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IntroductionThe cell membrane is a fluid structure that is made up of phospholipids and proteins. Its main function is to allow osmosis and diffusion to occur in a cell. It protects a cell from taking in molecules that are too large and other chemicals that are not permeable without energy being used. The cell membrane is considered to be selectively permeable because it does not allow the non-fat soluble chemicals and the larger molecules in, but it does allow fat soluble chemicals and small molecules to pass into the cell. In order for the larger molecules and non-fat chemicals to enter the cell protein channels and energy are needed. In this lab you will see the cell membrane working. The experiment will show the Osmosis of water and a sucrose solution. Osmosis is net movement of water molecules from a high to low concentration until equilibrium is reached. In other words, Osmosis is the diffusion of water. Through the diffusion of water Isotonic solutions may occur. This is where both sides of the membrane have an equal amount of water. There may also be a Hypertonic solution. That is where the membrane has more water and the concentration will move down a gradient causing the membrane to shrink. Another solution that may occur is a Hypotonic solution. This type of solution allows the water molecules to pass through the cell membrane into the solution causing the cell to increase in size. Diffusion of dye in agar and water will be studied in this lab. Diffusion is the movement of a concentration from a high gradient to a lower gradient until area is at same level. We will also study the permeability of the cell membrane when different solutions are used inside and outside of the cell. In this lab, we will observe the changes taking place during the diffusion of dye through agar gel and through water. We will determine what type of solution is formed when placing the mock cell membrane in different levels of solution. We will calculate the rate at which the dye diffused and plot the findings in a chart to show the different rates each cell changed.


In Part A of the lab the cell membrane of bags 2 through 4 will gain mass because of the use of sucrose solution in the cell. The water will move through the dialysis tubing to form equilibrium between the membrane and outer concentration. Bag 5 will be a Hypertonic solution, the water is at a high gradient and the solution surrounding the cell is at a low concentration gradient, causing the bag to shrink. Bag 1 will have an Isotonic solution. In Part B of the lab, the potassium permanganate will diffuse faster in water then in the agar gel. In Part C of the lab, the solutions in the bag and the solutions around the bag will be the same after the testing is done. Starch, chloride, protein, and sulfate ions will be found in both areas tested.

Materials and Methods

See the attached sheets for materials and methods used.


Part A: In bag 1 the mass changed 1/10 of a gram. In bag 2 the mass changed 4.4 grams. In bag 3 the mass changed 6.3 grams. In bag 4 the mass changed 8.3 grams, and in bag 5 the mass changed to a negative 6.0 grams.

Part B: The methylene blue diffused through the agar gel a total of 4.5 mm and the potassium permanganate diffused 10.5 mm. The potassium permanganate diffused through the water a total of 15 mm.

Part C: The solutions in the bag contained starch, which caused the solution to turn black. Sulfate ions and proteins were not found. Chloride ions were found in the solution, the solution turned into an orange-milky color. The solutions in the beaker contained no starch. There were sulfate ions found, which caused the solution to have white particles floating in it. Chloride was found in the solution, the solution turned into a yellow color. The beaker also contained proteins, the color of the solution turned to a violet color.

Discussion and Conclusion

The findings for Part A backed up my hypothesis. Bags 2 through 4 did have a Hypotonic solution. The 5th bag’s solution was Hypertonic and bag 1 involved an Isotonic solution. The relationship between sucrose solution and osmosis is that the higher the sucrose solution the faster osmosis occurs. The water molecules are moving faster through the sucrose solution so that equilibrium is met in the cell and surrounding solution. The water for bags 2 through 4 are moving into the dialysis tubing, that is why the dialysis tubing expanded and had a Hypotonic solution. For bag 5 the water was moving out of the dialysis tubing into the sucrose solution which is why there was a Hypertonic solution. The chart showed that the mass did increase steadily for bags 2 through 4 and the mass decreased steadily for bag 5. Bag 1 had a small decrease, which could be an error in reading the triple beam scale used to find the mass of the bag. Placing an amoeba into a jar of water for a certain time could cause the amoeba to burst. The amoeba contains 10% solutes, which would cause the water to flow into the cell to create equilibrium. This would be a Hypertonic solution. The Hypothesis for Part B was found to be true. The potassium permanganate diffused faster in water then in the agar gel. The agar gel has a thicker concentration making the movement of the dye slower than the movement of dye through the water. The attached sheet will show the results of the tests done in Part B to support the Hypothesis made. The questions concerning Part B are also included on the attached sheet. In Part C of the lab, my hypothesis did not hold up. There was a variance in which solutions were found in the beaker and in the bag. The findings in this experiment are outlined on the attached sheet. I believe the differences were caused by selective properties that the cell membrane has. The dialysis tube working like the cell membrane would allow the sodium molecules to be pushed out of the cell and back in to the cell with the attachment of other molecules. That is why sodium sulfate was not found in the bag but sodium chloride was. The bag pushed out the sulfate molecules through active transport and brought in the chloride molecules also through active transport. The starch molecules must play an important roll in the cell and the molecules were not allowed to pass through the cell membrane. The protein molecules were not allowed to pass through the cell membrane because they possibly could non-fat solubles or the particles were too big to pass through. They would need energy to pass through the cell membrane and protein channels that were not present in the dialysis tubing. The experiments done helped explain what was being discussed in the reading assignments and gave me a better understanding of how cells work. The work cells do keep our bodies healthy and maintain a balance in our bodies to help fight against infections. The plants, animals, and all other living organisms would not be able to survive if the cells did not follow the simple rules of which molecules are needed to maintain equilibrium in all living things.

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