LIMITATIONS/WEAKNESSES/ERROR IN LABORATORY INVESTIGATIONS
Improving the Investigation
MODIFICATION TO THE EXPERIMENT
HYPOTHESIS Solanum tuberosum L. in masses will decline as the concentration (2%, 5%, 10%, 20%, and 25%) of sodium chloride increases. Potato slices placed in distilled water will have a higher mass percentage due to the cells becoming turgid. BACKGROUND INFORMATION Diffusion is the movement of molecules from a hypertonic (high concentration solute) to the hypotonic (low concentration of solute). There are different types of diffusion one of which is osmosis. Osmosis is the movement of water molecules through a semipermeable membrane that allows only smaller molecules such as water to pass through and prevent larger molecules to enter such as glucose or sodium chloride. Bozeman Biology, 2012) Within osmosis comparison between the different solutions standard terminology is used to describe the differences such as Isotonic, hypertonic, and hypotonic as mentioned earlier. Isotonic is when the solution has an equal concentration of solutes. Hypertonic is when the solution has a concentration of the solute. In contrast, hypotonic is when the solution has a lower concentration of the solute. (Bowen, 2002) Plant cells are known to have strong cell walls that when osmosis allows water to be taken up it swells. However, to prevent the cell from bursting the cells become turgid.
The pressure within the cell rises and gradually the internal pressure has increased to an extent which even water molecules cannot enter. (Nigel D Purchon, 2012) This is convenient for plants as they do not have skeletons, thus their leaves and stems are supported by the pressure of the water. Loss of water by osmosis causes the plant to become flaccid which the plasma membrane withers from the cell wall. (BBC, 2012)
1. Collect the required apparatus.
2. Label five test tubes Distilled Water and place in one column in the test tube stand.
3. Repeat step 2 for 2%, 5%, 10%, 20% and 25%. Place them side-by-side in chronological order. Each row is now the number of trials. Label all the test tubes in the first row “1” then repeat with the other rows with, 2, 3, 4, and 5.
4. Set up the scale.
5. Cut the potato with the cork borer and use the metal rod to push the potato onto a piece of paper towel. Using the ruler measure cut the pieces into 2cm.
6. Place the weight tray on the scale then press “Tare”. Place the potato piece on the scales.
Record results for ‘Initial Mass’. Repeat for every piece of potato.
7. Repeat steps 6 and 7 for all the potatoes.
8. Pour 25cm3 of distilled water into each of the Distilled Water labeled test tubes.
9. Pour 25cm3 of 2% solution into each of the 2% labeled test tubes.
10. Repeat step 8 for 10%, 15%, 20% and 25%.
11. Place one piece of potato into a test tube with distilled water. Repeat using potato pieces from the same pile for the other trials.
12. Repeat step 12 with 2%, 5%, 10%, 20% and 25%.
13. Leave for 24 hours.
14. Record observations.
15. Place the weight tray on the scale then press “Tare”
It appears that Graph 1 represents the relationship between the mass changes and the sodium chloride concentrations (0%, 2%, 5%, 10%, 20% and 25%). The graph displays that there was a major decrease in size mainly in the 2% and only potato pieces in the distilled water were able to increase in mass. 3 Conclusions and Evaluation 3. 1 Conclusion CONCLUSION STATEMENT The aim of this investigation was to test the effect of the varied sodium concentration on the osmosis of potato. This aim of the investigation was accomplished as there were significant differences in the effect of the varied sodium chloride solutions.
Although the data has proven the hypothesis to be false.
Data produced from this investigation reveals that the hypothesis suggested earlier is incorrect. As shown in Graph 1, the average for 2% concentration had a more drastic decrease than the 25% concentration. Thus, disproving the hypothesis which states as the concentration level of sodium chloride increases the masses will decrease in relation. On the contrary, the results suggested a decrease in the concentration of the solution will greater the decrease in mass after a period of time.
For example, the average percentages change for the 2% concentration decreased by approximately 27. 77% in comparison to the average percentages change of 10. 91% of the 25% concentration of sodium chloride. This would suggest that any concentration higher than 2% concentration of sodium chloride would cause the potato cell to become turgid and hypotonic as a result of the higher concentration of water entering the potato cell. By becoming turgid the cell is no longer allowing the diffusion of any molecules into the cell thus preventing osmosis to occur.
The higher the percentage the faster the occurrence of the osmosis causing the cell to become turgid faster and preventing the water molecules enter. With this in mind, questions the reliability of the data despite the evidence of the balanced error bars. The effects of “sodium chloride concentration had decreased the mass as the concentration levels increased. ” (Roberts, et al. , 2009) This investigation supports the hypothesis stated earlier. In this investigation, the results as the researchers were able to conclude on the results of their 0. % decreasing the lease and with their maximum concentration of 2% giving the largest change in mass. However, this investigation was conducted in the time of only 30 minutes, not 24 hours. On the other hand, research “The Effect of Salinity on Osmosis in Solanum tuberosum (potatoes)” provided many similar results and was also conducted in a similar environment. This investigation supports the results obtained in this experiment justifying “0. 1% and 0. 5% declined in mass with a rapid rate” and “10% and increasing, the rate was much slower” (Holler, 2012) . 2 Evaluation Procedures RELIABILITY Measurements were measured with by only one researcher and thus eliminated the possible chances of human error that may occur if the measurements were recorded by multiple people. The trials of this investigation were conducted in chronological order and one-by-one. This process was also repeated five times for each concentration to increase reliability. The standard deviation displayed quite minimal and well balanced which shows there were minimal significant errors that may have occurred throughout the experiment.
However some of the errors that perhaps occurred due to some of the pieces were penetrated by the rod in removing them from the corer, this may have caused some significant error and decreases the reliability of the experiment. Due to the use of the same size potato, it can be assumed that the reliability of this investigation is dependable as there is little differentiation in size. Also, all the potato pieces were from the same potato meaning they were also from the source limiting any uncontrolled variables to occur and increase the reliability of this investigation.
The uncertainties of this experiment were quite minimal however perhaps may have occurred during the process of weighing the mass of the potato pieces due to not pressing ‘tare’ before measuring the mass of each piece, therefore, altering the masses slightly and increasing the uncertainties.
LIMITATIONS/WEAKNESSES/ERROR IN LABORATORY INVESTIGATIONS
MODIFICATION TO THE EXPERIMENT
To decrease the uncertainties a different method could be used to cut the potato pieces simultaneously, therefore, limiting the slightly varied sized pieces. This new method could be lining all 30 potato pieces in a straight line then measuring 2cm and cutting all the pieces in one cut. This new method will likely decrease the uncertainty when cutting the potato pieces. Creating a longer time limit to the investigation would provide time to increase the reliability of this investigation.
By creating a different method to create the potato pieces so that there is no penetration of the use of the rod from the corer. In this investigation, a small corer was utilized along with a bent rod that was used to remove the pieces which caused penetrations in the potato pieces. If this investigation was to be replicated perhaps using a larger corer will be less difficult to remove the potato pieces and decreasing the chances of penetrating the pieces. Another method that could be considered is to not use the corer and cut the pieces manually from the potato, firstly into a rectangular prism or cube.
This method will completely eliminate the chances of penetration of the potato pieces thus, increasing the reliability of the data produced and of the investigation. Modifications to the experiment perhaps include an extension to explore different variables that would affect osmosis. These extensions could be exploring the effect of surface -area, temperature, and perhaps comparison on the use of sucrose solution against the salinity. An interesting extension would be to include a vice-versa investigation to test the effect of the potato pieces to return to its original massif placed in distilled water.