When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid"; this is the exact opposite of "turgid". If you put plant cells into concentrated sugar solutions and look at them under a microscope you would see that the contents of the cells have shrunk and pulled away from the cell wall: they are said to be plasmolysed.
When plant cells are placed in a solution, which has exactly the same osmotic strength as the cells, they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means, "about to be". Although the cells are not plasmolysed, they are not turgid and so they do not hold the leaves up into the sunlight, they droop.
APPARATUS: Cork borer, potato, test-tubes (6), salt solution NaCl (1M), water (H2O), measuring cylinder (10cm3).
DIAGRAM:
Table of Concentration:
TEST TUBE Volume (NaCl) Volume of water Conc.n Total Volume
(cm3) (cm3) (dm3) (cm3)
1 0 10 0.0 10
2 2 8 0.2 10
3 4 6 0.4 10
4 6 4 0.6 10
5 8 2 0.8 10
6 10 0 1.0 10
Fair Test:
I will keep these factors the same throughout the experiment: Length of potato chip, total volume of test-tube and the time of immersion.
Safety
In any experiment, safety is always a VERY important factor.
REMEMBER: Only use the cork borer when the potato is on a tile, and always point the borer downwards. There is also a use of sharp knives in this experiment. Take care when handling your knife. DO NOT be silly. DO NOT run around the room at any point, especially whilst holding sharp or dangerous apparatus.
Prediction:
I predict that due to more water entering the cell than leaving, the potato chip will swell up.
- If the medium surrounding the cell has a higher water concentration than the cell itself, the cell will gain water by osmosis.
Water molecules are free to pass across the cell membrane in both directions, but more water will come into the cell than will leave. The net result is that water enters the cell. The cell is likely to swell up.
- If the medium is exactly the same water concentration as the cell there will be no net movement of water across the cell membrane.
Water crosses the cell membrane in both directions, but the amount going in is the same as the amount going out, so there is no overall movement of water. The cell will stay the same size.
- If the medium has a lower concentration of water than the cell (a very concentrated solution) the cell will lose water by osmosis.
Again, water crosses the cell membrane in both directions, but this time more water leaves the cell than enters it. Therefore the cell will shrink.
RESULTS:
Results Table:
Results 2:
Graph:
Conclusion:
As we can tell from the graphs, there is a definite relationship between the dependent and independent variable; I.E. that as concentration of the NaCl salt solution increases, the length and change in length both decrease. I believe that this is because as concentration of salt solution increases, the cell will lose water by osmosis, become plasmolysed and shrink. In my prediction, I predicted the opposite of this because I did not take into account, the concentration of NaCl solution and what its effect would be.
Evaluation:
I feel that the procedure that I used was very effective. I used my time well and got everything that needed to be done, done in the time given.
The quality of my results was generally good. However, the graph flowed in the opposite direction that I had expected it to. One point is anomalous. At 0.8 concentration of NaCl, the change in length was –0.34, whereas both the previous and latter figures were both –0.54. I believe that this could be because of several reasons. It could have occurred from my measuring, I may not have measured the length accurately. Also, the potato chips in question may not have been fully immersed in the salt solution.
I feel that my evidence is valid. I think the experiment was overall a fair test. The time of immersion was kept the same, as were the total volume of the test tube and the original length of the potato chip. I think, however, that the anomalous point was not kept under fair test conditions. I, overall, believe that my results are sufficient to sustain my conclusion. When I was carrying out my experiment, I found that I had no difficulties in any aspect of the method. If I were to do the experiment again, I would not make any changes to the method, nor any equipment I selected, because I found out from the experiment that my results could be used to answer what I was trying to find out.
