Last Updated 16 Jun 2020

Diffusion and Osmosis

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The Effects of Osmosis and Diffusion The experimentation of last week’s lab was in order to test the many effects of diffusion and osmosis amongst four experiments. One such experiment was testing the effects of molecular weight on diffusion in relation to the use of Agar. The methods performed included the use of two acids, HCl and acetic acid. Both acids were placed into an Agar-filled dish and, over increments of 15 minutes, data collection was taken based off the diffusion rate and the diameter length of both the HCl and the Acetic Acid.

The resulting factor was the HCl exhibited a greater rate of diffusion, directly resulting in a lager diameter. This implies that the HCl ultimately has a smaller molecular weight. The next experiment was based off osmosis of an animal cell; a chicken egg. After submerging two different chicken eggs in distilled water and 10% salt water, once again intervals of 15 minute data collection was taken for a total of one hour. After each interval the weight in grams was taken and then the eggs were placed back into the solution for further analysis.

Ultimately, the egg in distilled water exhibited an increase in weight while the egg in salt water was the opposite; a decrease in weight. This conclusion proves that water diffusion occurs from a hypotonic solution to a hypertonic solution. Osmosis in a plant cell was tested by comparing an Elodea cell in pond, distilled, and salt water. After obtaining samples of the Elodea cell and preparing a wet mount of each leaf using all three types of water, observations of the cells in a compound microscope was the next step.

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From there, comparisons of all three types of solutions in order to determine the apparent differences in osmosis were needed. When examined, the cell in pond water was not as defined; this result implied that water left the hypotonic cytoplasm of the cells causing it to wither in a way. Introduction In order to conduct the experiments of this lab, a hypothesis is no doubt necessary. In reference to the effects of molecular weight on diffusion a person is lead to believe that since the atomic mass unit of Acetic Acid is greater than that of HCl, the rate of diffusion of Acetic Acid will be slower and therefore produce a smaller diameter.

As stated by Watson (2011), “larger molecules diffuse more slowly because of resistance from molecules of the medium. ” This “medium” is the means of passing through the spaces in between a molecule. This was as well stated by (Watson 2011). Reiterating what was described, unlike smaller molecules, which can fit through a medium more easily, in turn allowing for a faster and more sufficient means of diffusion, a larger molecule has the resistance from a specific medium, which in a way is pulling back molecules therefore causing a prolonged time of diffusion.

This resistance is a direct correlation and explanation as to why the diffusion rate of a relatively larger molecule exhibits a longer rate of diffusion, as with the comparison of hydrochloric acid and acetic acid, and ultimately the purpose of this experiment. Based on the background information acquired on osmosis of an animal cell, it is safe to assume that after each interval of fifteen minutes, the weight of the animal cell in distilled water will continually grow, while the egg in salt water will decrease in weight.

Derived from information provided by (Fisher, Williams, & Lineback 2011), an animal cell, which is hypertonic, placed into a hypotonic solution of distilled water will cause water to diffuse into the hypertonic cell, seeing as diffusion occurs from hypotonic to a hypertonic solution. With any type of diffusion process, the particles that are being diffused tend to travel from a concentration that is greater to one that is smaller; moving down in the concentration gradient. This is the direct result of the increase in weight of the animal cell in the experiment.

In relation to a chicken egg, the largest living cell, it is predicted that the containing molecules will be too large to pass the membrane and water will flow into the egg (Reece 2011). The matter of the animal egg being placed into a solution of 10% salt is the directly opposite of the above stated. Osmosis within a plant cell placed in pond water will show a wilted cell wall based on the continual impeding force of the water on the wall. Aquatic plants tend to be hypertonic in their natural environment causing the plant to exhibit a “swollen” or turgid structure.

Materials and Methods In order to accurately and sufficiently test the hypothesis of the effects of molecular weight on diffusion, agar was one substance that was used. Agar in the presence of acids turns from a yellowish color to a more violet color. This same dish contained to holes with which two acids could be placed-HCl and acetic acid. From basic chemistry knowledge one knows that the molecular weight of HCl in comparison to Acetic Acid is smaller in size; that information was given from Watson (2011).

This is significant because it will later give way to the rate of diffusion of the two different acids. Constant observations, recordings, and measurements were required for this experiment, only in the intervals of 15 minutes. Over a period of one hour it was noticeable that the HCl exhibited a greater rate of diffusion and a great length in diameter, in comparison to acetic acid. The most important factor when dealing with this diffusion experiment, was the methods taken to prove that HCl had a greater rate of diffusion than acetic acid.

Initially, soaking a chicken egg in a small solution of acetic acid and 2 parts tap water will allow for better experimentation of the rate of osmosis of an animal cell. The overall scope of this particular experiment was to weigh two eggs using a triple beam balance in order to get an initial weight of the eggs before beginning the process of the lab. After doing so, the eggs were placed into two solutions, one being distilled water and the other 10% salt. Proceeding these steps were the 15 minute intervals of time, and after, a recording of the weight of the egg.

