Discussion

Discussion

The results show that with increased haematocrit there's decreased osmolarity.  There's increased haematocrit with increased 1/osmolarity.

When cells are placed in a solution of lower osmolarity that themselves, water enters the cell and the cell will swell dn then the cell will burst if it gets large enough. If the cell is large then the haematocrit value wil be higher.  Hence high haematocrit corresponds to low osmolarity.

Cells are about 60 % water.  A cell can expland quite a bit befoe it rupturs.

Discussion

When red blood cells are suspended in solutions with an osmolarity lower than their internal environment, water enters the cells via osmosis causing the cells to swell. The greater the difference in osmolarity between the internal and external environment, the greater the amount of water entering the cell, and hence the greater the cell will swell. Therefore, the lower the osmolarity of the NaCl solution, the larger the red blood cells will be in that solution and the higher the haematocrit reading.

Haematocrit is a measure of the percent volume that red blood cells occupy in relation to the volume of the whole blood (Berne & Levy 1998).  If the cells are larger due to swelling, it follows that the haematocrit will be higher.  Hence, the lower osmolarities of the external solution corresponds to larger haematocrit values (Figure 1).

Cells placed in very hyposmotic solutions will swell so much that they will eventually burst. These cells will no longer contribute to the haematocrit values and hence a decrease in measured haematocrit should be observed at very low osmolarities.  This is not apparent from the trend line fitted to our data but if you examine the measured haematocrit values, the value obtained at an osmolarity of 0.19 Osm L^-1 (54 %) is lower than that obtained at 0.20 Osm L^-1 (56 %). A dotted line has been hand drawn on the graph to show this decrease in haematocrit. This suggests that if measurements had been made from solutions of even lower osmolarity we may have seen a consistent decline in haematocrit.

Note that on the graph of Haematocrit versus 1/Osmolarity, a line marking where the isotonic point lies has been inserted.  From these results, one can conclude that the haematocrit of a normal sized red blood cell is 37 %, which is similar to the text book value of 45 % (Berne & Levy 1998). Infinitely high NaCl solutions will cause the cell to shrink to a minimum volume corresponding to a haematocrit value of 5 % (Figure 2).  When the cell has shrunk to this theoretical volume, no water will remain inside the cell.

The study of osmosis is important not only to understand the meaning of the different terms but also to understand the conditions in which our cells will change shape and size in real life. Homeostasis, the maintenance of constant internal conditions, is very important in the body (Boron, 2007). Using red blood cells as an example, their biconcave shape is essential for their function in carrying oxygen in circulation and a decrease in red blood cells (due to hypotonic plasma or otherwise) can cause severe disorders like anaemia (Zohdi & Kuypers, 2006).