Exploring Decomposition

By Eve Pranis

Decomposers, the final links in food chains, use dead plants and animals as food, breaking them down into smaller particles. Among the decomposers are fungi, which include the familiar molds and mushrooms. Other decomposer -- called bacteria -- are so small that a mere teaspoon of soil could contain billions of them.

Composting happens when humans promote this natural process of decomposition and nutrient cycling by creating an environment in which particular decomposers thrive. As the decomposers use the organic matter for energy and maintenance, they break it down into simpler molecules that can be used again as nutrients for plants, and the cycle begins all over again. This process also give off heat, which in turn speeds up decomposition. While microorganisms accomplish most of the chemical decomposition in a compost pile, small invertebrates such as sowbugs and earthworms are responsible for much of the physical breakdown of materials.

Although your students can't actually see many of the decomposers, they can explore their behavior up close. Whether you plan to build an outdoor compost pile or not, you can lay the groundwork with some exploratory activities. Consider the following:

  • Fill a plastic bag with some "once living" materials (e.g., cut fruit, grass clippings, moist bread) and hang the bag on the bulletin board with a sign reading "What do you think is happening in this bag?" Encourage students to observe and to make and explain predictions.
  • Have students generate a list of things that they think will and will not decompose. To test predictions, create mini-decomposition chambers (e.g., sealed plastic bags or clear plastic shoeboxes) to leave in the classroom or bury outside. Students may want to experiment by providing air holes, blowing in air, or adding soil to some containers. Have them observe containers regularly, or dig them up after a month and examine the contents. (See the activity "FungusAmongus" on pages 210 - 213 in GrowLab: Activities for Growing Minds, in the KidsGardening store, for further ideas.)
  • Challenge students to work outdoors in small groups to identify examples of decomposition in action. Have them describe what they observe that leads them to think decomposition is occurring.

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