Factors affecting osmosis in potatoes cells.

In my preliminary work I was trying to find out whether NaCl solution would have an effect on osmosis. I thought after a few minutes the cell would go turgid and all stiff, and if I bent it, it would snap.

In my investigation I predict that the longer the potatoes are left in the solution the more osmosis will occur and thus the heavier the potatoes will become. They will also become more turgid.

Method

 My method in my preliminary work was;

1. Cut the potato into two small but fat pieces in similar size using a tile and a scalpel,
2. Once the potatoes were cut you weigh them in the digital scales,
3. Get a test tube and put 20cm³ of NaCl concentration and then get another tube and fill it 20cm³ of distilled water,
4. Put the potatoes in the test tube and leave for 10-15 minutes,
5. Take the potatoes out of the test tubes and leave to dry off the surface water and tip the concentration away,
6. Once the surface water is dried you weigh the potatoes again and that is your final weigh-in
7. you draw a table of results (as in the results section ) and then you obtain the weight gain and weight loss.
8. To see if there is any water in the potato you can snap it. If it bends the potato is plasmolysed and if it is dry and snaps easier than the other the potato is turgid.

Results

        Here is my results table for the preliminary work,

        

I did the experiment with 20cm³ of NaCl solution and 20cm³ of distilled water just to get one lot of results for my preliminary work so that I can make predictions. As you can see the NaCl solution made the potato plasmolysed because when in the test tube the NaCl is a higher concentration than the potato sap, so the sap was drained out making the potato flexible. On the other hand the distilled gained water which means that the cell became turgid and gained water because the water was a lower concentration than the sap and which led to the water being taken in.

When I do the final practical I will need to do the experiment with five different concentrations, which are;

1. 20cm³ 2.0 M/L NaCl
2. 10cm³ x 2.0M/L + 10cm³ distilled water (0.1M/L)
3. 15cm³ x 2.0M/L + 5cm³ distilled water (0.5 M/L)
4. 5cm³ x 2.0M/L + 15cm³ distilled water (1.5M/L)
5. 20cm³ distilled water

Conclusion

        I conclude that when the NaCl is the higher concentration on the outside it will always make the object i.e. potato cells the cell will become plasmolysed and very flexible. If the concentration on the outside is a lower concentration than the inside the cell will gain inn weight and absorb water making the cell very turgid and will snap easily. When I do the investigation for the final time I will make the time the potatoes are in the solutions 15 minutes then osmosis has time to perform.

The Investigation

Apparatus:

• Test tubes/Boiling tubes,
• Digital balances to 2dps,
• NaCl solution 2.0M/L, (for dilutions)
• Distilled water,
• Measuring cylinders,
• Rulers,
• Scalpels and Tiles.

Prediction

I predict that the longer the potatoes are left in the solution the more osmosis will occur and thus the heavier the potatoes will become. They will also become more turgid.

Method

1. I got my scalpel and my tile and cut out 40 pieces of potato out which were roughly the same size and weight.
2. once I had got my pieces of potato I went over to the scales and weighed them to get the weight of the potato before I put them in the solutions.
3. I then got my measuring cylinder and measured out my solutions they were,

                   20cm³ 2.0 M/L NaCl

10cm³ x 2.0M/L + 10cm³ distilled water (0.1M/L)

15cm³ x 2.0M/L + 5cm³ distilled water (0.5 M/L)

5cm³ x 2.0M/L + 15cm³ distilled water (1.5M/L)

20cm³-distilled water

4. once I had made my solutions I put the potatoes in their boiling tubes and left them for 15 minutes
5. Take the potatoes out of the test tubes and leave to dry off the surface water and tip the concentration away,

Once the surface water is dried you weigh the potatoes again and that is     your final weigh-in.

6.          once you have weighed the potatoes you put the results in the same table as the weight before so that you then can calculate the average weight for the potatoes weight gain or loss.

7.   To see if there is any water in the potato you can snap it. If it bends the   potato is plasmolysed and if it is dry and snaps easier than the other the potato is turgid.

Results

Here is my results table,

As you can see from my results table the tubes that had the NaCl solution in them the potatoes weight went down after being in the boiling tubes for 15 minutes rather than the weight increasing like in the distilled water. The weight went down because when the potatoes are in the solution there is a stronger solution on the outside drawing the water out of the potatoes. This happened when the potatoes were in the NaCl solution, but when the potatoes were in the distilled water their weight increased because there is a stronger solution in the potato thus drawing in water rather than losing it.

Here is my graph of the averages,

Conclusion

        I conclude that when the NaCl is the higher concentration on the outside it will always make the object i.e. potato cells the cell will become plasmolysed and very flexible. If the concentration on the outside is a lower concentration than the inside the cell will gain inn weight and absorb water making the cell very turgid and will snap easily.

        If I had to do this project again I would change the way in which we got the potato. I would get a potato borer and get it out that why because then the potato is the same thickness and it can be made the same weight easier than the squares of potato that I had done in my investigation. The evidence wasn’t that great because the potatoes were different size and width and that had an effect on the overall investigation.

        I think that if we done this investigation in the summer we might have had different results because in the summer the potato is a lot drier than in the winter and that might have had an effect on the overall readings. Also if we had a stronger solution perhaps the weight of the potatoes might have gone down even more than they did now because of the stronger solution being on the outside it might have drawn more water out.