Osmosis in Potato Cells

Based on this information, he process of OSMOSIS ought to do the following, dependant on the conditions:-

1. In water, the potato cells will gain mass, because the potato cells contain sucrose, which means it has a lower concentration compared to pure water. Thus, water will enter the cells in an attempt to equalise the concentrations. However, because sucrose molecules cannot pass through the semi-permeable membrane, the pure water will never gain any sucrose molecules to lower the concentration of water. The potato cells will not be able to lose sucrose molecules and increase the concentration of water, so the concentrations on either side will not equalise, but instead more water will enter the cell until the cells reach their maximum capacity (becoming turgid) and bursts. This will kill the cell. That is why we cannot leave the potato cells in the solution for too long.
2. In a 1.0 sucrose solution, the potato cells will lose mass. This is because potato cells have more water compared to the sucrose solution. The water molecules will generally migrate over to the sucrose solution (otherwise known as net migration, because some water molecules move the opposite way) in an attempt to equalise the concentrations. As the sucrose molecules from the molar solution cannot enter the membrane though, the concentration of sugar in the water is still too low, and the concentration of sugar in the solution is too high. The result is that more water will attempt to enter the sucrose solution, leaving less water in the cells. Remember, the water cannot be replaced by sucrose. The cells will lose water and become plasmolysed (flaccid).

Aim:                This is preliminary work to determine a suitable range for the

concentration of sugar solutions.

Variables:        Concentration of sugar solution

Constants:        Size of potato chips

                Amount of time for each chip

Equipment:        6 Test Tubes (3 for each solution and repeats)

                6 potato strips

                3 solutions

                Core borer        

                Potato

Results:        We decided to measure the change in mass only; as the length was difficult to measure the there was virtually no difference noticeable to the human eye.

We could not repeat any more due to time constraints.

All masses are in grammes.

All potato strips were of equal size, diameter and length (5 cm). We ensured this by using a No. 2 size core borer. The variation of the results could be due to the fact that not all potato strips were smoothly and perfectly cut, thus an extra bump may contain 500 extra cells.

Evaluation:        There was a change in the mass of the potato strips. In solution A, the mass of the potato chip decreased significantly (20%). In solution B, the mass of the potato chip decreased, but not as much as the chip in solution A (9%). In solution C, the mass of the potato chip increased by 6%. This was after the potato chip had been left in their respective solutions for 30 minutes.

We used 30 minutes because in previous experiments, 30 minutes was sufficient to give us reliable and accurate results.

Using the principles of OSMOSIS, we know that water molecule swill move from an area of low sugar concentration to an area of high sugar concentration to equalise the difference. We also know that water will cause the mass of the potato chip to increase, whilst a sugar solution of 1.0 will cause the mass of the potato chip to decrease.

Since the mass change went from negative to positive between 0.5 mol solution and 0.1 mol solution, we can determine that the solution of the sugar inside the potato cells is between 0.5 mol and 0.1 mol. The next experiment will study the range in smaller increments, thus greater accuracy.

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Aim:                This is the final work to determine the solution strength of the potato cells.

Variables:        Concentration of sugar solution

Constants:        Size of potato chips

                Amount of time for each chip

                Temperature of the solutions (hotter molecules will move faster)

                Standard Atmospheric  air pressure

                Type of potato used

* The whole potato chip must be completely immersed in the sugar solution

Equipment:        5 Test Tubes (each solution and repeat will use the same test tube for economical purposes)

                1.0 molar sucrose solution

                1 Core borer No. 2 size        

                1 Water bath (to keep temperatures constant)

1 Potato

1 Glass beaker (to mix together sucrose and water)

1 Measuring cylinder (for accurate readings)

1 core-borer

1 knife

Digital balance

Filter/Blotting paper

Method:

1. Prepare the solutions by diluting the 1 mol. Solution with the correct amount of water using a measuring cylinder. For example: The 0.3 mol solution will use 3 cc of 1.0 mol solution and 7 cc of distilled water for a total of 10cc. Total amount can change, as long as the proportions remain constant i.e 20cc made from 6 cc of 1.0 mol. Solution and 14 cc of distilled water. Pour into test tubes
2. Prepare the potato pieces. Using the core borer, pierce the potato and extract a roughly cylindrical potato chip. If necessary, cut the ends off with a bladed instrument (preferably a knife).
3. Weigh the potato pieces. The measurements are your starting masses.
4. Insert the potato chips into the test tubes, one every minute. This ensures all potato chips stay in for exactly 30 minutes.
5. Time the chips for 30 minuntes.
6. After 30 minutes, take each potato chip out, one every minutes.
7. Dry it carefully. Do not break the potato chips. Re-weigh the potato chips. The measurements are your end masses.
8. Repeat as necessary

Formulae:

       

This formula is necessary because the only way to properly measure the difference in mass is using percentages.

