FUNGI
A fungus (plural fungi) is a eukaryotic organism that digests its food externally and absorbs the nutrient molecules into its cells. Along with bacteria, fungi are the primary decomposers of dead organic matter in most terrestrial ecosystems. Many fungi have important symbiotic relationships with many other organisms. Mycorrhizal symbiosis between plants and fungi is particularly important; over 90% of all plant species engage in some kind of mycorrhizal relationship with fungi and are dependent upon this relationship for survival. Fungi are also used extensively by humans: yeasts are responsible for fermentation of beer and bread, and mushroom farming and gathering is a large industry in many countries.
The branch of biology involving the study of fungi is known as mycology.
Fungi were originally classified as plants, however have since been separated as they are heterotrophs. This means they do not fix their own carbon through photosynthesis, but use carbon fixed by other organisms for metabolism. Fungi are now thought to be more closely related to animals than to plants, and are placed with animals in the monophyletic group of opisthokonts. Fungi absorb their food while animals ingest it, and their cells have cell walls. For these reasons, these organisms are placed in their own kingdom, Fungi.
The Fungi are a monophyletic group, meaning all varieties of fungi come from a common ancestor. The monophyly of the fungi has been confirmed through repeated tests of molecular phylogenetics; shared ancestral traits include chitinous cell walls and heterotrophy by absorption, along with other shared characteristics.
The major divisions (phyla) of fungi are mainly classified based on their sexual reproductive structures. Currently, five divisions are recognized:
The Chytridiomycota are commonly known as chytrids. These fungi produce zoospores that are capable of moving on their own through liquid menstrua by simple flagella.
The Zygomycota are known as zygomycetes and reproduce sexually with meiospores called zygospores. Black bread mold (Rhizopus stolonifer) is a common species that belongs to this group; another is Pilobolus, which shoots specialized structures through the air for several meters.
Members of the Glomeromycota are also known as the arbuscular mycorrhizal fungi. Only one species has been observed forming zygospores; all other species only reproduce asexually. This is an ancient association, with evidence dating to 350 million years ago.
The Ascomycota, commonly known as sac fungi or ascomycetes, form meiotic spores called ascospores, which are enclosed in a special sac-like structure called an ascus. This division includes morels, some mushrooms and truffles, as well as single-celled yeasts and many species that have only been observed undergoing asexual reproduction. Because the products of meiosis are retained within the sac-like ascus, several ascomyctes have been used for elucidating principles of genetics and heredity (e.g. Neurospora crassa).
Members of the Basidiomycota, commonly known as the club fungi or basidiomycetes, produce meiospores called basidiospores on club-like stalks called basidia. Most common mushrooms belong to this group, as well as rust (fungus) and smut fungi, which are major pathogens of grains.
Although the water molds and slime molds have traditionally been placed in kingdom Fungi and are still studied by mycologists, they are not true fungi. Unlike true fungi, the water molds and slime molds do not have cell walls made of chitin. In the 5-kingdom system, they are currently placed in kingdom Protista.
Fungi may be single-celled or multicellular. Multicellular fungi are composed of networks of long hollow tubes called hyphae. The hyphae often aggregate in a dense network known as mycelium. The mycelium grows through the medium on which the fungus feeds. Because fungi are embedded in the medium in which they grow, they are often not visible to the naked eye.
Fungi growing in axenic culture (ascomycetes)Although fungi lack true organs, the mycelia of ascomycetes and basidiomycetes may become organized into more complex reproductive structures called fruiting bodies, or sporocarps, when conditions are right. "Mushroom" is the common name given to the above-ground fruiting bodies of many fungal species. Although these above-ground structures are the most conspicuous to humans, they make up only a small portion of the entire fungal body. Some fungi form rhizoids, which are underground root-like structures that provide support and transport nutrients from the soil to the rest of the mycelium.
