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Testing Water

Postby HopePressler1 » Tue Oct 09, 2018 4:29 am

My 3rd grade son is interested in looking at the difference in the water in 3 backyard ponds and a wetland behind our house. He wants to examine the water under a microscope and see if different organisms and the quantity of them live in the different water.

Do you have a suggestion about how to identify microscopic organisms and accurately count them? We do have a good microscope.

Thank you,
Hope Pressler

Former Student Expert
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Re: Testing Water

Postby AkaAlex » Sat Oct 13, 2018 4:42 pm

Thank you for your question!

In order to accurately assess the presence of a particular organism in water under a microscope, you will need to follow these steps:

1. After collecting samples in your separate jars, create slides of each sample by first stirring the water sample, then suck up a couple droplets with a sterile/clean dropper.
2. Drop the liquid onto the center of a sterile microscope slide.
3. Place a clean plastic cover on top of the drop slowly and carefully (at a 45 degree angle so as to avoid bubbles).
4. Blot any excess water that comes out from under the cover.
5. Practice using different microscope powers and adjusting them until they are clearly visible.

Note that certain organisms are smaller than others, therefore some powers will show different organisms. Commonly seen in ponds/standing water are protozoa, arthropods, hydras, algae, and LOTS of bacteria. In order to identify different organisms, a dichotomous key could be very useful. Note that many organisms look quite similar and if they are alive they will be moving. This link may be helpful: https://courses.lumenlearning.com/bound ... organisms/

Without staining or a strong microscope, it is difficult to differentiate between species (such as gram negative vs positive bacteria). However you should be able to recognize the different shapes and colony patterns!

Good Luck! :D

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