Results:        

We decided to measure the change in mass only; as the length was difficult to measure the there was virtually no difference noticeable to the human eye.

5 repeats are believed to sufficient for the time allocated.

All masses are in grammes.

All potato strips were of equal size, diameter and length (5 cm). We ensured this by using a No. 3 size core borer, because the No. 2 size borer was unavailable for usage. The variation of the results could be due to the fact that not all potato strips were smoothly and perfectly cut, thus an extra bump may contain 500 extra cells.

The ideal temperature for the water bath would be 50 degrees centigrade. Any colder and the OSMOSIS process will happen slower; any hotter and the water in the solution may evaporate. 

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Conclusion

From our results, we can safely conclude that the solution strength of the potato cells is in between 0.3 and 0.4 mol sugar solution. We could extend this experiment by repeating it with a smaller scale. Instead of using 0.1, 0.2 etc, we could use 0.30, 0.32, 0.34 etc up to 0.40. This would give us an even more accurate result. This could be repeated further as necessary for the required degree of accuracy.

There was a change in the mass of the potato strips. In solution A, the mass of the potato chip decreased significantly (20%). In solution B, the mass of the potato chip decreased, but not as much as the chip in solution A (9%). In solution C, the mass of the potato chip increased by 6%. This was after the potato chip had been left in their respective solutions for 30 minutes.

We used 30 minutes because in previous experiments, 30 minutes was sufficient to give us reliable and accurate results.

Using the principles of OSMOSIS, we know that water molecule swill move from an area of low sugar concentration to an area of high sugar concentration to equalise the difference. We also know that water will cause the mass of the potato chip to increase, whilst a sugar solution of 1.0 will cause the mass of the potato chip to decrease.

Since the mass change went from negative to positive between 0.5 mol solution and 0.1 mol solution, we can determine that the solution of the sugar inside the potato cells is between 0.5 mol and 0.1 mol. The next experiment will study the range in smaller increments, thus greater accuracy. The results confirmed my hypothesis.

Looking at the graph below, we find that the line is not straight; in fact it is a curve. However, 5 data points are insufficient to give us an accurate line of best fit. The curve of the graph indicates diminishing return, for as the solution strength increases, the mass increases but as the mass increases, the rate of increase decreases. So the mass change of a potato chip in a sucrose solution of 0.2 mol compared to a 0.3 mol may be significant, but the mass change of a potato chip in a sucrose solution of 3.4 mol compared to a 3.5 mol solution, although still positive, will be less pronounced.

Research

The potato strips changed mass due to OSMOSIS. When they were placed in a solution with a greater concentration of water, they had to take in water to equalise the concentration inside the cells with the concentration outside the cells. Thus, they absorbed water and increased in mass and turgor pressure the cells become turgid. However, when they were placed in a solution with less water, they needed to lose water to equalise the concentration in the cells with the concentration of the solution. Thus, the vacuole shrunk in size (contains water) and there was less water in the cytoplasm, causing the cell membrane to decrease in size.  Because the cell wall stays fairly rigid, the cell becomes limp and flaccid. The cell is kwon to be plasmolysed and they decreased in mass.

Equal concentrations are impossible to achieve, though. This is due to the fact that the concentration of sugar and water must be equal. However, sugar molecules are too big to fit through the cell membrane, so the sugar levels remain different. Only the water content can change. With OSMOSIS in general, however, when the concentrations are equal on either side of a membrane, it is known as ‘isotonic’.

The skin of the potato was not used, as it contains different cells along with impurities, which would affect the outcome of the experiment.

Evaluation

I believe that the experiments went very well, although the results did vary more than I expected. It could be due to the potato chips having extra cells, or dead/inactive ones. However, I managed to get a smooth curve on the graph. We could now investigate the rate of OSMOSIS, more accurate attempts at the solution strength, different types of vegetables, and the optimal temperature for OSMOSIS.

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