A fungus of the species Armillaria ostoyae may be the largest organism on the planet. It was discovered in the Malheur National Forest in Oregon, and its underground mycelial network covers an area of 8.9 km² (2200 acres). Whether or not this is an actual individual organism is disputed: some tests have indicated that they have the same genetic makeup, but this does not exclude its being a clonal colony of numerous smaller individuals.
Fungi may reproduce sexually or asexually. In asexual reproduction, the offspring are genetically identical to the “parent” organism (they are clones). During sexual reproduction, a mixing of genetic material occurs so that the offspring exhibit traits of both parents. Many species can use both strategies at different times, while others are apparently strictly sexual or strictly asexual. Sexual reproduction has not been observed in some fungi of the Glomeromycota and Ascomycota. These are commonly referred to as Fungi imperfecti or Deuteromycota.
Yeasts and other unicellular fungi can reproduce simply by budding, or “pinching off” a new cell. Many multicellular species produce a variety of different asexual spores that are easily dispersed and resistant to harsh environmental conditions. When the conditions are right, these spores will germinate and colonize new habitats.
Sexual reproduction in fungi is somewhat different from that of animals or plants, and each fungal division reproduces using different strategies. Fungi that are known to reproduce sexually all have a haploid stage and a diploid stage in their life cycles. Ascomycetes and basidiomycetes also go through a dikaryotic stage, in which the nuclei inherited by the two parents do not fuse right away, but remain separate in the hyphal cells (see heterokaryosis).
In zygomycetes, the haploid hyphae of two compatible individuals fuse, forming a zygote, which becomes a resistant zygospore. When this zygospore germinates, it quickly undergoes meiosis, generating new haploid hyphae and asexual sporangiospores. These sporangiospores may then be distributed and germinate into new genetically-identical individuals, each producing their own haploid hyphae. When the hyphae of two compatible individuals come into contact with one another, they will fuse and generate new zygospores, thus completing the cycle.
In ascomycetes, when compatible haploid hyphae fuse with one another, their nuclei do not immediately fuse. The dikaryotic hyphae form structures called asci (sing. ascus), in which karyogamy (nuclear fusion) occurs. These asci are embedded in an ascocarp, or fruiting body, of the fungus. Karyogamy in the asci is followed immediately by meiosis and the production of ascospores. The ascospores are disseminated and germinate to form new haploid mycelium. Asexual conidia may be produced by the haploid mycelium. Many ascomycetes appear to have lost the ability to reproduce sexually and reproduce only via conidia.
Sexual reproduction in basidiomycetes is similar to that of ascomycetes. Sexually compatible haploid hyphae fuse to produce a dikaryotic mycelium. This leads to the production of a basidiocarp. The most commonly-known basidiocarps are mushrooms, but they may also take many other forms. Club-like structures known as basidia generate haploid basidiospores following karyogamy and meiosis. These basidiospores then germinate to produce new haploid mycelia.
BACTERIA
Bacteria (singular: bacterium) are a major group of living organisms. The term "bacteria" has variously applied to all prokaryotes or to a major group of them, otherwise called the eubacteria, depending on ideas about their relationships. Here, bacteria is used specifically to refer to the eubacteria. Another major group of bacteria (used in the broadest, non-taxonomic sense) are the Archaea. The study of bacteria is known as bacteriology, a subfield of microbiology.
Bacteria are the most abundant of all organisms. They are ubiquitous in soil, water, and as symbionts of other organisms. Many pathogens are bacteria. Most are minute, usually only 0.5-5.0 μm in their longest dimension, although giant bacteria like Thiomargarita namibiensis and Epulopiscium fishelsoni may grow past 0.5 mm in size. They generally have cell walls, like plant and fungal cells, but bacterial cell walls are normally made out of peptidoglycan instead of cellulose (as in plants) or chitin (as in fungi), and are not homologous with eukaryotic cell walls. Many move around using flagella, which are different in structure from the flagella of other groups.
The first bacteria were observed by Anton van Leeuwenhoek in 1674 using a single-lens microscope of his own design. The name bacterium was introduced much later, by Ehrenberg in 1828, derived from the Greek word βακτηριον meaning "small stick". Because of the difficulty in describing individual bacteria and the importance of their discovery to fields such as medicine, biochemistry, and geochemistry, the history of bacteriology is generally described as the history of microbiology.
