Cell Membranes and Osmosis


The interaction between cells and the aspects encompassing the environment is defined by the ability for cells to permit or restrict the movement of such aspects through the cell membrane. As such, it is evident that cells require reacting with biological facets such as water and chemicals and other elements that constitute the environment. Thus, in order for them to interact, movement is facilitated by the cell membrane. This movement of water and other solubles to and from the cell through the cell membrane is defined by the processes of diffusion and osmosis. Specifically, diffusion describes the process of movement in which molecules move from a highly concentrated region to a low-concentrated region within or outside the cell. Osmosis, on the other hand, describes movement of particles below the concentration gradient and across the cell membrane (Sadava, Hillis, Heller and Berenbaum, 114-115). The movement of molecules within and outside the cell is determined by the permeability of the cell membrane. Simply, molecules are allowed or disallowed from transiting between cells because of the selective permeability of the cell membrane. Cell membranes permit certain molecules to cross in and out of a cell. For instance, the cell membrane allows water to cross but prohibits ionized salts from entering the cell. Consequently, if the quantity of salt is greater than the amount of water within a cell than outside, the water will move from the cell to the encompassing environment. Similarly, if there is low concentration of dissolved molecules in the environment than within the cell, the water will transit from the environment to the cell, thus terming the solution as hypotonic. In addition, a hypertonic solution illustrates the movement of water into a highly concentrated solution from the cell. An isotonic solution describes the equilibrium between concentration within and outside the cell. Thus, determining the processes of osmosis and diffusion within cell membranes requires formulation of a hypothesis based on the effect of the concentration of a solution on movement across cell membranes (n.a, 2012).


Determining the movement of molecules across cell membranes will be illustrated by an experiment. The experiment will comprise four tubes, which will be indicated with the letters A, B, C and D. Consequently, the tube A is expected to have a reduction in weight while tubes C and D will be expected to depict an increase in weight. Alternately, tube B is supposed to be constant. Separately, tube A will be hypotonic, tubes C and D will be hypertonic and tube B will be isotonic. Thus, the experiment will determine if the four tubes comprise hypotonic, hypertonic and isotonic solutions.


The experimental design was divided into two parts. The first part was based on the observations of osmosis within cells. The second part was based on determining the osmotic behavior within cells. The first section of the experiment involved the use of tubes and solutions in observing osmosis in cells. In the experiment, four tubes were used. These tubes were filled with variable quantities of solutions in different containers that also possessed different quantities. 200ml of DI water was poured into a 250 ml beaker; 150ml of a 25 percent sucrose solution was poured into a 250ml beaker while 450ml of 1 percent sucrose solution was poured into a 1l beaker. Consequently, a piece of 40cm dialysis tubing was cut into four pieces of 10cm each. A 10ml pipette was used to dispense 3ml of 1 percent sucrose solution into two cut pieces of the tied dialysis tubes. Additionally, the top of the tubes were folded loosely and squeezed to dispel air bubbles. Moreover, the folded tops were tied with strings and parts of masking tape were attached to the strings in order to enable the labeling of tube A and tube B. Consequently, a piece of glassine paper was positioned on top of a loading balance to secure it from sugar and water. Accordingly, the tubes were weighed to 0.1g. Utilizing the similar procedure, tube C was created by allotting 3ml of 10 percent sucrose and tube D was created by allotting 3ml of 25 percent sucrose. Tube A was positioned within the beaker with 25 percent sucrose while tubes B, C and D were placed within the beaker with 1 percent sucrose. The weight was recorded after one hour (Fultz, 8).

The second section of the experiment commenced through creation of a blood cell through the Wet Mount technique, which involved dropping 1ul of blood on a slide while using a 40X objective lens. The technique was redone but with extra amounts of 10 percent or 0.9 percent of Sodium Chloride (NaCl) or water. This procedure was repeated using plant cells from the Elodea leaf within the slide (n.a, 2012).


The results for the first part of the experiment were recorded in Table 5-1. The experiment, which was based on the use of different tubes and different containers each with different concentrated solutions, did not match the hypothesis of the first experiment. Table 5-1 illustrated the Weight in Time that ranged from periods of 0 to 60 against the Sucrose solutions within the tubes and the containers.

Table 5-1: Observations of Osmosis

Sucrose SolutionWeight (g) of tube at time (min)LabelTube Container015304560A1%25%


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