Background

Decomposition is the process of an organism breaking down into simpler forms of matter. Those smallest parts are the nutrients in the soil that plants need to grow! Fungus, bacteria, and invertebrates (F.B.I.) are three different groups that help with decomposition. Fungi are organisms in their own separate kingdom. The part we see above ground is the reproductive body, which produces the spores. The mycelium is the main part of the fungus that is located in the soil and helps decompose plants and animals. The largest living organism on earth may be a fungus. A culture of the species Armillaria bulbosa has spread through an 86-hectare (35 acre) woodland in northern Michigan. It could be 1,500 years old!

The two other members of the “F.B.I.” are bacteria and invertebrates. Bacteria are microscopic organisms that help decompose living things. They are considered “helpful” as opposed to “harmful” bacteria that can make us sick. Invertebrates are animals without a backbone. This includes insects and earthworms. These creatures eat the dead matter and break it down into its smaller parts through their digestive system. Their excrements help add nutrients to the soil. A fun way to teach this to children is to pretend your hand and arm is worm and say, “Munch, munch, munch. Wiggle, wiggle, wiggle. Poop, poop, poop!” Students are pretty quick to pick up the fact that worm poop is in the soil.

Decomposition is a natural phenomenon that occurs at rates that depend on environmental conditions. Different conditions slow down or speed up decomposition. Moisture helps speed up decomposition. Things decompose VERY slowly in the desert. Warmer temperatures (but not too hot!) also help to speed up the rate of decomposition. Things hardly decompose in freezing temperatures where the F.B.I. cannot survive. This is why scientists have been able to find frozen remains in glaciers.
 

Composting

Worm composting (or vermiculture) creates a rich compost that can be used as a liquid fertilizer (add about a ½ cup of worm compost to a gallon of water) or sprinkle a small amount of compost in soil. Worm composting can be started in an opaque Tupperware container with holes in the lid (for air) and bottom (to release extra liquid). A thick, moist bedding of shredded newspaper, cardboard, or sawdust should be added to the bottom. Add the food scraps with cardboard over the top to help keep out flies. Red wiggler worms are the type of worms best suited for this closed environment. When ready to harvest the compost, you can either dump out the material and separate out the worms OR add food just in one small area of the compost bin and let the worms migrate to the food. You can use the same worms and eggs to start a new bin. Worm eggs look like miniature lemons (about half the size of the little fingernail).

If you make a compost pile, have the students layer the different ingredients evenly with rakes and shovels. The richest compost piles have equal parts of “brown” materials to “green” materials. Generally, “brown” materials add carbon to the compost. Good sources of carbon include straw, wood chips, and shredded cardboard. “Green” materials generally add nitrogen to the pile. This includes kitchen scraps and grass clippings. Adding some soil throughout each layers helps the F.B.I. work more evenly. Keep the pile evenly moist. Have the students turn to the pile infrequently to help with even decomposition. When the pile looks like soil, have the students sift out the larger pieces. This type of compost is not as strong as worm compost and can be added in larger amounts to the soil. Naturally, the fungus, bacteria, and invertebrates in the environment will come to concentrated areas of compostable items and help break them down. This can be helpful for students to see that the F.B.I. exists naturally almost everywhere, even at their school!


 

Vocabulary

Decomposition: to break down into a simpler form of matter.
Decomposers: Small living organisms that help decompose dead matter.
Invertebrates: organisms without a backbone.
Fungus: a multicellular organism with a chitinous cell. Fungus gain energy by decomposing dead matter.
Bacteria: Microorganisms that play a major role in decomposing matter.
Nutrients: A nutrient is a substance a living being needs to live and grow. Nutrients help living things by helping repair tissue and regulating body processes. Nutrients can only be obtained outside of the animal’s environment.
 
 

Attention Grabber

Have students read some fun facts about the F.B.I. Let them practice before they read it in front of the class.

•    The largest living organism on earth is said to be a fungus. A culture of the species Armillaria bulbosa has spread through 35 acres (about 33 football fields) of woodland in northern Michigan. Scientists estimate it to be 1,500 years old.
•    Some fungus can shoot its spores 8 feet!
•    The largest earthworm ever found was in South Africa. It was 22 feet long!
•    Houseflies find sugar with their feet, which are 10 million times more sensitive than the human tongue.
•    When the droppings of millions of cattle started ruining the land in Australia, dung beetles were imported to reduce the problem.
•    There are about 91,000 different kinds (species) of insects in the United States. In the world, some 1.5 million different kinds (species) that have been named, with more being discovered.
•    The honey mushroom is one of several fungus species that glows in the dark.


