Osmosis Egg Lab
The Effect of Salt Solutions on Decalcified Eggs
The cell membrane forms a boundary between a cell and the outside environment, it surrounds the cytoplasm of a cell. It is made up of a double layer of phospholipids embedded with proteins. The arrangement of the molecules that make up a cell membrane are described as a fluid mosaic, because it is flexible and floats, and the variety of molecules stud the membrane similar to the arrangement of tiles in a mosaic. The cell membrane is selectively permeable, which means that the cell membrane controls what substances pass in and out through the membrane. This characteristic of cell membranes plays a big role in passive transport; the movement of substances across the cell membrane without any input of energy by the cell. The energy for passive transport comes entirely from kinetic energy that the molecules have. Because of kinetic energy, molecules are in constant motion. The simplest type of passive transport is diffusion, which is the movement of small molecules from an area of high concentration to an area of lower concentration. Diffusion always moves down a concentration gradient, the difference between the concentration (or the strength of) of a solute in one place and its concentration in an adjacent area.
Osmosis is a type of diffusion in which water molecules diffuse across a semi-permeable membrane from a region of high concentration to one of low concentration. The net direction of osmosis depends on the concentration of solutes (the particles which are dissolved in a solvent) on the two sides of the cell membrane. In a hypertonic solution, the concentration of solutes in the solution that the cell is in is higher than the solute concentration of a cell’s cytoplasm. This causes the cell to shrink or shrivel due to water leaving the cell, and turgor pressure is lost. In plants, when this occurs, plasmolysis occurs, which is the reason plants wilt. A hypotonic solution is a solution where the solute concentration of the solution that the cell is in is lower than the solute concentration of a cell’s cytoplasm.The net movement of water is from the outside to the inside of the cell. The effect on the cell is that the cell swells and may burst, and eventually die. In an isotonic solution, the concentration of solutes on both sides of the membrane is the same and so the net movement of water is zero. When the concentration of dissolved substances is equal inside the cell to outside the cell this is known as dynamic equilibrium. Cells in an isotonic environment have no difficulty keeping the movement of water across the cell membrane in balance.
In this lab we are exploring the transport of water across the membrane of an egg by osmosis. The membrane of the egg is permeable to water and depending on the extracellular environment, water will move into or out of the egg. The egg resembles how cells in the body regulate the flow of molecules across the cell membrane. The purpose of this experiment is to understand osmosis and water transport using eggs.
How does the mass of an egg change after being submerged in distilled water, 5% salt solution & 15% salt solutions for 15 minutes?
If an egg is placed in the 5% salt solution then its mass will decrease slightly. If an egg is placed in the 15% salt solution then its mass will decrease and it will become even smaller than the egg placed in the 5% salt solution. If an egg is place in distilled water then it will swell and its mass will increase.
- Collect three decalcified eggs (eggs without their outer shell) and determine the dry mass of each egg by individually putting the eggs into a weighing boat and placing them on a balance.
- Record the weight of each egg on the data table (on Mac Airs)
- Get three 250mL beakers
- Fill one beaker with 150mL of 5% salt solution and, using a Sharpie, label it (indicating it’s the 5% salt solution)
- Fill a second beaker with 150mL of 15% salt solution and, using a Sharpie, label it (indicating it’s the 15% salt solution)
- Fill the 3rd beaker with 150mL of distilled water and, using a Sharpie, label it (indicating it’s the distilled water)
- Making sure to record which egg is being placed into what beaker, carefully place the 3 individual eggs into their own beaker using the spoon.
- After the eggs have been in the beakers 15 minutes, remove them from the beakers using the spoon, and place them back into the weighing boat and weigh them on the balance.
- Record the weight of each egg and any qualitative data in the appropriate column on the data table.
- Subtract the ‘before’ mass from the ‘after’ mass and record the results in the appropriate column on the data table.
- Calculate the percent change in mass and record it in the appropriate column on the data table.
- Analyze the information using a data table.
The independent variable is the salt concentration of the solutions, the thing added to an experiment that causes the dependent variable to change.
The dependent variable is the eggs, the variable being observed.
The control is the egg’s mass without any solution, what is used to show what would happen if nothing was done to the egg.
