fungi

Page written by Matthew Bogen = __Kingdom Fungi__ =



**Diagnostic Characteristics of Fungi:**
Fungi (singular, fungus) are heterotrophic, eukaryotic cells with cell walls. “Eukaryotic” means that a cell has a nucleus, and its organelles are enclosed by membranes, a layer of lipids that selectively allows certain nutrients in or out. “Heterotrophs” are organisms that cannot make their own food, and obtain it from other sources in their environment. In the case of fungi, they have a method called absorption (see ‘transport of materials’)

In contrast to plants, which use cellulose in their cell walls, fungi use **chitin**, the same material that is found in the exoskeletons of insects.

In the past, an absence of flagella (singular, flagellum) was required in order to be a member of Kingdom Fungi. However, one of the phyla (singular, phylum) in Kingdom Fungi, Phylum Chytridiomycota, has flagella as a distinctive characteristic. When evidence arose to suggest that this phylum, which at the time had been grouped with protists, was more closely related to fungi than other protists, the phylum was shifted in classification.

Note: “-mycete” is a suffix used to denote fungi. Anything-mycete means that it’s a fungus or fungus-related.

**Habitats:**
Fungi are present in both aquatic and terrestrial areas. In aquatic, species have been found in both marine and freshwater environments. In terrestrial environments, fungi act as primary decomposers in an ecosystem.

Fungi require moist environments to thrive. They frequently appear on old food (hence black bread mold) that is left out in the open. Due to fungi’s method of reproduction (see the section), nearly anything in open air can become a location for fungi to settle. This ranges from rotting logs to shower curtains.

The fossil record indicates that fungi appeared in terrestrial habitats around the same time as plants. //Fungi can live on soil, dead matter, plants, animals, and bacteria. (CM)//

Fungi need food, air, and moisture to thrive. However, fungi do not die if these conditions are not met. If an area is unsuitable for a mold spore to open up and grow, it will wait until the conditions are right. Mold spores can remain alive for years simply living inside of their cases, even without food, air, and moisture. (JS 11)

**Major Types:**
There are four phyla within Kingdom Fungi.



Phylum Chytridiomycota: The earliest phylum to diverge in fungal phylogeny. Chytrids, as members of this phylum are called, live in aqutic environments. They are noted to have //flagella//, whip-like tails used for movement. For this reason, chytrids used to be classified as protists. The loss of flagella is considered an evolutionary change that affects the other three phyla. Chytrids prey on different food sources. Some are decomposers, while others parasitize other aquatic organisms. These parasitic chytrids are a factor in why amphibian populations have declined worldwide.

Phylum Zygomycota: Named for zygosporangiua, the structure used by species in this taxon for reproduction. (Covered in the reproduction section) Zygomycetes live in soil. Like chytrids, zygomycetes have different food sources. Some get nutrients from decaying plant or animal material. Others forms **mycorrhizae**. Mycorrhizae is a mutualistic relation between fungi and plants. In exchange for getting material, a zygomycete can aid the plant in taking nutrients from the soil.

Phylum Ascoymycote: Present in marine, freshwater, and terrestrial areas, ascomycetes are named for their **asci**, a saclike container of spores for sexual reproduction. Ascomycetes are noted for an extensive heterokaryotic stage during reproduction. (See more in reproduction) Ascomycetes include many decomposers, but also count in their number many plant pathogens. A pathogen is an organism that causes disease in its host.

Phylum Basidiomycota: Named for **basidiocarps**, a fruting body used in reproduction, basidiomycetes are the best saprobes of wood. This is due to their ability to decompose lignin, a complex polymer abundantly present in wood. Basidiomycetes are noted for their long-lived dikaryotic mycelia (see anatomy).

Basidiomycetes include mushrooms, shelf fungi, puffballs, rusts, and smuts. These fungi are dispersed by spores that come from the tips of the basidia (origin of the Phyla name). These mushrooms are essentially chunks of interwoven hyphae growing up from a main mass of mycelium underground. Basidia grow on the undersides and release spores into the air. (JP- Source 3)

Separate from these four phyla are the deuteromycetes, or **imperfect fungi**. These are fungi that don’t demonstrate stages in sexual reproduction that would lead it to be classified in one of the four phyla. (If a stage is discovered, the species will be relocated into one of the four phyla.)

