Fungi and other organisms that feed on dead or decaying matter are called detritivores . Many species of fungi are predators , catching their prey with tiny lassos or miniature missiles or toxic chemicals. Fungi and bacteria are vital to the continuation of life on Earth. They are the planetary decomposers, breaking down organic matter into a form usable by other organisms. Only fungi are capable of breaking down lignin , the compound that adds stiffness to the cell walls of plants.
Fungi also participate in two important symbiotic relationships.
Fungi can form lichens , an association of a fungus with a green algae or a cyanobacteria. Lichens are usually presented as a classic example of mutualism , where each partner benefits from the relationship, but some authorities believe that this relationship might be a form of controlled parasitism. Certain fungi are also symbiotic with the roots or gametophyte stages of many types of plants. The body of a fungi consists of many small threads called hyphae , which intertwine to form a larger body called a mycelium . The cell walls of fungal hyphae are made of polysaccharides, like those of plants or bacteria, but they also contain chitin .