Fungi

Fungi are a group of many-celled organisms that live by absorbing food and are neither plant nor animal. They are so different that biologists have given them their own separate kingdom among the five kingdoms or forms of life (monerans, protists, fungi, plants, and animals). Fungi play a key role as decomposers and recyclers, but they can also cause disease in plants and animals.

The kingdom Fungi is made up of yeasts, molds, and mushrooms. Most are many-celled organisms with a complex cell structure. Although some fungi resemble plants and have roots, they lack leaves and chlorophyll and cannot make their own food. Instead, they absorb their food directly from their surroundings, including living or dead matter. Fungi also digest their food outside their bodies. They do this by releasing enzymes onto their food, which breaks down the food for absorption. Fungi are different in the way they reproduce. Nearly all species of fungi reproduce asexually by forming special reproductive cells called spores. They do not produce embryos as plants and animals do. Instead, every fungus produces powdery spore cells that are so light they can be dispersed by the wind. These microscopic spores can resist harsh conditions and remain ready to germinate when conditions are right.

Fungi play an essential role in the cycles of nature because they break down organic matter like dead plants or animals and allow their basic nutrients to be recycled. Without fungi in the soil acting as nature's decomposers, we would be living in a sea of waste. When fungi eat, they break down or decompose organic matter into simple substances like carbon, nitrogen, and hydrogen, which become available for other living things to use. Fungi are usually too small to see, but when they form fruiting bodies (such as mushrooms growing on a rotting log), they become obvious. Those mushrooms we notice on a log are hard at work breaking down the dead wood.

Although beneficial, fungi can also be harmful to certain forms of life. This kind of fungi are parasitic and are known as biotrophs. Biotrophs are organisms that live by absorbing organic compounds from living matter. These fungi can destroy crops by attacking a plant's major systems, or they can contribute to plant diseases. Certain fungi, like molds, can cause foods to spoil, sneakers to smell, and toes to itch from athlete's foot. Other fungi, like yeast, are put to good use and are essential to making bread, wine, beer, and certain cheeses, since they cause the all-important fermentation process (the breaking down of carbohydrates into alcohol and carbon dioxide). In the twentieth century, scientists discovered that important drugs could be derived from fungi. Antibiotics—like penicillin as well as the wonder drug cyclosporin, which makes organ transplants possible—are good examples. Finally, mushrooms are cultivated like any crop and are sold commercially to be eaten as a food.

The main groups of fungi are chyrids, water molds, sporangium fungi, sac fungi, and club fungi. Chyrids live in muddy or aquatic habitats and feed on decaying plants, although some live as parasites. Water molds are important decomposers in watery environments. Sporangium fungi are commonly known as bread mold and are also found in soil and manure. Sac fungi, which comprise more than 30,000 species, include the yeast used to leaven bread and to make alcoholic beverages. Club fungi include the familiar mushroom as well as stinkhorns and puffballs. All fungi can reproduce asexually, and making spores is the most common method of reproduction. Spores are similar to seeds but much smaller and simpler since they usually contain only one or two cells. Fungi are able to respond to changes in their environment and can produce a large amount of spores in a short time if necessary (as in drought conditions). Most fungi release their spores into the air; the wind carries the ultralight spores into the atmosphere where they can travel great distances. If a spore lands on organic matter and conditions are good, it will germinate or sprout and produce a new fungus. With a typical mushroom, the part we notice aboveground is the spore-producing part of the organism. When a fungus is mature enough, a good rainfall will cause this spore-bearing part to swell and push aboveground, making mushrooms appear where there were none the day before.

A world with no fungi would be a world full of dead plants and animals that would neither rot and nor disappear naturally. It would be a world in constant need of basic substances since it could not break down organic matter and therefore could not recycle. It would also be a world without mushrooms. Mushroom farming is a large industry since people in all parts of the world eat mushrooms both raw and cooked. Wild mushrooms should never be eaten, however, since it takes an expert to know the difference between an edible mushroom and a poisonous one.

[See alsoAntibiotics; Decomposition ]