**lichens**
Llichens are not a individual organism. Lichens are made of millions of photosynthetic microorganisms. Lichens are a mixture of algea and fungus. They live where neither fungus nor algea can. They act as a pioneer species in primary and secondary secussion. They help with the fixation, making an inorganic compound an organic molecule, of nitrogen. Lichens can absorb up to ten times their weight in water. Lichens are known to have reproduced sexaully although some do not. Lichens are able to survive the extreme cold and live in places like the tundra. There the phylum is often mistaken for moss. They often have a hard time growing in arid climates due to the lack of water, growing only one or two centimeters a year. Lichens can not survive in a polluted in environment because they are sensitive to sulfur dioxide that is readily accepted because of lichens passive intake of water and minerals.(RJ)

**Basic Anatomy:**
A fungus’s main structure is its hyphae (singular hypha). Hyphae are tube-like walls that surround the cytoplasm and plasma membranes. Comprised of all these hyphae is the mycelium (plural mycelia), an interwoven network of an organism’s hyphae. Due to fungi’s method of obtaining nutrients, mycelia are noted for having incredibly high surface area, and can grow rapidly – even at the pace of a kilometer a day. Some fungi have **septa**, cross-walls that divide the hyphae. They are porous, which allows ribosomes, mitochondria, and even nuclei to filter between them. However, other fungi are **coenocytic**, meaning that there are no such divisions. Most fungi are multicellular. Some, however, are unicellular. For example, yeast is a unicellular fungus. Phylum Chrytidiomycota is the only phylum of fungi to possess flagella.

For reproduction, different phyla have unique structures (see ‘Major types’ and ‘Reproduction’)

Fungi have cell walls (like plants) but the cell walls are composed of //**chitin**//, which is what arthropod (insects, crayfish, etc.) exoskeletons are composed of. The cell walls of plants and some protists are composed of cellulose.The hyphae of some symbiotic fungi become specialized for penetrating the cells of the host. These hyphae are called //**haustoria. (RW)**//

**Transport of Materials:**
Fungi gain their materials through **absorption**. Different nutrients pass through hyphae from their environment. Hence, hyphae have a massive surface area, especially compared to volume. Materials can also traverse different cells through the septa, cross-walls in the hyphae.

In order to digest their food, fungi secrete **exoenzymes** outside their body. (hence the prefix ‘exo-’) These exoenzymes break down molecules into simpler ones that can be absorbed by the fungus.

Different fungi obtain these materials from varying environments. **Saprobes**, decomposers, absorb nutrients from dead organic matter. An example would be if a basidiomycete absorbed nutrients from a dead, rotting log.

Parasitic fungi, on the other hand, take nutrients from live plant or animal hosts. Those that parasitize plants can develop **haustoria** (singular haustorium), hyphae that penetrate the cell wall of a plant cell.

Mutualistic fungi will similarly take nutrients from their hosts, but will aid its host in some way. For instance, many fungi can aid plants in getting nutrients from the soil.

Fungi’s digestive enzymes are very strong and can easily break down cellulose and lignin in decaying plant tissues. In order to prevent themselves from also digesting themselves, fungi have cell walls that resistant to their own enzymes. (CP source 2).

Locomotion is defined as an organisms movement or ability to move from one place to another. Fungi have rather limited locomotion and are described as being sessile, meaning they are fixed in one place and overall immobile.
 * Locomotion: **

**Reproduction:**
Fungi reproduce either sexually or asexually.

At its core, fungi produce spores, a haploid set of chromosomes, and release them. The wind will then carry the spores across a distance. If the environment a spore lands in is moist and has plenty of nutrients, it will germinate and begin creating hyphae of its own.

Different phyla of fungi are more or less likely to produce either sexually or asexually. This is also dependent on conditions in the fungus’s environment.

For sexual reproduction in fungi, there are two primary stages: **plasmogamy** and **karyogamy**. In plasmogamy, the cytoplasm of two parent fungi fuses when their mycelia meet. In karyogamy, the haploid nuclei fuse and undergo meiosis. Then, the specialized structures (depending on the phylum) produce and disperse these haploid spores.

It should be noted that a normal nucleus in fungi is **haploid**, or only has one set of chromosomes. (By contrast, humans have two sets of 23 chromosomes each. This state of paired DNA sets is diploidy.)

In addition, plasmogamy and karyogamy do not happen immediately after each other. Even when the mycelia come together, the nuclei may not fuse for some time, ranging from days to decades. In these instances, the mycelium is considered **dikaryotic** – it has two distinct nuclei.

Different phyla have different structures for producing and releasing spores.

Phylum Zygomycota: Structures called zygosporangia (singular zygosporangium) are produced, where plasmogamy and karyogamy take place. Mucor is a genus within the zygosporangiua class. There are about 2000 known types of mucor. They are molds, usually white, beige, or grey. They undergo sexual and asexual reproduction in plants, digestive systems, vegetables, and plants, although they cannot usually infect humans. They are, however, very prevalent in Europe and the culprit of mold allergies for many Europeans. (LPE)

Phylum Ascomycota: Plasmogamy produces an ascognium (female) and an antheridium (male). The ascognium extends hyphae, and dikaryotic cells will form. Asci, the saclike containers for spores, will develop at the tips of these dikaryotic hyphae.

