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1. Outline the classification and include living examples at all levels of classification.

The vegetative filament of a fungus is called a hypha. Hyphae may or may not be divided into cells by perforated cross walls, each of which is called a septum. A hypha grows at its tip, where new membrane material is added by the action of Golgi bodies. A mat of interwoven hyphae is known as mycelium. Branches form in areas away from the tip. Hyphae cell walls are made of chitin, a complex polysaccharide also found in the external skeleton of insects and other invertebrates. Fungi differ from plants, which have cellulose in their cell walls. Fungi, like animals, store food as glycogen, while plants store food as starch.

Fungi reproduce both sexually and asexually. Sexual reproduction in many fungi begins when cells or gametes from two mating strains undergo cytoplasmic fusion. The nuclei, however, may not immediately fuse, but will divide independently. When genetically different nuclei coexist within a hypha, the hypha is said to be heterokaryotic. A hypha with genetically similar nuclei is called homokaryotic.

Fungi reproduce asexually by producing spores, usually on special branches or modified cells of the hyphae. The small, lightweight spores are often released into the air. They may be carried long distances before they land and germinate into new hyphae. Fungi also reproduce asexually by the fragmentation, or breaking apart, of the hyphae.

Members of the kingdom fungi are classified into four divisions based primarily on the structure of the hyphae or on the type of reproduction.

Zygomycota

The approximately 600 species of the Division Zygomycota are mostly terrestrial organisms. They are commonly found in soil and dung. Zygomycetes are coenocytic - that is their hyphae lack septa. However their reproductive structures are blocked off from the rest of the hyphae by unperforated cross walls.

The division Zygomycota includes Rhizopus stolonifer, the common black bread mold. Rhizopus appears as a fuzzy growth on bread and consists of three different types of hyphae. Rhizoids are anchoring hyphae that penetrate the bread, produce digestive enzymes and absorb nutrients. The hyphae that grows across the surface of the bread are called stolons. Specialized upright hyphae called sporangiophores produce sporangia at their tips.

Asexual reproduction in zygomycetes occurs when hormonal action causes upright sporangiophores to form. Sporangia form at the tips of the sporangiophores. The sporangia produce spores that are dispersed by wind.

Sexual reproduction in Rhizopus is called conjugation. Conjugation in fungi is a sexual process that occurs when two filaments line up to each other. A similar kind of conjugation occurs in filamentous algae such as Spirogyra. In Rhizopus hyphae of two mating strains come close together. Each hypha encloses haploid nuclei. Hormones cause short branches to form on each phyla and grow outward until they touch. Then septa form near the tip of each branch. Each resulting cell is a gametangium that contains several nuclei. The gametangia fuse; then the nuclei fuse in pairs. Each pair contains one nucleus from each mating strain. Thus the zygote contains many diploid nuclei.

The wall surrounding the zygote then thickens. The resulting protective, temporarily dormant structure is called zygospore. Meiosis occurs when the zygospore germinates. Germination usually takes place after one to three months, depending on environmental conditions.

Reproducing sexually and asexually provides an adaptive advantage. During periods when the environment is favorable, the rapid, asexual formation of spores ensures the quick spread of the species. In periods of environmental stress, sexual reproduction ensures genetic recombination before the hyphae die.

Basidiomycota

Scientists place about 25000 species in the Division Basidiomycota, or club fungi. Mushrooms, toadstools, and puffballs are classified as basidiomycetes, as are rusts and smuts.

Under proper conditions, such as after a warm rain in the spring, underground hyphae grow upward, intertwine, and produce a basidiocarp, the reproductive body of a basidiomycete. A mushroom is a basidiocarp with a flattened cap attached to a stem that is called a stalk.

On the outside of the cap are radiating rows of gills. A specialized club-shaped reproductive cell called a basidium forms on the gills. Each gill contains thousands of basidia. In each basidium two nuclei become isolated by a complete septum. The nuclei fuse and form a diploid zygote. Meiosis then results in four nuclei that are pushed into cytoplasmic extensions to form basidiospores. At maturity basidiospores are released and germinate into new homokaryotic hyphae.

