Science Buddies: "Ask an Expert"

I have some questions about some of the steps in my procedure for science fair. My project will test the effects of two different kinds of toothpaste (one containing Triclosan and one without) on Daphnia and five different kinds of protists: Euglena, Stentor, Paramecia, Blepharisma, and Spirostomum. I will pipet small cultures of each organism onto a recessed slide. The control set will consist of six slides total--one for each organism. A set amount of pure distilled water will be added to each slide before it is covered. There will be two test sets, each containing probably eighteen slides--three slides for each kind of organism. Each of these three slides will be exposed to a different dilution of toothpaste that either contains Triclosan, or does not contain Triclosan, depending on which set that particular slide belongs to. Each slide will be covered with a cover slip. Every slide will be placed under a microscope, and five photographs will be taken at 30-second intervals at several different points in the experiment: once before the cultures are exposed to aything new, once at 1 minute after initial exposure, once at 5 minutes after initial exposure, once at 15 minutes after initial exposure, once at 30 minutes after initial exposure to the distilled water and/or toothpaste, once at 45 minutes after initial exposure, once at 1 hour after initial exposure, and once at 24 hours after initial exposure. Not only will photographs be taken to track movement of the organisms, but at these different intervals, the heartbeats of the Daphnia will be counted as well. In my research, I was unable to come across any answers to these major questions:
1) What dilutions should I expose the organisms to? Which dilutions will most accurately show the effects of toothpaste and Triclosan on Daphnia and protists? If possible, I would like to narrow it down to three dilutions.
2) How long will it take these different organisms to respond to the toothpaste and/or distilled water? Do my time intervals sound like they would give me the most accurate data?
These are all the questions I have for the time being...Thank you soooo much for your help!!! I really appreciate it!!!

Hi,

This sounds like an interesting experiment! The only thing I would suggest is that you perhaps think about doing more replicates so that you don't have just one slide per organism and treatment.

Unfortunately, I don't have good answers to your questions; I don't think anyone has thought of adding toothpaste to solutions containing these creatures before. I suspect that your time intervals will be just fine, though you might consider checking immediately after adding the solution as well. I think you will probably find that any change occurs quickly (within ~5 min), but it's usually best to keep checking just in case.

As to what concentrations to use, I don't know. You may need to do some pilot experiments to figure out what concentration(s) is/are best. I would probably start with obvious multiples, like half toothpaste/half water (you should definitely see an effect there!), one-quarter toothpaste and three-quarters water, etc. and see how the organisms react.

Thanks so much for getting back to me so quickly!
Yes, I was planning on repeating the experiment twice...Thanks for the suggestion!
I will definitely take your advice into consideration.
I have another question...You know how I am taking five pictures at 30 second intervals at each time interval (1 minute, 5 minutes, 15 minutes, etc.)? How do I show their movement and activity in a quantitative way? Do I measure (from each photo) how far they moved? Or if they moved in and out of view by simply counting the number of organisms? I do not know how to most accurately and quanitatively display this data...I want to somehow be able to show when they stop moving, because that would show that they are dead. Do you have any more ideas? I hope this makes sense. Thanks in advance!

Hmm, this is an interesting problem. Again, I think you will need to just do a pilot study and see how far they move and whether either of your methods (looking at turnover rate on the slide or trying to measure the movement of individuals between pictures) will work. I might suggest just describing this qualitatively, because I can imagine that in your control you will have some movement, but in the treatments you might get two extremes of movement (no movement because they're dead, and very fast movement away from the contaminant). So rating movement on a scale (0-5) or something like that may not work very well.

If you can get the same individuals in the photos, then you can draw a line between the initial position of an individual and the final position, and measure that--as long as you have some sort of scale on the microscope. This would probably be easiest--but it requires your animals to cooperate, and animals don't always do what you expect them to do!

Thank you! I'll see how it goes!