Classification
Why do we classify?
1. To study the diversity of life.
2. To group organisms in a logical manner.
The process of classifying is known as taxonomy. A taxa is a group or level of
organization. From largest to smallest the current taxa are:
Mnemonic Device:
King
Example
Polar Bears
Kingdom
Animalia
Animals
Phillip
Phyla
Chordata
with backbones
Came
Class
Mammalia
who have milk
Over
Order
Carnivora
and eat meat
For
Family
Ursidae
bears
Great
Ursus
Bear
Genus
Spaghetti
maritimus
sea
Species
The very first person to classify organisms was Aristotle. His system consisted of two
categories: Animals or Plants
Our current naming system was developed by Carolus Linneaus in the 18th century. He
developed a two-word naming system called binomial nomenclature. This was based
on the genus and species of the organism.
Rules for naming:
1. Scientific names are always written in italics. If hand written, then they need to be
in cursive and/or underlined.
2. The genus name is always capitalized.
Example: Mephitis mephitis
3. The species name is always lowercase.
So how did we go from two groups to the current six? The problem with Aristotle’s
method is he did not have an understanding of genetics or evolution; organisms were
classified by what they looked like. We now group organisms based off of evolutionary
descent as well as by their DNA.
So how do you show similarities
among organisms?
A cladogram is a diagram that
depicts evolutionary relationships
of derived characteristics among
organisms. They are useful in
showing how one organism
branches off from another during
evolution (like an evolutionary
family tree).
How do you know if you have found a new species?
Dichotomous keys are field guides that distinguish between different species that have
been classified. It is a series of paired statements that describe physical characteristics
of organisms. You follow the statements until it gives you the scientific name.
1. a. Organism is living ...... go to 4.
1. b. Organism is nonliving ........go to 2.
2. a. Object is metallic ..............go to 3.
2. b. Object is nonmetallic ............ROCK.
So what is our current classification system?
Kingdom
Cell Type
Eubacteria
Prokaryote
Archaebacteria
Prokaryote
Cell
Structure
Cell wall with
peptidoglycan
Cell walls
without
peptidoglycan
Number of
Cells
Unicellular
Unicellular
Mode of
Nutrition
Auto or
heterotroph
Auto or
heterotroph
Examples
Streptococcus
, E. coli
Halophiles
Protista
Eukaryote
Cell walls
with
cellulose in
some; some
have
chloroplasts
Most
unicellular;
some
colonial;
some
multicellular
Auto or
heterotroph
Amoeba,
Paramecium
Fungi
Eukaryote
Plantae
Eukaryote
Animalia
Eukaryote
Cells walls of
chitin
Cell walls of
cellulose;
chloroplast
No cell wall
or
chloroplast
Most
multicellular;
some
unicellular
Multicellular
Multicellular
Heterotroph
Autotroph
heterotroph
Mushroom,
yeast
Mosses,
ferns, trees
Sponges,
fish,
mammals