As the homokaryotic hyphae grow, septa form so that each cell contains one nucleus. These homokaryotic, septate hyphae are called the primary mycelium. These hyphae grow and fuse with hyphae from another mating strain. When separate mating strains fuse, a secondary mycelium results. Hyphae of these mycelia are heterokaryotic, containing from each mating strain in each cell. Secondary mycelium intertwines and forms a basidiocarp. A mushroom for example is a basidiocarp.

Rusts are a group of parasitic basidiomycetes that cause diseases in plants. Rusts attack many plants but are of particular concern to us when they infect cereal crops such as wheat and oats. Infected plants look rusty because they are covered with reddish brown fungal spores. Rusts do not form basidiocarps. Instead basidia develop on the surface of infected plants.

Smuts, like rusts, are plant pathogens that do not form basidiocarps. The approximately 1,000 species of smuts cover infected organisms with dark masses of spores.

Ascomycota

The division ascomycota or sac fungi contains over 30,000 species this is the largest division of fungi, and some biologists suspect it may have been the most recent group to evolve sac fungi live in a variety of habitats, including salt and fresh water. In terrestrial environments ascomycetes live in soil dung, and rotting logs. Common ascomycetes are morels, powdery mildews, yeast's, and cup fungi.

Sexual reproduction begins when the hyphae of two mating strains form either male or female gametangia the female gametangium is called an ascogonium and the male gametangium is called an antheridium. The gametangia fuse, and male nuclei move into the ascogonium. Male and female nuclei pair but do not fuse. These cells divide, and the resulting heterocaryotic hyphae grow and intertwine, forming an ascocarp. The ascocarp is the reproductive body of an ascomycete. It has various forms, depending on the species.

Sacs called asci on the surface of the ascocarp near the tips of some hyphae. Each ascus encloses two nuclei. The nuclei fuse in the ascus, and the resulting diploid nucleus immediately undergoes meiosis, producing four haploid nuclei. Each nucleus usually then divides once by mitosis, so each ascus finally contains eight haploid ascospores. When ascus raptures it releases ascospores, usually into the air these land on the ground and germinate forming new hyphae.

Asexual reproduction in ascomycetes involves the production of spores, each of which is called a conidium. Many conidia are formed on the ends of specialized branches called conidiophores.

In unicellular ascomycetes called yeast's asexual reproduction occurs by bud formation. Sexual reproduction involves the formation of a diploid zygote. The zygote results from the fusion of two ascospores. The zygote either may function as an ascus, producing eight ascsores, or may produce diploid cells by budding. If the zygote undergoes meiosis and it produces ascospores, the haploid ascospores can reproduce in one of two ways. They can either produce new haploid cells by budding, or they can fuse in sexual reproduction.

Humans are interested in approximately 600 species of yeast's because of their ability to break down carbohydrates. This ability makes yeast important to the food industry. When carbohydrates are thus broken down, they form alcohol and carbon dioxide. This process causes bread dough to rise and grapes to ferment. Domesticated yeast, usually a strain of saccharomyces cerevisie, is used in most modern brewing processes.

Yeast's are also important to some genetic engineering.

Deuteromycota

Deuteromycetes, sometimes called the imperfect fungi, or fungi imperfecti, are a group of about 10,000 species of fungi in which a sexual reproductive phase has not been discovered. In effect, the division deuteromycota is a taxonomic " holding tank ". Biologist can classify these organisms on the basis of their type of asexual reproduction. However they will not assign deuteromycetes to another division unless they can identify a sexual reproductive phase. The group contains forms that probably have evolved from several different strains. Today it appears that most imperfect fungi have characteristics similar to those of ascomyscetes. Deuteromycetes are the organisms that cause ring worm and athleteís foot.

Aspergilus and penicillium are two deuteromycetes that have recently been reclassified into the division ascomycota. Each of these organisms is valuable to humans. Humans use aspergilus to ferment soy beans and make Soya sauce. Penycilium produces the antibiotic penicilin and gives flavor to Roquefort cheese. These organism have been renamed as a result of their reclassification.

