MicrobeWorld

Now You See It... Now You Don't! - Experiment

Maybe you’ve heard the term "biodegradable." It basically means something capable of being broken apart into simpler substances by natural biological processes.

But what are these biological processes that break some things down? Why do some things biodegrade more readily than others?

In this experiment, you’ll investigate the biodegrading process of commercial packing peanuts. 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 experiment will take you about 30 minutes to 1 hour to do on the first day, and about 10-20 minutes each successive day over five days.

You’ll Need:

• 6 clear plastic or glass jars (minimum 1-cup volume)
• marker
• masking tape
• teaspoon
• measuring cup for liquids
• eye dropper (you may wish to have more than one on hand)
• test tube (if you can’t find a test tube, use a thin, clear glass instead)
• large spoon or other stirring utensil
• 7 biodegradable packing peanuts made of starch (visit a packaging service store such as Mail Boxes Etc. if you don’t have starch peanuts at home)
• 7 polystyrene, or Styrofoam, peanuts (also available at a packaging store)
• iodine tincture solution (drugstore antiseptic version that contains iodine and iodide salts; should be brown)
• 1 1/2 cups aged tap water (let tap water sit out overnight to "age" and lose its chlorine)
• compost activator that contains live microorganisms (available at garden supply stores; be sure the label says it contains live microorganisms and not just extra nutrients)
• corn starch or flour
• slice of raw potato

What To Do:

1.  Wash your hands before starting.

2.  Lay the potato slice on your table. Using the eye dropper, put a drop of iodine at four separate locations on the slice and watch what happens. The resulting blue-black color is caused by a chemical reaction between the starch in the potato and the iodine. An iodine test like this is often used to confirm whether there is starch in a sample.

3.  Put a drop of iodine on a polystyrene peanut and a drop on a a biodegradable peanut and observe what happens. What does this tell you about the make up of each kind of peanut? Throw away the potato slice and peanuts and wash your hands.

4.  Using the masking tape, label your jars 1 through 6. Put 1/4 cup (50 mL) of aged water in each. Put one teaspoon of corn starch in jars 1 and 2. Clean your teaspoon. Put two biodegradable peanuts in jars 3 and 4 and two polystyrene peanuts in jars 5 and 6. Add one teaspoon of compost activator to jars 2, 4 and 6. Mix the contents of each jar, cleaning your stirring utensil between jars.

5.  Test the contents from each of your jars for starch. Put five drops of the mixture from jar 1 in a test tube. Add a drop of iodine to the tube. Record the results. Repeat this procedure for each of the other jars. Be sure to rinse out your test tube thoroughly before testing the contents of the next jar or use a new eye dropper for each jar. Wash your hands when you finish this part of the experiment.

Questions

1. Why does a polystyrene peanut not degrade the same way the starch peanut does?   Answer
2. Are live bacteria necessary for breakdown?  Answer
3. What would happen if you buried a polystyrene peanut and a starch peanut in your yard during the fall and dug up the spot in the spring?  Answer

This experiment is based on an activity developed by the National Association of Biology Teachers.