Download Classification Hierarchy

LS 4 Classification of living organisms
There are at least 1.7 million living organism on Earth. To help keep track of
them, scientists have developed a system of classifying or grouping them. When
grouping organisms scientists will first look at structural similarities and in some
cases they will use DNA comparisons to determine grouping. The field of science
that involves classification is called Taxonomy.
The first scientist who worked on a system of classification was the Greek
scientist Aristotle. He classified organisms based on the ability to walk, swim or
fly.
You have learned how living things are grouped using the current
classification hierarchy system. In this classification system, organisms are
arranged into groups that have one or more characteristics in common. Within this
scientific classification of living organisms there is also a hierarchy. A hierarchy
is a system of things that are ranked one above the other. All organisms on Earth
are placed on levels in this hierarchy according to their physical characteristics and
activities. The levels of hierarchy include: domain, kingdom, phylum, class,
order, family, genus, and species. As one goes down the hierarchy from the
Domain to the Species there is an increase in the similarity between organisms.
There are also fewer numbers of different kinds of organisms in each level.
Classification Hierarchy
Domain: The highest level most inclusive group
Kingdom: A subdivision of Domain
Phylum: A subdivision of a kingdom
Class: Each phylum is divided into classes
Order: Each class is divided into orders
Family: Each order is divided into families
Genus: Each family is divided into genera
Species: Lowest level (represents a single type of organism)
At the top of the hierarchy is the broad classification level of Domain. The
three domains are the Eukarya, Archaea and Bacteria. The organisms within a
domain share certain physical characteristics and activities such as the presence or
absence of cellular structures like a nucleus or a cell wall; whether they are
unicellular or multicellular; and how they get their food.
Today scientists recognize six different kingdoms of organisms. These
kingdoms include the animal kingdom, the plant kingdom, the protist kingdom, the
fungi kingdom, the archaea kingdom, and the bacteria kingdom.
The six kingdoms used today are divided into a number of smaller groups
called phyla. A phylum is a group of organisms that share more specific
characteristics and activities. The organisms in a phylum have more in common
with each other than with the other members of their kingdom. For example,
spiders and birds are members of the animal kingdom, but they are placed in
different phyla. Birds have an internal skeleton with a back bone, so they are
grouped in the phyla chordata. Spiders have a segmented body covered by a hard
outer skeleton, so they are grouped in the phyla arthropod.
Some organisms in the animal kingdom share more characteristics than the
spider and bird. The more levels of the classification system shared by two
organisms, the more closely they are related. For example, a dog and a wolf share
the same kingdom (Animalia), the same phylum (Chordata), the same class
(Mammalian), the same order (Carnivore), the same family (Canidae), and the
same genus (Canis). They are not members of the same species, however. Dogs
are members of the species familiaris and wolves are members of the species lupis.
Because they have more levels of the classification system in common, they are
more closely related than the bird and spider which only share one level in
common.
Scientists now have a system for naming all the living organisms on earth.
The system was created by a Swedish scientist named Carolus Linnaeus over 200
years ago is called Binomial nomenclature. With this system Linnaeus gave each
organism a two-word Latin name. This two-part name consists of an organism’s
genus name followed by its species name. It is similar to you having a first and
last name. For example, the scientific name of the dog is Canis familiaris. Canis
being the genus the organism belongs to and familiaris being the name of the
species. This naming system makes it easier for scientists around the world to
communicate. The rules of binomial nomenclature are simple. The first word is
always capitalized and the second one is not. Both words are either italicized or
underlined and Latin is always used
Dichotomous keys are a tool used to help identify organisms. At each step of the
key you must decide on one of two choices based on the characteristics of the
organisms.
Example of a dichotomous key
1. Organism is an autotroph......................go to 2.
Organism is a heterotroph................. go to 5.
2. Organism is aquatic................................ go to 3.
Organism is terrestrial........................go to 4
3. Organisms can swim ...............................Sharkus baskingas.
Organisms cannot swim..........................Sero crudum.