Mycorrhizae and lichens

Mycorrhizae and lichens represent two types of symbiotic relationships between fungi and autotrophic organisms. These relationships are of great ecological significance: they are instances of mutualism a type of symbiosis in which both organisms benefit. A mycorhisa is a symbiotic association between fungi and plant roots. They occur in more then 80 percent of plants. Mycorhysae help plants absorb water and nutrients, such as phosphorous and potassium, by forming extensive networks of fungal hyphae in the soil. The fungus increases the surface area in the soil available for absorption. The digestive action of fungal enzymes provides nutrients that can be readily absorbed by the plant. The fungi absorb some of the sugars created by the plant during photosynthesis.

Fungal hyphae penetrate roots. Mycorrhizae that contain fungi that penetrate the root cortex cells are called endomycorhyzae, the most common type. The fungus is usually a zygomycete. Micorrhizae with fungal hyphae that do not penetrate cortex cells are called ectomycorhyzae. They are less common then endomycorrhizae and the fungus is usually a basidiomycete. Ectomycorhyzae are most common in coniferous forests, especially those with nutrient poor soils. Mycorrhizae help plant absorb nutrients in such environments and also offer the plant some protection from harsh conditions such as cold and draught.

About 20,000 species of fungi form lichens. A lichen is a symbiotic association between a fungus, usually and ascomycete, and a green alga or cyanobateria. Although the relationship is mutualistic, it may also be thought of as controlled parasitism. The fungal hyphae penetrate the cells of the photosynthetic partner and absorb food.

Biologists classify lichens into groups according to the nature of their thallus, or body. Crustose lichens grow as a layer on the surfaces of rocks or trees. Foliose lichens, are loosely attached to the substrate and have thin leafy thalli. A shrubby lichens with upright growth are called two fold lichens. Long, thin growths hanging from tree branches are foliose lichens.

2. Discuss the phylogeny and evolutionary status.

The oldest fossils that resemble modern fungi are found in Precambrian rocks that are about 900 million years old. The earliest fossils that are distinctly fungi are about 500 millions years old, from the Ordovician period. By about 300 million years ago, in the late Carboniferous period, all modern divisions of fungi had evolved. Since most present day fungi are terrestrial, scientists speculate that fungi underwent adaptive radiation shortly after plants and animals colonized the land. Scientists reason that fungi, like all other eukaryotes, arose from prokaryotes. Fungi are heterotrophic - they cannot make their own food - and therefore probably arose from other heterotrophs. Some scientists, however, theorize that some fungi evolved from red algae.

It seems possible that the first fungi were unicellular and gave rise to coenocytic fungi. Coenocytic refers to filaments without internal cross wall. A coenocytic filament contains many nuclei that move through the cytoplasm. Coenocytes may have given rise to club fungi. Club fungi in turn may have given rise to sac fungi. Club fungi and sac fungi have bodies that are divided into distinct cells by perforated cross walls.

3. Describe the main characteristics displayed by the phyla.

Members of the kingdom fungi are a diverse group of over 65,000 species living in many different environments. Molds, mildews, rusts, smuts, mushrooms and yeast's are all fungi. Most fungi are microscopic. Some microscopic fungi, such as the pathogens responsible for athleteís foot, ringworm, and chestnut blight are harmful. Many microscopic fungi, such as yeast's, are beneficial. Yeast's cause bread to rise and are among the most widely used research organisms. Not all fungi are entirely microscopic. Some fungi produce fruiting bodies that are visible to the unaided eye, such as puffballs, mushrooms and morels.

Most fungi are saprophytic or parasitic, and a few species are predatory. A saprophyte is an organism that feeds on dead organic material. As fungi digest this material, they recycle the nutrient molecules in it. Organisms that break down organic materials are decomposes. For example, fungi release carbon, nitrogen and phosphorus molecules when they digest dead plants and animals. These molecules are used by the fungus or by other organisms. Without decomposers, nutrients would not be reused and life could not continue on earth.

A parasite derives its nutrients from a living host organisms at the hostís expense. Parasitic fungi harm host organisms and cause many plant and animal diseases. For example, the fetal Dutch elm disease is caused by the fungus Ceratocystis ulmi. Other fungi, such as wheat rusts, attack crops and cause serious economic loss. Fungi that attack animals cause a variety of diseases, such as histoplasmosis, a serious lung disease.

