Background

Objectives

Students will start a compost to observe fungus, bacteria, and invertebrates decomposing materials.
Students will learn the role of fungus, bacteria and invertebrates in decomposition.

Materials

Shovels
Rakes
Magnifying lenses

Season

Any season

Group Size

Whole class

California State
Content Standards

L.S. 2.c, 3.d

Things under normal conditions decompose. To decompose means it breaks into its smallest parts. Those smallest parts happen to be the nutrients that plants need to grow. These nutrients mix with the ground and add nutrients to the soil. There are three groups that help with decomposition. Those things are fungus, bacteria, and invertebrates (F.B.I.). Fungi are organisms in their own kingdom. The part we see above ground is the reproductive body and produces spores. The mycelium is the main part of the fungus that is located in the ground and helps decompose plants and animals. The largest living organism is said to be a fungus, called the honey mushroom, located in the state of Oregon. It is 3.5 miles wide and would cover 1,665 football fields! Bacteria are microscopic organisms that help decompose living things. These are considered “helpful” bacteria as opposed to bacteria that make us sick. Invertebrates are animals without a backbone. This includes insects and earthworms. These creatures eat the dead material and break it down into its smaller parts in their body. Their excrement are the nutrients added to the soil. A fun way to say this 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 on the fact that worm poop is part of what makes soil.

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 speed up 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.

Worm composting (or vermiculture) creates very 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 on 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 can be used. Add the food scraps with cardboard over the top to help keep out flies. Red wriggler worms are the type of worms to keep in this setting. They are best adapted to 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 to soil. “Brown” materials add nitrogen to the compost. A good source of nitrogen would be manure. “Green” materials would include kitchen scraps and adds carbon. Soil helps the F.B.I. agents spread throughout the compost pile. Keep the pile evenly moist. When the pile looks like soil, have the students remove the larger pieces. This type of compost is not as strong as worm compost and can be added in larger amounts to add nutrients to the soil.

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. Fungi eat to gain energy by decomposing dead matter.
Bacteria: Microorganisms that play a major role in decomposing matter.

Attention Grabber

Have you ever heard of the F.B.I.? I’m not talking about the Federal Bureau of Investigation. I’m talking about the F.B.I. of nature. These special agents help our forests, gardens, farms, and other habitats grow. Without them, our forests would look messy. They’d be filled with dead trees, leaves that have fallen, dead animals! And, our gardens and farms would look sick because they wouldn’t have the nutrients in the soil that they need. Does anyone have an idea what the special agents do? They help turn dead things like plants and even animals (yuck!) into soil. I know that’s very hard to believe so we are going to study these F.B.I. agents and then observe how they are able to turn a dead plant into new soil.

Garden Activity

Introduce the word decomposers and decomposition. A fun term for decomposers is F.B.I. (fungus, bacteria, invertebrate). Explain what the role of decomposers is for the environment. You can give an example of fungus as mushrooms on their pizza. Some bacteria, like germs, make us sick, but this bacteria helps us. Invertebrates do not have a backbone (you can have students pretend they don’t have a backbone and can’t stand up straight). Worms are a good example of an invertebrate that helps with decomposition.

Start a worm compost container. See above 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 and vegetables, eggshells (in very small pieces), teabags (remove the staple) and coffee grinds are great things to add. Do not add dairy, meat, citrus fruits or lots of oily food. These 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 problem when you add the compost to your garden beds). Keep the container moist. To start a compost pile, the same things can be added as to the worm bin, but citrus is okay as well. Add water to help speed up the compost pile.
- NOTE: Some students can work on shredding the paper for the worm bin while other students are observing the worms. Then, they can switch.

The invertebrates (worms and insects) in the compost can be observed using a magnifying lens.

After a week or more, they will observe that the 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.

Wrap Up

Review what decomposition means. Review the decomposers. What do decomposers do? They help recycle plants and other dead things back into new soil, for new plants to grow.
Have students make F.B.I. badges in the shape of an invertebrate they saw.

What's Next?

To further this study, have students examine playground wood chips or another similar area where decomposers would be found. They can often find invertebrates, fungus, and wood chips turning into new soil when the push away the top later.
Start a compost pile with food from student lunches. Students can observe how they can recycle their own food.

Download Materials

Lesson Materials

Fungus

Bacteria

Invertebrates