A fungus (plural: fungi) is a living organism that includes yeasts, moulds, mushrooms and others. Fungi have thin thread-like cells called hyphae that absorb nutrients and hold the fungus in place. Some, such as mushrooms, also have a body containing many cells. Fungi do not have chlorophyll to capture energy from sunlight as plants do. Instead, they are nourished by digesting dead organic matter around them and absorbing it. The study of fungi is called mycology.

The fungi are a separate kingdom of living things, different from animals and plants.

The cells of fungi have nuclei, unlike the cells of bacteria. Hyphae sometimes have many nuclei. Their cell walls contain chitin, unlike the cell walls of plants, which contain cellulose. These and other differences show that the fungi form a single group of related organisms. The group of fungi is called the Eumycota or Eumycetes. They share a common ancestor: they are a monophyletic group.

Fungi are saprophytic: a fungus breaks down dead organic matter around it, and uses it as food. It absorbs the molecules of food through its cell wall.p107 Some fungi are parasitic or symbiotic.

Fungi reproduce sexually and asexually in several different ways. Many fungi make spores that grow into new fungi. 

Fungi came into existence about 1000 million years ago. They are found in fossils from the Devonian period, and they are probably much older. They are hard to find in older fossils because they decay rapidly.

Structure

Reproduction 
Fungi reproduce both sexually and asexually. Some fungi grow mushrooms: these are fruiting bodies.  Under the cap there are gills; the gills bear spores that will disperse, and may develop into new fungi.  Otherwise, fungi use a sporangium to bear asexual spores by mitosis, or sexual spores by meiosis. The spores are haploid.

Fungi may be single celled or multicellular. Yeast is single-celled, and reproduces either sexually or asexually. Asexual reproduction occurs by simple budding (binary fission).

Mycelium 

The mycelium is the vegetative (non-reproductive) part of a fungus. It is usually underground (or inside some other substance), and made of filaments called hyphae (singluar: hypha).

Hyphae 
Hyphae look like threads or tiny roots. The mycelium is a mat of hyphae that may be very thickly woven. The fungus uses them to extract nutrients. Each hypha is a long cell inside a tube-shaped cell wall that grows from the end. 

Hyphae are usually syncytia. This means the cell walls (septa) are mostly not complete, and the cell nuclei are not separated from each other as in normal cells. Details differ between species.

Symbiosis 
Symbiosis means living together. Lichens are a symbiosis between a fungus and an alga or bacterium. In this partnership the algal cells live inside the fungus tissue. The end result is a new mat-like life-form which clings to rock and other surfaces. About 20% of all fungi live as part of a lichen.

Another important kind of symbiosis is mycorrhiza. This is when a fungus lives inside plant roots; most trees have mycorrhizal roots, and so do many crop plants. Both the fungus and the plant benefit in this arrangement.

Pathogens 

Some fungi cause crop diseases; others cause serious disease in humans. Some are highly poisonous: never eat a mushroom picked in the wild unless you know what you are doing.

Uses 
 Edible fungi are widely used as human food. Certain types of cheese need a fungal species to be added. Blue cheese and Camembert cheese are examples of those types of cheese. The fungi give a unique flavor and texture to the cheese. 
 Some fungi produce psychotropic (mind-altering) substances. Some people take these fungi recreationally for their psychedelic properties. These psychedelic mushrooms are often called magic mushrooms because they can cause hallucinations. As with any drug, their effect ends after a certain amount of time. Most "magic mushrooms" last for 4 to 6 hours. Because of their mind-altering effects they are illegal in many countries around the world. However, scientists are also researching ways to use "magic mushrooms" as medicine.
 In modern times, some fungi (for example, penicillin) have been used as a source of antibiotics. The antibiotics are produced by many fungi as a natural defence against bacteria.

Related pages 
 Mycorrhiza
 Mould
 Lichen
 Candida

References