Final answer:
The thread-like filaments making up a fungus are called hyphae, which group together to form a mycelium. Fungi have a cell wall largely composed of chitin and contribute significantly to nutrient cycling in ecosystems.
Step-by-step explanation:
The filaments of cells that make up all parts of a typical fungus are called hyphae. Fungi typically grow as thread-like filaments that form a network. This network, composed of hyphae, is referred to as a mycelium. Hyphae are essential because they help the fungus absorb nutrients from different sources, such as soil, decomposing organic matter, and even living organisms. Fungi have a cell wall made largely of chitin and other polysaccharides, which is somewhat similar to the cell wall of plant cells that contains cellulose. A mass of hyphae, the mycelium, is the primary vegetative growth stage of a fungus, and it's often extensive, spreading through large areas to mine substrates for nutrients.
Fungi can also produce specialized reproductive structures like fruiting bodies, of which mushrooms are a well-known example. These structures are involved in the reproduction of fungi by producing and releasing spores. Although most fungi are multicellular during their lifecycle, some, like yeasts, can also exist as single cells. Fungi play a crucial role in ecosystems, as they decompose organic matter and recycle nutrients back into the environment.