Semipermeability of Cell Membranes

A basic function of membranes is to separate the contents of a cell from the environment. However, it is always necessary for cells to take up nutrients from the surroundings; therefore, the enclosing membrane of a cell must be permeable, (Malacinski, G.M, Freifelder D. 1998). Semi permeable means that the cell membrane acts like a net with very little holes. It filters the molecules that pass through it. Molecules that are fine can pass through like water. The lipid bilayer membrane is impermeable to ions, yet it is permeable to water; this result in a movement of water called Osmosis, (Minkoff E.C, Baker P. J, 1996). When considering the behavior of a cell in a solution, both solute concentration and membrane permeability must be considered. These two factors are taken to account in the concept of tonicity, the ability of a solution to cause a cell to gain or lose water. The tonicity of a solution depends in the part of its concentration of solutes that cannot cross the membrane, relative to that inside of the cell. If there is a higher concentration of nonpenetrating solutes in the surrounding solution, water will tend to leave the cell, and vice versa (Campbell N. ,2008). Models in the form of a dialyzing bag is used to analyze the concept of semipermeability. Dialysis tubing can come in various pore sizes that allow selective passage of materials. The selectiveness of a dialyzing bag is the same as the cell membrane which is also selective, but no really in terms of size of the material. It has to do with polarity. The cell membrane is bipolar- has polar head with long, non-polar tail, but two chains of this with non-polar ends facing inward on the membrane. Polar molecules need to go through membrane-bound protein channels or receptors.*!!!@ The study is limited to only analyzing the concept of semipermeability with the use of a dialyzing bag as a model. Also, it was only directed to knowing the responses of animal and plant cells exposed in different concentrations.

The study was focus on achieving its objectives of:

1. Demonstrating the effect of different concentrations on the cell and the dialysis bag.

2. Measure the effects of exposure on various concentration of solutes in the process of Osmosis.

3. Differentiate Hypertonic, Hypotonic, and Isotonic environments.

4. Prove the hypothesis that the cell membrane is semipermeable.