The organisms in kingdom fungi include mushrooms, yeasts, molds, rusts, smuts, puffballs, truffles, morels, and molds. More than 70,000 species of fungi have been identified. The fungi constitute and independent group to that of plants and animals. They live everywhere in air, in water, on land, in soil, and on or in plants and animals. Some fungi are microscopic and other extend for more than a thousand acres. Mycology is a discipline of biology which deals with the study of fungi. Fungi appear like plants but are closely related to animals. Fungi are not capable of producing their own food,so they get their nourishment from other sources. Fungi are in a wide variety of sizes and forms and have great economic importance.
Fungi show a great diversityin morphology and habitat. Fungi are heterotrophic organisms, they obtain their nutrients by absorption. The cell wall of fungi are mostly made up of carbohydrate chitin, while the cell wall in plants is made of cellulose. The carbohydrates stored in fungi is in the form of glycogen. The 'fruit' body of fungus is only seen, while the living body of the fungus is a mycelium, it is made of tiny filaments called hyphae. The mycelium is hidden. Nutrition in fungi is by absorbing nutrients from the organic material in which they live. Fungi do not have stomachs, they digest their food before it pass through the cell wall into the hyphae. The hyphae secrets enzymes and acids that break down the organic material into simple compounds.
Based on the spore case in which the spores are produced fungi are classified into four divisions.
Division Ascomycota: Sac Fungi
The sac-fungi produce spores in small cup-shaped sacs called asci, hence the name ascomycota. The mature sac fungi spores are known as ascospores, they are released at the tip of the ascus breaks open. Yeast is the most common one-celled fungi. Yeast reproduces through asexual process called budding. The buds form at the side of the parent cell, they pinch-off and grow into new yeast cell which is identical to the parent cell. Examples of sac-fungi are morels, truffles, cup fungi and powdery mildews. Example: Aspergillus, Claviceps, Neurospora.
Division Basidiomycota: Club Fungi
Basidiomycota includes the mushrooms, puff-balls, smuts, rusts and toadstools. The spores are borne on a club-shaped spore case called basidium. In mushrooms the basidia are lined at the gills under the cap. Huge numbers of spores are produced by the club fungi. In fact, an average sized mushroom produces over 16 billion spores. These spores rarely germinate or mature. Example: Agaricus(mushroom), Ustilago(smut), and Puccinia(rust fungus).
Division Zygomycota: Zygote forming Fungi
These fungi are usually found on cheese, bread, and other decaying food. They are zygote forming fungi, hence the name zygomycota. The spores are produced in round-shaped case called sporangium. The grayish fuzz seen on bread and decaying food is actually mass of mature sporangia mold. Under the microscope they are seen as pinheads. When the sporangium breaks open hundreds of spores are released. Example: Mucor, Rhizopus (the bread mould) and Albugo.
Division Deuteromycota: Imperfect Fungi
These organisms are known as imperfect fungi because they lack sexual reproduction. They reproduce by asexual spores known as conidia. Most of the fungi causes diseases to humans like ringworm, athlete's foot. Economically important imperfect fungi are Penicillium and Aspergillus. Other examples are Alternaria, Colletotrichum and Trichoderma.