Osmosis Investigation

December 00 Osmosis Investigation Andrew Muckles

My Understanding of Osmosis

Osmosis is the diffusion of water from a dilute solution (with many water molecules) to a more concentrated solution (containing less water molecules) through a semi permeable membrane. The semi permeable membrane only allows the passage of the water molecules from the solutions and not the solute molecules. The movement of the water molecules will continue until they are evenly spread on both sides of the semi permeable membrane.

Below is a diagram of a turgid plant cell that cannot hold any more water. This is a healthy plant cell.

It is important that a plant has plenty of water in its cells in order to stay healthy. Below is a flaccid cell that does not contain much water. This is an unhealthy plant cell.

If a plants cells are flaccid the plant wilts. This is because it does not contain enough water in its cells to stay healthy.

Investigation Procedure

My practical investigation of osmosis will go as follows. Firstly I will cut the potato into six equal pieces. These will be approximately 30 millimetres in length and 4 millimetres in width. I will measure the length of each of these and record it in a result table. I will then pour 10mls of each of the solutions into six separate test tubes. The test tubes will be put onto a test tube rack. I will then put one piece of potato in each of the test tubes. When they are all immersed in the salt solutions I will start the stopwatch and wait for 30 minutes. After 30 minutes I will remove the potato out of each of the test tubes and measure them. I’ll record the measurements in a result table. These results will be plotted on a graph, which will show me where osmosis has occurred. The results will also show me where osmosis has not occurred and where the plant cells have became turgid, flaccid or plasmolysed. Further information I will gain from my investigation will be which strength solution matched that of the cytoplasm of the plant cells.

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To make my investigation fair I will have to take into account certain pointers: -

The pieces of potato are identical in size before testing.
The amount of salt solution in each test tube is the same.
The pieces of potato are immersed in the salt solution for the same amount of time.

Risk Assessment

Risk assessment is important for safety means in my investigation. Hazards are when cutting the potato, cutting someone nearby or myself, using the salt solutions, they could be spilled onto the floor and someone may slip over or getting a solution into ...

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To make my investigation fair I will have to take into account certain pointers: -

The pieces of potato are identical in size before testing.
The amount of salt solution in each test tube is the same.
The pieces of potato are immersed in the salt solution for the same amount of time.

Risk Assessment

Prediction

I predict that the potato immersed in the most dilute salt solution will grow the most. This is because diffusion of the water in the solution will move by osmosis into the potatoes plant cells and make them turgid. The extra water molecules will make it larger than before. I will also predict that the potato immersed in the most concentrated solution will decrease in size. This is because the potato contains more water molecules than the solution so will therefore, by the process of osmosis, move into the solution the potatoes water molecules. I think that one of the solutions at molar 0.3 or 0.4 will leave the potato at the same size because it will have roughly the same amount of water molecules as the potato contains in its cells. A solution with molar 0.6 is more concentrated than that of molar 0.1.

Equipment

Six pieces of potato
Measuring equipment
10 mls of each salt solution
Six test tubes
Test tube rack
Measuring cylinder
Scalpel
Safety Eyewear

Results

My experiment went well and I have gained two sets of results entirely for accuracy. Here is my result table: -

Conclusion

In conclusion I believe osmosis has occurred well in my experiment. From the result table above and the graph of results below, osmosis can easily be spotted. It seems that the cells gained the most water in the distilled water and the least concentrated 0.2 molar solution. Also the most concentrated 0.6 molar solution lost a lot of water. I think that the cells in the 0.3 and 0.4 molar solutions have a similar amount of water in them to the potato cells because they did not lose nor gain any water. So at these concentrations, there are equal numbers of water molecules on each side of the semi permeable cell membrane. The flow of water on each side is equal. The general pattern is that the stronger the salt solution, the most water lost and vice-versa.

Evaluation

In all experiments, improvements can be made. Noticing these improvements is the tricky job if your experiment went well. I have noticed a few improvements that could have been made to make a more accurate set of results for my investigation.

More accurate cutting and measuring with better equipment would have helped to make sure that the potatoes were already exactly the same size.
A wider range of salt solutions would have enabled me to carry out more tests and get more results to confirm that osmosis had occurred and where.
I could have collated my results with the rest of my class and worked out a better average from many different sets of results.
Odd results such as the result for the 0.2 molar solution that had got smaller could have been repeated and a new, more accurate result could have been found.
Lastly I could have used molar solutions like 0.25, 0.3, 0.35 etc. to make my results accurate.