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Classification of Organisms

Classification of Organisms

Author: Skylear Shields

To help explain the levels of taxonomy (classification) and explain the differences between Eukarya, Bacteria and Archeae.

Taxonomy, or the classification of living things, has tiers. From the most broad categorization to the most specific, the categories are; Domain, Kingdom, Phylum, Class, Order, Family and Species. There are only three domains, which are Eukarya (complex organisms), Archaea (a type of prokaryote) and Bacteria.

What are the differences between the three domains, you ask? Eukaryotes are complex cells; all the way down to their organelles. Archaea and Bacteria are simple, since they lack a nucleus. Archaea and Bacteria are only different due to the unique nature of Archaea's cell wall, as well as the biochemical bonds that Archaea can perform.

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Hey there! If you're reading this, then it must mean that you want to know how the classification - or taxonomy - of living things works. I'll explain it the best I can.

First, I'll be explaining the levels, or ranks, of "biological classification". Biological classification is the categorization of living things, all the way down to their species. I'll be using a green iguana - iguana iguana, if you prefer Latin - as an example.

Then, I'll explain the differences between the three Domains.

The Tiers of Taxonomy

Alright. There are a total of 8 ranks of taxonomy. Well, that isn't entirely accurate; there's 9, but I'll explain that in a second. The 8 major ranks start from the broadest category, Domain, to the most specific, Species. You can see the list of the major categories in the image to the right.

The "Life" category is the special 9th that I mentioned. Since Life is so broad it encompasses all life on Earth, we tend to not mention it.

The "Domain" rank gets split into three different "sub-ranks". These sub-ranks are Eukarya, Archaea, and Bacteria. Our green iguana (we'll nickname him Iggy) is a complex multicellular organism, and thus we'll place him under Eukarya.

Next we have the "Kingdom" rank. Kingdoms are a tad more specific than Domains, but have more sub-ranks. One popular sub-rank of Kingdom is the Animalia, or Animal kingdom. There is also the Plantae (plants) and the Fungi (mushrooms and such), just to name a couple. Since Iggy is an animal, we'd put him in the Animalia kingdom.

Then there's the "Phylum" category. There is a crazy amount of Phyla, so I'll only use one; Chordata. The Chordata Phylum is the Phylum that Iggy belongs to; it's the Phylum that classifies the animals which possess spinal cords and pre-anal tails. You can read the list of Phyla here.

Next is the "Class" rank. There are a few Classes, but here's the one Iggy belongs to; Reptilia. Reptilia, or the Reptile Class, is quite self-explanatory. Same goes for the Mammalia Class.

The "Order" rank is getting even more specific. Iggy, our friend iguana, is in the Squamata Order. Squamata encompasses pretty much all reptiles. You can read more on Orders here. Note that there are quite a few unlisted Orders.

"Families" are the next rank, and they are defined by the similarities between "Genus". Iggy the iguana belongs to the Iguanidae family, which comprises of all iguanas and related species!

"Genus" is the second-to-most specific category. Like how the Grizzly bear is under the Genus Ursus (bear in Latin), our pet iguana is in the Genus Iguana. Genus usually dictate a smaller cluster of certain organisms in Families.

The "Species" rank is exactly how it sounds; the specific group that the organism belongs to. Organisms get to Species when they have some unique trait(s) that separates them from their Genus siblings. Iggy is a common iguana, and his species is iguana.

Iggy's Conclusion

Now that we've explored the ranks of taxonomy, we can finally define completely what our pal Iggy is!

He is an Animalia Chordata Reptilia Squamata Iguandae Iguana Iguana. You could also say he's a Spined Animal that's a Lizard-class Reptile that is Thrice an Iguana. Either way, we have successfully taxonomy'd our pet Iggy.

Go ahead and post some taxonomies of your favorite animals in the comment section!

Eukarya vs. Archaea vs. Bacteria

The three Domains I talked about earlier are each different.

  • Eukarya - these guys are complex organisms. Their cells have nuclei, unlike the other two. Four Kingdoms fit under the Domain of the Eukaryotes; the Protista (Protists), the Fungi, the Plantae and the Anamalia.
  • Archaea - a sub-division of Prokaryotes, Archaea are somewhat different from their cousin Bacteria. These guys have a unique cell wall and a few unique organelles that enable them to live in quite extreme enviroments... sary, the Mariana Trench or the Sahara Desert.
  • Bacteria - the other sub-division of Prokaryotes, the Bacteria are cousins to the Archaea. They're found almost everywhere and also lack a nucleus and quite a few other organelles that Eukaryotes have. 

Now, the core differences between the Archaea and Bacteria are that; Archaea have three RNA enzymes, while Bacteria have only one. Bacteria reacts to antibiotics differently, and Archaea behave more like Eukaryotic cells.