UNIT+6+-+MICROBIOLOGY



__ INTRO __ Microbiology is the study of //[|microorganisms]//, which are [|unicellular] or cell-cluster [|microscopic] [|organisms]. This includes [|eukaryotes] such as [|fungi] and [|protists], and [|prokaryotes] such as [|bacteria] and certain algae. [|Viruses], though not strictly classed as living organisms, are also studied__. __ Microbiology is a broad term which includes [|virology], [|mycology], [|parasitology] and other branches. A [|microbiologist] is a specialist in microbiology. Microbiology is researched actively, and the field is advancing continually. We have probably only studied about one percent of all of the microbe species on Earth. Although microbes were first observed over three hundred years ago, the field of microbiology can be said to be in its infancy relative to older biological disciplines such as [|zoology] and [|botany].


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VIRUSES __** A **virus** (from the [|Latin] //virus// meaning "[|toxin]" or "[|poison]"), is a [|sub-microscopic] infectious agent that is unable to grow or reproduce outside a [|host] [|cell]. Each viral particle, or //virion//, consists of genetic material, [|DNA] or [|RNA], within a protective protein coat called a [|capsid]. The capsid shape varies from simple helical and icosahedral (polyhedral or near-spherical) forms, to more complex structures with tails or an [|envelope]. Viruses infect cellular life forms and are grouped into animal, plant and bacterial types, according to the type of host infected. [|Biologists] debate whether or not viruses are living [|organisms]. Some consider them non-living as they do not meet all the criteria used in the common definitions of [|life]. For example, unlike most organisms, viruses do not have [|cells]. However, viruses have genes and evolve by [|natural selection]. Others have described them as organisms at the edge of life. Viral infections in human and animal hosts usually result in an immune response and [|disease]. Often, a virus is completely eliminated by the [|immune system]. [|Antibiotics] have no effect on viruses, but [|antiviral drugs] have been developed to treat life-threatening infections. [|Vaccines] that produce lifelong [|immunity] can prevent viral infections.

__Bacteria** (singular: **bacterium**) are unicellular [|microorganisms]. Typically a few [|micrometres] in length, bacteria have a wide range of shapes, ranging from [|spheres] to rods to spirals. Bacteria are ubiquitous in every [|habitat] on [|Earth], growing in soil, [|acidic hot springs], [|radioactive waste], seawater, and deep in the [|Earth's crust]. There are typically 40 million bacterial [|cells] in a gram of soil and a million bacterial cells in a millilitre of fresh water; in all, there are approximately five [|nonillion] (5×1030) bacteria on Earth, forming much of the world's [|biomass].Bacteria are vital in recycling nutrients, and many important steps in [|nutrient cycles] depend on bacteria, such as the [|fixation of nitrogen] from the [|atmosphere]. However, most of these bacteria have not been characterized, and only about half of the [|phyla] of bacteria have species that can be [|cultured] in the [|laboratory].hThe study of bacteria is known as [|bacteriology], a branch of [|microbiology]. There are approximately ten times as many bacterial cells as [|human] cells in the human body, with large numbers of bacteria on the [|skin] and in the [|digestive tract]. Although the vast majority of these bacteria are rendered harmless by the protective effects of the [|immune system], and a few are [|beneficial], some are [|pathogenic bacteria] and cause [|infectious diseases], including [|cholera], [|syphilis], [|anthrax], [|leprosy] and [|bubonic plague]. The most common fatal bacterial diseases are [|respiratory infections], with [|tuberculosis] alone killing about 2 million people a year, mostly in [|sub-Saharan Africa]. In [|developed countries], [|antibiotics] are used to treat bacterial infections and in various agricultural processes, so [|antibiotic resistance] is becoming common. In industry, bacteria are important in processes such as [|sewage treatment], the production of [|cheese] and [|yoghurt], and the manufacture of antibiotics and other chemicals. Bacteria are [|prokaryotes]. Unlike cells of animals and other [|eukaryotes], bacterial cells do not contain a [|nucleus] and rarely harbour [|membrane-bound] [|organelles]. Although the term //bacteria// traditionally included all prokaryotes, the [|scientific classification] changed after the discovery in the 1990s that prokaryotic life consists of two very different groups of organisms that [|evolved] independently from an ancient common ancestor. These [|evolutionary domains] are called Bacteria and [|Archaea].
 * __ BACTERIA


 * __ THE HOT ZONE

http://student.ccbcmd.edu/courses/bio141/lecguide/unit1/shape/shape.html

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