A predatory fungus is one that captures pray for food. Pleurotus ostreatus is an example of a predatory fungus. Also called the oyster fungus, P. ostreatus obtains nitrogen by capturing roundworms. After secreting a substance that makes the roundworm sluggish the fungal cells engulf the worm, penetrate its body, and absorb its contents.

4. Explain in detail the reproductive patterns found in the phyla. How do these patterns increase the ability of the organisms to survive natural selection.

Fungi reproduce both sexually and asexually. Sexual reproduction in many fungi begins when cells or gametes from two mating strains undergo cytoplasmic fusion. The nuclei, however, may not immediately fuse, but will divide independently. When genetically different nuclei coexist within a hypha, the hypha is said to be heterokaryotic. A hypha with genetically similar nuclei is called homokaryotic.

Fungi reproduce asexually by producing spores, usually on special branches or modified cells of the hyphae. The small, lightweight spores are often released into the air. They may be carried long distances before they land and germinate into new hyphae. Fungi also reproduce asexually by the fragmentation, or breaking apart, of the hyphae.

This is how reproduction occurs in Division Zygomycota:

Asexual reproduction in zygomycetes occurs when hormonal action causes upright sporangiophores to form. Sporangia form at the tips of the sporangiophores. The sporangia produce spores that are dispersed by wind.

Sexual reproduction in Rhizopus is called conjugation. Conjugation in fungi is a sexual process that occurs when two filaments line up to each other. A similar kind of conjugation occurs in filamentous algae such as Spirogyra. In Rhizopus hyphae of two mating strains come close together. Each hypha encloses haploid nuclei. Hormones cause short branches to form on each phyla and grow outward until they touch. Then septa form near the tip of each branch. Each resulting cell is a gametangium that contains several nuclei. The gametangia fuse; then the nuclei fuse in pairs. Each pair contains one nucleus from each mating strain. Thus the zygote contains many diploid nuclei.

The wall surrounding the zygote then thickens. The resulting protective, temporarily dormant structure is called zygospore. Meiosis occurs when the zygospore germinates. Germination usually takes place after one to three months, depending on environmental conditions.

Reproducing sexually and asexually provides an adaptive advantage. During periods when the environment is favorable, the rapid, asexual formation of spores ensures the quick spread of the species. In periods of environmental stress, sexual reproduction ensures genetic recombination before the hyphae die.

This is how reproduction occurs in Division Basidiomycota:

Under proper conditions, such as after a warm rain in the spring, underground hyphae grow upward, intertwine, and produce a basidiocarp, the reproductive body of a basidiomycete. A mushroom is a basidiocarp with a flattened cap attached to a stem that is called a stalk.

On the outside of the cap are radiating rows of gills. A specialized club-shaped reproductive cell called a basidium forms on the gills. Each gill contains thousands of basidia. In each basidium two nuclei become isolated by a complete septum. The nuclei fuse and form a diploid zygote. Meiosis then results in four nuclei that are pushed into cytoplasmic extensions to form basidiospores. At maturity basidiospores are released and germinate into new homokaryotic hyphae.

As the homokaryotic hyphae grow, septa form so that each cell contains one nucleus. These homokaryotic, septate hyphae are called the primary mycelium. These hyphae grow and fuse with hyphae from another mating strain. When separate mating strains fuse, a secondary mycelium results. Hyphae of these mycelia are heterokaryotic, containing from each mating strain in each cell. Secondary mycelium intertwines and forms a basidiocarp. A mushroom for example is a basidiocarp.

This is how reproduction occurs in the Division Ascomycota:

Sexual reproduction begins when the hyphae of two mating strains form either male or female gametangia the female gametangium is called an ascogonium and the male gametangium is called an antheridium. The gametangia fuse, and male nuclei move into the ascogonium. Male and female nuclei pair but do not fuse. These cells divide, and the resulting heterocaryotic hyphae grow and intertwine, forming an ascocarp. The ascocarp is the reproductive body of an ascomycete. It has various forms, depending on the species.

