Fourth Grade NGSS
Biogeology and Heat Generation

Decomposers and Biogeology


  • Learning about  the food chain and decomposers role
  • Introducting the term, "biogeology."

  • Decomposers
  • producers
  • Scavengers
  • Carnivore
  • Omnivore

  • Decomposer worksheets
  • worm and ant life cycle worksheet
  • Food Chain by Cassy Fries


    “Earthworm:  Cocoon Formation”

    “Live Worm Birth”  earthworm hatching (shows 3 worms coming out of a single egg).  You also get sense of scale since there the egg is clearly about same size at tip of a ballpoint pen)


    The environment is full of different animals with different needs.  Students should learn early how these organisms are grouped.    Every organism needs to find food, which is the basis of the food chain (single chain) and food web (many chains).   In food webs there are many layers.  There are decomposers who make areas ready for producers to grow.  Decomposers can use their eating habits to produce heat (bacteria, actinomycetes) that further break down organic debris that helps other organisms like fungi to adsorb nutrients.

    Decomposers interact with the  lithosphere (rock layer) and the biosphere (life).  They not only break down organic matter but they mix into the rock layer.  This is called biogeology.

    There are many different food chains in a specific area.    If an organism relies solely on one organism for food, the first organism will be in trouble if the second dies out.   Individual organisms, however,  prefer specific food, but they usually vary their diets depending on what is available.  The food chain refers to  "who eats whom" relationship.  For instance, humans eat hamburger which comes from the meat of a cow, which eats only grass (herbivore).  But humans don't only eat meat, they eat many other items that come from both animals and plants (omnivore).  If you plotted the entire food habits of an organism this would be called a food web.  



    Prior to lab: Collect worms from  outside in the science garden so students can  observe worms.  May want to have a worm bin. 

    1. Read the poem “Working on a Food Chain.”  Make sure students understand the concepts of consumer, producer, and decomposer.  You can go through the poem again and include some of the concepts on the right including examples of primary, secondary and tertiary consumers.  

      There are many ways to refer to the components of a food web.  If you wish to determine the place that an organism has in a food chain you would use the terms decomposer, producer and consumer.

      A decomposer would be organisms like fungi, annelids, ants and bacteria.  A producer would be organisms that photosynthesize and a consumer is predator.  There are different levels when you develop a food web.

      These organisms help to produce soil, which is rocks plus organic matter.  Without soil many organisms and plants cannot survive.  This interaction of the rock layer (lithosphere) with organic matter (biosphere) is called biogeology and very important in understanding environmental science.

      2.  Hand out the picture on Decomposers in Compost.  Go over the different organisms.  Note that these are common groups.  Decomposers help to create a world for organisms to live on earth.  Decomposers use different strategies to accomplish this from those organisms that can break down organic matter and release a lot of heat energy (thermophilic - hot loving) to organisms that can slowly churn the lithosphere (cool composting.)

      Also look at the word "compost" and "decomposers."    Decomposers are responsible for compost.  The breakdown would not occur if the little critters did not do their job.

    3.     Hand out the plastic models and see if students can identify them on the Lab Worksheet (Compost Organisms).  Some they may be familiar with like beetles and worms, and others like Fungi and Actinomycetes, might  be foreign to them.  Key concept:  many little organisms are responsible for decomposition on the Earth's surface.

    4.     Hand out models of “Life Cycle of Worms,” and “Life Cycle of Ants.”  Ants (Insect) and Worms (annelids) are very important in cool composting.  Use worksheet to put the models on the correct phase.  Read the information below.  These animals are some of the most important organisms that gets soil ready for plants to grow.  Ants are one of the few animals that can digest wood (as students will learn later)  and worms help to churn up the ground and add nutrient as they go their  life cycle.  Students studied ants in the 3rd grade, so this should be a review.  Spend more time on worms as this is new. Students studied ants in the 3rd grade, so this should be a review.  Spend more time on worms as this is new. 


    Eggs: (Can change the information to your comfort level.) After mating, a princess ant is considered a queen ant.  She finds a good nesting site to start a colony, where she lays thousands of tiny eggs.  She won’t leave the nest until the first generation of worker ants are ready to search for food.  Once her colony is established, a queen ant may lay thousands of eggs each day.

    Larva:  Eventually, ant eggs develop into larvae, which resemble tiny pieces of rice.  They have no eyes, only a mouth and they are fed by worker ants that bring food to the nesting site.  It takes between a week and a month for eggs to turn into larvae, depending on the species.

    Pupa:  A few weeks to a month after becoming larvae, the growing ants will be ready to spin cocoons, called pupae.  Within a week or so, pale yellow ants will emerge.  They turn their normal color once their exoskeleton hardens.  A queen’s first batch of ants will be smaller because they have not been fed by other worker ants within the colony.

    Ant:  Once its exoskeleton hardens, an ant is ready to begin supporting the colony. Worker ants are by far the most common, but some ants can also develop into soldier ants, drones, or princesses.  The worker ants have distinct tasks, including caring for eggs, finding food, or expanding and maintaining the colony.



    Earthworms are hermaphroditic, meaning they have both male and female characteristics, so they can both fertilize and lay eggs.  Eggs are contained in a sheath (clitellum)that slides off the worm after fertilization.  The sheath becomes a cocoon that is deposited in the soil, where it hardened to protect the eggs inside. 

    NOTE:  The eggs and cocoons in the model sets are not to scale, eggs and cocoons are much smaller  --see videos.


    Worm hatchlings emerge from their protective cocoon at different rates depending on the species, but the range is from three weeks to five months.  Temperature and moisture also impact the amount of time it takes hatchlings to emerge.  Only a few hatchlings survive to exit the cocoon.

    Juvenile Worm:

    Depending on the species, it takes anywhere from 10 to 55 weeks for worms to mature.  They grow daily and are mature once they have the ability to lay and fertilize eggs.

    There are thousands of species that are considered worms, including varieties of annelids like earthworms and red worms, and parasites like hookworms and pinworms.   In nature, worms  are vital to ecosystem because they act as decomposers, moving decaying material back into the soil where it can feed plants and continue the cycle of life.


    5.  Play the “Earthworm:  Cocoon Formation” video.  Play this video with the sound off and just talk through through the stages.  Video has great visuals for cocoon formation and worm birth but the narrator talks very slowly and has a very monotone voice.  It does show the size of the cocoon compared to the size of the worm (about the size of the last couple segments after the clitellum falls away).

    Play the worm hatching video  from 1:00 min to 3:00 and stop.  They will get to see three worms hatching from a single worm cocoon. 

    6.    Find some worms from outside and put a few at each table.  Students can use hand lens to look at worm parts in detail.  You need to find worms ahead of time.  If you get them ahead and keep them in dirt you may get some worm eggs for students to look at.  Ideally you would need a clear container tso students can look at the worms.   If you take worms out of dirt to look at, they should go back in dirt between classes or they will get too dry.


    If you see some worm cocoons, you can set up a couple of microscopes in the back so students can take turns looking at them under the microscope.  Sometimes the multiple baby worms are visible moving around inside the cocoon.


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