Decomposers include certain types of bacteria, worms, slugs, snails and fungi. All of these organisms break down or eat dead or decomposing organisms to help carry out the process of decomposition. They are the last step in the food chain, which recycles nutrients and breaks down wastes and organic matter in the ecosystem.
Decomposers are known as heterotrophs because they eat organic substrates to obtain carbon, energy and other nutrients to grow and thrive. Decomposers break down the organic substrates via biochemical reactions that convert the substrates into metabolically useful products. This removes the need for internal digestive organs in decomposers. For this reason, most decomposers are bacteria and fungi. Bacteria are widespread and can break down a myriad of organic matter. Typically 1 gram of soil contains around 40 million bacterial cells that can break down organic molecules in the soil, which in turn produce more soil. Fungi primarily decompose litter and work it into the ecosystem, while worms, slugs and snails decompose fruits and vegetables. Bacteria, fungi and other decomposers help recycle many nutrients in nutrient cycles such as the carbon cycle, the nitrogen cycle, the iron cycle and the sulfur cycle.
Scavengers are sometimes considered decomposers. While consuming dead animals or plants, they break them into small pieces, which aids the process of decomposition.