Cell membranes are a selectively permeable phospholipid layer that act as a barrier between the internal and external environments of the cell (Singer and Nicolson 1972). Osmosis is the movement of solvent across a semipermeable membrane from low solute to high solute concentration; osmolarity is the concentration of an osmotic solution. Tonicity describes the relative concentrations of two solutions to determine movement of diffusion of solute across the membrane separating the solutions.
The permeability of the rabbit red blood cell membrane is explored, factors varying the degrees of permeability to different solutes, and the effects on the cell from this movement of solutes and water across the membrane. The resultant effects when rabbit red blood cells are introduced to solutions of varying tonicity – isotonic, hypotonic, and hypertonic – are also observed. The permeability of the cell membrane to various organic solutes based on factors like molecular weights and lipid-water partition coefficients is also studied. The permeability of a cell membrane to a solute does not appear to show a high dependence on the molecular weight of said solute (Finkelstein 1976). The lipid-water partition coefficient, on the other hand, does affect the ease and speed at which molecules cross the cell membrane. It is a measure of the solubility difference of a particular solute between the two immiscible phases of lipid and water; a coefficient equal to less than 1 means a greater amount of that solute is found in water and is hydrophilic, whereas a coefficient equal to more than 1 indicates a greater amount of solute in the lipid phase thus showing hydrophobicity and greater permeability of the membrane to this solute (Leo et al. 1971).
It is hypothesized that this experiment will show crenation of cells in hypotonic solutions, while hemolysis will occur in hypertonic solutions; additionally, while molecular weight will not have a significant effect on permeability to the membrane and resultant hemolysis, a greater lipid-water partition coefficient will result in faster hemolysis.