Decomposition is the process where microscopic organisms called detrivores consume break down materials into their constituent molecular components. Proteins are broken into ammonia, carbon dioxide, and other elements such as phosphorus and sulfur. Fats and carbohydrates are broken into carbon dioxide and waters. Detrivores play the critical role of returning nutrients locked inside of dead organisms to the environment so they can be used again by plants and other producers. Without detrivores, the world would be piled high with dead organisms while the rest of the planet would run out of nutrients. These are the organisms that connect the end of the food chain back to the beginning. Detrivores include bacteria and fungi.
Essentially, decomposition is the opposite of everything life is trying to accomplish, and you can’t have one without the other.
- Some type of clear, sealable container. Best option is glass mason jars with lids. Other options could be plastic water bottles (16 oz), 2 liter soda bottles with labels removed, Large Ziplock freezer bags (not ideal but will work).
- Food Waste. (carrot or potato peelings, apple cores, old lettuce, orange peels, egg shells) - orange peels are nice because they take longer to decompose. Note: Different types of food materials should be used such as potatoes and carrots and fruits. When compared to high cellulose content plant waste such as straw or sticks, students will see that the food waste breaks down much more quickly than the plant waste. This is important to observe because it shows why food materials such as corn and soy beans are easier to turn into biofuels than cellulosic plant materials. - NO MEAT OR DAIRY
- Plant waste (grass clippings, pulled weeds, plant cuttings, hay) Students could bring waste in from home as an assignment.
- Paper: newspaper, used copies – these could be cut into different sizes or shredded to show how surface area affects decomposition – Paper could be “stacked” (a pile of small squares paper clipped or stapled together) to show how this slows decomposition.
- Other types of trash: aluminum foil, small bits of plastic, Styrofoam. These will not decompose, but that is the point.
- Optional - Non-latex gloves: it could get gross.
- Each student or student group takes one container and fills it with a variety of different materials. Students should record/observe the condition of the materials at their initial state.
- Seal the containers and place them in a location.Note: At this point different experimental conditions could be established. Students could place the jars in different locations: a sunny spot, a dark spot, a cold, dark spot (inside a refrigerator), and/or a warm, dark spot (behind a refrigerator). Some containers could be left open. Some could be dried out. The end result of this would show that dark, warm, and moist environments favor decomposition. This can be tied into the rate of decomposition in different biomes showing that the tropical rain forest floor (dark, warm, and moist) has the fastest decomposition while places like hot deserts and cold deserts (Arctic) have very slow rates of decomposition. Other optional variables: waste materials can be layered between soil, sand, and lime stone dust to simulate what happens in a landfill. This will show that the layering and packing a materials in a landfill slows the decomposition process.
- Observe the changes each day. Look for liquid being formed, fungus growing,changes in the structure and appearance of the materials. The composting mixtures can be churned (shaking the containers) which will facilitate decomposition, but materials will get on the sides of the container obscuring the view.
Changes to be expected:
- Fungal growth: gray and white fuzzy stuff
- Possible insect growth: eggs of fruit flies and other insects may have already been laid on the waste
- Color changes
- Formation of dark liquids at the bottom of the container