Fungi: An Overview of Molds, Yeasts & Mushrooms

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Fungi

Fungi, (singular: Fungus), a large group of organisms, including molds, yeasts, and mushrooms. Some scientists consider slime molds to be fungi, but most classify them as protists. Fungi lack chlorophyll and cannot make their own food; they must live as parasites (that is, on living organisms) or as saprophytes (on dead or decaying matter). Fungi directly absorb some nutrients, such as sugar, and secrete enzymes to break down nutrients too complex for direct absorption. They then absorb the simplified products.

Mushrooms are types of fungi.

There are about 100,000 classified species of fungi. Fungi are widely distributed in freshwater and saltwater, in soil, and in the air. Many of the molds grow on such foods as bread and cheese. Some fungi live in close association with certain algae. The two organisms are dependent on each other and live as one organism, known as a lichen.

Many of the fungi are destructivethey damage crops, spoil stored food products, and cause plant diseases such as chestnut blight, Dutch elm disease, and apple scab. Ergot, a fungus that which infects rye plants, can be fatal to humans. It is from ergot that the drug lysergic acid diethylamide (LSD) is extracted. Useful fungi include the mold penicillium (from which the antibiotic penicillin is extracted) and various fungi used in making cheeses. Many types of mushrooms are edible.

Most fungi are multicelled but their cell walls have gaps in them. The body of a typical multicelled fungus consists of long, slender filaments called hyphae, which form a many-branched network called the mycelium. Reproductive cells are produced in structures that develop from the mycelium. Yeasts are single-celled.

The life cycles of most fungi are complex, and usually include a sexual and an asexual phase. An important characteristic of the fungi is that they produce spores at some time during their life cycle. A spore is a reproductive cell capable of developing into a new organism.

Fungi make up the kingdom Fungi. Most mycologists (scientists who study fungi) separate the kingdom into the following divisions.

Ascomycota

Members of this group form an ascus, a sac-like reproductive structure that bears spores inside. Included in this group are ergot, powdery mildews, morels, truffles, most yeasts, and certain molds.

Basidiomycota

Members of this group form a basidium, a club-shaped reproductive structure that bears spores at one end. Included in this group are rusts and smuts, most mushrooms, and the fungi that cause dry rot.

Deuteromycota, or Fungi Imperfecti

This group includes all the fungi in which a sexual phase has not been observed. Among its members are certain yeasts; the mold penicillium; and the fungi that cause athlete's foot, damping-off, and ringworm.

Mycophycophyta

This group includes the lichens.

Zygomycota

This group includes many molds, such as the black bread mold and various molds that are parasitic on insects, nematodes, and certain other organisms.