Fungi Including Some Yeasts example essay topic

Fungus The Latin word for mushroom is fungus (plural, fungi). The word fungus has come to stand for a whole group of simple plants that contain no chlorophyll and lack such complex plant structures as roots, stems, leaves, and flowers. Included among the fungi, along with mushrooms, are molds, mildews, rusts, smuts, truffles, and yeasts. Toadstool is another name for mushroom.

Some people use the name toadstool only when referring to poisonous mushrooms, but botanists make no such distinction. A general scientific term for fungi is, from the Greek word for mushroom, makes, and the study of these organisms is called mycology. Because they lack chlorophyll, fungi are unable to manufacture food out of the raw materials around them as other plants do. They must therefore get nutrition from other plants and from animals. When they get their food from living plants or animals, fungi are called parasites. When they get it from dead plant or animal matter, they are called saprophytes.

Fungi are very widely distributed throughout the world, particularly in the temperate and tropical regions where there is sufficient moisture for them to grow. They are less likely to be found in dry areas. Some few types of fungi have been reported in Arctic and Antarctic areas (some molds, after all, thrive on refrigerated food). There are about 50,000 known species of fungus.

Although any single typical fungus may not be uniform in appearance -- a mushroom, for example, has a cap, stem, and rootlike components -- it has, in fact, a uniform structure throughout. The typical fungus consists of a mass of tubular, branched filaments, or strands, called hyphae (singular, hypha). The mass of hyphae is called the mycelium, and it is this that makes up the thallus, or body, of the fungus. In order to grow, the mycelium uses the organic matter, either living or dead, in its environment. As the mycelium matures, it forms spores. These are seed like reproductive bodies, each normally consisting of one cell, that become detached from the parent fungus and start new organisms.

As the spore grows, it develops into a hypha that branches out and eventually forms the mycelium of a new fungus. In some fungi the spores may be produced directly by any portion of the mycelium; in others, such as the mushroom, they are formed in a special fruiting section, such as the mushroom cap. This section, normally the only visible or most visible section of the fungus, is called the sporophore. Fungi live both on land and in the water. Only a small portion of those that live on land is normally visible. Most of the fungus, a complex network of hyphae, grows underground, near the surface.

The visible parts of fungi vary greatly in size. Some are so tiny that they cannot be seen without the aid of magnification. Others are quite large. Some mushrooms reach diameters of 8 to 10 inches (20 to 25 centimeters) and heights of 10 to 12 inches (25 to 30 centimeters). Bracket fungi that are 15 inches (38 centimeters) in diameter are fairly common; and mushrooms called puffballs have been known to grow to 60 inches (152 centimeters) in diameter. Although fungi are distributed worldwide, the distribution of a specific species is limited by temperature and moisture conditions of an area coupled with the available food supply.

The best temperature for most fungi to thrive is from 68^0 to 86^0 F (20^0 to 30^0 C). Some types of fungi, however, do perfectly well at them- as high as 120^0 F (48^0 C), while a fairly large number of them do well at freezing temperatures, 32^0 F (0^0 C) or below. The reproduction of fungi can be either sexual or asexual. Sexual reproduction, as with other organisms, involves the fusion of two nuclei when two sex cells unite.

This joining produces spores that can grow into new organisms. Asexual reproduction is by fragmentation, cell division, or budding. The simplest process is direct fragmentation, or breaking up, of the fungus body, the thallus. Each of the fragments develops into a new individual organism if environmental conditions are favorable. Such fragmentation usually is the result of outside natural forces. Some yeasts, which are single-celled fungi, reproduce by simple cell division.

A yeast cell divides into two complete yeast cells. Other fungi, including some yeasts, reproduce by a method that is called budding. A bud develops on the surface of a yeast cell; the nucleus of the cell then divides into two, one of which moves into the bud. The bud is capable of starting a life of its own as a new fungus How Fungi Obtain Food fungus secretes enzymes into the living or dead plant or animal material on which it grows. The enzymes digest the material, which is then absorbed through the walls of the hyphae.

A common example of this action is the rotting of fruits such as peaches or apples. The brown, softened area on the fruit has been subjected to the enzyme secretions of the hyphae. Some fungi, more specialized in their food-absorbing techniques, produce tiny hyphae called rhizoids. These rootlike structures anchor the fungus to its food source and probably also absorb food. Other fungi produce absorptive structures called haustoria, another type of hypha outgrowth. Fungi are classified as parasites or saprophytes (or sa probes), depending on whether they feed on living or dead organic matter.

Because parasites attack living organisms for their nutrition, they are a leading cause of disease in plants. Some cause diseases in animals, including humans. Among the fungal diseases that attack plants are downy mildew on grapes, onions, and tobacco; powdery mildew on grapes, apples, cherries, lilacs, peaches, and roses; smut on corn, wheat, and onions; rust on wheat, oats, beans, asparagus, and some flowers; brown rot on some fruits; and various spots, blights, and wilts on leaves. Because they attack only dead organic matter, saprophytes are in good measure responsible for the decomposition of much plant and animal residue. They also attack foodstuffs such as bread, processed meat and cheese, and picked fruits and vegetables. Some saprophytes are responsible for the destruction of timber, textiles, paper, and leather.

