Osmosis in potato cells.

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Roxana Jahanshahi

Osmosis in potato cells.

I will be using potatoes to find out the rate of osmosis in plant cells as the concentrations in a solution increase.

Preliminary Test

Apparatus:

  • Ruler
  • Scalpel
  • 1 Potato
  • 3 Test Tubes
  • 10cm³ Measuring Cylinder
  • Test Tube rack
  • Distilled Water
  • Weak sodium chloride solution (8.5%)
  • Strong sodium chloride solution (17%)

Method:

  • Cut 3 chips of potato to the exact same size
  • Using a ruler measure their length and record it on a table.
  • Fill 3/4 of the test tubes
  • One with Distilled Water
  • One with Weak Sodium Chloride Solution
  • One with Strong Sodium Chloride Solution
  • Place a potato chip into each test tube and record it onto your table and leave them there for 30minutes
  • Remove the chips from the test tube after 30 minutes have passed
  • In order to remove any excess liquid place the potato chips on a paper towel
  • Measure each chip and re-measure the length and record it on the table.

Results:

 

Conclusion:

There was a variation of osmosis in each of the potato chips depending on the concentration of the solution. As the concentration of solute increased the length of the potato chip decreased. The potato chip that was in the least concentrated solution (distilled water) increased in length by 7.5% and the chip in the most concentrated solution (strong sodium chloride solution) decreased in length by 5%.

I believe that the reason for the increase in length of the chip in distilled water was due to the turgidity.  The cell sap in the vacuole is a strong solution and is more concentrated than the solution surrounding the cell. The partially permeable membrane permits the water molecules to move into the potato cell. When this happens the cell swells up and eventually the cell is saturated with water and is unable to hold anymore. When there is an increase in length the cell is turgid.

There is no change in the weak sodium chloride solution this may be due to the fact that the solution inside the cell and surrounding the cell have an equal concentration.

The potato chip in the strong sodium chloride solution decreased in size. From our knowledge of plasmolysis we can understand that the concentration of solution inside the potato cell is higher than that surrounding the cell. As the water molecules pass out of the cell the sap vacuole begins to shrink and the cell becomes flaccid.

Planning:

The effect of varying solute concentrations on the process of osmosis in potato cells.

The aim of this experiment is to see the effects of various concentrations of sodium chloride on osmosis. I will be looking at how potato chips are affected by varying concentrations of sodium chloride solution. I will use my preliminary results as a guideline for what to expect on my final experiment. In the final experiment the potato chip will decrease in length/mass as the concentration of solute in the solution increases. The potato chips placed in an isotonic solution will show little/ no change, the chips placed in a hypertonic solution will lose mass.

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For my final experiment I will:

  • Take more readings at more frequent intervals. Every 30minutes for 4 hours.
  • Measure my potatoes in a more accurate way
  • Use a larger gradient of solution concentration ranging from 0M(Distilled water), 0.2M, 0.4M, 0.6M, 0.8M, 1M, 1.2M, 1.4M, 1.6M, 1.8M 2M. The Distilled water will act as a control to compare the results with.  
  • Use more potato chips for each concentration. E.g. 3chips per concentration.
  • Measure my chips by mass instead of length, as it is more accurate.
  • Use a cork borer to cut the chips to ensure that ...

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