Most species of fungi grow on land and obtain their nutrients from dead organic matter. Some fungi are symbionts or parasites on other organisms. The majority of species feed by secreting enzymes, which partially digest the food extracellularly, and then absorbing the partially digested food to complete digestion internally.
As with animals, the major storage carbohydrate of fungi is glycogen. Fungi lack the complex vascular system found in higher plants, so their transport of food and water is less efficient.
Along with bacteria, fungi have an important ecological role in the decomposition of dead plants, animals, and other organic matter. Thus, fungi are ecologically important because they release large amounts of carbon dioxide into the atmosphere and recycle nitrogen and other important nutrients within ecosystems for use by plants and other organisms. Some fungi are parasitic, in that they obtain their nutrients from a living host organism, a relationship which usually harms the host.
Such parasitic fungi usually have specialized tissues called haustoria, which penetrate the host’s body. Most of the diseases which afflict agricultural plants are caused by parasitic fungi. Some examples are corn smut, black stem rust of wheat and barley, and cotton root rot. Some species of fungi can also parasitize animals. Even humans can be parasitized by fungi which cause diseases such as athlete’s foot, ringworm, and yeast infections.
Use of fungi in human affairs.
Fungi have a profound influence on human affairs, and their use in food is a very ancient practice; mushrooms, truffles and puffballs must have been, in their season, part of every hunter-gatherer’s collection.
The written record starts with the ancient Greeks, as early as the fifth century BC, where records in the classical writings of Hippocrates and Euripides mention fungus poisoning; from which we can deduce sufficiently long and wide usage of collected field fungi for the few poisonous mushrooms to be distinguished from the non-poisonous. During the years of the Roman Empire, the death of the emperor Claudius was said to be due to the eating of a plate of poisoned mushrooms. Some of the fungi were even regarded as great luxuries with magical properties, considered food of the gods.
The cultivation of macrofungi to yield fruit bodies began to flourish in the beginning of the seventeenth century, and today over six million tonnes of edible mushrooms are produced commercially each year around the world.
Many fungi are of considerable medical significance. For thousands of years, Eastern cultures have revered mushrooms as both food and medicine. Mushrooms or their extracts are made into a soup or tea, research suggesting they may aid in the treatment of certain types of cancer, boost the immune system and reduce the risk of coronary heart disease.
Other fungi are used to modify food to make it more nutritious or palatable. Tuber melanosporum, known to most as the truffle, has a taste and aroma so intense that it is used as flavouring instead of a separate dish. Soy sauce is also produced by growing a filamentous fungus on cooked soya beans. It is used extensively as a flavouring and condiment in Chinese cuisine.