while carrying out the practical experiments.
The purpose of the experiment was to simulate the idea, make observations of water osmosis and if solutes could diffuse through the selective semi permeable membrane. We expect the experiment to portray diffusion as the large size solutes cannot pass through the membrane whereas water molecules can. The dialysis tubing acted like either an animal or plant cell by shrinking or bulging when placed to different solutions.
MATERIALS AND METHODS
The following materials where used for the osmosis experiment;
- Dialysis tubing, three 250 mL beakers and a syringe.
- Scissors, water, thread, sugar syrup (use regular, granulated sugar; dextrose), metric ruler and a balance.
With the above materials, the following procedural steps where followed;
- The three beakers were label as follows and each filled about three-quarter full.
Beaker # 1with water, beaker # 2 and # 3 with syrup (prepared by dissolving 250g of sugar in 250mL water) using the balance to weight the sugar quantity.
- Three segments about 10 cm long were cut from the dialysis tubing, submerged in water until the tubing unfold. In order to prevent leakage, one end of each segments were tightly tied with a string.
- The tubes free ends were moistened and using the syringe, for tube # 1 and 2, filled with sugar solution, while tube # 3, filled water. Free ends were tightly tired and rinsed
- The tubes were then placed in their respective beakers as follows; tube #1 in beaker #1, tube #2 in beaker #2, and tube #3 in beaker #3, forming model cells.
- Changes were observed and noted at an interval of one hour for three hours.
DISCUSSION OF THE RESULT
The transportation of solvent molecules and water across the semi permeable membrane requires energy; osmotic pressure, to drive the process. In the process that pure water was used on both sides of the dialysis tubing, the osmotic pressure difference would have been zero and therefore, the turgidity of the membrane remains unchanged. Moreover, this may be attributed to the fact the osmosis gradient between them is constant (Pretorius, Hopkins, and Schieke 29).
The difference in concentration between the solutions in beaker 1, 2 and 3 at either side of the semi permeable membranes are different and will cause the solution with low concentration to diffuse to higher concentration solution. The process shall endlessly occur to create equilibrium for continuous flow of water on both sides. In beaker model cell #1, the solution (water) has a lower solute concentration compared to solute concentration in the dialysis tubing. As a result therefore, the water shall therefore enter the tube becoming big and turgid. If it were an animal cell, it would have swollen and can at times even burst (Mauro 252). Whereas if it were a plant cell placed on a hypotonic solution, its vacuoles would have too swollen thereby pushing its content against the cell wall.
Beaker model cell #2 contains isotonic solutions because the sugar solute concentration on both the tube and its surrounding are the same. The dialysis tube will therefore not lose nor gain water from the solution. This is because the osmotic gradient between the two solutions in constant and therefore there is no change in the osmotic pressure caused by the solute molecules to propagate movement (Davis et al. 890).
In beaker model cell #3, the water and syrup solution contains a higher solute concentration than the tube content; this will result in water diffusing from the dialysis tube to the solution. The tube will shrink and similarly, if it were an animal cell. Whereas, for plant cells, the cell’s vacuoles would collapse (Kylstra et al.289).
Cumulative percentage change shows better difference in weight change and is computed as follows; the difference between final weight (g) and Initial weight (g) divided by the initial weight (g) and multiplying the final value with 100. For hypertonic solutions, the value could be negative because the dialysis tube will lose water, but for hypotonic solutions, the value would be positive as the tubes (cells) absorb water from the solution (Pretorius et al. 24). Whereas for isotonic solutions, the value remains constant for the gradient concentration is perpetual.
OSMOSIS DATA TABLE OBSERVATIONS.
The following bar graph shows the dynamic changes that occur to dialysis tube when placed into different solution with respect to time change. The yellow bars represent the initial size of the tube, when dipped in hypertonic, hypotonic and isotonic solutions respectively, the red, green and blue colors show the result changes on the dialysis tubes (Kim et al.314).
In conclusion therefore, the selective permeability capability of dialysis tube is based on size and only allows for free flow of solvent to reach equilibrium on the inside and its environs but blocks the passage of large solutes. Osmosis can occur under normal circumstances but environmental changes can affect its rate, it is an important process to plants and animals body reaction and should therefore be kept at normal conditions.
Work Cited.
Davis, I. S. et al. “Osmosis in Semi-permeable Pores: An Examination of the Basic Flow Equations Based on an Experimental and Molecular Dynamics Study.” Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science 463.2079 (2007): 881–896. rspa.royalsocietypublishing.org. Web. 19 Oct. 2013.
Kim, Young M. et al. “Overview of Systems Engineering Approaches for a Large-scale Seawater Desalination Plant with a Reverse Osmosis Network.” Desalination 238.1–3 (2009): 312–332. ScienceDirect. Web. 19 Oct. 2013.
Kylstra, Johannes A., Ian S. Longmuir, and Michael Grace. “Dysbarism: Osmosis Caused by Dissolved Gas?” Science 161.3838 (1968): 289–289. www.sciencemag.org. Web. 19 Oct. 2013.
Mauro, Alexander. “Nature of Solvent Transfer in Osmosis.” Science 126.3267 (1957): 252–253. www.sciencemag.org. Web. 19 Oct. 2013.
Pretorius, Victor, B.J. Hopkins, and J.D. Schieke. “Electro-osmosis: A New Concept for High-speed Liquid Chromatography.” Journal of Chromatography A 99 (1974): 23–30. ScienceDirect. Web. 19 Oct. 2013.
