Fungus Facts

Fungi are very different from green plants, as they contain no chlorophyll or chloroplasts. These are simple plants that include the yeast, molds, rusts, smuts, and mushrooms.

Fungi are very different from green plants, as they contain no chlorophyll or chloroplasts. These are simple plants that include the yeast, molds, rusts, smuts, and mushrooms. Some biologists place fungi in a different kingdom separate from plants, while others don't. Most fungi are decomposers and cause decay. Some are parasites and get their food from a host.

Most fungal species are saprophytes: they feed on remains of dead organisms or their by-products (such as leaf litter on a forest floor). Most forest soil has too much acid for bacteria to grow well, and so the fungi are the main decay producers. They will cause decay of dead leaves. They secrete enzymes that break down these organic remains, then they absorb soluble breakdown products. Saprophytic fungi are the best of decomposers as they help recycle substances through communities of life.

Mycelium is the vegetative body of most true fungi. The basic unit of a fungus is not a cell but a threadlike tubular structure called a hypha. These structures have cross-walls that give them a "cellular" structure and in these the divisions are not true cells. The hyphae usually contain chitin, a very resistant nitrogenous substance. The composition may vary with age and environmental conditions. The tips of the hyphae are full of cytoplasm, but in other regions there may be a central vacuole. Many very small nuclei are present in the cytoplasm. In some of the species, multinucleate cytoplasm runs continuously through the tubes; in others, perforated cross-walls compartmentalize the hyphae into separate cells, yet allow chemical communication and movement of nuclei between body parts. The hyphae threads spread out and grow over and into their food material and may make up a visible mesh or mycelium.

Fungi must take in food materials synthesized by other organisms due to the absence of chlorophyll; the fungi cannot photosynthesize their food from simple substances. Saprophytic fungi derive food from dead and decaying materials. The molds are such an example as they develop on stale, damp food and the many fungi that live in the soil feed on the humus there. If there were no soil fungi, there would be large amounts of dead wood and organic litter that would not decay or be returned to the soil. The parasitic fungi live on or in the tissues of another living organism or host, absorbing nourishment from its body.

There are growing tips on the hyphae, on the saprophytic and parasitic fund, that can break down complex organic materials into simpler soluble substances absorb in the cell walls. The process enables parasitic hyphae to break down and penetrate the cell walls of the host.

Most of the true fungi can reproduce asexually through spore formation, fission and budding (by single-celled yeast), or fragmentation from a parent mycelium. They are many that are able to reproduce sexually. Asexual reproduction takes place rapidly after the establishment of a mycelium. Vertical hyphae are a little thicker than the rest, they grow up and become swollen at their ends. These swellings contain the dense cytoplasm and many nuclei. The swelling becomes the sporangium and the protoplasm inside breaks up into elliptical spores, each containing several nuclei, surrounded by a wall. In species of Mucor the sporangium wall breaks away causing the powdery spore mass to be dispersed by air currents. In other Mucor species, the sporangium wall liquefies, releasing the spores, but the method of spore dispersal is uncertain. Other species such as gametes are all potentially compatible. In others, only gametes of different mating types can fuse.

The yeast is a one-celled fungus with cells that divide in a manner called budding. This is a widely distributed and rather unusual family of fungi. Only a few of the several species can form true hyphae; the majority of them consist of single-celled organisms. The nucleus first divides by mitosis, then one nucleus moves out against the cell membrane. The wall bulges outward, and the nucleus moves into the bulge, then slowly the bulge (called a bud) grows and becomes an entirely new cell. There may be more than one bud on a cell when growing rapidly. One bud can even appear on another bud resulting in a many-celled appearance, then before long the cells separate and become one-celled yeast plants again. Yeast will reproduce by spores. In certain conditions, two cells may conjugate, that is, they join and their cell contents fuse. Then later, the cell contents divide into four individuals, each developing a thick wall. These are spores and may constitute a resting stage. The old cell wall enclosing them opens letting the spores free to germinate and form normally budding cells. Such spores often arise without any previous conjugation.

These fungi contain a group of enzymes that break down sugar into carbon dioxide and ethanol ("alcohol"), making energy available for metabolism. The later stages of fermentation are a type of anaerobic respiration. Unless fermentable sugars are present the yeast cells require oxygen for the preliminary conversion of other available carbohydrates into compounds that become energy sources. Yeast added to the dough makes carbon dioxide; since the carbon dioxide cannot escape the dough swells up or rises.

Mold is any fungus that has a threadlike form of growth and a fuzzy appearance. The common type grows on bread and develops from spores, which drift in the air. The spore after it falls onto the damp bread grows by sending out branching threads. A cell membrane and cell wall contain cytoplasm and many nuclei surround the threads. The threads grow down into the bread and produce digestive enzymes that will change the bread into a liquid form. Growing mold absorbs the liquid. Mold grows across the surface of the bread. At the ends, a new set of branching threads moves down into the bread, spreading the mold.

Mucor is the name given to a group of mold fungi, which grow on the surface of decaying fruit, bread, horse manure, and other organic matter. The hyphae, which have no cross-walls, grow rapidly under favorable conditions and branch repeatedly, within a few days forming a dense white or gray mycelium covering the surface of the food. The spores of Mucor are very resistant to conditions such as drought or cold, and can remain dormant for years. When conditions are favorable the wall of the spore breaks open and the protoplasm inside grows out into a new hypha and eventually into a mycelium. Germination favors warm, damp conditions.

Species of Penicillin of certain mold fungi have become important to antibacterial chemicals or antibiotics they produce. Penicillin is made growing the appropriate species of mold on nutrients; the active compound is then extracted from the culture fluid and purified. Soil-dwelling microorganisms called actinomycetes, which have characteristics of both bacteria and fungi, produce streptomycin and other antibiotics.

Parasitic fungi are the disease-causing organisms in plants and fungal attacks can result in devastating agricultural losses. They can also produce diseases in animals, some of them very serious. In the moist tropics there are countless fungal disease in humans.

A parasitic fungus, Phytophora infestans, causes the disease late blight in potatoes and tomatoes. This disease was responsible for the Irish potato famines of the mid-nineteenth century. If a spore of the fungus lands on a leaf of a healthy potato plant in warm moist conditions, a new hypha grows out of it and enters the leaf through a stoma. Then short branches will grow out of the hypha and penetrate the walls of the leaf cells with the aid of enzymes. The hyphae absorb nutrients from the cell contents and grow rapidly, spreading throughout the tissues of the plant. This parasite can kill the entire plant.

Lichens are single plants that consist of a fungus and an alga growing together. The threads of the fungus give the lichen its shape. The cells of the alga mix in among these fungus threads, giving the lichen its green color. The fungus absorbs water from the air allowing the alga to grow then the fungus gets food from the alga.

The mushrooms are fungi that are larger and more complex than the molds. In this group there are also puffballs and shelf fungi. In the rotting leaves on the forest floor the strands of fungus tissue digest and absorb their food. When these fungus plants have grown strong enough the cells multiply and form the fruiting body, the spore-producing organ of the fungus. Often the mushrooms appear in the same spot on a lawn each year where some old roots or logs lie buried, as this is the food of the hidden fungus body.

Some fungi have fruiting bodes that are good to eat such as the favorite of all fungi, the mushrooms. Be very careful if you are around sheds or caves or even in an open field and find wild mushrooms as some can not only make you sick but also can kill.

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