Lab #5: Serial Dilution and Experimental Design

9/20/18

Purpose: The purpose of this lab was to learn about the process of serial dilution, learning more in depth about experimental design and correctly storing soil samples. Students gained experience with the 1000 microliter pipette during the process of serial dilution. Serial dilution makes counting cells in a sample easier with less to count. Throughout this lab, the students formed new lab groups and became more comfortable with creating an experiment and planning out the methods and different aspects of the future experiment such as timing, variables and materials. Before lab, students were asked to collect a soil sample from a specific location which will be used for a future experiment. In this lab, students correctly labeled the soil samples and put them into petri dishes to store for a later experiment.

Procedure:

1. Begin the process of storing your soil sample by obtaining a petri-dish and label your name and soil identification onto the top and bottom of the petri-dish.
2. Record the mass of the bottom of the petri-dish.
3. Add a small sample of the soil into the petri-dish and weight both the bottom of container and soil.
4. Place the soil and petri-dish in designated location
5. Start the process of serial dilution by first obtaining a 1000 microliter micropipette and practice transferring water to a petri-dish with this larger micropipette.
6. Then, locate the stock culture in the well plate and view it on the dissecting microscope and note any observations.
7. Add 900 microliters of culture media with a micropipette to 4 empty wells on the well plate
8. Add 1000 microliters of stock culture with a 1000 microliter micropipette to the first well and mix briefly by moving the solution up and down with the micropipette.
9. Eject the tip of micropipette and take 100 microliters of the first well and place into second well, mix briefly.
10. Then eject tip and add 1000 microliters of the second well and add it to the third well, mix briefly.
11. Eject tip and take 1000 microliters from the third well and add it into the fourth well and mix briefly.
12. View the diluted samples under a dissecting microscope and choose the optimal samples to observe and note which ones have less cells to count.
13. Observe each dilution and count the number of cells in each on a concavity slide on the compound microscope. Record data
14. Record the cell count in 5 microliters then find the number of cells per microliter, the number of cells in an undiluted sample and lastly the number of cells in milliliters in an undiluted sample.
15. Clean slides, put away microscopes, pipettes, and micropipette tips.
16. Next, go to the computer lab and create class spreadsheet with each student’s serial dilution average.
17. Get with lab group and talk about a possible experiment to do with Tetrahymena and microplastics.
18. Come up with a question and falsifiable hypothesis
19. Then describe the methods and treatment for the experiment utilizing the given examples of article methods.
20. Lastly, plan out how you would conduct the experiment using a 24 well plate and what each well would hold also including how you would measure the effect of the treatment.

Data:Serial Dilution

 Data: Soil Sample

Sketch:

Where Final Sample is Stored:

The sample of my soil is stored in a petri-dish labeled mo34fall18

The remaining soil sample is stored in a plastic bag

Conclusion: Throughout this lab I learned the process of serial dilution and how it can make it easier to count the amount of cells on a microscope. I was able to observe the decrease in amount of cells in the tetrahymena sample as each dilution factor increased. By going to the computer lab and researching a new experiment to do in the future I gained insight into how to form a falsifiable hypothesis and create methods and treatment for my own possible experiment. My group came up with an experiment that will measure the population change after being exposed to microplastics. As we were brainstorming the methods for this experiment I learned that in order to keep the concentrations the same between the two variables being used, you must add culture media to equal the addition of amount of microplastics being added to one variable. Overall, I hope to keep learning new lab techniques that I will be able to utilize for my group’s future experiment. I also plan on furthering my research about microplastics and scientific articles overall to become comfortable enough to write my own scientific article.