Science Buddies: "Ask an Expert"

Could you look at this procedure and see if it makes sense?

Procedure for finding the average heart beat of a Daphnia with and without an energy drink.

1. Using an pipette or eye dropper, put a Daphnia on a depression slide. Remove excess water so the Daphnia cannot swim out of the view.
2. Using the microscope, focus on the Daphnia on 4X magnification. Locate the heart. If needed, look at a picture that shows the anatomy of a Daphnia to aid in locating the heart.
3. Count the heartbeats of the Daphnia. On the keyboard of a computer, for ten seconds, type a letter for every heartbeat.
4. Repeat step three two more times for a total of three times for the same Daphnia.
5. Using the pipette or eye dropper, put the Daphnia into a recovery container for five minutes.
6. Average the number of heartbeats and multiple by six to obtain the average beats per minute (bpm).
7. After the five minutes is over, place the same Daphnia in a small Petri dish filled with the energy drink being tested. Allow it to swim in the energy drink for one minute.
8. Using a pipette or eye dropper, put the Daphnia on a depression slide. Remove excess liquid so the Daphnia cannot swim out of view.
9. Using the microscope, focus on the Daphnia on 4X magnification. Locate the heart.
10. Count the heartbeats of the Daphnia. On the keyboard of a computer, for ten seconds, type a letter for every heartbeat.
12. Repeat step nine two more times for a total of three times for the same Daphnia.
13. Return the Daphnia to the recovery container.
14. Average the number of heartbeats and multiply by ten to obtain the average beats per minute. (bpm)

Repeat the procedure for each energy drink being tested.


Make the measurements of the Daphnia quickly to avoid stressing the Daphnia in the small amount of liquid and to avoid heating the solution with the microscope light.

Water Water Water Water Drink Drink Drink Drink
Solution Test A Test B Test C Average Test A Test B Test C Average
1 A. Water n/a n/a n/a n/a
B. n/a n/a n/a n/a
C. n/a n/a n/a n/a
2 A. Rockstar
B.
C.
3 A. Red Bull
B.
C.
4 A. Jamba
B.
C.
5 A. Amp
B.
C.
6 A. Coca-Cola
B.
C.
7 A. Xyience
B.
C.
8 A. Monster
B.
C.
9 A. 5 Hour Energy
B.
C.
10 A. iChill
B.
C.
11 A. No Fear
B.
C.

So, we have done a few of the tests and the same thing almost always happens, once the daphnia is in the energy drink for one min. and I take it and put it under the microscope it seems as if it is dead- it doesn't move and its heart isn't beating- but after I put him in the recovery jar he "comes back to life". I am wondering what your thoughts on this are and if you have any ideas on how I should revise the test. Thanks.

Hello Starkiller,

Congratulations for having laid out your experiment so clearly!

I would have some suggestions to improve it:

1. to get the number of heartbeat per minute, multiply the number you get per 10 seconds by 6 (and not ten) to get a number per minute
2. If you have the choice, I think it would be preferable to run each experiment with a different daphnia. The idea behind that is that manipulation of the same Daphnia can also affect its behavior. (You basically have to choose between two assumptions, if you don't test those: the first one being that you can dismiss the effect of the manipulation on the animal, the second one being that all Daphnia behave roughly the same). Also, I would probably try to have more than 3 trials for each conditions. It is more important to have a well supported conclusion than to make several for which support might not be this high.
3. About the fact that the energy drink doesn't seem to be that good for the Daphnia: based on the results you observe (which are results, even if there are negative), it looks like you should try to focus first on one energy drink, and try several dilutions. It could be that there are ingredients in those drinks that inhibit heartbeats at a high concentration. Testing different dilutions would also test this.

I hope this helps. If not, or if you have more questions, don't hesitate to ask again!

Heloise

I did times six, but forgot to change it on the procedure...thanks!

I have most of the tests done using the same Daphnia for one test; I did test three Daphnia for each drink though.

Is there a way to attach our chart that is filled in so you can see the results? When I copied and pasted the last time it changed the view.

I found that the Daphnia "died" after being in caffeine and I was considering diluting it by 50%.

This week is the end of winter break so I was hoping to get most of the experiment and fair stuff finished..... during school it is pretty busy. So I am feeling stressed that I might have to retest them all again. (Besides the fact that the Daphnia are not as plentiful- my first two shipments died a day after I got them so the company has shipped them one day express...that put me behind during the week.

Anything you can suggest I would appreciate!

I copied and pasted the tests.... I think you might be able to read it.
Water Water Water Water Drink Drink Drink Drink
Solution Caffeine Test A Test B Test C Average Test A Test B Test C Average
1 A. Water 0mg 31 33 31 31.66666667 n/a n/a n/a n/a
B. 24 26 25 25 n/a n/a n/a n/a
C. 26 26 26 26 n/a n/a n/a n/a
2 A. Rockstar 80mg
B.
C.
3 A. Red Bull 80mg 41 35 42 39.33333333 0 0 0 0 13bpm
B. 0 0
C. 0 0
4 A. Jamba 80mg 31 32 32 31.66666667 0 0 0 0
B. 47 44 43 44.66666667 0 0 0 0
C. 30 27 28 28.33333333 2 0 0 0.666666667 30bpm
5 A. Amp 71mg 33 34 37 34.66666667 0 0 0 0 0bpm
B. 23 24 24 23.66666667 0 0 0 0
C. 49 51 49 49.66666667 0 0 0 0
6 A. Coca-Cola 57mg 28 30 33 30.33333333 0 0 0 0 22bpm
B. 44 45 42 43.66666667 3 0 0 1 30bpm started moving after 1 minute
C. 31 33 35 33 12 7 5 8 13bpm
7 A. Xyience 13mg 24 28 26 26 2 0 0 0.666666667 15bpm started moving after ten minutes
B. 23 25 25 24.33333333 0 0 0 0 15bpm
C. 37 30 34 33.66666667 0 0 0 0
8 A. Monster 160mg 18 18 18 18 0 0 0 0
B. 29 34 36 33 0 0 0 0
C. 30 32 36 32.66666667 11 9 9 9.5
9 A. 5 Hour Energy 20 22 24 22 27 18 0 15
B. 23 21 23 22.33 10 10 8 9.33
C. 38 42 43 41.25 22 19 21 20.67
10 A. iChill 0mg
B.
C.
11 A. No Fear 87mg 29 33 32 31.33333333 13 12 12 12.33333333
B. 32 32 30 31.33333333 2 0 0 0.666666667
C. 29 30 29 29.33333333 6 7 11 8

Hi starkiller,

Thank you for sharing your data so thoroughly! The formatting is still a bit difficult to read, but I think I get the gist. One question I have is: do the second set of numbers represent the recovery heartbeat, or a different test?

It is difficult to interpret your data just by looking at it. Have you tried graphing the averages to compare the heartbeats? Nowadays, science fair judges also want to see some basic statistics. In your case, you would need to use a test called ANOVA (ANalysis Of VAriance), which allows you to compare more than two groups. You can do an ANOVA with the Data Analysis TookPak in Excel. However, if you get a significant result (P<0.05), you will need to do pairwise comparisons to find out which groups caused the differences, and you may need a statistical program to do that. Let me know if you are trying to analyze your data at that level.

Heather