Cell Membrane Diffusion Report

ii. Diffusion (Dialysis) through model membranes
Cell membranes play a major role in the differences in composition and concentration of the extracellular and intracellular fluid. Cells are selective for which molecules can diffuse through their membranes. Nonpolar, hydrophobic molecules such as O2 can cross the phospholipid bilayer with ease. Small molecules such as water can also cross the membrane but at a slower rate due to its polarity which make it difficult to pass through the hydrophobic regions of the membrane. Ions and large polar molecules that are hydrophilic require another form of entry into the cell membrane. Proteins that function in transportation can permit the passing of these types of molecules as needed. Transport proteins

After 8 minutes the three cubes were removed and we measured the distance the vinegar diffused. We then calculated the percent of the cube which vinegar entered for each cube. As observed from our results, the size of the cubes did not change the rate at which vinegar diffused. The rate of diffusion was the same for all cube sizes. The distance the vinegar diffused was the same for all cubes because the rate of diffusion was not affected by the size of the agar cubes. Factors that may have affected rate of diffusion would be heat or concentration gradient, but these variables were kept the same in our experiment. We did however observe a difference in the percent of the cube that vinegar entered. At the same rate of diffusion, we saw that vinegar could diffuse through a greater value of surface area with smaller cubes. An increase in cube size lowered the percent of cube that vinegar entered. This is because the larger cube has a greater volume, so at the same rate of diffusion the vinegar would take longer to cross through a greater volume than it would a smaller volume. Eventually the vinegar would be able to diffuse through the entire cube, but the larger the cube size the longer it would take the vinegar to diffuse through entire volume of cube, even at the same rate of