This process was done until a total of 60 minutes was reached for both the distilled water solution and the 10% salt solution. After acquiring all results and data, a conclusion could be based. Once acquiring three samples of Elodea leaves, preparing three different wet mounts was the following step. From there, after ten minutes an observation of all the samples under a compound microscope was the following method needed in order to determine the characteristics of the leaves. The leaf in the pond water demonstrated the leaf cell in “normal” conditions, while the distilled water and NaCl were not “normal” conditions.

Results The findings of the effects of molecular weight diffusion conclude that ultimately the molecular weight of a molecule affects the rate of diffusion directly. The greater the weight, the slower the diffusion process will be; that was the case for acetic acid, and it was in part due to the diffusion of particles through the medium. In addition to that, the measurement of the diameter of both acids also was directly affected by the molecular rate. All the comparisons in the diameter readings of the two acids can be found in table 2.

All readings for both acids were taken over an increment of 15 minutes for an hour. In total, HCl produced a larger diameter due to its smaller amu. See table 2. In comparing the affects of distilled water to 10% salt water and the rate of osmosis of an animal cell, the rate of osmosis proved most sufficient in distilled water, rather than in the salt water, with an apparent increasing weight distribution in the distilled water, and a decrease in weight in the salt water. These changes in weight loss and gain are exhibited in Table 1.

Even though it is obvious that both eggs exhibited either weight loss or gain, both eggs also showed a sudden spike it the gain or loss around the time frame of 15 minutes and 45 minutes, yet again illustrated in Table 1. Discussion After conducting the diffusion experiment using agar and examining the results, it is apparent what the outcome of diffusion is when comparing HCl and acetic acid atomic weights. It is as well safe to assume the resulting outcomes of future comparisons of two molecules of with different atomic mass units.

The use of agar in this specific experiment is much useful due to the properties and characteristics of the extract. The agar, in the presence of an acid, turns from a yellowish color to one that is pink; because of this characteristic, it was possible to measure the distance from the center outward of the agar when placed into a dish of HCl and acetic acid (Watson 2011). As explained before, these measurements allowed for sufficient data in determining the rate off diffusion for both acids. Table 2 will provide a visual for the data that was collected from the experiment.

In the end, a conclusion was established that the rate of diffusion was most prominent in HCl, the acid with the smallest amu. Simply the definition of diffusion itself will aid in understanding why molecules of a higher molecular weight will diffuse slower in comparison to one of a smaller weight. Any substance will diffuse down its concentration gradient, the region along which the density of a chemical substance decreases (Reece 2011). It is understood that the molecular weight is how much mass a substance has, and mass can be determined by how tightly packed particles are-density.

A molecule with a high mass, ultimately a high density, will illustrate a slower rate of diffusion. With regards to the cell that is the egg, the rate of osmosis proved to be greater in the distilled water as compared to that of the 10% salt. This is in part due to the size of the particles that make up the egg as well as surround the egg. If there is a higher concentration of nonpenetrating solutes in the surrounding solution, then water will tend to leave the cell (Reece 2011). This definition provides an understanding of what is happening to the egg when it is submerged into the 10% salt solution.

Comparing the egg to the salt solution, there is a higher concentration of nonpenetrating solute in the salt solution, nonpenetrating being the particles that cannot cross the membrane, and this in return allows water to leave the egg which ultimately causes dehydration for the egg, resulting in weight loss recorded in Table 1. The complete opposite is the case for the distilled water which would result in weight gain for the egg. Literature Cited Fisher, K. , Williams, K. , & Lineback, J. (2011). Osmosis and diffusion conceptual assessment. CBE Life Sciences Education, 10(4), 418-429. doi: 10. 187/cbe. 11-04-0038 Reece, J. B. 2011. Campbell Biology. 9th ed. San Francisco (CA): Pearson Education Inc. 125-139 p. Watson, C. M. (2011). Diffusion and osmosis. In Biology 1441 Laboratory: Cellular and Molecular Biology (pp. 76-91). Boston: Pearson Learning Solutions. Tables and Figures Figure 1 percentage change in wait of eggs between 15 minute intervals [pic] |Weight of Egg (grams) | |Time Water 10% Salt | |0 75. 60 91. 65 | |15 76. 00 91. 46 | |30 76. 10 91. 39 | |45 76. 10 91. 5 | |60 76. 10 91. 23 | Table 1 A comparison in weight and change of each egg in DI water and a 10% salt solution. |Start time |HCl |Acetic Acid | | |15 min |16 mm |16 mm | | |30 min |18 mm |19 mm | | |45 min |23 mm |22mm | | Table 2 ----------------------- 60 min26mm23 mm

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