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The Impact of Sodium Chloride Concentration on the Mass of Potato and Sweet Potato Cells

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The impact of sodium chloride concentration on the mass of potato and sweet potato cells


Osmosis is the process of diffusion of water molecules. Through osmosis, water molecules travel from areas of high concentration, to areas of low concentration through a semi-permeable membrane. (BBC. 2014) It also describes the movement of a solvent across a semi permeable membrane. (GCSE (2016) Water moves both ways, depending on whether solution is hypertonic or hypotonic determines whether the water molecules enter, or escape the cell. If the solution is hypotonic (meaning less than) to the cell, the water molecules enter the cell. If the cell solution is hypertonic (meaning greater than) to the cell, the net flow of water escapes the cell. If the solution is Isotonic (meaning the same to) to the cell, there is no net movement of water. (Khan. (2018). Potatoes contain water and starch, and will gain water mass when submerged in watery solutions, contrarily, when immersed in concentrated solutions such as Sodium Chloride (NaCl) the potatoes will lose water mass. (Lobo, T. (2018).  Sweet potatoes have a higher concentration of sucrose, therefore the sweet potato strips has a lower solute concentration. Thus, when submerged amongst the NaCl solutions, there is less of a drastic change in weight due to the hypo and hypertonic solutions (Botanical Online. (2018). 


To investigate the effect of osmosis on the average percent change in mass on potatoes and and sweet potatoes.


As the concentration of the NaCl solute increases, the mass of both potatoes will change due to osmosis. However, the potato will reach an isotonic point at a smaller concentration of NaCl, in comparison to the sweet potato.

Independent Variable:

The change in concentration of the NaCl

Dependent Variable:

The average percent change in mass of potatoes.

Constant Variable:


How they are kept constant

Why they are kept constant

Time of each trial

  • each trial is left for exactly 20 minutes
  • This factor ensures that it is a fair trial.
  • Keeping this the same makes sure that as each trial is tested the same period of time, it allows the data to be similar among the three trials

NaCl concentration

  • 20mL of each solution is used
  • Keeping this consistent is important as different amounts of concentrations have different effects
  • If 10mL of solute is used, the potato strip might not be fully exposed, causing an effect on the results

Size of the test tube

  • test tubes used include the same dimensions
  • allows the same room for each potato strip to be covered by each solution


  • 15 test tubes
  • 3 test tube rack
  • concentrations of NaCl (0, 0.5, 1, 2.5, 5)
  • scales
  • knife
  • sweet potato
  • potato
  • measuring cylinder
  • paper towel
  • labels
  • timer


Step 1: Label 5 test tubes with the different concentrations of NaCl (0, 0.5, 1, 2.5, 5)

Step 2: fill the 5 test tubes with the required solution measurements, 20mL of each solution

Step 3: Cut 5 strips of potato and sweet potato (ensure they are approximately the same size)

Step 4: cover the scales with a piece of paper towel, and tare the scales

Step 5: weigh each strip of potato, and record the data

Step 6: At the same time, place one strip of potato and one strip of sweet potato in each test tube

Step 7:  Start timer for 20 minutes and leave the trial aside

Step 8: (repeat steps 1-7 until two replicated trials are made)

Step 9: Once the timer has finished, immediately pour out the solution, while ensuring that the strips of potato remain in the test tubes

Step 10: cover the scales with a piece of paper towel, and tare the scales

Step 11: One by one, remove each strip of potato and sweet potato, and lightly blot them with paper towel

Step 12: weigh each strip of potato, and record new results

Step 13: (Repeat steps 9-12 until the results of all replicated trials have been recorded)

Risk Assessment:

Generally, this practical is fairly safe. However, it is crucial that the knife is used with caution in order to prevent injuries. It is also important that the NaCl solutions are kept a safe distance away from the electrical outlet, to prevent the solute from spilling into the outlet.


The results given in table one shows that the results throughout trial two there were traces of random error. In order to minimise the effect, the data from trial 2 was not included in the figure 1. Figure 1 shows that the sweet potato reached an isotonic point with a higher solution which is at approximately 4% NaCl in comparison to the potato with an isotonic point of approximately 1.1% NaCl.


The results given in both table 1 and figure 1, support the scientific theory that forms the hypothesis. The sweet potato and potato had different isotonic points, and a clear indication that there was less of a difference in percent change of the mass of the sweet potato in comparison to the mass of the potato. The two experiments had different isotonic points due to their different characteristics and densities. Therefore, the sweet potato requires a higher concentration solution, in order for the solution to be hypertonic to the cell. In table 1, it is evident that in trials 1,2,3 of the change in mass of the potato with the NaCl concentrations of 2.5 and 5%, these results show minimal traces of scatter, and there is no clear outlier. Therefore, these results are considered precise. However, the data given in the average percent change of trial two for both sweet potato and potato, there were large amounts of scatter. Thus, these results are not precise, and were not included in figure 1. These results are due to random error. By excluding the data from trial two, it removes scatter, therefore making the results more precise and more reliable. In order to determine accuracy amongst the results, the data given in table 1 and figure 1 were compared to the results of the same experiment conducted. Figure 2 shows a graph that displays data from another experiment conducted with similar concentrations of NaCl The data in figure 2 indicates that there was an isotonic point of the potato at approximately 0.25% NaCl, however, the data in figure 1 displays an isotonic point of approximately 1.1% NaCl. Although, this comparison in results do not take into consideration the initial weight and final weight of the potatoes across both experiments, and the time that the potato strips were left in the solute’. Therefore, in order to deem these results accurate, the experiment will need to be conducted again, where the weight of the potato strips are approximately the same, and the potato strips were left in the isotonic solution for equal periods of time. Random errors that may have caused variation amongst the results include inconsistency among the blotting of the potatoes, when drying the potato. There may have been large droplets of water that remained on the potato strips when recording the data of the final mass. This error may have had an affect on the data, by causing variation amongst the mass of the potatoes. Therefore, minimising the precision of the data. An example of systematic error that may have caused the results to be inaccurate amongst trial two, was an error in the method. An example of this is during trial two, when placing the sweet potato strips in the test tube, some strips did not fit properly into the test tube, therefore causing a percentage of the solution to overflow, from the test tube, therefore there was inconsistency in the amounts of solute amongst each trials. Thus, having an effect on the results which caused inaccurate results.



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