Fungi, << FUHN jy, >> are organisms that obtain food by absorbing it from other living organisms or from parts of formerly living things. According to mycologists (scientists who study fungi), thousands of fungus species (types) exist. A number of fungi are too small to be seen without a microscope. But many types can be seen with the unaided eye. Some of the most common fungi include mildews, molds, mushrooms, rusts, and smuts.
Parts of a fungus.
Except for yeasts, chytrids, and other one-celled fungi, the main part of a fungus consists of thousands of threadlike cells called hyphae. These tiny, branching cells sometimes form a tangled mass called a mycelium. In many kinds of fungi, the mycelium grows beneath the surface of the material on which the organism is feeding. For example, the mycelium of a mushroom often grows just beneath the surface of the soil. The umbrella-shaped growth known as a mushroom is actually the fruiting body of the fungus. The fruiting body produces cells called spores, which develop into new hyphae. Spores are smaller and simpler than the seeds of plants, but both enable an organism to reproduce.
Certain fungi, including some types of molds, bear spores in tiny structures called sporangia. In black bread mold, the sporangia form at the tips of upright hyphae called sporangiophores. Other hyphae called stolons spread over the surface of the bread. They are anchored by rhizoids (rootlike structures). Groups of sporangia usually form above the rhizoids. Such fungi as the green mold Penicillium notatum produce chains of spores from branched hyphae called conidiophores. Still other fungi, including cup fungi, produce spores that they shoot into the air from individual saclike cells.
How a fungus lives.
Since fungi cannot produce their own food, they take carbohydrates, proteins, and other nutrients from the living organisms or dead organic matter on which they live. Fungi discharge chemicals called enzymes into the material on which they feed. The enzymes break down complex carbohydrates and proteins into simple compounds that the hyphae can absorb.
Fungi live almost everywhere on land and in water. Mushrooms belong to a large group of fungi called saprophytes, which live on dead or decaying matter. Such fungi as mildews and smuts are parasites that feed on living organisms. Some fungi live together with other organisms in ways that are mutually beneficial. For example, a fungus and an organism called an alga may live together to form a lichen (see Lichen ). Some fungi also live with the roots of plants in a relationship known as a mycorrhiza. The fungus takes carbohydrates from the plant. In return, the fungus helps supply the plant with water and such important minerals as phosphorus, potassium, iron, copper, and zinc. Most trees, shrubs, and herbs have mycorrhizal relationships with fungi.
Fungi generally reproduce by forming spores. Some spores are produced by the union of gametes (sex cells). Others, called asexual or imperfect spores, develop without the union of gametes. Many fungi produce spores both sexually and asexually. Numerous spores are scattered by the wind, and others are transported by water or by animals. Mushrooms, cup fungi, and some other fungi forcefully discharge their spores. A spore that lands in a favorable location germinates (starts to grow) and eventually produces a new mycelium.
Yeasts can reproduce by forming sexual spores, but many kinds of yeasts reproduce by budding. When a yeast buds, a bulge forms on the cell. A cell wall grows and separates the bud from the original yeast cell. The bud then develops into a new cell. Budding produces a large number of yeast cells rapidly.
The importance of fungi.
Many fungi break down complex animal and plant matter into simple compounds. This process of decomposition enriches the soil and makes essential substances available to plants and other organisms in a usable form. Through decomposition, fungi also return carbon dioxide to the atmosphere, where green plants can reuse it to make food.
Fungi play a major role in a number of foods. For example, mushrooms and truffles are considered delicacies by many people (see Truffle ). Cheese manufacturers add molds to Camembert and Roquefort cheeses to ripen them and provide their distinctive flavors. Yeasts cause the fermentation that produces alcoholic beverages. In the fermentation process, yeasts break down sugar into carbon dioxide and alcohol. Baker’s yeast causes bread to rise by producing carbon dioxide from the carbohydrates in the dough. The carbon dioxide gas bubbles up through the dough, causing the rise. Some people eat yeasts as a rich source of protein and B vitamins.
Some molds produce important drugs called antibiotics. Antibiotics weaken or destroy bacteria and other organisms that cause disease. Penicillin, the first and most important antibiotic, was discovered in 1928 by Sir Alexander Fleming, a British bacteriologist. Penicillium notatum is one of several green molds that produce penicillin, which physicians use in treating many diseases caused by bacteria. See Penicillin .
Some fungi may cause extensive damage. Parasitic fungi destroy many crops and other plants. Important parasitic fungi that attack plants include mildews, rusts, and smuts. Others produce diseases in animals and people. Some mushrooms are poisonous and can cause serious illness or death if eaten. Molds spoil many kinds of food, and they may also prove poisonous. In damp climates, mildews and other fungi can ruin clothing, bookbindings, and other materials. Fungi may also cause wood to decay or rot.
