Classifying Organisms

Taxonomy
Taxonomy is the science of classifying organisms. Carol von Linne, mostly known as Carolus Linnaeus, was the Swedish botanist who began working on a system for the classification of organisms. This system evolved and became the most common system used today. The system consists of organizing different groups which are inside other groups. Each organism would be labeled with a species, related species would be organized in the same genus, similar genera would be in the same family, then families in an order, orders in a class, classes in a phylum (or a division), and phyla in a kingdom.

The Kingdoms, which are the largest groups, were only two in the beginning but have developed and now 6 Kindoms are usually accepted: Animalia, Plantae, Fungi, Protista, Monera, Archaea. 

• Kingdom Monera: Prokaryotes; Bacteria; May have fungus, plant, or animal characteristics; includes Eubacteria and Cyanobacteria; around 10,000 species
• Kingdom Archaea: Prokaryotes; always unicellular and living under rough or extreme conditions and environments; different chemical characteristics than Monera
• Kingdom Protista: Slime molds and algae; mostly unicellular; eukaryote; around 250,000 species
• Kingdom Fungi: Mushrooms, molds, mildew; multicellular; heterotrophic; almost never capable of movement; 100,000 species
• Kingdom Plantae: Multicellular and eukaryotes; producers of complex molecules using light (photosynthesis); 250,000 species
• Kingdom Animalia: Multicellular and eukaryotes; without cell walls which reduces stiffness; unable to produce food, need to take energy from external sources; 1,000,000 species (largest kingdom) 

A very important part of the classification are the homologous structures. Internal structures which may be similar to those of other organisms may help classify the groups. Characteristics such as reproduction methods, backbone existence, type of food consumed, body parts and covering, and others may also help in the grouping. There are other three ways of classifying including: systematics, cladistics, and molecular evolutionary taxonomy. Systematics and Cladistics use tree diagrams to explain relationships between organisms and find their way to a common ancestor. The difference between these two is that cladistics usually divide the branches when special traits are found. Molecular Evolutionary Taxonomy classifies by the presence of specific genetic changes in organisms. Still the anatomical classification (Linnaeus method) is the most common. It keeps changing because of the new discoveries available because of new technology.

A common example of Linnaeus's method are humans:

• Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia
• Order: Primata
• Family: Hominidae
• Genus: Homo
• Species: sapiens sapiens

A species is the one who breed exclusively inside a group and produces fertile offspring. The name of the species would be used with the genus name in the binomial nomenclature to make up the official name of a certain organism. In the past example the species's name would be Homo sapiens sapiens.




Sources:
Chester, T., W. Armstrong, and K. Madore. 2007. The Five Kingdoms of Life. Available at: http://waynesword.palomar.edu/trfeb98.htm.
Rode Island College Faculty. 2010. The Six Kingdoms and Taxonomy. http://www.ric.edu/faculty/ptiskus/six_kingdoms/index.htm
McDarby, Micheal. 2010. Classifying Living Things - Taxonomy. http://faculty.fmcc.suny.edu/mcdarby/animals&plantsbook/History/02-Explaining-Life-Classification.htm#Systematics & Cladistics