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Cell Membranes and Osmosis Analysis


Gaseous exchange, excretion, and intake of water and minerals are essential processes in all living things. The above process takes place at the molecular level and molecules have to move across the membrane (Alters, 1999). The cell membrane is semi-permeable or selectively permeable. The function of the cell membrane is to regulate the movement of molecules in and out of the cell (Yager, 2009).

The molecules move across the membrane through passive transport and active transport. Active transport is as a result of different in the concentration gradient while active transport energy is required to facilitate the molecule movements. The active transport is also referred to as diffusion, which is the molecule movement from a region with more concentration of molecules to that with less concentration (Scott and Fong, 2009). The movement of water molecules from a solution of high concentration, to a region of low concentration and across a semi permeable membrane is known as osmosis (Alters, 1999).

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The objectives of the experiment were to illustrate the movement of molecules across a semi permeable membrane. Dialysis tubing was used as the semi permeable membrane. The concentration of water molecules was regulated by the use of sucrose solution so as to create different levels of water concentration (Stoker, 2010). The experiment hypothesis was that the water molecule would move in and out of the dialysis tubing depending on the different in the concentration gradients between the two solutions. The hypothesis was tested by carrying out the experiment.


200ml of the deionized water was put in a 250ml beaker and the beaker labeled using a wax pen. In another beaker, 150ml of 25% sucrose solution was put, and the beaker labeled. 450 ml of 1% sucrose solution was put into a third beaker which was subsequently labeled.

A 40cm dialysis tubing was cut into four equal pieces of 10cm each, which were then soaked with deionized water. One end of the 10cm dialysis tubing was sealed by tying tightly with a string.

In two of the tubes, tube A and B, 3ml of 1% solution of sucrose was added and the weight of the tubing taken and recorded. In the remaining two tubes, C and D, 3ml of 10% and 25% were added respectively and their weight taken and recorded. Tube A was then immersed in a beaker containing 25% sucrose solution. The remaining tubes were immersed in a beaker containing 1% sucrose. The tubes were removed after 15 minutes and their weight taken. The procedure was repeated after 30, 45 and 60 minutes and the weight recorded in the table. All the change in weight was recorded in the table and a graph of weight against time used to analysis the observations.


The weight of tube A decreased, while in tube B, C and D the weight shown in the table below.

Tubes 0 minutes 15 minutes 30 minutes 45 minutes 60 minutes
A 12.3g 9.4g 9.5g 9.5g 9.4g
B 12.3g 13.1g 12.5g 12.7g 12.5g
C 12.2g 12.6g 12.4g 12.8g 12.8g
D 12.5g 13.4g 13.4g 13.5g 14.0g

The weight of the tubes changes with time as shown by the graph below.

Comulative Change
Figure 1

Discussion and conclusion

The experiment supported my hypothesis on the change of weight when a solution in a semi permeable membrane is immersed in solution with different concentration of water molecules. The weight of tube A decreases when immersed in a solution containing 25% sucrose solution. There is a high concentration of water molecules in the dialysis tubing than in sucrose solution. The water molecules move across the membrane to a low water concentration region causing a reduction in weight.

The weight of tube C and D increases as there is less concentration of water in the tubes than in the solution it is immersed. Tube C and D had a low concentration of water molecules with a 10% and 25% sucrose concentration respectively. The water moved from beaker to the dialysis tube where the water molecule concentration was low.

Tube B is the control experiment through there is a relative increase in weight. The weight of tube B was expected not to change as the concentration of the water molecule is equal in the both in the dialysis tube and the solution in the beaker. It raises the question on the accuracy of the experiment. There is a need to ensure accurate measurement of the weight collected and ensuring that no outside factor caused bias in the results.

The graph of fig 1 above on, the cumulative change in weight (g) of the tube at time (min), shows there was a drastic increase in weight of the tube in the first 15 minutes. The increased in almost all the tubes stagnated after 15 minutes showing there was a balance in concentration of water molecules between the tube and he beakers.

In conclusion, the experiment was a success. It illustrated the osmosis process and the influence of the water molecule concentration to the process. The change in weight of the tubing illustrated there was a movement of water molecules in and out of the tubes depending on the concentration of water molecules.


Alters, S. (1999). Biology: Understanding life. Sudbury, Mass: Jones and Barlette.

Scott, A. S., & Fong, E. (2009). Body structures & functions. Clifton Park, N.Y: Delmar.

Stoker, H. S. (2010). General, organic, and biological chemistry. Australia: Brooks/Cole Cengage Learning

Yager, R. E. (2009). Inquiry: The key to exemplary science. Arlington, Va: NSTA Press.