The World Beneath Your Feet:The Rotten Truth

Adapted from Shelburne Farms Project Seasons, Deborah Parella

Post-Visit Activity, All Grades  

Objective

Students will learn about and observe the decomposition process 

Materials

  • Lunch leftovers
  • Zip-lock sandwich bags (one for each student)
  • Scissors
  • Paper and pencil
  • Soil
  • Plant misters
  • Rubber or latex gloves (have students bring their own, but have a few extras)

Background

Decomposition is a fundamental process on which all life depends.  We'd all be knee deep in garbage without it.  Bacteria, fungi, and other microscopic organisms that live in the soil, air, and water are responsible for turning once living plants and animals into nutrients that can be used again.  Think of them as nature's recyclers.  They have the ability to produce special enzymes which allow them to break down these dead plants and animals and use them for food.  As they eat, they grow and multiply at an amazing rate.  In just four hours one bacteria can grow into a colony of 5096.  Despite their microscopic size you've probably seen evidence of them in your own homes.  Remember that lemon with the blue-green mold in the back of the refrigerator?  Or that black fuzzy slice of bread hidden in the bread box?  These are colonies of our microbial friends hard at work at the fine art of decomposition. 

Procedure

  1. Ask the students to name some things they or their family have thrown away the past few days.  What happens to these things?  Do they disappear?  Decompose?  Remain in the same form forever?  Record the students' ideas on the blackboard.  Explain they will conduct an experiment with their lunch leftovers to learn the fate of some common throw-away items.
  2. Give each student a zip-lock lunch bag.  Explain that they will place one small leftover piece of each item from their lunch into the bag.  This includes food, peelings, a corner of the lunch bag, paper napkins, plastic bags, straws, juice boxes, etc.  Have them use scissors to cut items up if necessary.  Stress that they may not add any meat to their bag as potentially harmful bacteria could grow.
  3. Have older students create compost bag journals.  As they add items to their compost bag, have them record the exact contents in their journal.  Each student should also predict what will happen to each item over time.  Will it rot?  Smell yucky?  Stay the same?  Younger students can do this as a class exercise rather than individuals.
  4. Ask the students to add a sprinkling of soil to their bags and to lightly mist the contents with a plant mister.  Have the students breathe air into the bags and carefully seal them.  Explain that they will leave the bags for 2-8 weeks.  You may decide to keep all the bags together, or place them in various locations with differing conditions (hanging in a sunny window, hidden inside a dark closet, in a cool basement, etc.)  Ask the students if these varying conditions will have a different effect on what occurs inside the bags.  If locations of the bags vary, be sure to have everyone register their location on a class master list and in their journals or you may be unpleasantly surprised when a missing bag finally makes its presence known.
  5. Ask students to observe their bags periodically and record in their journal what they see happening inside.  Remind the students that they are not to open the bags until the designated time is up.
  6. On the selected date, have the students bring their compost bags and rubber gloves outdoors.  Distribute extra rubber gloves to students without.  Have students wear gloves while sorting through the contents of their bags.  Record any items still identifiable and their present state.  Are any items missing?  Provide plant misters so items can be cleaned off for closer observation and identification.  How did the results compare to the predictions?
  7. Define and discuss the process of decomposition or decay.  Explain how certain materials are broken down by microorganisms, mainly bacteria and fungi, into basic nutrients and recycled back into the soil.  Talk about composting as an alternative to the garbage dump for many items.  Introduce the terms biodegradable (capable of being broken down by living microorganisms into simpler compounds), non-biodegradable (materials that can not be broken by natural processes), recyclable (an item that can be collected from the waste stream and reprocessed to be made into new products), photodegradable (material capable of being broken down by exposure to sunlight), and reusable (a product that can be used over and over again in the same form).  Have the students sort the items in their compost bags into these categories.

Extensions

  1. Start an outdoor compost pile with lunch leftovers.  Loosen an area of soil at least 3 feet by 3 feet with a spading fork.  Line the bottom with drainage materials such as cornstalks or thin branches.  Add dead and dried plant matter including dried leaves, hay, sawdust, or pine needles.  These materials are high in carbon.  Next add nitrogen rich materials like lunch scraps.  Have students weigh the amount of waste generated.  Cover with a layer of soil or old compost.  Continue layers until 3 feet high, then moisten with water.  Now as decomposers start working the temperature rises.  Mix it up at least once a week and let it decompose for at least 4 to 6 weeks until you have rich, dark soil.  Add to your school garden!
  2. Place a variety of fruits or vegetables inside an empty aquarium in the classroom.  Ad soil, leaves, and even soil creatures to the aquarium.  Mist with water.  Cover with Plexiglas and observe the changes that occur over time.  Read the book Mousekin's Golden House by Edna Miller (Prentice-Hall, 1964) and discuss what happens to Mousekin's pumpkin.