Wednesday, December 16, 2009

Effect of Oil Spills on Underwater Plant Growth and Photosynthetic Rate?'s that dreaded time of year again. Science fair. I'm looking to do ';Effect of Oil Spills on Underwater Plant Growth and Photosynthetic Rate';. I'm planning to put each plant in a water-filled test tube. My control group will have no oil in the water, and my other group will have a certain amount of oil in the water.

1. How do I measure photosynthetic rate of the plants? What are the variables in this project? Is it the type of oil?

2. And what else can I measure besides mass and photosynthetic rate?

3. What plant should I use???

Thanks so much!!Effect of Oil Spills on Underwater Plant Growth and Photosynthetic Rate?
Elodea is a good standby for test involving aquatic plants. It grows fast, is readily available, and is nearly impossible to kill. (You can get it at any local pet grow in long ';vines'; with leaves all around it).

To measure photosynthetic rate, you could put an inverted, water filled tube (called a Durham tube) above the plant. As the plant produces oxygen from photosynthesis, a bubble will appear in the tube. Another method is to use a pH indicator like bromothymol blue, though this is also sensitive to respiration.

You could also use a Winkler kit to test for dissolved oxygen - remember the oil is probably going to change the rate at which gases can dissolve into the water in your tubes. Make sure you dry your plant completely before weighing it, and try to make the mass of the plant going into the tubes as close as possible.

Your variable here should be ';Elodea with Oil'; and ';Elodea without Oil.';

Remember that your control is the ';without oil.'; Addition of the oil is your independent variable, and photosynthesis rate (observed by gas production) is your dependent variable.

I hope this helps. If you can get your hands on clear glass funnels that are large enough to turn upside down and put your plants in, you could put them in small fish bowls, and cover the tip of the funnel with an empty water balloon (or any small balloon) and use that as a measure of gas production - that would be easier than using a Durham tube, but you'd need a larger setup than test tubes. Good luck! Let me know how it turns out or if you have any more questions.
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