Decomposers are organisms that break down dead or decaying organisms, and in doing so carry out the natural process of decomposition

Decomposition

Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...

. Like herbivores and predators, decomposers are heterotrophic, meaning that they use organic substrates to get their energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

, carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 and nutrients for growth and development. Decomposers use deceased organisms and non-living organic compounds as their food source. The primary examples are:

Bacteria

Bacteria are important decomposers; they are widely distributed and can break down just about any type of organic matter. A gram of soil typically contains 40 million bacterial cells, and the bacteria on Earth form a biomass

Biomass

Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 that exceeds that of all living plants and animals. Bacteria are vital in the recycling nutrients, and many steps in nutrient cycles depend on these organisms.

Fungi

The primary decomposers of litter in many ecosystems are fungi. Unlike bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

, which are unicellular organisms, most saprotrophic fungi grow as a branching network of hypha

Hypha

A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...

e. While bacteria are restricted to growing and feeding on the exposed surfaces of organic matter, fungi can use their hyphae to penetrate larger pieces of organic matter. Additionally, only wood-decay fungi

Wood-decay fungus

A wood-decay fungus is a variety of fungus that digests moist wood, causing it to rot. Some wood-decay fungi attack dead wood, such as brown rot, and some, such as Armillaria , are parasitic and colonize living trees. Fungi that not only grow on wood but actually cause it to decay, are called...

 have evolved the enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s necessary to decompose lignin

Lignin

Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...

, a chemically complex substance found in wood. These two factors make fungi the primary decomposers in forest

Forest

A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...

s, where litter has high concentrations of lignin and often occurs in large pieces

Coarse woody debris

Coarse woody debris is a term used in English-speaking countries for fallen dead trees and the remains of large branches on the ground in forests. Some prefer the term coarse woody habitat . A dead standing tree is known as a snag and provides many of the same functions as coarse woody debris...

. Fungi eat the dead matter by releasing acid found in their body to melt the decaying material, then sucking in all the acid, along with the melted material. Over time, the fungi will eat all the material left. Hyphae are used to drain the melted material and acid are also used in sexual reproduction. When two fungi's hyphae grow close to each other, they will then fuse together and form another fungus. That new fungus will then mature.

Worms

Various types of worms are also considered decomposers, as they act as scavengers. For example, a worm that begins to consume an apple helps to hasten its decay by removing parts of the skin and flesh, exposing the interior of the fruit to the elements and to other decomposers. Certain species of roundworms will also help to decompose the bodies of animals .