e RBCs, and the loss of their contents (largely haemoglobin) into the surrounding solution (termed haemolysis). If RBC's are placed into solutions of penetrating solutes, the time to haemolysis is an indication of the rate at which the solute is able to cross the cell membrane.
             As the solute enters the RBC's the osmotic gradient for water is increased, causing water to move more rapidly into the cells. Solutions of penetrating solutes are therefore hypotonic, regardless of their osmolarity (Boron & Boulpaep, 2009). Methods Stock solutions of RBCs, washed and re-suspended in isotonic saline, were provided. These were used as osmometers for investigating the membrane transport properties of cells. Changes in cell volume were measured using a light intensity meter (LIM) that gave a voltage output in response to changes in cell volume. The voltage was then recorded using the Power Lab system and the Scope and Chart software. Three sets of experiments were carried out.
             First, the LIM was calibrated using test tubes of isotonic solution with varying volumes of RBC suspension (ranging from 0-200 µL) and recording the voltage output using Chart software. A calibration curve was constructed and used to determine the concentration of RBCs in an unknown solution. The second set of experiments was then carried out in which 200 µL of RBCs
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