What two types of organisms are responsible for decomposition?

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

• Differentiate between compostable waste and non-biodegradable waste.

• Explore the active process of decomposition.

• Create a worm compost farm.

Materials

• See activities for materials.

Background

Energy enters the food chain from the sun.

Producers (e.g. plants) create complex organic substances (essentially food) using energy from sunlight and other materials.

Consumers (e.g. animals) get their energy by eating the producers and/or other consumers.

Scavengers and decomposers get their energy by eating dead plants or animals.

Rotting food (or food that’s gone ‘bad’) doesn’t look or smell great but it contains a wealth of nutrients, including carbon, nitrogen, and phosphorous. Living organisms require these nutrients to create cells, tissues and to provide energy for life processes.

When a plant or animal dies, nutrients would remain forever locked in the dead tissues if it weren’t for decomposers. The decomposers complete the cycle by returning essential molecules to the plant producers.

Decomposers (fungi, bacteria, invertebrates such as worms and insects) have the ability to break down dead organisms into smaller particles and create new compounds. We use decomposers to restore the natural nutrient cycle through controlled composting.

Decomposers are the link that keeps the circle of life in motion. The nutrients that decomposers release into the environment become part of the soil, making it fertile and good for plant growth. These nutrients become a part of new plants that grow from the fertile soil.

Vocabulary

Biodegradability: Biological and biochemical breakdown of organic materials by the environment. Biodegradability simply means that soil micro-organisms and natural weathering processes are capable of decomposing the material into soil nutrients without leaving any harmful residues behind. Or: something that rots.

Bioplastics: Plastics made from renewable plant material or plant products like cornstarch, potato starch, or tapioca. These can biodegrade.

Bioremediation: Any process that uses micro-organisms, fungi, algae, green plants or their enzymes to improve the state of a natural environment altered by contaminants.

Compost: Verb: the controlled process of decomposing organic material. Noun: organic material that can be used as a medium to grow plants. Humus (mature compost) is a stable material that is dark brown or black and has a soil-like, earthy smell. Given enough time, all biodegradable material will oxidize to humus.

Decomposer: An organism, often a bacterium, fungus, or invertebrate that feeds on and breaks down dead plant or animal matter, making organic nutrients available to the ecosystem. Or: ‘FBI’ (fungi, bacteria, invertebrates)

Decomposition: The action or process of breaking down; the rotting or decaying of plant or animal matter.

Invertebrate: An animal that lacks a backbone or spinal column.

Nutrients: Organic and inorganic compounds that a living organism needs to live and grow or a substance used in an organism’s metabolism which must be taken in from its environment. Or: food.

Organic waste: Waste created by or from a once-living organism. It is capable of decay and is composed of carbon compounds.

Vermicomposting: Using earthworms/red wiggler worms to turn organic waste into very high quality compost.

Other Resources

Science World | Decomposer Photo Cards

UN Food &Agriculture Organization | Soil Biodiversity: Enter a Hidden World

Crash Course Kids | Video | The Dirt on Decomposers

BC Green Games

Metro Vancouver | Worm Composting Brochure 

US Department of Agriculture | Ask the Answer Worm!

Recycling Council of British Columbia | Recycling Fact Sheets

Victoria Compost & Conservation Education Society | Fact Sheets

Worms Eat My Garbage by Mary Appelhof

A decomposer is an organism that decomposes, or breaks down, organic material such as the remains of dead organisms. Decomposers include bacteria and fungi. These organisms carry out the process of decomposition, which all living organisms undergo after death. Decomposition is an important process because it allows organic material to be recycled in an ecosystem.

Mushrooms, such as those in the image above, are a type of fungus and play a role in decomposition.

Decomposers play an important role in every ecosystem. Without decomposers, dead organisms would not be broken down and recycled into other living matter. The reason decomposers decompose, however, is simply because they need to survive. Decomposers are heterotrophic, which means they get their energy from ingesting organic material. A dead organism provides nutrients for decomposers like bacteria and fungi to use in order to grow and reproduce, propagating their own species. The side effect of this basic need to survive is that organic material and nutrients are cycled throughout the ecosystem as other organisms consume the bacteria and fungi.

Some organisms perform a similar function as decomposers, and are sometimes called decomposers, but are technically detritivores. The difference lies in the way decomposers and detritivores break down organic material. Detritivores must digest organic material within their bodies in order to break it down and gain nutrients from it. Decomposers do not need to digest organic material internally in order to break it down; instead, they can break down matter through biochemical reactions. Organisms that are detritivores include invertebrates such as earthworms, woodlice, sea stars, slugs, and fiddler crabs.