Most saprophytes need oxygen in order to survive and feed. Some few, such as those that cause fermentation, can survive without it. Plant and Animal Associations Some types of fungi live in close, mutually dep en dent association with plants or animals. Lichens, for example, are combinations of fungi and algae living in such close association that they seem to be a single plant form.

Certain scale insects embed themselves in the bark of trees and remain there sucking sap from the tree for the rest of their lives. A type of fungus will spread itself in a network over the bark of the tree, covering the insects and feeding off them, without killing them. This is a case of double parasitism: the insects live off the tree and the fungus off the insects, both to the disadvantage of the tree. An interesting kind of reverse parasitism occurs in certain ant colonies.

Texas leaf-cutter ants cultivate fungi in their underground colonies by feeding the organisms tiny bits of leaves. The ants feed entirely on the fungi. Types of fungi called sooty molds live on the surfaces of plants in association with scale insects. They do not live as parasites on either the insects or the plants, but they obtain nourishment from the secretions of the insects. The extensive growth of the mold's mycelium, however, may prevent light from reaching the plant's surface and thus cause it to die because photosynthesis is inhibited.

Some Familiar Fungi casual walk through a forest is sufficient to bring one into contact with many familiar fungi, such as varieties of mushrooms and the familiar bracket fungus that grows on wood. Other types of fungi are brought to one's attention largely in association with food: the mold that covers stale bread, the yeast that is used for baking or brewing, and the mushrooms and truffles that are available in supermarkets or offered as delicacies in many restaurants. Molds: One chief difference between molds and other fungi is that molds, in their life cycles, alternate between animal and plant behavior. The fact that they are able, at certain stages of their lives, to move about gives them a similarity to protozoa, or tiny one-celled animals. Yet in most of their functions and by their appearance, they resemble other fungi.

Most of them are saprophytic, obtaining their nutrition from dead organic matter such as meat, cheese, bread, fruits, and vegetables. One group, the, is parasitic and frequently causes serious crop diseases, particularly in cabbage, cauliflower, brussels sprouts, turnips, and radishes. Mushrooms: Among the mushrooms are the puffballs and earthstars, which grow in soil or on rotting wood in forests and grassy areas. Many of these are edible while young. When they mature, they dry out and become powdery inside. Rural children know that if they kick these mushrooms when they are dry, a powdery burst of spores will swirl into the slightest breeze.

The largest of the puffballs, Calavatia gigantes, may be as large as 4 feet (120 centimeters) or more across. The earthstars are so named because, in addition to the puffball effect, they have a leaf like expanded base that resembles a star. Since some mushrooms are poisonous, only an expert in mushroom identification should collect mushrooms that are intended for people to eat. Truffles: For centuries this fungus, which grows underground, has been prized as a food delicacy. Truffles are saprophytes and grow in association with the roots of trees, particularly oaks.

They range in size from the size of a pea to as large as an orange. Three countries are famed for their truffles: France, Italy, and England. Mature French truffles are black with white veins; Italian truffles are white; and English truffles are either black or brown, depending on the species. Because truffles grow underground, they are not always easy to locate, so hunting them is usually carried out with the aid of pigs or dogs. Yeasts: There are about 160 species of single-celled fungi commonly called yeasts. Some yeasts are commercially significant because they are used in baking, brewing, and fermentation.

Yeast does its work primarily by interacting with the carbohydrates (sugar and starches) in either dough for bread or liquid for brewing and fermentation. Brewers' yeast has long been considered nutritionally useful to humans because it contains a high quantity of B vitamins. Some yeasts cause decay in fruits and vegetables, as do other saprophytic fungi. Fungi and People Fungi are everywhere in the human environment -- in the soil; in lakes, rivers, and the seas; in the air (some are so tiny that they are carried by currents of wind or on the bodies of insects); and in and on plants and animals, including humans.

They, along with bacteria, are responsible for the decay of organic matter and the release into the atmosphere of carbon, oxygen, nitrogen, and phosphorous. Many of them are eaten at the dinner table. One of the most beneficial uses of a fungus came with the virtually accidental discovery of the antibiotic penicillin by Sir Alexander Fleming in 1928. Antibiotics, many of them derived from fungi, have helped revolutionize the practice of medicine in the 20th century.

Not all fungi are beneficial. Some, as has been noted, can cause serious diseases in plants and wreak havoc on whole segments of an agricultural economy. One of the best-known instances of fungus devastation in the 20th century was the destruction of elm trees in Europe and the United States by Dutch elm disease. The fungus responsible, Ceratocystis ulm i, probably arrived in Europe from Asia about the time of World War I. By the 1930's it had spread throughout Europe and Great Britain and killed thousands of trees. It appeared in the United States in 1930 and has since destroyed millions of elm trees. Overland spread of the disease normally occurs through transmission by elm bark beetles.

One serious fungus-caused disease that may attack people and animals is ergotism. The fungus ergot develops on grasses, especially on rye. It contains a number of poisons called alkaloids. If the grain is harvested and the ergot is not removed, it will get into bread made from the rye and cause ergotism -- also known as St. Anthony's fire -- for which there is no known cure. The disease may also infect cattle that eat the rye grains left in a field. Ergot also contains acid, the principle active agent in the drug LSD (acid).

The fungus does have some positive uses however. It has been used to develop medicines that induce labor in pregnant women and curtail hemorrhaging after birth.