Scientific
Classification
CLASSIFICATION

Defn. The grouping of organisms by
similarities

TAXONOMY: the branch of
biology concerned with the
grouping and naming of organisms;
the study of classification
Taxonomy

Organisms are
classified into a
hierarchy of groups
and subgroups
based on
similarities that
reflect their
relationships over a
period of time.
Cladogram or Phylogenic Tree


A branching, treelike
diagram in which the
endpoints of the branches
represent specific species
of organisms.
It is used to illustrate
relationships and show
points at which various
species have diverged
from common ancestral
forms.
What is wrong with this picture?
Think-Pair-Share:
Why was Aristotle’s
system flawed? Why
does it not “work”?
HISTORY:




Aristotle- developed the 1st method of
classification
He divided all living things into 2 major
groups
1. Plants
 classified by size and structure
2. Animals
 classified by habitat (where they lived)
HISTORY: Aristotle

Problems with his system:

Frogs live in both water and on land
HISTORY: Aristotle

Problems with his system:

Bats, birds and flying insects were
grouped together
HISTORY:


Carolus Linnaeusdeveloped the
modern system of
classification
Father of Taxonomy
MODERN CLASSIFICATION SYSTEM
Organisms are grouped together on the basis of:
1. Similarity in structure
Panthera leo
Felis rufus
Felis domesticus
2. Similarity in genetic makeup (biochemistry)


Similarities among
organisms on the structural
and metabolic levels are
reflected in the large degree
of similarity in proteins and
nucleic acids of different
organisms.
Diversity is the product of
variations in these
molecules.
3. Similarity of embryonic development
4. Similarity in evolutionary history

Phylogeny: the evolutionary history
of a species based on comparing
relationships between species using
the fossil record
5. Similarity in behavior
Check for Understanding:


With your partner, develop 2 possible
explanations as to why the modern system
of classification is “better” and easier to
use than the original system of
classification.
TIME: 2 minutes

Classification is based on close
evolutionary relationships of
organisms.

Organisms classified in the same taxa
(pl.) (taxon, sing.) share a common
ancestry. They have evolved from the
same common ancestral organism.
Evolutionary Relationships
Levels of Classification








Domain- highest level; bacteria, archaea &
Eukarya
Kingdom – 6 Kingdoms
Phylum (sing.)
 Phyla (pl.)(Plants don’t have phyla, they
have divisions.)
Class
Order
Family
Genus
These two taxa make up the
Species
scientific name.
Binomial Nomenclature



This system was developed by Linnaeus
Binomial nomenclature is a standard way
of identifying a species with a scientific
two-word name.
The first word is the genus name and the
second the species name.
Binomial Nomenclature





Scientific name - 2 Latin names
Genus and species
Capitalize the first letter of the genus
Do NOT capitalize the species
ALWAYS underline or use italics
Ex. Homo sapiens
Binomial Nomenclature
Scientific Name:
Pinus virginianis
Common Name:
Virginia Pine
What defines a “Species”?

organisms that belong to the same
species can mate AND produce FERTILE
offspring.
Why use scientific names?

Common names do not indicate how
organisms are related or classified.

Common names can be misleading.
(e.g., seahorse, weeping willow)

Organisms with more than one
common name leads to mass
confusion.
Why Latin?
 Latin is no longer spoken, and
therefore, does not change as spoken
languages do.
 So, scientific names remain the same
forever.
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Scientific Classification