As prokaryotes (organisms without the cell nucleus)all bacteria have a relatively simple cell structure lacking a cell nucleus and organelles such as mitochondria and chloroplasts. Most bacteria are relatively small and possess distinctive cell and colony morphologies (shapes) as described below. The most important bacterial structural characteristic is the cell wall. Bacteria can be divided into two groups (Gram positive and Gram negative) based on differences in cell wall structure as revealed by Gram staining. Gram positive bacteria possess a cell wall containing a thick peptidoglycan (called Murein in older sources) layer and teichoic acids while Gram negative bacteria have an outer, lipopolysaccharide-containing membrane and a thin peptidoglycan layer located in the periplasm (the region between the outer and cytoplasmic membranes). Many bacteria contain other extracellular structures such as flagella and fimbriae which are used for motility (movement), attachment, and conjugation respectively. Some bacteria also contain capsules or slime layers that also facilitate bacterial attachment to surfaces and biofilm formation. Bacteria contain relatively few intracellular structures compared to eukaryotes but do contain a tightly supercoiled chromosome, ribosomes, and several other species-specific structures such as intracellular membranes, nutrient storage structures, gas vesicles, and magnetosomes. Some bacteria are capable of forming endospores which allows them to survive extreme environmental and chemical stresses. This property is restricted to specific Gram positive organisms such as Bacillus and Clostridium.
In contrast to higher organisms, bacteria exhibit an extremely wide variety of metabolic types. In fact, it is widely accepted that eukaryotic metabolism is largely a derivative of bacterial metabolism with mitochondria having descended from a lineage within the α-Proteobacteria and chloroplasts from the Cyanobacteria by ancient endosymbiotic events. Bacterial metabolism can be divided broadly on the basis of the kind of energy used for growth, electron donors and electron acceptors and by the source of carbon used. Most bacteria are heterotrophic; using organic carbon compounds as both carbon and energy sources. In aerobic organisms, oxygen is used as the terminal electron acceptor. In anaerobic organisms other inorganic compounds, such as nitrate, sulfate or carbon dioxide as terminal electron acceptors leading to the environmentally important processes of denitrification, sulfate reduction and acetogenesis, respectively. Non-respiratory anaerobes use fermentation to generate energy and reducing power, secreting metabolic by-products (such as ethanol in brewing) as waste. Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves. As an alternative to heterotrophy many bacteria are autotrophic, fixing carbon dioxide into cell mass. Energy metabolism of bacteria is either based on phototrophy or chemotrophy, i. e. the use of either light or exergonic chemical reactions for fueling life processes. Lithotrophic bacteria use inorganic electron donors for respiration (chemolthotrophs) or biosynthesis and carbon dioxide fixation (photolithotrophs), opposed by organotrophs which need organic compounds as electron donors for biosynthetic reactions (and mostly as well as carbon sources). Common inorganic electron donors are hydrogen, ammonia (leading to nitrification), iron and several reduced sulfur compounds. In both aerobic phototrophy and chemolithotrophy oxygen is used as a terminal electron acceptor, while under anaerobic conditions inorganic compounds (see above) are used instead. Most photolithotrophic and chemolithotrophic organisms are autotrophic, meaning that they obtain cellular carbon by fixation of carbon dioxide, whereas photoorganotrophic and chemoorganotrophic organisms are heterotrophic. In addition to carbon, some organisms also fix nitrogen gas (nitrogen fixation). This environmentally important trait can be found in bacteria of nearly all the metabolic types listed above but is not universal. The distribution of metabolic traits within a group of organisms has traditionally been used to define their taxonomy, although these traits often do not correspond with genetic techniques
All bacteria reproduce through asexual reproduction (binary fission) which results in cell division. Two identical clone daughter cells are produced. Some bacteria, while still reproducing asexually, form more complex reproductive structures that facilitate the dispersal of the newly-formed daughter cells. Examples include fruiting body formation by Myxococcus and arial hyphae formation by Streptomyces.
