Fungi are a group of eukaryotic organisms that includes yeasts, molds, and mushrooms. They are distinguished from other eukaryotes by their cell walls, which are composed of chitin, a polymer of N-acetylglucosamine. Fungi are the most diverse group of eukaryotes, with over 1.5 million species described. They range in size from single cells to large multicellular structures, such as the fruiting bodies of some mushrooms.
Fungi play an important role in many ecosystems. They break down dead organic matter and recycle nutrients back into the soil. Many fungi form symbiotic relationships with plants, helping them to obtain water and minerals from the soil. Others are parasites of plants or animals, causing disease. Some fungi have economic importance; for example, yeasts are used in brewing and baking, while molds are used in the production of cheese and antibiotics.
The study of fungi is known as mycology. Mycologists use various techniques to identify and classify fungi; these include studying their morphology (shape), physiology (growth and metabolism), ultrastructure (cellular structure), biochemistry (chemicals produced), ecology (environmental interactions), and genetics (DNA).