Osmosis Internal Assessment (Biology)

5. Materials and Apparatus

6. Procedure

1. Pour 10ml of distilled water (H20) into the 10ml measuring cylinder. Pour the 10ml of distilled water into a test tube.
2. Repeat step 1 24 times such that there are 25 test tubes (5 to every test tube rack) each containing 10ml of distilled water (H20).
3. Using a cylindrical borer, bore 5 cylindrical strips (1cm in diameter) out of a Potato.
4. Using the ruler, measure each strip and cut into pieces that are 4 cm long.
5. Place each potato strip on a fresh paper towel to drain off excess juices.
6. Place a fresh paper towel on the electronic weighing scale, set the scale to zero, then weigh each potato strip on the fresh paper towel, ensuring each weighs 3 grams. Cut off any excess with a scalpel if necessary.
7. Place each of the 5 potato strips into a test tube containing 10ml of distilled water on the same test rube rack.
8. Immediately cover the test tubes with a 3cm by 3cm piece of aluminium foil. Start the stopwatch.
9. Label the test tube rack: “immersion duration of 5 hours”.
10. Repeat steps 3 to 9 4 times with a label for 4 hours, 3 hours, 2 hours, and 1 hour accordingly, in descending order (label the first repeat 4 hours, the second repeat 3 hours, the third repeat 2 hours, and the final repeat 1 hour).
11. After 1 hour from the starting time, using forceps, remove the potato strips labelled “immersion duration of 1 hour” from the respective 5 test tubes. Place them on fresh paper towels to allow excess juices to be drained.
12. Place a fresh paper towel on the electronic weighing scale, set the scale to zero, then weigh each potato strip on the fresh paper towel, record their respective weights.
13. Repeat steps 11 to 12 for the potato strips labelled “immersion duration of 2 hours”, followed by those labelled 3 hours, 4 hours, and lastly, 5 hours.
14. Dispose of all used material appropriately. 

7. Results

Table 1. Initial and final mass of the potato strips after immersion in distilled water () over a period of five hours at one hour intervals

        *Note that the initial mass of all the potato strips are the same

Table 2. Mean, standard deviation, and 33.33% of the mean for the final mass of potato strips immersed in distilled water ()

*As the Standard Deviation is less than 33.33% of the mean for all the values of final mass of the potato strips, it can be seen that these mean values are accurate.

Graph 1. Mean and Standard Deviation for the final mass of potato strips immersed in Distilled Water ()

Table 3. Change in mass of potato strips immersed in distilled water () with mean ±0.1g, standard deviation, and 33.33% of mean

*The + and – signs indicate increase and decrease in weight respectively
*As the Standard Deviation is less than 33.33% of the mean for all the values of final mass of the potato strips, it can be seen that these mean values are accurate.

Table 4. Percent change in mass and mean percent change in mass of potato strips immersed in distilled water ()

Graph 2. Mean percent change in mass of potato strips immersed in distilled water

8. Calculations Involved

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9. Conclusion

As seen in graph 1, as the duration of the immersion of potato strips in the solution increased, the mass of the potato strips generally increased. This was in line with my predictions because the distilled water had a higher water concentration than the potato strip, thus making it hypotonic, and allowing water to travel from the region of higher water concentration (water solution) to the region of lower water concentration (potato strip). When a longer period of time was given for osmosis to occur, a plateau in the mass of the potato strips could be seen whereby most of the potato strips stopped increasing in mass at 3.6 grams, indicating that after 4 hours of immersion in the distilled water, the potato cells had become turgid and that the net movement of water molecules was equal to zero. Here, the water solution had turned isotonic and the movement of water into the cell equaled the movement of water out of the cell, resulting in a general trend where no further changes in the mass of the potato strips were observed after 4 hours.

        For all of the values for which standard deviation and 33.33% of the mean were calculated, the standard deviation was less than 33% of the mean, indicating that the results were accurate and reliable. Therefore, no anamolous results were removed from the processing of the raw data. However, there was a noticeable difference in the change in mass of the potato strips between those that has been left in the distilled water for 2 hours and 3 hours.  The difference between the two was 0.3 grams while the differences between the one hour intervals for all the other time intervals was only 0.1 grams, and after processsing the raw data, mean percent change of the mass of the potato strip at 2 hours did not fit in graph 2 as well as the other values did, this is to be discused in the evaluation.*

10. Evaluation

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