Bacteria
Bacteria (bacteria, singular bacterium) are microorganisms characterized by the absence of a clear nuclear membrane, as a result, considered more primitive compared to animal and plant cells (the overwhelming number of antibiotics are aimed at destroying the walls of bacterial cells). Most bacteria are unicellular, and cells can have the following shapes: spherical (coccus), spiral (spirilla), rod-shaped (bacillus), helical (spirochete) and comma (vibrio). Bacteria usually range in size from 0.5 to 6 microns. Mobile individuals have one or more antennae extending from their surface (from the cell wall). Many bacteria have a capsule - a thick layer of much hydrated material; some of them have the property of forming resting forms under unfavorable conditions,retaining viability for a long period (such as endospores). Bacteria multiply by simple cell division (asexual); with incomplete separation of daughter cells, the formation of chains and other forms can occur. In the presence of a dense nutrient medium, as a result of the multiplication of bacteria, colonies appear, which are visible concentrations of cells. Some of them have a filamentous shape, similar to that of a fungus. Certain types of bacteria are able to reproduce sexually through mating (conjugation). Bacteria are found almost everywhere. They can live in water, soil or air, as well as parasitize in the body of plants, animals or humans. Some species do not harm their hosts, while others can cause various diseases.
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