Selective permeability is a function and a feature of the cell membrane, which is crucial to regulate homeostasis. According to Turksen (132), the plasma membrane function by controlling specific passing of some substances and at the same time hinders entry of some substances into the cell. As high school students, we were curious of a cell membrane could do this function. We, therefore, performed an experiment to test how a chicken eggshell membrane could allow some substances to pass through it while hinders the passage of some substances. We dissolved the eggshell in vinegar. After a thorough reading, the book by Turksen (143), we found out that vinegar dissolves the chicken membrane leaving all the cells in the eggshell intact. The vinegar bounds the internal structure of the eggshell enabling us to carry out the experiment.
We carefully analyzed the experiment and found out that several processes are involved in the performance of the cell membrane permeability. According to Goodman (101), the process of osmosis enables the success of this experiment. We found out that osmosis is a process that allows diffusion of water through a selective permeable membrane. The water diffuses from a region where concentration of solute is low to a region where the concentration of solute is high. The surrounding of the eggshell is in a low concentration, therefore, diffusion of water from the low concentration area to the high concentrate, area in the eggshell content.
We also learnt about several terms involved in this process. The processes include solvent, solute, solution and osmotic pressure. According to Goodman (45), a solvent dissolves a solute. A solvent can be either a liquid or a gas. Solvent dissolves solutes depending on temperatures. The higher the temperature, the higher the amount of solute that can dissolve in a solvent. The maximum amount of solute that dissolves in a solvent depends on the temperature. A solution is a mixture that we got from the combination of a solvent and a solute. The concentration of the solution depends on the amount of solute dissolved in the solvent. When a high amount of solute is dissolvent in a solvent, the solution is to be concentrated.
We also learnt that osmotic pressure played a major role in the determining of the cell membrane permeability. In the book by Turksen (68), a solution applies osmotic pressure to hinder water flowing into the cell membrane. Osmotic pressure works to nullify osmosis. Hypotonic, hypertonic and isotonic solutions enabled the success of this experiment. Hypotonic solution is a solution that has a low concentration for solutes. A cell has a higher concentration of solutes when dissolved in a hypotonic solution. Therefore, allowing water to flow into the cell. Goodman (82) confirmed that a hypertonic is solution with a higher concentration. A cell decreases its water to the surrounding through osmosis. Cell shrinks because water flowing out of the cell into the hypertonic solution. An Isotonic solution has the same concentration like the concentration of the cell. Therefore, the cell retains its contents. The concentration of water and the solute molecules are equal to the external concentration of cell content.
Material and methods
The technician provided us with four 500ml beakers. The beakers are labeled 1, 2, 3 and 4. We used the beakers to hold solution contents of the experiment. We used four de- shelled eggshells. The eggshells were the main substances that we used to perform the experiment. We used the shells to confirm the permeability of the cell membrane. We also had solutions of different concentrations, a twenty percent sucrose concentration and a forty percent sucrose concentration solution, which we used to perform the experiment to prove the permeability of the membrane. We also had unknown sucrose solution labeled A and B. The metric machine provided used to measure the weights of the contents of the substances that we used in the experiment. According to Goodman, (134) similar experiment showed that that using metric machine provided accurate results for the success of the experiment.
During the experiment, we drained the eggshell from the vinegar. We used a slotted spoon to carry out the procedure. We placed an empty tray on the metric machine and later placed the eggshell that we drained from the vinegar solution, into the tray. We then read the reading on the metric scale and rounded the readings to the nearest 0.1. According Turksen (90), the paper towel beneath the spoon drained the vinegar keeping the eggshells dry. We placed the entire eggshell on the tray and recorded the initial reading on a table.
We analyzed their readings and recorded their readings on a table. When we finished recording, we took each eggshell and put it in each of the four beakers. The beakers had labels on them. We recorded the process of every beaker for 15 minutes. After every 15 minutes in every beaker, we took out the eggshell with sorted spoons and put them on the tray on the metric machine. We then read the readings of the process and recorded them on the table. We repeated this process for all the four eggshells, and for every 15 minutes, we recorded the readings.
After performing the experiment for all the four eggshells, we found our readings and recorded them in the table.
Weight in Grams
EGGS IN TAP WATER
EGGS IN 20% SUCROSE SOLUTION
EGGS IN 40% SUCROSE SOLUTION
EGGS IN #4 UNKNOWN SOLUTION
Total WT change
We analyzed the table and found out that the weight of the eggshell varied depending on the time.
Eggs in tap water
The weight of the eggshell in tap varied with time. The initial weight of the eggshell was 93.2 but changed during the entire 60 minutes. At the end of the 60th minute, the weight we recorded was 98.4. This showed that the weight increased. Confirming that water has a lower concentration than the shell content, hence water flowing into the cell. According to Goodman (127), we proved that water flows from a region of lower solute concentration to a higher solute concentrated area.
Eggs in 20% sucrose solution.
The weight of the eggshell in the 20% sucrose solution reduces from 88.3 to 86.6. According to Turksen (76), we found out that osmosis occur that, solution flow from a region of low solute concentration to a high solute concentration area. Therefore, we confirmed that the eggshell content had a lower concentration than the 20% sucrose solution, leading to the eggshell losing water to the 20% solution, confirming the loss of weight from 88.6 to 86.6.
Eggs in 40% sucrose solution
We found out that the weight of the eggshell reduced from 82.4 to 80.7. This means that the total weight change was 1.7. The slight change in weight showed that the concentration of the water and 40% sucrose was almost the same. However, the change in weight still proved that osmosis occurred. According to Goodman (83), osmosis occurs when water flows from a lower concentration to a higher concentration, proving the loss in weight of the shell. This also proved that the shell is permeable.
Eggs in unknown solution.
We found out that out that the eggshell reduced in weight. We recorded a total weight loss of 4.7. This showed that the eggshell lost water to the unknown solution. According to Turksen (127), osmosis occurs when water flow from a region of low concentration to a high concentration. We confirmed that the unknown solution has a higher concentration than the eggshell content leading to loss of water from the eggshell proving that the eggshell is permeable.
Goodman, Steven R. Medical Cell Biology, Third Edition (MEDICAL CELL BIOLOGY
(GOODMAN). London: Academic Press, 2007, print.
Turksen, Kursad. Permeability Barrier: Methods and Protocols (Methods in Molecular Biology).
New York: Humana Press, 2011, print.