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Electrolytes: How much and which ones to test on Daphnia?
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goalmachine
- Posts: 19
- Joined: Mon Oct 17, 2005 4:16 pm
Electrolytes: How much and which ones to test on Daphnia?
As you may know from my last post, I'm testing the effects of electrolytes on Daphnia. One solution that we plan on using and introudicng the daphnia to is salt water because sodium is an electrolyte. I have two questions. First, what concentration of salt do I use? Also, what other electrolytes can I use and what concentration. All help is greatly appreciated.
Thanks,
Alex
Let's Go Islanders
Alex
Let's Go Islanders
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Lise Byrd
- Former Expert
- Posts: 95
- Joined: Sun Sep 18, 2005 10:00 pm
Here is a website that might help you:
http://www.caudata.org/daphnia/
Look under the "Physical Requirements" section. ppt is a unit of proportion that means "part per trillion" (1 X 10^(-9)), and ppm stands for "parts per million" (1 X 10^(-6)). It seems that daphnia is extremely sensitive to changes in the environment, so you would not have to use very high concentrations of electrolytes.
The website may also give you other ideas for things you can use as electrolytes. If you want a weaker electrolyte than sodium, you can try acetic acid, citric acid, or carbonate.
Sonia
http://www.caudata.org/daphnia/
Look under the "Physical Requirements" section. ppt is a unit of proportion that means "part per trillion" (1 X 10^(-9)), and ppm stands for "parts per million" (1 X 10^(-6)). It seems that daphnia is extremely sensitive to changes in the environment, so you would not have to use very high concentrations of electrolytes.
The website may also give you other ideas for things you can use as electrolytes. If you want a weaker electrolyte than sodium, you can try acetic acid, citric acid, or carbonate.
Sonia
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donnahardy2
- Former Expert
- Posts: 2671
- Joined: Mon Nov 14, 2005 12:45 pm
Suggestions for Daphnia Project
Hi Alex,
I read through part of the information in the website suggested by Sonia, and it appears that daphnia are very sensitive to most electrolytes, including sodium chloride, so you would probably want to work with concentrations from 0 to 10 ppm (1 ppm = 1 mg/liter). But I have no experience in this area, so you should see if you can get more information.
What is the purpose of your project? In looking through the information on this topic, I noticed the author suggested using Miracle Grow fertilizer to feed the algae that the daphnia grow on. Miracle Grow contains inorganic salts (of nitrogen and phosphorus compounds, I believe), so perhaps you could test the effect of varying concentration of Miracle Grow on your daphnia cultures (0 to 2 tsp/gallon). Or, perhaps you could collect water from various sources in your community and test the effect of the water on the daphnia. These organisms are very sensitive to environmental toxins (detergents, pesticides, etc) so this would be a good way to determine if there is anything in the water that inhibits daphnia.
How are you going to measure your results? Ideally, you want to have a quantitative measure that you can graph.
I would not recommend using an organic acid or carbonate salts as these will change the pH of the water, and daphnia are very sensitive to a shift in pH. When you set up your experiment, be sure to keep the pH, temperature, amount of sunlight, population density, amount of algae the same (controlled). You will want to have just one variable in your experiment. Remember to use metric measurements in your project. If you use a teaspoon of fertilizer, or something similar, it would be best to weigh it in grams.
I hope these suggestions will help. Let us know if you have any other questions.
Donna Hardy
I read through part of the information in the website suggested by Sonia, and it appears that daphnia are very sensitive to most electrolytes, including sodium chloride, so you would probably want to work with concentrations from 0 to 10 ppm (1 ppm = 1 mg/liter). But I have no experience in this area, so you should see if you can get more information.
What is the purpose of your project? In looking through the information on this topic, I noticed the author suggested using Miracle Grow fertilizer to feed the algae that the daphnia grow on. Miracle Grow contains inorganic salts (of nitrogen and phosphorus compounds, I believe), so perhaps you could test the effect of varying concentration of Miracle Grow on your daphnia cultures (0 to 2 tsp/gallon). Or, perhaps you could collect water from various sources in your community and test the effect of the water on the daphnia. These organisms are very sensitive to environmental toxins (detergents, pesticides, etc) so this would be a good way to determine if there is anything in the water that inhibits daphnia.
How are you going to measure your results? Ideally, you want to have a quantitative measure that you can graph.
I would not recommend using an organic acid or carbonate salts as these will change the pH of the water, and daphnia are very sensitive to a shift in pH. When you set up your experiment, be sure to keep the pH, temperature, amount of sunlight, population density, amount of algae the same (controlled). You will want to have just one variable in your experiment. Remember to use metric measurements in your project. If you use a teaspoon of fertilizer, or something similar, it would be best to weigh it in grams.
I hope these suggestions will help. Let us know if you have any other questions.
Donna Hardy
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carolinethorn
- Former Expert
- Posts: 393
- Joined: Tue Sep 20, 2005 2:40 pm
Hi Goal Machine,
Often when a scientist is trying to show that there is a specific effect from a particular sustance (ie of the electrolyte)they do what is called a dose-response curve. Ideally this shows that, the more of the substance you use, the greater effect you can measure until it reaches a plateau. So to use the range that Donna suggested for sodium chloride you would test 0ppm, 1ppm, 2ppm, 3ppm, 4ppm all the way to 10ppm. If thats too costly you could just choose a few across the range eg. 0ppm, 2.5ppm, 5ppm, 7.5ppm, 10ppm
A couple of things you should be cautious about is how many replicants you are going to do. Animals often vary a lot in how they respond so its a good idea to do each concentration at least 3 times.
Also you need to think about if you can use the same animals for more than one part of the experiment - being a part of the experiment and being exposed to the electrolyte may alter the daphnia permanently, (We call this becoming "sensitized") and then they wouldn't be independent experiments. So while it should be ok to use them in the 0ppm and one other concentration, you might need a fresh set of daphnia to measure another concentration. If that isn't feasable cost-wise you could do what is known as a "wash-out period", where the daphnia are in the 0ppm and you monitor them until the heart rate goes back to normal for a certain period of time.
best of luck,
caroline
Often when a scientist is trying to show that there is a specific effect from a particular sustance (ie of the electrolyte)they do what is called a dose-response curve. Ideally this shows that, the more of the substance you use, the greater effect you can measure until it reaches a plateau. So to use the range that Donna suggested for sodium chloride you would test 0ppm, 1ppm, 2ppm, 3ppm, 4ppm all the way to 10ppm. If thats too costly you could just choose a few across the range eg. 0ppm, 2.5ppm, 5ppm, 7.5ppm, 10ppm
A couple of things you should be cautious about is how many replicants you are going to do. Animals often vary a lot in how they respond so its a good idea to do each concentration at least 3 times.
Also you need to think about if you can use the same animals for more than one part of the experiment - being a part of the experiment and being exposed to the electrolyte may alter the daphnia permanently, (We call this becoming "sensitized") and then they wouldn't be independent experiments. So while it should be ok to use them in the 0ppm and one other concentration, you might need a fresh set of daphnia to measure another concentration. If that isn't feasable cost-wise you could do what is known as a "wash-out period", where the daphnia are in the 0ppm and you monitor them until the heart rate goes back to normal for a certain period of time.
best of luck,
caroline