Lab #2 - Egg Osmosis (1)

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University of Ottawa *

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Biology

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Jan 9, 2024

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Lab #2 Egg Osmosis OBSERVATIONS: INDIVIDUAL DATA 10% Salt 5% Salt Tap Water Starting Mass (g) 77.0 77.1 77.2 Final Mass (g) 77.1 77.2 77.7 Change in mass (g) (final - mass) 0.1 0.1 0.5 CLASS DATA 10% Salt (Mass in g) 5% Salt (Mass in g) Tap Water (Mass in g) Change in mass (g) -3.66 0.23 0.4 QUESTIONS: 1. How do your data compare with the class data? In terms of the 10 % salt solution, our data was quite different from the class data, our egg seemed to have gained weight (+0.1) while for the rest of the groups, their mass went down significantly (-3.66). I presume this had something to do with our mass balance either being inaccurate or, the weight of the excess water in the container we were supposed to put our egg in on the mass balance hindered our results. However, for the 5% salt solution, the results from my group (+0.1) compared to the class were almost the same (+0.23). There was an increase in mass, but only by a little bit. Finally, the same can be said about the results for the tap water, the mass change that my group encountered (+0.5) was about the same as the class data (+0.4). Though our mass changed a little bit more than everyone else’s. 2. Define osmosis. Osmosis is a process by which molecules of a solvent pass through the membrane of a cell from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane. 3. Explain, in terms of osmosis, the change in mass of the egg for the… a. 10% solution When placed in a 10% salt solution, which is hypertonic in comparison to the egg, the egg’s mass will decrease. The concentration difference, (higher concentration in the extracellular fluid than in the egg) will need to be compensated, and thus, water will move out of the egg through the process of osmosis to balance out the difference and in turn, will lose some mass.
b. 5% solution Now, when the egg is placed into the 5% salt solution from the 10% salt solution, the egg will gain mass. This is because after coming out of the 10% salt solution it now contains a higher concentration of salt than the 5% salt solution. The environment has now become hypotonic. When the concentration of the extracellular fluid is less than the concentration of the cytoplasm inside the egg’s cells, water will move into the egg (through the process of osmosis) to take care of the imbalance of concentrations, thus increasing the mass of the egg. c. Tap water Finally, when the egg is placed into the tap water, the environment once again becomes hypotonic as the the concentration of extracellular fluid is lower than that of the concentrations of the cell cytoplasms within the egg. Once again the concentrations aren’t equal, and so through osmosis, the solvent, water, will enter the cells of the egg to compensate for the imbalance. This moving of water into the egg’s cells will increase the mass of the egg. 4. What do you think would happen if you left the egg in distilled water overnight? I think what would happen to the egg if you left it in distilled water overnight is that water would continue entering the egg’s cells until it reached an isotonic environment. Through the process of osmosis water would enter the egg’s cells until the concentration of the extracellular fluid and the concentration of cytoplasm of the egg's cells were equal. 5. What do you think would happen if you put an egg in distilled water for eight minutes, then placed it in a 10 percent salt solution for eight minutes? I think that if you placed the egg in distilled water for 8 minutes, then placed it into a 10% salt solution for 8 minutes, the egg would have a similar mass to that of what it started with. Hypothetically, when the egg is placed into the distilled water, it will expand due to osmosis as the water will enter the egg’s cells to compensate for the imbalance of solvent concentration, than for the same amount of time (8 minutes) it will lose water when placed into the 10% salt solution to again compensate for the concentration difference (Solute ECF > Solute CYTO ). In a perfect world I’d assume that the mass of the egg would end up exactly the same, however, in the real world, I’m sure other factors will come into play (such as rate of absorption & desorption) so I predict that the mass of the egg will be close to that of the initial mass but not the exact same. 6. In the procedure, do you think anything other than water passed between the egg and the solutions? What information would you need to have in order to determine this experimentally? During the procedure I do not believe that anything other than water passed through the egg and out. Eggs have semi permeable membranes, which means that only selective things can pass through them, water being one of them. The information that we would need to have in order to determine my theory experimentally would be the initial concentration of the salt solution, and the final concentration (after leaving the egg in it for a bit). If we subtract the two, we would be able to determine whether any salt passed through the membrane or not. If the concentration lowered, salt passed through and if it remained the same, salt did not pass through.
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