Investigating the osmotic effect of different solutions on red blood cells

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Investigating the osmotic effect of different solutions on red blood cells


In this lab we wanted to understand the osmotic effect that varying solute concentration has on erythrocytes. Osmosis is the way water molecules pass a selectively permeable membrane down a concentration gradient. Osmosis was demonstrated when six different solutions of glucose, sodium chloride and distilled water were mixed with red blood cells and the clarity of the solution against printed text was recorded and viewed under the light microscope, recording any changes to the cells observed and expecting a change in blood cells with varying solute concentrations. The results obtained indicate that water molecules indeed move from high concentrated solutions to a low concentrated one and imbalance in water in solution can lead to cell bursting or shrinking.


The purpose of the lab was to test the effect that change in solute concentration of the environment have on red blood cells , The hypothesis tested was that osmosis should occur based on the solute concentration on the outside of the red blood cells. The membrane of blood cells are permeable to water molecules therefore there is a constant movement of water molecules across the membrane of the blood cell in a process of Osmosis, Osmosis is the net movement of water molecules from a region of high water potential to a region of low water potential (Bradley and Calvert, 2006), the movement of water around various parts of the body is governed by an importance force known as the osmotic pressure (Joshi, 2009). Osmosis is vital for living organisms, influencing the distribution of nutrients with the release of metabolic waste products such as urea. Blood is the connective tissue which carries the nutrients in its non-living matrix called the plasma (Marieb, 2012) if blood cells were to be surrounded in an isotonic solution, they will neither shrink nor swell which is ideal. However, if the solution is hypertonic, the cells will lose water and shrink; our body’s physiology will try to maintain a balanced environment so that blood cells remain unaffected.

Areal life example of osmosis occurring is during the filtration process, which takes place in the kidneys. Over 80% of the filtrate is reabsorbed into the tissue fluid and thenintothe blood which ensures that majority of the useful materials such as glucose and amino acids that were filtered out of the blood get returned back to the blood. Patients with kidney failure are unable to remove such waste products however hemodialysis acts as an “artificial kidney” (Schrier, 2007) which circulates the patient’s blood through a membrane tubing immersed in a solution in order to get rid of the waste products in the blood (Marieb,2012 Page 520) giving a person with a chronic illness such a useful treatment.


A table is drawn out to record the results. Six test tubes individually labelled A-F were prepared. 2ml of the following solutions were measured using Pasteur pipettes -0.9% sodium chloride, 10% sodium chloride, distilled water, 20% glucose, 5% glucose and 0.5% glucose. An immaculate Pasteur pipette was used to add 2 drops of horse blood into test tube labelled A, the tube is inverted in order to mix the content. Test tube is held in front of some text and the clarity of print seen through the test tube is recorded. The same procedure is repeated on remaining test tubes and the clarity was also recorded. Small sample from test tube A is obtained and one drop is placed on a microscope slide, a cover slip is placed on top and the slide is viewed under a light microscope at x400 magnification, the shape of the cell and the effect of the solution is observed and recorded, This is repeated for the other test tube samples.


Table 1 are the results for each test tube which contained different solutions with 2ml of horse blood mixed, the concentration of the solution in the test tube were determined by the clarity of the print and also describe the slides when viewed under the microscope.



Clarity of print

Cell under the microscope (x400 magnification)

Hypertonic ,Hypotonic or Isotonic

A 0.9 % Sodium chloride solution

Not Clear

No change to cells


B 10% Sodium chloride solution

Not Clear

The cell shrunk in size

Addition of distilled water decreased the number of cells present.


C Distilled water


The cells got bigger in size and number of cell under microscope decreased after a while


D 20% Glucose solution

Not clear

The cell shrunk in size


E 5% Glucose Solution

Not clear

No change to cell shape or number


F 0.5% Glucose solution


The cells shrunk in size and an increase in surrounding moving cells



Results obtained from the experiment clearly show how osmotic pressure can make a difference to the cells based in the solution that it is in supporting my hypothesis. The blood cells in the 10% NaCl solution were crenated; we know this because all the cells viewed were considerably smaller. The cells in the 0.9% NaCl were viewed as normal with few or no changes. The cells in the distilled water were either enlarged, or haemolysed. We know this because the cells in the viewing field were much bigger, but there were very few of them because many had burst. The cells placed in hypotonic solution lead the solution to become clear red and the print to become visible where as the cells placed in hypertonic and isotonic solution was very cloudy and the print was not visible.

The human kidney is a complex organ primarily responsible for osmoregulation of fluids and electrolyte whilst also excreting waste products from the blood through the production of urine (Bradley and Calvert, 2006) The kidneys also perform other vital roles such as maintaining the internal conditions known as homeostasis, regulating blood pressure and osmotic pressure (Stellman, 1998) therefore the movement of water in and out of blood cells are important in order to fulfil these roles.

Cells placed in 5% glucose and 0.9 NaCl also known as saline are isotonic which had no change to the cells because the solution has the same solute and water concentration as the plasma fluid therefore the movement of water is balanced due to the equal osmotic pressures, interstitial fluid and most intravenous fluids are isotonic to the cells so that the blood cells remain unchanged, the table shows that cells infused in distilled water lead the blood cells to become larger as water keeps entering the cell due to the solution being hypotonic to the cell with low solute concentration causing the cells to swell (Clayden, 2001), the number of cells also decreased as too much water entering the blood cells caused the cells to burst and release haemoglobin in a process called haemolysis (Guyton and Hall, 2006) and the print becomes clear because the red blood cells have haemolysed and thus do not diffract light. Cells placed in hypertonic solution such as the 20% glucose causes the cells to shrink in size since water moves from inside the cells to the outside because the solution has greater tendency to pull water but the print was blurry as the cells were intact causing light to diffract (Marieb, 2012 page 84).

The methodology used to see the clarity of the print was subjective for each person however using a colorimeter would have been a better way of determining whether the solution was clear or not, however using the samples on the microscope was a very precise way on measuring the effect as it was easier to observe the changes in the cells nonetheless a haemocytometer could have been used in order to measure the blood cell concentration quantitatively.

The body requires minimum water intake of 1 Litre and dehydration occurs when fluid loss becomes greater than amount consumed , during dehydration the loss of body fluids causes a rise in blood solute concentration that increases in osmolality,In attempt to regain fluid balance the levels of sodium rises by shifting water molecules out of the cells and into the blood, usually reforming the imbalance but without sufficient water in the extracellular space ,water continues to shift out of the cells and into the space, causing the cells to shrivel as established in the hypertonic test tubes which leads to a decrease in blood volume and also affecting thermoregulation leading to other serious complications such as life-threatening hypovolemic shock (Sembulingam and Sembulingam, n.d.)

In conclusion from the lab conducted it can be seen how osmosis can make a difference to cells based on the solution it is in, In an isotonic solution the cells did not change in size, in a hypertonic solution the cells experience shrinking and in a hypotonic solution the cells haemolysed. The findings provide explanation as to what happens to blood cells in surroundings of different osmotic pressures and the movement of water molecules during osmoregulation and abnormal function of homeostasis controls may cause conditions such as edema.


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