Sacs called asci on the surface of the ascocarp near the tips of some hyphae. Each ascus encloses two nuclei. The nuclei fuse in the ascus, and the resulting diploid nucleus immediately undergoes meiosis, producing four haploid nuclei. Each nucleus usually then divides once by mitosis, so each ascus finally contains eight haploid ascospores. When ascus raptures it releases ascospores, usually into the air these land on the ground and germinate forming new hyphae.

Asexual reproduction in ascomycetes involves the production of spores, each of which is called a conidium. Many conidia are formed on the ends of specialized branches called conidiophores.

In unicellular ascomycetes called yeast's asexual reproduction occurs by bud formation. Sexual reproduction involves the formation of a diploid zygote. The zygote results from the fusion of two ascospores. The zygote either may function as an ascus, producing eight ascsores, or may produce diploid cells by budding. If the zygote undergoes meiosis and it produces ascospores, the haploid ascospores can reproduce in one of two ways. They can either produce new haploid cells by budding, or they can fuse in sexual reproduction.

5. Describe the relationship of these phyla with humans both positive and negative.

Positive

One of the main positive factors fungi acts as is as a decomposer. Decomposers are necessary to change dead organic bodies into minerals and nutrients and also contribute toward the carbon cycle. The carbon cycle is when a fungus decomposes an organism it forms a byproduct carbon dioxide, which can be later used by trees to develop oxygen and this way the cycle continues.

Yeast's are used for rising dough by producing carbon dioxide.

yeast's are used to produce alcohol

A good share of antibiotics are a chemical produced by different types of fungi.

Lichens are the symbiosis of algae and fungus and because they are very sensitive to pollution they can be used to determine the amount of pollution in the air.

Negative

Many fungi are poisonous and deadly, it is not advised to eat any without good knowledge of them.

Some types of fungus exists as parasites and cause many wood and plant diseases, which cause problems in our agriculture and forest industries. Many pesticides are being used to prevent parasite fungi from destroying our crops.

6. Explain something you found interesting about fungi.

I was very interested by the symbiotic relationship of fungus and algae in lichens.

About 20,000 species of fungi form lichens. A lichen is a symbiotic association between a fungus, usually and ascomycete, and a green alga or cyanobateria. Although the relationship is mutualistic, it may also be thought of as controlled parasitism. The fungal hyphae penetrate the cells of the photosynthetic partner and absorb food.

Biologists classify lichens into groups according to the nature of their thallus, or body. Crustose lichens grow as a layer on the surfaces of rocks or trees. Foliose lichens, are loosely attached to the substrate and have thin leafy thalli. A shrubby lichens with upright growth are called two fold lichens. Long, thin growths hanging from tree branches are foliose lichens.

 

7. Make a running list of the organisms for each phyla.

Division Oomycota : water molds, white rusts, downy mildews. Saprolegnia, Phytophthora, Albugo

Division Zygomycota

Class Zygomycetes : Rhizopus, Mucor, Phycomyces, Choanephora, Entomophthora

Class Trichomycetes : Stachylina

Division Ascomycota

Class Hemiascomycetes : Yeast's and their relatives. Saccharomyces, Schizosaccharomyces, Endomyces, Eremascus, Taphrina

Class Plectomycetes : Powdery Mildews, fruit molds, etc. Erysiphe, Podosphaera, Aspergillus, Penicillium, Ceratocystis

Class Pyrenomycetes : Sordaria, Neurospora, Chaetomium, Xylaria, Hypoxylon

Class Discomycetes : Sclerotinia, Trichoscyphella, Rhytisma, Xanthoria, Pyronema

Class Laboulbeniomycetes : Herpomyces, Laboulbenia

Class Loculoascomycetes : Cochliobolus, Pyrenophora, Leptosphaeria, Pleospora

Division Basidiomycota

Class Heterobasidiomycetes : Rusts and smuts, Ustilago, Urocystis, Puccinia. Phragmidium, Melampsora

Class Homobasidiomycetes : Toadstools, bracket fungi, mushrooms, puffballs, stinkhorns, etc. Coprinus, Marasmius, Amanita, Agaricus, Lycoperdon, Phallus.