Phylum Basidiomycota: Basidiocarps, fruting bodies, are the source of sexual spores. From these, basidia, where meiosis occurs, and basidiospores, the fungus’s spores that will be carried by wind, are developed. Asexual reproduction in basidiomycetes is far less common than in ascomycetes.

The hetrokaryotic stage is the stage where fungi fuse together to create one cell with two nuclei. (MP)

media type="youtube" key="qDwgSWDqKoQ?version=3" height="315" width="420"(VN) Reproduction in Fungi

media type="youtube" key="puDkLFcCZyI" height="315" width="420" (IL) The above video depicts growth in fungus, while at the end there is footage of fungus beginning reproduction.

media type="youtube" key="Y4n0b5rMqE0" height="314" width="420"(AR)

**Environmental Adaptations:**
Fungi have developed mutualistic associations in a number of cases. For instance, **lichens** are a combination of fungi and photosynthetic autotrohps (usually green algae or cyanobacteria). The fungus provides the structure to held everything together. It acts as a physical environment that algae can grow on, and can provide protection from some intense sunlight. Meanwhile, the algae provides energy. Cyanobacteria can fix nitrogen. Lichens are so merged that they have their own classification system, with over 25,000 ‘species’ listed.

There are also mutualistic associations with plants, called **mycorrhizae**, as exemplified with the aid in getting nutrients from the soil.

Fungi have adapted in other ways. They have developed a method to secrete exoenzymes to digest food outside the hyphae, and haustoria can penetrate dead organic matter to obtain resources.

Fungi are of great importance and value to all life on Earth, especially so to humans. Fungi decompose dead, organic matter (without fungi and other decomposers, Earth would be buried in waste); recycle carbon and nitrogen; and release carbon dioxide into the atmosphere. Various forms of fungi can be used in food industries, too; for example, yeast is used in baking bread and brewing alcohol, and mushrooms and truffles are used as a source of food. Many fungi have also been used for medicinal purposes, particularly in the case of penicillin and cyclosporine, a drug that “makes organ transplants possible.” (MR; Sources 13, 14, 15, and 16) However, fungi also have many negative implications for Earth’s organisms; they parasitize a number of organisms, including humans (e.g. athlete’s foot, yeast infections, and ringworm), and cause devastating agricultural disease, such as Ireland’s potato famine in the mid-1840s, which led to the death of over 250,000 Irish people. (MR; Sources 13, 14, 15, and 16) In more recent times, some of you may be aware of the honey bee colony collapse crisis that started in 2006, a tragedy in which approximately 20-40% of honey bee colonies present in the United States have died for no obvious reason. This colony collapse phenomenon threatens to have devastating effects on our environment and our agricultural system. Scientists have since identified a certain viral strain and fungus that, in tandem, have been responsible for this catastrophe. (MR; Sources 13, 14, 15, and 16)

__**Review Questions**__ 1. Define the term "sessile". How can this trait affect the reproductive success of fungi or other organisms? State an example. (MB) 2. How does the structure of fungi help it obtain and transport food and other materials? (AP) 3. What types of habitats would be suitable for fungi? 4. How do fungi carry out sexual and asexual reproduction and what is need for these to be successful in forming a new individual? (MS)

Sources: Campbell, Neil A., and Jane B. Reece. "Fungi." //Biology//. San Francisco: Benjamin Cummings, 2002. 616-31. Print. http://www.uwlax.edu/biology/volk/fungi3/sld001.htm (TB) 2. [] (CP) 3. [] mucor.org (LPE) 4. [] (MM) 5. http://www.mun.ca/biology/scarr/141985_Fungi.jpg (Matt B) 6. [] (AR) 7. [] (AR) 8. // Reproduction in Fungi - YouTube //. // YouTube - Broadcast Yourself. // Web. 11 Nov. 2011. . (VN) 9. [] (ZJ) 10.[] (MP) 11. [] (JS) 12.[|http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/fungi/fungi.htm#Structure] (RW) 13. "Fungi." Biology. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Gale Science In Context. Web. 1 Dec. 2011. 14. "Fungi." Biology. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Gale Science In Context. Web. 1 Dec. 2011. 15. "Fungi." World of Biology. Gale, 2010. Gale Science In Context. Web. 1 Dec. 2011. 16. "Fungi." UXL Complete Life Science Resource. Ed. Julie Carnagie and Leonard C. Bruno. Detroit: UXL, 2009. Gale Science In Context. Web. 1 Dec. 2011.