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Introducing Decomposers

This activity introduces characteristics of various decomposers, such as fungi, bacteria and invertebrates.

Fungi release chemicals externally to break down dead plants or animals into simpler substances. They absorb some of these substances for growth, but others are utilized by other organisms, including plants.

Bacteria are tiny, microscopic organisms. The ones that live on dead materials help break them down into nutrients which are returned to the soil.

There are many invertebrate decomposers, the most common are worms, flies, millipedes, and sow bugs (woodlice).

Earthworms digest rotting plants, animal matter, fungi, and bacteria as they swallow soil. The waste that comes out of their bodies at the other end contains important minerals and nutrients ready for plants to absorb. 

Millipedes, sow bugs, and fly larvae (maggots) do a similar process, at different rates, but they rely on a different food source.

Centipedes are part of the decomposer group because they eat other invertebrate decomposers, thereby keeping the decomposer populations balanced.

Objectives

  • List and identify examples of decomposers and describe their role within a simple food web.

Materials

  • Per class:
    pictures of various decomposers
    1 bag of composted or mostly composted material
    1 tarp or plastic bag
    3 big bowls that can get dirty
    10 clear plastic containers

  • Per student:
    1 spoon

Key Questions

  • What do these decomposers have in common?
  • What do decomposers need to survive?
  • Where do decomposers live?
  • What common organisms are in this group?

What To Do

Preparation

  1. Collect composted material from a compost pile. If it is being managed properly it should not have a strong smell.
  2. Place tarp on the table. Put the three bowls on the table.
  3. Pour the composted material into the three bowls. Place the spoons and plastic containers around the edge of the table.

Part 1: Group discussion

  1. Discuss any known examples of living things that break down waste.
  2. Show pictures and discuss the different types.

Part 2: Activity

  1. Use spoons to explore the compost in the bowls. Look for organisms breaking down the food waste.
  2. Place any organisms the students find into the plastic containers. Share the plastic containers with the group.
  3. See if students can find and name all the organisms using the pictures. See if they  can find other decomposers they are learning about
  4. After students are done exploring, put the organisms back in the compost bowls. Later, return them to their natural environment.

Variation

  • Go for a walk to a nearby forest or park and look for signs of natural breakdown due to decomposers (e.g. mushrooms or other fungus, partially broken down decay, soft ground).

Extensions

  • Count how many of each type of organism you found to determine if a compost bin promotes biodiversity.
  • Dissect a mushroom. Make mushroom prints with different types of mushrooms and tempera paints.
  • Examine dirt and compost. Compare and contrast how they look and feel. Discuss what each is made out of.
  • Compare the organisms found in compost with those found in soil. Why could these be different?