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Think about the different places various kinds of plants and animal live. As you know, many, like penguins and cacti, can only live in certain places.
Now think about times you’ve dug a hole in the ground. Did you notice differences in the color of the soil layers? Did you wonder what causes those color differences?
Lots of different kinds of bacteria make their home in the soil. Some are photosynthetic (foe-toe-sin-the-tick). Light provides the energy they need to grow. Photosynthetic microbes live in specific kinds of light. To some, too much light is as harmful to them as no light at all.
Different bacteria also need different amounts of oxygen. In mud, the surface area has lots of oxygen. Further below the surface, the mud lacks oxygen. Bacteria that need oxygen to live are called aerobic /air-oh-bick/ and live at or near the surface, while bacteria that don’t need oxygen are called anaerobic (an-air-oh-bick) and live deeper in the earth.
In this experiment you’ll explore some of the factors that determine where bacteria can live. Print out these pages and follow the directions to do this experiment at home. When you're done, come back to this page to test your newfound knowledge by answering the questions below. (No fair peeking at the answers before you've done the activity!)
Note: This is a long-term experiment. It will take 3-4 weeks for bacteria to grow before you can get full results.
What To Do:
1. Wash your hands before starting. (If you have a cut or wound, you should wear latex or rubber gloves when collecting and working with soil.)
2. Shred a sheet of newspaper into thin strips and set it aside.
3. In the 2-gallon bucket, add five or six cups of soil or mud from one of your collection buckets. Pick out all the sticks, leaves and pebbles. While stirring, slowly add water (collected from the same source) to the soil until your mixture becomes like thick cream. The amount of water you need to add will depend on how wet your soil is at the start. Add the shredded newspaper and one tablespoon of powdered chalk. Mix the contents gently. Make sure the mixture is wet enough that it will flow easily through the funnel.
4. Using masking tape, make a label for one jar or bottle with the name of the soil source on it (e.g. My Backyard). Using the funnel, pour approximately a half-inch of your mixture into the jar or bottle.
5. With one hand covering the opening of your jar and the other holding the base, gently tap the base a few times on a hard surface to allow the mixture to settle evenly. Continue to fill the jar, gently tapping the base every few inches, until it is filled to within two inches from the top. Close the lid or cover the bottle tightly with plastic wrap secured by rubberbands.
6. Repeat the process to fill each of your jars/bottles with soil or mud collected from a different place. (Rinse out your 2-gallon bucket well in between mixing each new batch.) Be sure each new jar/bottle is labeled properly.
7. Place your jars/bottles in a well-lit place, but not in direct sunlight. If you wish, shine indirect light on the jars/bottles with your lamps. Keep them out of heat and at room temperature.
8. For three or four weeks, observe the jars/bottles daily looking for color changes in the mixtures. Record your observations in a notebook. Draw, label and color a picture of each of the jars at the end of each week.
This experiment is based on an activity developed by the National Association of Biology Teachers.