Classification of Microorganisms
General Classification
Introduction
This Article is concerned with?classification, also known as?taxonomy, which is the arrangement of organisms into related groups.? we will explain the categories into which microorganisms can be placed - bacteria, algae, fungi, protozoa, and viruses.?In addition, briefly consider a few larger organisms such as rotifers and worms.?But before we consider the different types of microorganisms, you need to understand how scientists classify all living organisms.
Categories
Taxonomists place every organism in the world into a series of categories, such as those shown below.?These categories are based on relationships, with closely related organisms placed in the same category.?
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As you can see,?kingdom?is the most general category used to describe an organism.?A cat is in the kingdom Animalia, also known as the animal kingdom.?A variety of other organisms such as worms, insects, and snails are also in the animal kingdom.?By saying that cats and snails are in the same kingdom, we are saying that they are more closely related to each other than either is related to, for example, a fern in the plant kingdom.?
Each category below kingdom narrows down the types of characteristics which an organism has.?The phylum Chordata, for example, includes only animals with backbones, while the class Mammalia contains animals with backbones which also have hair and feed their young with milk.?
The narrowest category is?species, which is a group of organisms that have similar traits and can interbreed.?Scientists usually refer to a certain species of organism using its?scientific name, which consists of both its genus and species names with the genus name capitalized and with both names italicized.?For example, the scientific name of the domestic cat is?Felis catus, the scientific name of humans is?Homo sapiens, and the scientific name of the organism which causes giardiasis is?Giardia lamblia.?
In addition to the categories shown on the pyramid above, there are a few other categories which you may come in contact with.??Subspecies,?strain, and?variety?are all terms used to refer to categories smaller than species.?For example, the grizzly bear is a subspecies of the brown bear.?In microbiology, we often talk about different strains of bacteria, some of which can cause disease and some of which cannot.?
The chart above shows how microorganisms are related.?The three most general groups into which the organisms are placed are prokaryotes, eukaryotes, and non-living organisms.?We will explain what each of these categories mean in a later Article.?For now, you should just be aware that prokaryotes are more primitive organisms than eukaryotes.?
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10 个月Hi, based on what I have read, Archaea and Bacteria are now considered to be two separate types of Procaryotes although Archaea were once classified as Bacteria.