Scavengers are the first to arrive at a dead organism’s remains, and they directly eat the dead plant and animal material. Once scavengers are done with the remains, decomposers and detritivores take over and consume the parts that the scavengers have left behind. Many predators will scavenge on occasion; examples of these sometime scavengers include lions, jackals, wolves, raccoons, and opossums. Vultures are obligate scavengers, meaning that scavenging is how they obtain all of their food. They are the only members of the animal kingdom that have to scavenge in order to eat.

When an organism dies and decomposers do the work of decomposition, the organism’s remains go through five stages of decomposition: fresh, bloat, active decay, advanced decay, and dry/remains. There are two main processes that occur in a decomposing organism: autolysis and putrefaction. Autolysis is when cellular enzymes in the dead organism’s own body break down cells and tissues, while putrefaction is when microbes grow and reproduce throughout the body after death. Here is a brief summary of the five stages.

This stage begins as soon as an organism’s heart stops beating. With no more oxygen coming into the body and a buildup of carbon dioxide, autolysis begins to occur. Putrefaction also begins to occur.

Due to putrefaction, a buildup of gases occurs and the organism’s remains appear bloated in what is known as the bloat stage. Some gases and fluids are purged from the body.

The remains lose mass, and liquefaction and disintegration of tissues begins to occur. Bacteria produce chemicals such as ammonia, hydrogen sulfide, and methane, which cause strong odors.

The organism has lost a lot of mass, so there is not much left to be decomposed. If the organism is on or in soil, the surrounding soil will show an increase in nitrogen, an important nutrient for plants.

Dry/Remains

In this stage, only dry skin, cartilage, and bones are left. Plant growth may occur around the remains because of the increased nutrient levels in the soil. Eventually, only the bones of the organism will remain.

Bacteria are microscopic, unicellular organisms found nearly everywhere on Earth, including inside the human body. When an organism dies, it provides many nutrients for bacteria to grow and reproduce, and they become numerous in the process of putrefaction during decomposition. Bacteria are themselves a cause of sickness and even death when they infect organisms. Serious and often fatal diseases such as typhus, tuberculosis, and cholera are caused by bacterial infections. Bacteria that kill their hosts end up inadvertently providing nutrients for other bacteria during decomposition.

Fungi are the main decomposers in many environments. Some examples of fungi are yeasts, molds, and mushrooms. Fungi have hyphae, which are branching filaments, and these hyphae are able to enter organic matter, making fungi effective decomposers. Wood-decay fungi have specific enzymes that digest compounds in wood, and are the main decomposers in forests. In fact, wood-decay fungi are the only producers of these enzymes, so they play a very important role in decomposition.

• Detritivore – An organism that eats detritus, which is decomposing plant and animal matter as well as feces; it has a similar function in an ecosystem as a decomposer.
• Ecosystem – A community of living organisms along with all the non-living parts of their environment.
• Putrefaction – A process that occurs during decomposition when microbes proliferate throughout the remains of a dead organism.
• Hyphae – Long, branching filaments on fungi that make them better able to decompose organic material and are also used in reproduction.

1. Which organism is NOT a decomposer?
A. Bacterium
B. Mold
C. Mushroom
D. Earthworm

D is correct. Although earthworms eat decaying plant and animal matter, they are technically detritivores since they cannot break down organic material externally. True decomposers are bacteria and fungi. Choices B and C are two types of fungi.

2. What are the stages of decomposition in order?
A. Fresh, bloat, active decay, advanced decay, dry/remains
B. Fresh, dry/remains, advanced decay, active decay, bloat
C. Active decay, advanced decay, bloat, fresh, dry/remains
D. Bloat, dry/remains, fresh, active decay, advanced decay

A is correct. Fresh, bloat, active decay, advanced decay, and dry/remains are the five stages of decomposition that an organism goes through after it dies.

3. Which is a process that does not directly occur during the process of decomposition?
A. Autolysis
B. Putrefaction
C. Photosynthesis
D. Nutrient cycling

C is correct. Autolysis and putrefaction occur within an organism’s remains during decomposition. Nutrient cycling occurs during decomposition because decomposers are themselves food sources for other organisms and also because they release the dead organism’s nutrients such as nitrogen into the soil. Photosynthesis is how plants make energy; it is not a process that is directly tied to decomposition.