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.
