Fungus and Single-celled Fungi

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  • Topic: Fungus, Yeast, Mushroom
  • Pages : 6 (2138 words )
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  • Published : October 8, 1999
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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 mycota, from the Greek word for mushroom, mykes, 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 seedlike 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° to 86°F (20° to 30°C). Some types of fungi, however, do perfectly well at tem- peratures as high as 120°F (48°C), while a fairly large number of them do well at freezing temperatures, 32°F (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...
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