Osmosis Lab Report

Osmosis is a passive movement of water through a selectively permeable membrane moves from an area of higher concentration to an area of lower concentration. In this lab, we can determine the direction of diffusion of small molecules by measuring the diffusion of small molecules through dialysis tubing. This tubing acts as a selectively permeable membrane, and allow to pass larger molecules slowly. Introduction:
Cells have kinetic energy and it causes the molecules of the cell to move around and bump into each other. Diffusion is one result of this molecular movement. Diffusion is the passive movement of molecules from an area of higher concentration to lower concentration. Osmosis is a passive movement of water through a selectively permeable
membrane moves from an area of higher concentration to an area of lower concentration. Diffusion or osmosis occurs until dynamic equilibrium has been reached. This is the point where the concentrations in both areas are equal and no net movement will occur from one area to another. If two solutions have the same solute concentration, the solutions are said to be isotonic. If the solutions differ in concentration, the area with the higher solute concentration is hypertonic and the area with the lower solute concentration is hypotonic. Since a hypotonic solution contains a higher level of solute, it has a high solute potential and low water potential. This is because water potential and solute potential are inversely proportional.
A hypotonic solution would have a high water potential and a low solute potential. An isotonic solution would have equal solute and water potentials. Water
potential is composed of two main things, a physical pressure component, and pressure potential. Water will always move from areas of high water potential to areas of low water potential. This experiment will prove that diffusion and osmosis occur between solutions of different concentrations until dynamic equilibrium is reached, affecting the cell by causing plasmolysis or increased turgor pressure during the process.

Materials and Methods: To begin Lab, first gather the materials.
The materials needed are dialysis tubing from Fisher Scientific (S413003A) with. We also used four tubes of Spectra/Por® which has a 32mm width and 20.4mm diameter. We also used ~127mm strips. The dialysis tubing has a 12,000 molecular weight cutoff and diameters of 4.8 angstroms. Sucrose has a weight of 342 and solution of 9.3 angstroms. We also need distilled water,
And five 100mL beakers. Start the lab by labeling the beakers 1 through 5, and fill with 4 tap water and one 40% sucrose. Then make up five different solution:2 tap water, 20% sucrose, 40% sucrose, and 60% sucrose. Soak the dialysis tubing and clamp one end of each tube. Pour 10mL of each solution into bags and clamp other end carefully to get any air bubbles out. Rinse off each bag and remove moisture on the surface and record the intial mass of the bags. Fill each beaker with enough water or solution to cover the bag. Weight the bags every 10 min.

Results: Bag Weights (g)
Time
(min) 1 2 3 4 5 Water 20% 40% 60% Water
0 21.54 15.32 16.19 20.48 21.61
10 22.0 16.28 17.55 22.63 22.45
20 22.17 16.67 18.26 23.43 20.63
30 21.98 17.10 19.22 24.44 19.39
40 21.83 17.44 19.75 25.41 18.77
50 22.02 17.76 Bag open 26.62 18.20
60 22.14 17.99 Bag open 27.47 17.52

Cumulative Change in Weight (g)
1 2 3 4 5
Water 20% 40% 60% Water
0 0 0 0 0
0.46 0.96 1.36 2.15 0.84
0.63 1.35 2.07 2.95 -0.98
0.44 1.78 3.03 3.96 -2.22
0.29 2.16 1.52 4.93 -2.84
0.48 2.44 X 6.14 -3.41
0.6 2.67 X 6.99 -4.09

Corrected Cumulative Change in Weight (g)
2 3 4 5
20% 40% 60% Water
0 0 0 0
0.5 0.9 1.69 0.38
0.72 1.44 2.32 -1.61
1.34 2.59 3.52 -2.66
1.83 1.27 4.64 -3.13
1.96 X 5.66 -3.89
2.07 X 6.39 -4.69

Figure 1
Corrected cumulative change in weight. At each time subtract the change in weight of bag 1 (water) from the weight of the bag 2(20%), bag 3 (40%), bag 4 (60%), and bag 5 (water) in 60 min but bag 3 leaked after 40 min so no data.

Discussion: In this experiment, it was proven that water move faster than sucrose across the cell membrane. It means that sucrose cannot pass through a selectively permeable membrane, but water molecules can move across the membrane to the area of lower water potential to reach dynamic equilibrium.

Reference:

- Campbell et al. 2008 and Traxler 1928
- McCutcheon, M. and Lucke, B. 1926. The kinetics of osmotic swelling in living cells. J. Gen. Phys. 9: 696-707
- Traxler, R. 1928. The effect of the temperature on rate of osmosis. J.Phys. Chem. 32 (1) 128-141