The constants are the 250mL beakers, the temperature of the solutions, the amount of solution (150mL), the type of eggs, the time in the solutions, and the balance.
- Three decalcified eggs
- 150mL distilled water
- 150mL 5% salt water
- 150mL 15% salt water
- 3 – 250mL beakers
- Masking tape
- Weighing boat
- Mac Airs
How Does the Mass of Decalcified Eggs Change After Being Submerged in Distilled Water and 5% & 15% Salt Solutions for 15 Minutes?
This lab studied how the percentage of salt solute effects the mass of an egg. The hypothesis stated that the egg in the 5% salt solution would have a slight decrease in mass size, that the egg in the 15% salt solution would have the largest amount of change (and would have the largest decrease in mass), and that the egg in the 0% salt solution/distilled water would be the only egg to increase its mass size. The data from the experiment contradicted the hypothesis.
After collecting three decalcified eggs and weighing each egg separately; three test groups were created. Each individual egg was placed in one of three beakers: #1 with distilled water had an egg initially weighing 90.50 grams, beaker #2 with 5% salt solution had an egg initially weighing 83.87 grams, and beaker #3 with 15% salt solution had an egg initially weighing 86.25 grams at the start of the experiment. Each beaker contained 150mL of solution. After sitting in the solutions for 15 minutes the eggs were removed and weighed again. The egg in beaker #1 then weighed 92.98 grams, resulting in a +2.48 gram change in mass. The egg in beaker #2 then weighed 85.57 grams, resulting in a +1.7 gram change in mass. Lastly, the egg in beaker #3 then weighed 87.47 grams, resulting in a +1.22 gram change in mass. The comparison of the percentage change of the three eggs in this experiment resulted in the following overall percent change in mass: egg #1= +2.74%, egg#2= +2.02%, and egg #3= +1.41% change. To recap, osmosis is the flow of water through a semi-permeable membrane from an area of higher water concentration to an area of lower water concentration. The experiment results showed that all the eggs increased in mass size, slightly swelling, showing the effects that osmosis has on a solution. Osmosis has taken place in the eggs in the 5% salt solution and 15% salt solution. The water has moved from an area of higher concentration (the beaker) to an area of lower concentration (egg). The mass of the eggs increased because the water concentration of the salt water solution in the beakers is higher than the water concentration inside the eggs. In beaker #1, the beaker with distilled water, the concentration of water outside the egg was greater than the concentration of water inside the egg. Therefore, the water moved from the beaker to the egg.
The main limitation in this experiment was the short amount of time the eggs sat in the solutions. This may have caused some inaccurate data since there wasn’t a lot of time for osmosis to occur dramatically. It would be interesting to do this experiment again, allowing more time to see how much time would have been needed to reach a state of equilibrium, an isotonic environment. Also, the difference in the initial size/mass of the eggs varied somewhat which may have contributed to the rate at which osmosis occured. If doing this experiment again, including a broader sampling of the independent variable (the salt) and more dependent variables (the eggs) would allow a larger population to be tested and then averaged. Also, measuring the remaining volume of the solutions after the eggs have been removed would help to chart the changes in mass. It would also be interesting to see the results if other independent variables (such as sugar or corn syrup or vinegar) were included. Errors may have occurred due to incorrect measurements of the weights of the eggs. Recording wrong measurements could lead to a false interpretation of the results.
One example of osmosis in the human body involves water and nutrient absorption in the stomach, small intestine, and colon. Osmosis gradients lead water to flow into the body through tiny gaps between the cells in the intestines and absorb nutrients and food into the blood to keep humans alive. Another example of osmosis in the human body is the instinct of thirst. If the water volume in the body falls below a certain threshold, or if the salt concentration becomes too high, the brain signals thirst. Also, the kidneys use osmotic gradient to make urine more concentrated or more diluted, regulating the bodies fluids. The kidneys expel water and salt to maintain optimal levels for the cells in the body to function. Overall, this was a fun and beneficial lab which demonstrated how osmosis occurs in the human body.
“The Cell Membrane”. Web. 3 November 2011.
“Biology 12 – Cell Membrane and Cell Wall Function: Chapter Notes”. Web. 3 November 2011.
“Cell Organization and Functions”. Web. 3 November 2011.