Using “Deshelled” Chicken Eggs
Introduction
Osmosis can be defined as the diffusion of water from an area where the concentration of water molecules is high, through a semi-permeable membrane to an area where the concentration of water molecules is low (1). Alternatively, osmosis can be thought of as a process by which water leaves an area of low solute concentration to an area of high solute concentration, in an effort to create an equilibrium. In a living cell, water molecules can move through the cell membrane, which is semi-permeable. In certain situations, solutions which are higher in solute concentration than a living cell will cause the water to leave the cell and make the external environment more dilute. This will cause the cell to shrink and the solution is considered to be in a hypertonic state. On the other hand, if the surrounding environment has less solute than the cell itself, then the cell will become swollen and the solution is considered to be in a hypotonic state. If both cell and the surrounding solution have equal concentrations of solute, then the solution is in an isotonic state, and an equal number of water molecules move into and out of the cell.
Unshelled eggs can be utilized as biological systems to study osmosis because each cell in the egg will either take up or release water, based on the concentration of solute within the external environment. The sum of these cells that take up or release water can be measured by the total weight that is gained or released by the egg as a whole. The experiment described in this report uses unshelled eggs and solutions of increasing sucrose concentrations to determine the osmolarity of a sucrose solution of unknown concentration. The hypothesis is that the eggs can be used as a system to adequately illustrate osmosis, and that the concentration of an unknown sucrose solution can be determined.
Materials and Methods
Eggs that had been deshelled were each blotted with paper towels to remove excess water and weighed. This initial weight was considered to be the weight at t=0. Eggs were placed in separate dishes containing either 0%, 20% or 40% sucrose solution. An egg was also placed in a dish containing an unknown sucrose concentration. At fifteen minute time intervals, the eggs were gently taken out of the dishes, excess water was removed by blotting with paper towels, and the eggs were each weighed. Each weight was determined from time= 0 to time= 60 minutes and recorded in Table 1.
Results
The relative weight of each egg at each timepoint of incubation in the different sucrose solutions was recorded in Table 1. The increase or decrease in egg weights for each sucrose concentration over time are presented in Table 2 as a value of the difference between egg weight at a particular time from its initial time point. The differences in egg weight over time for each sucrose concentration are illustrated in Figure 1. The total weight changes are presented in Table 3. These results are also depicted in Figure 2. Based on these results, it appears that at 0% sucrose concentration, the eggs steadily gained weight over time. Egg weight was virtually identical after incubation in the 20% sucrose solution as before incubation, however, weight steadily decreased when the egg was incubated in the 40% sucrose solution. The egg incubated in the unknown solution gained weight over time, but to a smaller extent than the egg incubated in a 0% sucrose solution. The changes in weight vs concentration of sucrose is illustrated in Figure 2 as a straight line. The weight change is inversely proportional to the concentration of sucrose. By examining the change in weight of the egg in the unknown sucrose solution, the line of the graph could be used to determine the concentration of the unknown. This graph was used to identify the unknown solution as having a solute concentration of 10% sucrose.
Answers to Questions
- The original solute concentration is approximately 20% sucrose. This is based on the fact that there was little change in the weight of the egg after incubation in the 20% sucrose solution, indicating that the egg is isotonic with the solution.
- The solute concentration of the unknown solution is approximately 10% sucrose. This value was interpolated from the data in Figures 1 and 2. The egg incubated in the unknown sucrose solution appeared to weigh somewhere halfway between the eggs incubated in 0% and 20% sucrose solutions. This would suggest that the unknown sucrose solution was 10%.
Discussion
The results of this study illustrate that osmosis is taking place with the deshelled eggs and sucrose solutions of different concentrations. The egg exposed to the 0% sucrose solution became swollen and took in water, thus increasing in weight over time. This egg became hypotonic, indicating that the sucrose concentration in the egg is greater than that in the solution and so water from the solution was transported into the egg. The egg exposed to the 40% sucrose solution, on the other hand, became lower in weight. This egg was in an environment which was greater in sucrose concentration than the egg itself, and thus the water from the egg was released into the surrounding solution. The egg which was incubated in 20% sucrose solution exhibited the least change in weight; this suggests that 20% sucrose is very close to the sucrose concentration within the egg itself. This egg is isotonic because it has an equal osmolarity to the surrounding environment.
The data of Table 3 could be used to generate a standard curve of egg osmolarity to increasing sucrose solutions. This is depicted in Figure 2 as a straight line, indicating that sucrose concentration was inversely proportional to the changes in egg weight. The osmolarity of the egg which was incubated at an unknown sucrose concentration could be determined and the sucrose concentration was interpolated from the graph to be approximately 10%. The osmolarity could be more accurately determined by providing additional solutions of increasing sucrose concentrations in smaller increments (eg. 2.5%, 5%, 7.5%, 10%, 12.5%, etc). Repeating the experiment several times could also help to provide more accuracy. It would also be very interesting to try this experiment out with different types of solutions besides sucrose, such as a salt solution, for example, and at different temperatures, to see how quickly or slowly the rate of osmosis takes place (2, 3).
References
- Mirriam Webster Dictoionary online; http://www.merriam-webster.com/dictionary/osmosis
- http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
- http://sps.k12.ar.us/massengale/egg_osmosis_sample1_lab.htm