Solid agar plate with bacterial coloniesIn the laboratory, bacteria are usually grown using two methods, solid and liquid. Solid growth media such as agar plates are used to isolate pure cultures of a bacterial strain. When quantitation of growth or large volumes of cells are required liquid growth media are generally used. Growth in liquid media, with stirring, most often occurs as an even cell suspension making the cultures easier to divide and transfer compared to solid media, although the isolation of individual cells from liquid media is extremely difficult. In both liquid and solid media there exist a finite amount of nutrients, which allows for the study of the bacterial cell cycle. These limitations can be avoided by the use of a chemostat, which maintains a bacterial culture under steady-state conditions by the continuous addition of nutrients and the removal of waste products and cells. Large chemostats are often used for industrial-scale microbial processes.
Most techniques commonly used to grow bacteria are designed to optimise the amount of cells produced, the amount of time needed to produce them, and the cost to produce them. In a bacterium's natural environment nutrients are limited, meaning that bacteria cannot continue to reproduce indefinitely. This constant limitation of nutrients has led the evolution of many different growth strategies in different types of organisms. Some possess the ability to grow extremely rapidly when nutrients become available, such as the formation of algal (and cyanobacterial) blooms that often occur in lakes during the summer. Other organisms have devised more specialized strategies to make them more successful in a harsh environment, such as the production of antibiotics by Streptomyces; often at the expense of a slower growth rate. In a natural environment, many organisms live in communities (e.g. biofilms) which may allow for increased supply of nutrients and protection of environmental stresses. Often these relationships are essential for growth of a particular organism or group of organisms (syntrophy). These evolutionary tactics to overcome nutrient limitation must be accounted for in an industrial/laboratory bacterial growth experiment. For instance bacteria that tend to agglutinate may need more vigorous stirring to break apart any large bacterial masses. The main growth attribute that must be understood for controlled growth is that bacteria have defined growth phases.
A controlled bacterial growth will follow three distinct phases. Nearly all cultures start from taking a relatively old stock of bacteria and diluting them in to fresh media; these cells need to adapt to the nutrient rich environment. The first phase of growth is the lag phase. The lag phase is a period of slow growth. The slow growth is most often attributed the need for cells to adapt to fast growth. The lag phase has high biosynthesis rates; enzymes needed to metabolise a variety of substrates are produced. The second phase of growth is the logarithmic phase (log phase), also known as the exponential phase. The log phase is marked by rapid exponential growth. The rate at which cells grow during this phase is known as the growth rate. The time it takes the cells to double during the log phase is known as the generation time. During the log phase, nutrients are metabolised at maximum speed until they are all gone. The final phase of growth is the stationary phase. This phase of growth is caused by depleted nutrients. The cells begin to shut down their metabolic activity, as well as break-down their own non-essential proteins. The stationary phase is a transition from rapid growth to dormancy. The cells turn off all none essential functions, such as bacterial conjugation.
2006-08-06 22:22:50
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answer #1
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answered by cookie 2
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Ok, Hey, im names Dan Btw Fungi-many types of it, some are yeast, etc, they are single celled and can only be seen through a microscope, others like mould , can be seen with a naked eye Mouldss are made of tiny threads called hyphae, growing from the threads are fruiting bodies which make spores, wind blow on spores, and as they fall, if suitable they can reproduce, ( fungus), some with very large fruiting bodies, best known is Mushrooms. Yeast is made for beer, wine and bread, they can be used very effectively, some microscopispecieses of fungi are grown in large tanks, the protein in them are mycoprotein, used for artificial meat products Bacteria Big enough to be seen in a light microscope, single celled, found in water,soil and even inside animals.Bacteria help to decay dead animals and plants, help break down sewage, some are made to make foods, yogurt and cheese, thereproduceue by dividing in half, this is called binary fission.
2016-04-02 03:58:57
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answer #4
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answered by Anonymous
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