Osmolarity of Red Blood Cells

Lab: Assessment of Human Plasma Osmolality and the Effects of varying Tonicities on Red Blood Cells

Alberto Herrera

10/01/2013

BIOL 3321 AA

Chrystal Pristell

Purpose:

The purpose of this laboratory experiment was to evaluate the morphology of red blood cells under hypotonic, isotonic and hypertonic solutions of sucrose and NaCl prepared using a literature value for the range of human blood osmolarity.

Background:

Due to their own thermal motion and physics, molecules tend to move down their concentration gradients, from an area of high concentration to an area of low concentration. This process, referred to as diffusion, continues until an equilibrium is reached and no net movement of molecules is seen (although they are still moving back and forth due to their own thermal motion). In this experiment, the effects of different tonicities of sucrose and NaCl solutions on red blood cells were evaluated. When two aqueous solutions of different concentrations are separated by a semipermeable membrane, water moves from the area where it is in its highest concentration toward the area where it is in its lowest concentration by a process known as osmosis (1).

The term tonicity refers to the osmotic pressure gradient of two solutions separated by a semipermeable membrane. Cells are enclosed by such a semipermeable membrane, their plasma membrane, which acts as a physical barrier between the cells internal and external environment. The plasma membrane is partially permeable to water as it is a small uncharged polar molecule. Water is able to cross the plasma membrane freely despite its polarity through integral pore protein known as aquaporins. This is done via facilitated diffusion, as water still goes down its concentration gradient but at a rate much higher than what would be allowed by the chemistry of the phospholipid bilayer without aquaporins (2).

This transport of water across the...