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Chapter 18
Classification
Classification
Every year, thousands of new species
are discovered
 Biologists classify them with similar
organisms
 The ways we group organisms continue
to change
 Today’s methods reflect an organism’s
evolutionary history

Classification
Taxonomy- The branch of biology that
names and groups organisms according
to their characteristics and evolutionary
history
 This allows us to keep track of all of the
millions of different species.
 Between 2-25 million!! Most extinct
now.

History of Classification
Aristotle first classified organisms over
2,000 years ago
 Grouped them as:

– Animals
• Land, water, or air dwellers
– Plants
• 3 types based on stems
History of Classification

As more and more species
were discovered, the existing
categories weren’t adequate
– Common names – not accurate (jellyfish is
really not a fish)
– Common names varied from country to
country
– Some early scientific names were too long
and complicated
History of Classification
Swedish naturalist
Carolus Linnaeus
(1707-1778) – devised a system of
grouping organisms into hierarchical
categories
 He used an organism’s form and
structure (morphology) to classify it

Classification

7 levels
– Kingdom
– Phylum
– Class
– Order
– Family
– Genus
– Species
*King Phillip Came Over For Good Spaghetti
Binomial Nomenclature
Two part name
 1st name capitalized
 2nd name lowercase
 underlined or italicized
 1st name is the genus, the second is a
describer word

– Example: Homo sapiens which means
(wise)
Phylogeny

Modern taxonomists
consider:
– 1. morphology
– 2. chromosomal characteristics
– 3. nucleotide and amino acid sequences
– 4. embryological development
– 5. fossil record
Phylogenic Tree

Phylogenic tree – a family tree that shows
the evolutionary relationships thought to exist
among groups of organisms
Fossil Record
Provides clues to evolutionary
relationships
 But, some organisms have incomplete
fossil records
 There may be strata where no fossils of
an organism appear
 Need other evidence to support the
phylogenetic tree

Morphology
Study organism’s
structure and
compare it to other living organisms
 Homologous features suggest a
common ancestor
 The greater the number of homologous
features, the more closely related the
organisms

Embryological Development

Early patterns of embryological development
provide evidence of phylogeny
– Egg is fertilized and zygote starts to divide
by mitosis
– Hours later a ball of cells called a blastula
is formed
– Soon after, an indentation called a
blastopore forms
– Blastopore becomes the mouth in most
animals, but the other end in echinoderms
(starfish, sand dollars)
Chromosomes & Macromolecules
Taxonomists use comparisons of
macromolecules such as DNA, RNA,
and proteins as a kind of molecular
clock
 The number of differences is a clue to
how long ago the species diverged
 Biologists can also compare karyotypes
or patterns of chromosomes
 In our human history lab, we saw how
similar the amino acid sequences were
between humans and chimps

Cladistics
Cladistics – a system of phylogenic
classification using shared derived
characters
 A derived characters is a feature that
only evolved in a specific group (birds
have feathers)
 A group of shared derived characters is
strong evidence for common ancestry
 Cladograms - Ancestry diagrams

Six Kingdoms
1) Archaebacteria
 2) Eubacteria
 3) Protista
 4) Fungi
 5) Plantae
 6) Animalia

Archaebacteria
Unicellular prokaryotes
 Some are autotrophic (chemosynthesis)

– Waste products may include flammable
gasses – methane)

Many live in harsh environments
– Sulfurous hot springs, salty lakes,
anaerobic conditions (intestines)

Directly descended from the first
organisms on earth (before oxygen and
photosynthesis)
Eubacteria
Unicellular prokaryotes
 Most are aerobic
 True bacteria – can affect your life:

– Cause tooth decay
– Make yogurt
– Cause food poisoning
Protista
Eukaryotic
 Mostly single celled (amoeba, euglena)
 Some multicellular (giant kelp)
 All eukaryotes that are not plants,
animals or fungi
 Some look like plants, but lack
specialized tissues

Fungi
Heterotrophic
 Can be unicellular or multicellular
 They absorb nutrients rather than
ingesting them
 There are over 100,000 species:

– Mushrooms
– Mildews
– Molds
– rusts
Plantae

Use the term Division
instead of Kingdom
 Eukaryotic and Multicellular
 Most are autotrophic and use photosynthesis
to get energy
 There are over 350,000 species:
– Mosses
– Ferns
– Conifers
– Flowering plants
Animalia
Eukaryotic
 Multicellular
 Heterotrophic
 Most have symmetrical bodies and are
able to move around their environment
 Examples:

– Humans
– Dogs
– Fish
– Insects