Red blood cell permeability—factors that influence the diffusion across a membrane Table 1: Mean and standard error time observed for sheep red blood cell population to achieve transparency. Time is in seconds. Amount of trials (N) is in parentheses. a Solution Distilled water Urea 0.3M a Time of achieved transparency Mean b(N) Standard error <2 0 3.337 0.754 Ethylene glycerol 0.3M 946 7.977 Glycerol 0.3M 1146.1 29.516 Sucrose 0.3M >1200 0 Transparency of red blood cells was obtained when 75% of the sheep red blood population has hemolysed b Three trials were carried out for every solution (N=3) 1. All solutions in this lab are made of penetrating substances. Since the solutes can cross though the cell membrane, it creates an environment where osmosis causes water to rush into the red blood cells, leading to hemolysis. This hyposmotic environment is what caused the suspension of red blood cells to become transparent. A factor that influences this diffusion is the permeability of the erythrocyte to the solute. Factors of the solute that would influence diffusion include the temperature and the pH of the solution, the size of the molecule, and the polarity of the solute. Non-polar molecules diffuse across the membrane more easily than polar molecules. Solutes that contain functional groups such as hydroxide also had an effect on diffusion since these functional groups would make the solute polar. In addition, smaller molecules diffuse across the membrane more easily, where as larger molecules decreases the ability of diffusion. Size has the greatest effect on diffusion. 2. Distilled water is a small and non-polar molecule. Since both factors of the small and nonpolar molecule increase the diffusion of a substance though a cell, distilled water diffused quickly causing hemolysis in the cell instantaneously. Urea similarly obtained hemolysis rapidly since it is a small molecule. Although urea is polar, size has a greater influence on diffusion. The small size of urea allows it to diffuse easily across the cell membrane. Ethylene glycol contains many hydroxide functional groups, which makes it polar. This molecule is also larger in relevance to water and urea. These factors make the molecule diffuse more poorly than distilled water and urea. Glycerol contains a larger amount of hydroxide groups, therefore it is a more polar and larger molecule. These factors caused glycerol to diffuse across the cell membrane poorly, and hemolysis was achieved at a slow rate. Sucrose took the longest time to diffuse since it contains the most hydroxide groups making it the most polar. In addition this, sucrose is a relatively large molecule. Due the polarity and exceptionally large size, diffusion of sucrose is tremendously poor, and transparency of the red blood cells was not achieved in the duration of the lab.
