Taxonomy: Kingdom Mycetae (Fungi)
By Lhenn on Jan 25, 2010 with Comments 0
You may not be aware of it but a fungus has saved many people’s lives. The most famous antibiotic, penicillin, was derived from a fungus named Penicillium chrysogenum. Fungi are important to humans in many ways. They are valuable sources of food, chemicals, fuels, and medicine. Some fungi, however, cause plant and animal diseases.
What are Fungi?
A quick survey of your backyard and household will make you encounter some members of Kingdom Mycetae. You will see them growing on soil, barks of trees, decaying logs, under a heap of decaying leaves, and even on your leather bags and shoes, bathroom curtains, and rotten foods in the kitchen.
Most fungi are multicellular. They were once classified as plants because of their appearance. The mushroom, for instance, looks like a small plant. However, the mushroom and all the other fungi lack chlorophyll. Thus, they cannot produce their own food, unlike most plants. They also lack the specialized tissues and organs that plants possess.
The body of a fungus is usually a mass of threadlike tubes called hyphae. A mass of hyphae is called mycelium. A part of the mycelium, the descending hypha, grows downward to the substrate. The part which grows upward and which bears the reproductive structures is called ascending hypha or the fruiting body. In the case of the mushroom, the structure that grows above the ground is its fruiting body. It looks solid but is actually made up of interwoven mass ascending hyphae. Its descending hyphae form a network that penetrates the ground.
The cell walls of fungi are made of cellulose or chitin, a strong, flexible polysaccharide that it is also found in the body covering of insects. Most fungi are saprophytic, that is, they feed on dead organisms. A fungus secretes enzymes from its descending hyphae to digest food outside of itself. Then the fungus cells absorb the digested food. Some fungi are parasitic. Examples are the fungi that cause athlete’s foot and ringworm. Fungi grow best in warm and humid places. This is the reason why they grow on moist towels, leather shoes and bags, and even between your toes.
Fungi generally reproduce asexually by means of fragmentation or by sporulation. In fragmentation, filaments break off from the fungal body and grow into new individuals. Spores are microscopic reproductive cells that disperse and germinate into new organisms under favorable conditions. The spores are enclosed in a spore-bearing structure, or spore case, which breaks when mature, releasing a number of spores that are dispersed by the wind. These spores are able to withstand extreme conditions of dryness and cold. They germinate into new organisms when environmental conditions become favorable. Fungi may also reproduce sexually by means of the haploid spores developing into haploid hyphae that are capable of fertilization.
Classification of Fungi
Fungi are classified into four divisions based on the spore case in which spores are produced. The first three division exhibit asexual as well as sexual reproduction while the fourth division lacks sexual stage.
1. Division Ascomycota: Sac Fungi
The spores of sac fungi are produced in small cup-shaped sacs called asci, thus, the term ascomycota. When sac fungi mature, the spores called ascospores are released as the tip of an ascus breaks open. The most common one-celled sac fungi is yeast. Yeast also reproduces through as asexual process called budding. Buds form at the side of the parent cell, pinch off, and grow into new yeast cells that are identical to the parent cell. Other common examples of sac fungi are morels, truffles, cup fungi, and powdery mildews.
2. Division Basidiomycota: Club Fungi
This includes the mushroom, puffballs, bracket or shelf fungi, toadstools, rusts and smuts. They bear spores in a club-shaped spore case called basidium. In mushrooms, the basidia are lined at the gills found under the cap. Club fungi produce spores in tremendous numbers. In fact, an average-sized mushroom could produce up to 16 billion spores. If all these spores would germinate into adult mushrooms, the Earth would probably be covered with mushrooms. The spores rarely germinate nor reach maturity.
3. Division Zygomycota: Zygote-forming Fungi
Zygote-forming fungi are usually seen on bread, cheese, and other decaying foods. Their name implies the presence of sexual spores called zygospores. They produce spores in a round-shaped spore case called sporangium. The black, white, or grayish fuzz you see on bread and decaying food is actually a mass of mature sporangia of mold. Under the microscope, they look like pinheads. Hundreds of spores are released into the air when a sporangium breaks open. The black mold, Rhizopus nigricans, is a common example of a zygote-forming fungus.
4. Division Deuteromycota: Imperfect Fungi
Organisms under this division are called imperfect fungi because they lack sexual reproduction. Most of the fungi that cause diseases in humans, like ringworm and athlete’s foot belong to this group. Among the economically important imperfect fungi are Penicillium and Aspergillus.
Importance of Fungi
Recycling. Fungi are most important in their role as decomposers. They break down organic materials from food scraps, dead plants and animals, and return them to the soil where they are reabsorbed by plants.
Mycorrhizae. Some fungi form associations with plant roots, forming fungus roots or mycorrhizae. They expand the surface area of roots for absorption of water and minerals. Plants with mycorrhizae can absorb ten times more than those without mycorrhizae.
Food. Fungi are widely used in the production of many foods and drinks. Yeast are economically important because they are used in the production of bread, beer, wine, cheese, and soy sauce. Yeast cells metabolize sugar and release carbon dioxide, acids, and have alcohol as by-products. The carbon dioxide form bubbles in the dough causing it to rise. Aspergillus, an imperfect fungi, is also used in the production of soy sauce and soy paste. Mushroom, like taingang daga and morels are fungi that have become a delicacy in many parts of the world. Many mushrooms are cultivated for sale worldwide.
Medicines. The importance of fungi in the field of medicine cannot be underestimated. The imperfect fungus, Penicillium chrysogenum, is the source of the very useful antibiotic, penicillin. Vidarabine, the fist antiviral drug used to treat encephalitis or the inflammation of the brain and spinal cord, was produced from a species of fungi.
Biological Control. Some fungi which parasitize insects can be useful for controlling insect pests of crops. The spores of the fungi are sprayed on the crop pests, such as caterpillars, beetles, leafhoppers, and mites. This method is generally cheaper and safer to the environment than the use of chemical pesticides.
Harmful Effects of Fungi
Although most fungi are beneficial, some of its members are harmful to both plants and humans. Fungi, such as molds, are the common cause of food spoilage and the rotting of many household items, such as furniture, leather seats, shoes, bags, and clothes.
A certain species of yeast, Candida albicans, causes vaginal yeast infection called candidiasis. Candidiasis can also occur in other parts of the body such as the mouth, hands, feet, skin, and nails.
Other common fungal infections are athlete’s foot and ringworm. Athlete’s foot is an itchy, painful skin infection of the foot caused by the fungus Tinea pedis. Ringworm is any fungal infection of the skin, scalp, and nails. Some groups of fungi may also cause diseases of the brain.
Some species of mushrooms produce poisonous substances known as mycotoxins. The poisonous ones are commonly called toadstools and the non-poisonous, mushrooms.
Mycotoxins are extremely dangerous when ingested. They may cause hallucinations then finally death. It is safer to rely on the mushroom sold in the grocery stores because they have passed the hands of mushroom experts rather than harvesting one from the wild.
Certain fungi are parasites to plants. Powdery mildews are destructive to fruit trees as well as grain crops. Rusts are common pathogens to wheat. The infected plant looks like it is covered with rusts, thus the name. corn smuts are also a common problem to farmers because they damage corn crops and decrease the yield.
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Filed Under: Biology