 

Garden Activity

•    Introduce the lesson by pretending your hand is a worm and have the students repeat after you, “Munch, munch, munch. Wiggle, wiggle, wiggle. Poop, poop, poop!” Ask if they can guess what you all are. Pass around a worm in a small container and ask the students to use their eyes to observe the worm. Let students know that they will have the opportunity to observe the worm more closely in this activity.
•    Introduce the idea that the students are looking at a member of the F.B.I. The F.B.I. are decomposers and stands for: fungus, bacteria, and invertebrates. Show the students pictures of each type of decomposer.  Relate each to something the students relate to in their daily lives (fungus is a kind of mushroom- have they eaten mushrooms? Bacteria is used to make cheese and yogurt. Have they eaten cheese or yogurt? Have they seen an earthworm after it rains?) Explain the role of decomposers.

 

Activity 1: Start a worm compost container.
 

•    See below for more details in how to start a worm pile. Add fruit (no citrus) and vegetable scraps to the worm bin. You can help the students understand that the bedding is made of trees, so this too will decompose.  All fruits, vegetables, eggshells (in very small pieces), teabags (remove the staple) and coffee grounds are great things to add. Do not add dairy, meat, citrus fruits or lots of oily food. These things cause the pile to smell badly and can attract unwelcome animals. You can also add scraps from the garden, excluding weeds (you don’t want to add weeds to the compost because their seeds usually don’t decompose and can cause a weed problem when you add the compost to your garden beds). Keep the container moist.

Divide students into four groups. Have groups switch after about 5-7 minutes at each station.
o    Station 1: will work on shredding old newspaper. Model for students how large the pieces should be. They can use a ruler or scissors to help them if necessary.
o    Station 2: will take the shredded pieces of paper, put them in a small bucket to get them wet and carefully squeeze out the excess water. Have students carefully open up the pieces of paper and spread it out in the bottom of the worm bin.
o    Station 3: will observe the worms in small containers. If they would like, they can gently hold a worm. Model how to do this for the students.
o    Station 4: Students can work in pairs to go over the F.B.I. cards. Their partner can use it as a flash card and they can use it to practice identifying and remembering the words fungus, bacteria, and invertebrates. This is good practice since these are challenging words to remember and pronounce!
•    Have student volunteers bring scraps from home to feed the worms. This would probably only be necessary once a week. When feeding the worms, put the food in one area of the bin so it can easier to find the worms. They usually can be found closest to the food source.

Activity 2: Start an Outdoor Compost Bin:
 

•    If you have an outdoor area, you can start a compost bin. It is fun to have students bring food scraps from home to help add to the compost. You can add the same things as added to the worm bin, but citrus can be added as well.  You can also observe decomposition by having a small pile of compostable items in an area that is relatively undisturbed for a few weeks if you do not have the ability to create the layered compost pile. Adding water to the small pile can help keep the environment more hospitable for the F.B.I.
•    Have students observe the invertebrates (worms and insects) by using a hand lens. Use a small sheet of plastic and have a student take a shovel from the compost bin. Plastic spoons can be used as tools to help move around the compost for observation. Be sure to show students how to use a hand lens. It’s a good idea to remind students to only use the hand lens to look at the F.B.I. Please don’t use it as a tool to sort through the compost (supply plastic spoons or other similar tools for this).
•    After about a month, students can observe the decomposition process by seeing fruit and vegetable scraps turn into new soil.  The F.B.I break down all of the organic material into their smallest parts and are recycled back into soil.  Students can bring home the recycled nutrients in small bags to take home and feed their plants or they can use the compost to feed plants in their school.

 

Wrap Up & Assessment

•    Review what decomposition means. Review the different decomposers. What do decomposers do? Students can work in groups to make a body motion or dance for each type of decomposer.
•    Have students create a picture story showing how a worm makes new soil.
•    Have students make F.B.I. badges in the shape of an F.B.I. agent they found if they bring compost from their homes or their school lunches.
•    Have students fill out the F.B.I. worksheet included in the appendix.
•    As a class, have students work on ABC Compost Cards. They can use this to help educate others about what can be composted.

 

What’s Next?

•    Have students start a composting pile from their school lunches. They can make posters, use their ABC Compost Cards, and create a short presentation to help educate and encourage other students at their school to also “recycle” their food.
•    The Banana Slug String Band has a great song about decomposers called the “F.B.I.” You can find this song online. This would be a great song for students to sing along with while reading the words.
•    Have students examine playground woodchips or another similar area where decomposers would be found.  They can often find invertebrates, fungus, and woodchips turning into new soil when the push away the top later.
 

Download Materials

Student Worksheets

 F.B.I. Worksheet