Fungi

Most species of fungi grow on land and obtain their nutrients from dead organic matter. Some fungi are symbionts or parasites on other organisms. The majority of species feed by secreting enzymes, which partially digest the food extracellularly, and then absorbing the partially digested food to complete digestion internally. As with animals, the major storage carbohydrate of fungi is glycogen. Fungi lack the complex vascular system found in higher plants, so their transport of food and water is less efficient.

Along with bacteria, fungi have an important ecological role in the decomposition of dead plants, animals, and other organic matter. Thus, fungi are ecologically important because they release large amounts of carbon dioxide into the atmosphere and recycle nitrogen and other important nutrients within ecosystems for use by plants and other organisms. Some fungi are parasitic, in that they obtain their nutrients from a living host organism, a relationship which usually harms the host. Such parasitic fungi usually have specialized tissues called haustoria, which penetrate the host's body. Most of the diseases which afflict agricultural plants are caused by parasitic fungi. Some examples are corn smut, black stem rust of wheat and barley, and cotton root rot. Some species of fungi can also parasitize animals. Even humans can be parasitized by fungi which cause diseases such as athlete's foot, ringworm, and yeast infections.