Systems of Biological Classification
Biological Classification Systems
Organisms are divided into three domains: Eukaryotes belong in Eukarya. Prokaryotes are divided into the domains Archaea and Bacteria. Beneath domains there are other rankings that organisms are divided into, so we can keep all the organisms organized and see how they’re grouped together, see which organisms are related to other organisms and from that determine which characteristics they may have in common.
Let’s look at the rest of them. After domain, you’ve got Kingdom, Phylum/Division, and phylum is going to be referred to in Eukarya, where divisions are going to be referred to more in the Archaea and Bacteria domains. Then, you have Class, Order, Family, Genus, and Species. Species is the most specific, where the domains are going to be the most general.
The domains are going to hold everything that fits under that category, where each species is going to hold just a small, very specific organism. Organisms are named scientifically with binomial nomenclature in eukaryotes. Binomial nomenclature is used to name eukaryotic organisms. That means that you use these last two (bi- meaning “two”), these last two names to name an organism.
You would use the genus and species of an organism to give it its scientific name. You will have a more common name most of the time for a creature or an organism, but there is also a scientific name where you will be able to see what the species and genus is and from that see which family, order, class, phylum, kingdom, and domain that organism would fit into.
A species is defined as a population of organisms capable of interbreeding with each other and producing viable and fertile offspring, which means that they are producing offspring that is both alive and healthy and is able to reproduce in itself. If the organisms are producing offspring that aren’t capable of reproducing, then that species is not going to be able to continue, or that organism’s growth isn’t going to be able to continue and it’s not going to be considered a species in itself.
Each species is only going to consist of organisms that can breed with each other and produce viable and fertile offspring, offspring that can also reproduce. Let’s look at an example. Before we do that, I’m going to give you all an acronym to help you remember the order of these. You’ve got your three domains. Under each domain you’re going to have kingdom, phylum, class, order, family, genus, species.
Well, it may be hard to keep track of what order those go in, so here is a helpful little saying that should help you: “Keep Ponds Clean Or Frogs Get Sick.” If you look at the first letter of each of those, they will remind you what the order of our rankings are. Kingdom, phylum, class, order, family, genus, species. Let’s go through and see if you can figure out what this is a classification of.
This organism is in the kingdom Animalia, which is going to be all animals. It’s going to be in the phylum Chordata, which is going to be organisms with spinal cords. We’re going along with this and this. Look wherever you like, but we want to remember which order we’re going in. I have them listed here, but if you want to say the acronym in your head to get used to the order of the rankings, then you can definitely do that.
Kingdom, phylum. Next, we’ve got our class, Mammalia, which is going to be all mammals, all organisms that are able to produce milk for their young and give birth to live young in most situations (we have a couple of egg-laying mammals). Then, you’ve got your order, Carnivora, which is going to be carnivores (animals that can eat meat). Family is Felidae. Genus is Felis. Species is Catus.
Your scientific name is going to be found using binomial nomenclature. You know this is a eukaryotic organism, because it’s in the kingdom Animalia, which is a eukaryote. It would go into domain eukarya. Binomial nomenclature means we use these last two. Using our genus and species, our creature is going to be known as Felis catus. What do we think that is? If you guess a housecat, you are correct.
This was the classification of a house cat. “Felis” kind of sounds like “feline”, which you’ve probably heard before. “Catus” sounds like “cat”. A house cat belongs to the kingdom Animalia, phylum Chordata, class Mammalia, order Carnivora, family Felidae, genus Felis, and species Catus, giving it the name Felis catus. The common name of house cat. This would be the common name.
Whenever you are looking at an organism and you see some latin words like this, two latin words together, you are probably looking at the scientific name for that organism. If you know the genus and species of an organism, you can figure out which other group, which other organisms are members of that group, and figure out what they might have in common and slowly build up and figure out what family, order, class, phylum, kingdom, and domain that organism is in.
The more things that you know about an organism, the more you can break it down and put it into different kingdoms, phylums, classes, orders, a family, a genus, and species. This classification system is used internationally, so that anywhere in the world if you saw this Latin name, any scientists, whether they spoke English or another language, would be able to know what species that scientific name was referring to.
This classification system is used by all scientists, that way all scientists will be on the same page if they’re trying to classify a new organism or figure out which rankings an organism that they find might fit into, to see if it is indeed a new organism or something that’s already been discovered and they are just trying to classify it.
Whenever you are trying to remember the order, keep in mind this handy acronym: Keep Ponds Clean Or Frogs Get Sick. That should help you keep these guys in order. Remember our three domains: Eukarya, archaea, and Bacteria. The most important thing to remember about your biological classification system is that it’s there to classify these organisms. It’s there to keep you organized.