You and Your Students!
Vicki Cobb, Education World Science Editor
Discover the true meaning of “biodegradable.”
Earth Science, Microbiology
Setting the Scene (Background)
This experiment was inspired when a child asked me, “What happens to your body after you’re buried?” This may seem like morbid curiosity, but children are working out their own struggles with mortality. Why not use this child’s curiosity to teach science? Soil is full of all kinds of bacteria that can rot stuff. So a good way to rot something is to bury it. Of course, it takes a long time for soil bacteria to finish rotting something, but you can see the beginning of rot over a period of several weeks.
This is activity is a good opportunity for cooperative learning. Your students might complete the activity in pairs. Let kids choose the items they wish to bury, but make sure the class has a representative sampling of many different things. That way, they will have a “heap” of information to share.
This procedure is very simple. Have students select a wide variety of things to bury. [See Required Props for some ideas.] They will bury one item to a flowerpot.
Important: Items must be buried in garden dirt, not store-bought potting soil.
Have students make a label for each item they bury. They can do that by writing the item name on a small piece of paper and sticking a toothpick through the paper to create a flag-like label.
Water daily for a week to keep the dirt moist.
Act II [one week later]
After a week, dig everything up. Wash the dirt of buried items as much as possible. The dirt will stick to places where things are starting to get rotten because bacteria are growing into the "food"; the soil sticks to the bacteria and the bacteria stick to the food.
Have students feel the rotting fruits and vegetables. How do they feel? Are they getting soft? If there is a peel, is the peel not as rotten as the flesh inside it? How does a peel protect apples, potatoes, and other foods before we eat them? (Peels often have a coat of wax that keeps the bacteria from getting in and rotting the foods too quickly.)
Bury everything again, keep it watered, and dig it up in another week. Or leave it buried for a month or so. (Just be sure to keep it watered.) Then dig it up again and see how the rotting process is progressing.
I'm a big believer in introducing technical terminology in an "as needed" basis. This is the perfect time to introduce an important vocabulary word: biodegradable. Explain to students that everything that rots is called biodegradable. Each part of that long word has a separate special meaning. Bio means living, degrade means to break down, and able means having the power to do something. "Biodegradable" is a term bandied about in popular lingo, but it has real implications for the future of our planet. When the term is learned in the context of this kind of activity, it will not be forgotten.
Introduction of this term can lead into discussions of the problems of garbage disposal, littering, full landfills, and even over-population. The possibilities are endless!
Article By Vicki Cobb
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