Video: Taxonomic Hierarchy

In this video, we will learn how to recall the levels in the taxonomic hierarchy, and apply this knowledge to example organisms.

10:20

Video Transcript

In this video, we’ll learn what taxonomic hierarchy is. We’ll learn the levels of taxonomic hierarchy from kingdom to species. And we’ll look at some examples of how organisms are classified using this hierarchical system.

Taxonomy is the study of naming, defining, and classifying groups of organisms. Scientists classify living things because it makes them easier to identify and to learn about. Classifications is when we put organisms together into groups based on meaningful similarities. We’re able to generalize, to contrast, and to compare between categories. Taxonomy was originally based on physical characteristics. And now we refer to those methods of classification as artificial classification.

With advancing technology, we now group organisms based on evolutionary relationships, a method that we refer to as natural or phylogenetic classification. We classify organisms into groups called taxa. And those groups are arranged into levels or ranks. The arrangement is hierarchical, going from large, general groups to smaller, more specific groups. One way to imagine this is to pretend that you want to send a package to the home of one of your friends. In order to get the package to the correct destination, your address will include the country, the more specific state or region, the even more specific city or town, and then the street that the house is located on and finally the actual number of your friend’s house.

Another similar concept that you may be familiar with is how organisms are made of organ systems, which are made of organs, which are made of tissues, which are made of cells. Not only are we going from large to small, but each specific rank contains several of the rank beneath it. Species is the most specific of our taxonomic levels. In fact, the word species kind of sounds like specific. Several related species make up one genus. And there are several related genera in one family. Families are grouped into orders. Orders are grouped into classes. There are several classes in one phylum and several phyla in one kingdom.

Modern classification systems may also include super groups, often referred to as domain. A domain is a rank even more general than a kingdom. Some students like to use a mnemonic device to help them to remember the order of the taxonomic levels. One that’s quite common is “King Philip came over for good soup.” Another one that I particularly like is “keen penguins congregate on frozen ground sometimes,” or even “kids prefer candy over fancy green salad.” You can use one of these or even come up with a mnemonic device of your own.

Next, let’s look at an example of the classification of an organism. Here we have an ant whose scientific name is Solenopsis invicta. Ants are members of the animal kingdom, which tells us that they’re multicellular, heterotrophic, likely able to move around, and likely to reproduce sexually. Their phylum is Arthropoda. Arthropods have exoskeletons and jointed legs. Their class, Insecta, lets us know that these particular arthropods have three pairs of legs and three body segments.

Their order, Hymenoptera, also includes the related families of bees and wasps. This lets us know that ants have many things in common with bees and wasps but also many important differences. Formicidae is the name of the family of ants. This particular ant genus is Solenopsis, which identifies it as a type of fire ant, which brings us to the scientific name for the species, Solenopsis invicta. The scientific name for an organism consists of both its genus and its species. This is a naming system that we refer to as binomial nomenclature, since each species is designated using two names.

We can see that as the taxonomic levels become more specific, they begin to include fewer and fewer organisms. If I were to discover a new species of fire ant, it would likely be classified similarly, since it would share many of these relationships and characteristics.

Let’s look at another example. Quercus virginiana is the scientific name for a species of oak tree found in the southern United States. This genus name tells us that this oak tree is an evergreen oak tree, also often referred to as a live oak. The family Fagaceae includes oak trees and the related genus of beach trees, just as the order Fagales will include several other related families of trees. The class of this tree is Angiosperm, which means that it’s a type of flowering plant. And the phylum, Tracheophyte, identifies it as a type of vascular plant. And the fact that it’s a plant tells us that our oak tree is a photosynthetic, multicellular land organism.

Before we move on to our practice question, let’s take a closer look at what constitutes a species. We often refer to a species as a group of closely related organisms which are able to reproduce together and produce fertile offspring. Sometimes organisms from the same genus but different species are able to successfully reproduce. For example, when a male lion and a female tiger mate, they produce an offspring that we refer to as a liger. However, ligers cannot reproduce together to make more ligers. Since lions and tigers belong to two different species, their offspring will not be fertile, meaning that they can’t have offspring of their own.

Now that we’ve learned about hierarchical classification, the taxonomic levels, and what constitutes a species, let’s try a practice question.

The binomial naming system provides each organism with two names. For example, the binomial name for humans is Homo sapiens. In the binomial system, what taxonomic rank does the first name represent? In the binomial system, what taxonomic rank does the second name represent?

Binomial is a word that actually means two names, and it’s the way that scientists name organisms. The first part of the name is more general, and the last part is more specific. It’s sort of how most people are given a family name, which tells us who they’re related to, and a given name, which sets them apart as an individual. However, in the instance of organisms, as with many cultures, the family name comes first and the more specific given name comes second.

Well, if you know which taxonomic rank is the very most specific and which one is the next most general, this would be enough information to answer our question with. But just in case you’d like another hint, we’ll go ahead and look at the taxonomic hierarchy for the human species. Humans belong to the animal kingdom. Our phylum is chordate, and our class is mammal. We are members of the primate order and the hominid family. Our genus is Homo, and our species is sapiens, or Homo sapiens. Now we have everything we need to answer our questions.

The first name in the binomial naming system, Homo, represents the genus. And the second name, sapiens, represents the species. If you remember that in binomial nomenclature, the general name comes first, that’ll help you to remember that the first name is actually the genus. And if you remember that the specific names come second, that’ll help you to remember that the second name is the species.

Let’s wrap up our lesson by taking a moment to review what we’ve learned. In this video, we learned about the hierarchical arrangement of the taxonomic ranks. In order from largest to smallest, these are kingdom, phylum, class, order, family, genus, and species. We looked at some examples of the classification of different types of organisms and also what their classification can tell us about their traits.

We learned that artificial classification is based on physical characteristics, while natural classification is based on evolutionary relationships determined by genetic analysis. We also reviewed that a species is a group of closely related organisms which can reproduce together and produce fertile offspring.

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