Fourth Grade NGSS
Biogeology and Heat Generation

Decomposer Identification


  •  Identifying microorganisms in compost. 
  • ·    Exploring the ecosystem of rot.  

  • thermophilic
  •  actinomyetes
  • fungi
  • Bacteria 
  • mesophilic


    ·         Microscope 

    ·         Petri dishes or paper plates

    ·         White spoons

    ·         Compost from local composter

    ·        Decomposer worksheets

    Draw Decomposers worksheet

    “Compost” Powerpoint



    Bacteria and fungi digest organic matter and convert it into different chemical forms that are used by other microbes, invertebrates and plants.  During thermophilic composting the populations of various types of microorganisms will change as conditions change. The world of microbes in compost is diverse and mysterious.  The energy that they release during their struggle to stay alive, creates another ecosystem that helps to further digest and change organic material.  

    There is always a challenge in compost in that your mixture produces an end product that has carbon and nitrogen in balance.  Making compost at the beginning can produce “smells” but once it gets an “earthy smell” then the compost is ready.  

    In this lesson we will have the student explore the different microbes that they can find.  It is not important what their names are, but that students look for organisms that help this complex chemical process.  Below are some of the organisms the students may see.  Drawing pictures can help them look at the organism careful. 

    Nematodes, or roundworms, are an abundant invertebrates in the soil. Typically less than one millimeter in length, they prey on bacteria, protozoa, fungal spores, and each other. Though there are pest forms of nematodes, most of those found in soil and compost are beneficial.

    Fermentation Mites

    Fermentation mites, also called mold mites, are transparent-bodied creatures that feed primarily on yeast in fermenting masses or organic debris. Literally thousands of these individuals can develop into a seething mass over a fermenting surface. As a result, they often become pest species in fermenting industries, such as wineries and cheese factories. They are not pests in the compost pile.

    Springtails, or collembola, along with nematodes and mites, dominate in numbers among the soil invertebrates. They are a major factor in controlling fungi populations. They feed principally on fungi, but also on nematodes and small bits of organic detritus

    Redworms and Earthworms
    Redworms and earthworms play an important part in the break-down of organic materials and in forming finished compost. Red worms are usually 2-3 inches long and are important in warm composting debris.  The more common earthworms are important in natural soil.  As worms process organic materials, they coat the material with a mucus film that binds small particles together into stable
    aggregates and helps to protect nutrients from being leached out by rain. These stable aggregates give soil a loose and well-draining structure.

    Ground Beetles
    Ground beetles have many representatives lurking through litter and soil spaces. Most of them feed on other organisms, but some feed on seeds and other vegetable matter.

    Wolf Spiders
    Wolf spiders are truly "wolves" of the soil and compost communities. They don't build webs, but run freely, hunting their prey. Depending on the size of the spider, their prey can include all sizes of arthropods- invertebrate animals with jointed legs and segmented bodies.

    Centipedes are frequently found in soil and in compost communities. They prey on almost any type of soil invertebrate near their size or slightly larger


    Before the lab

    Collect a sample of compost that has various types of organisms.  You can get the compost from the black compost bin behind the composter in the garden or from the composter directly. The bin in the back will have a greater variety of cool compost organisms.

    To get a good assortment of organisms, one method of collecting invertebrates is to take grab samples of compost from various locations in the heap. Some organisms such as centipedes and sowbugs will be more likely to be found near the surface. Others will be found deeper in the heap.

    For the heat loving decomposers you will need to look for actinomycetes in the compost.  These look like white and fuzzy.


    Lab intro: 

    Tell them today they are going to learn about and examine organisms found in the various phases of composting         

    1.      Go over the compost powerpoint.  Be sure to point out that there are two phases, a hot thermophilic (heat producing phase) and a cool phase.     


    2.      ACTIVITY:

    a.      provide the students with sets of compost food chain sheets and the cards  (students should work in teams of two or three) and ask them to look for the ones that are thermophilic (heat loving).  These are the organisms from the first phase (includes actinomycetes, mold, bacteria, protozoa).  Have them set those cards aside separate from the rest.

    b.     Ask them how are these thermophilic organisms similar:  (all are tiny simple organisms)

    c.     pass out the trays of compost with actinomycetes on them.  Have them use magnifying lens to look.  they should be able to see the strands that are formed by the bacteria


    a.      ask them to review the other cards (the ones that are NOT thermophilic) 

    b.     ask them to look for separate primary consumers--the ones that eat the compost residue from secondary and tertiary consumers.

    c.     put the cards to one side on the table but keep them handy so students can use them to figure out their organisms


    a.      provide the students with the trays of compost.  This compost should have an assortment of types of organisms in it.


    b.      Students should look for a variety of organisms.  They can use wooden tongue depressors, plastic spoons, or other instruments that will not hurt the organisms, to sort through the compost. Flashlights and magnifying lenses can be used to enhance the observation. The larger organisms, such as worms, centipedes, millipedes, sowbugs, earwigs, spiders, ants, beetles, snails, slugs, some mites, etc., can be observed with the naked eye. To get a closer look, they can pull the organism out and put them in the petri dish for closer observation.  You can also allow them to place samples of the compost in petri dishes or watch glasses and observe them under a microscope.

    c.      Have students use the Decomposer Worksheets and cards to identify different organisms that they find.  Have them observe the organisms with their magnifying glasses or microscope and then draw some of their organisms on the worksheet.  Tell them to draw as many details as possible.  (Some students are very detail oriented and will only draw one or two.  For those that draw quickly, ask them first to put in more details and then to keep drawing other organisms.)  They can color the drawings as well.


    d.     When they are done, have them carefully put their organisms in the petri dishes back in the dirt for the next class.


    5.  Wrap up (5 minutes)


    Discuss what animals they have seen and what part the organisms play in the process of decomposition.



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