The Effect of Salt Concentration on Osmosis in Potato Cells

 

The potatoes in the lower salt concentration will expand. The concentration of water outside the potatoes has a low salt concentration.  The water outside the potatoes will permeate the cell membrane and the potato cell will swell which is known as hypertonic.

 

The potatoes in a solution where the water concentration would be equal outside and inside the semi-permeable membrane of the potato cell is an example of isotonic; that is, there would be no net movement of water. 

           

 

Method

 

Each of the glasses were labeled with the following: 0%, 1.75%, 3.5% and 7%

1 ½ level teaspoons of salt was place into the beaker containing 100 ml of distilled water and mixed completely. 

50ml was poured into the glass labeled 7%

Distilled water was added to the 100 ml mark for the 3.5 % solution

50ml was poured into the glass labeled 3.5%

Distilled water was added to the 100 ml mark for the 1.75 % solution

50ml was poured into the glass labeled 1.75%

Eight pieces of potato were cut 1 cm x 1cm x 4cm

It was important that the potatoes were cut to this size as exactly as possible.

2 pieces of potato were placed into each of the 4 glasses for 8 hours. 

The potatoes were removed from each glass and patted dry with a paper towel.

The labels from the glasses were removed and placed by the potatoes to identify each set of potatoes

The potatoes were measured and averaged for each set.

 

The variable in this experiment is the water/salt content of the solution.  The assumptions are that time, water temperature and surface area are constant.

 

 

 

Results

 

The findings were that where the salt concentration in the solution was high, the volume of the potato sample declined; that is, the potato sample shrank in size.   Where the salt concentration

was lowest, the volume of the potato increased; that is, the potato swelled.

 

The results are summarized as follows:  

              

 

           

 

Discussion

 

The results can be explained by the theory of osmosis which is the diffusion of water molecules across a semi-permeable membrane.  The tendency of a cell to lose or gain water in a given solution is known as toxicity. The desired state is balance.

 

When the cell is immersed in a solution where solute concentration is essentially equal to the cell it is said to be isotonic; that is, there is no net movement of water. 

 

When the solute concentration is lower than that of the cell, the cell gains water and swells known as hypotonic.   There is a movement of water into the cell that causes the swelling.

 

When the solute concentration is higher than that of the cell, the cell loses water and shrinks known as hypertonic.  There is a movement of water from the cell causes the shrinking.

 

The 0% solution was hypotonic and the 1.75%, 3.5% and 7% solutions were hypertonic.  An incidence of isotonic was not displayed. 

The hypothesis prediction made prior to the experiment were correct except that an isotonic state was not found.

 

The results could have been impacted by the accuracy in the size of the potato samples.  Additionally, the measurement of the potato samples after the experiment was conducted were not exact, the volume calculations could be effected.  The water temperature also could have an impact as the salt must dissolve in the solution.            

 

In a research study to purchase a water filter, knowing about osmosis would be helpful.  Understanding osmosis helped me to understand process of reverse osmosis which basically is osmosis with pressure.  In reverse osmosis, the membrane is used to form a very fine filter. The water is put on one side of the membrane and pressure is applied to stop, and then reverse, the osmotic process. It generally takes a lot of pressure and is fairly slow, but it works.