Lab 7: Materials and Methods: Performing the Experiment: Direction Change Assay and the Effects of Polypropyelene
Objective:
The objective of this lab is to observe the effects, if there are any, of polypropylene microplastic on the behaviors of Tetrahymena. We observed the simple swim speed assay, the direction change assay, and the vacuole formation assay. I was assigned to focus on the direction change assay. The other objective of this lab was to apply the skills we learned last lab to our lab this week. We also learned how to use serological pipettes with the electronic pump. We continued to strengthen our understanding of calculating concentrations of a solution.
The Tetrahymena medium is made up of the following components:
- Proteose peptone – 5.0 g
- Tryptone – 5.0 g
- Dipotassium phosphate – .02 g
- Distilled water – 1.0 L
Procedure for Direction Change Assay:
- Add a 5 µl of culture to a clean flat microscope slide.
- Place the slide on the dissecting scope.
- Choose a cell to follow for 10 seconds.
- Keep track of how many times the cell changes direction by more than 17% during this time period.
- Record the number of direction changes.
- Repeat for at least 10 cells.
- Record the numbers and calculate the average number of direction changes/second.
- Repeat this process for the cilia exposed to the polypropylene microplastic.
Data:
Table 1: Cell Count Number in 2 µl of Culture:
| Trial | Number of Cells (cells/2µl) |
| 1 | 16 |
| 2 | 5 |
| 3 | 16 |
Cell count: 61667 cells/ml
Table 1: Data on the Direction Change Assay of Tetrahymena:
| Cell # | # of direction changes/10 seconds//seconds spinning |
| 1 | 3//0 |
| 2 | 5//0 |
| 3 | 7//2 |
| 4 | 7//0 |
| 5 | 8//3 |
| 6 | 3//1 |
| 7 | 5//2 |
| 8 | 4//0 |
| 9 | 3//0 |
| 10 | 4//0 |
| Average | 4.9//0.8 |
Table 2: Data on the Direction Change Assay of Tetrahymena Exposed to the Polypropylene Twine Juice:
| Cell # | # of direction changes/10 seconds//seconds spinning |
| 1 | 4//0 |
| 2 | 3//0 |
| 3 | 4//0 |
| 4 | 1//0 |
| 5 | 2//2.2 |
| 6 | 6//0 |
| 7 | 1//2.59 |
| 8 | 2//0 |
| 9 | 3//2.48 |
| 10 | 3//3.13 |
| Average | 2.9//1.04 |
Conclusion:
Based on the recorded data, it can be reasonably stated that there may be a correlation between the presence of polypropylene microplastic and the direction change behavior of the Tetrahymena. As shown by Table 1, the average amount of direction changes per 10 seconds is significantly higher than the average amount of direction changes per 10 seconds of the Tetrahymena exposed to twine juice. Thus, there is a correlation between the presence of twine juice and the amount of direction changes made by the Tetrahymena. The duration of time that the observed cells spent spinning were lower when they were exposed to the polypropylene. That means that there is a correlation between the the presence of the polypropylene and the increase of time spinning.