Essential question:

How and why do we classify organisms?

Why Classify?• To study the diversity

of life• Used to name

organisms and group them

Taxonomy = classify organisms and give

them universally accepted name

NamingEarly Attempts:• Used physical description• Ex: “Oak with deeply

divided leaves that have no hairs on their undersides and no teeth around their edges.”

• Common names vary among languagesEx: Mountain Lion or puma

or cougar

Solution:Carolus Linnaeus developed

BINOMIAL NOMENCLATURE = two part scientific name.

1. Written in italics with Greek and Latinized words

2. First word Capitalized, second word lower case

3. Genus – 1st word, species – 2nd word

Ex: Scientific Name – Felis concolor Common Name – Mountain Lion

Grizzly BearUrsus arctos

Polar BearUrsus maritimus

Panda BearAiluropoda melanoleuca

Which two bears are more closely related?

Binomial Nomenclature

1. Each organism has 2 scientific names

2. Genus and species3. Always in italics4. Genus – upper case,

species-lower case5. Genus can be

abbreviated. Tyrannosaurus rex = T. rex

Classification• Linnaeus’ hierarchical system:

Kingdom general

PhylumClass

OrderFamily

GenusSpecies

specific(King Philip Came Over For Grape Soda)

Taxons

Linnaeus’s System of Classification“King Philip Came Over For Grape Soda”

Kingdom

Phylum

Class

Order

Family

Genus

Species

Kingdoms and Domains1st attempts to make the Tree of Life were too

inclusive: plant vs. animal• Modern tree contains the six kingdoms and

their phyla: Eubacteria, Archaebacteria, Protista, Fungi,

Plantae, Animalia• Domains – newest, largest inclusive category

developed from comparing r-RNA subunits.Bacteria, Archaea, Eukarya

Phylogeny – evolutionary history of an organism (how it changed over time)

Cladogram• shows ancestral

relations between organisms= evolutionary tree of life.

• DNA and RNA, computational phylogenetics are now used

Modern Classification• Just using appearance can be misleading.• New system uses:

1. Fossils

2. Dissections/comparative anatomy

3. Molecular similarities/DNA/enzymes-The more genes that are similar, the more closely related

4. Evolutionary similarities or milestonesEx: amniotic sac, jaws, endothermic

Molecular Clocks

• Used to estimate how long ago two species shared a common ancestor.

• The more dissimilar the genes, the longer ago they shared a common ancestor

How do we diagram these evolutionary relationships???

Using a……..

….Cladogram• Uses derived characteristics, those that appear in

recent parts of a lineage but not in its older members, to construct diagram of evolutionary relationships.

KingdomsEubacteria

Archaebacteria

Protista

Plantae

Fungi

Animalia

DOMAIN EUKARYA

DOMAIN ARCHAEA

DOMAIN BACTERIA

Section 18-3

Figure 18-13 Cladogram of Six Kingdoms and Three Domains

DICHOTOMOUS KEYS

• a tool to determine the identity of ORGANISMS.

• Keys consist of a series of choices that lead the user to the correct name of a given item.

• "Dichotomous" means "divided into two parts". Therefore, dichotomous keys always give two choices in each step.