Chapter 18: Classification
18-1 Finding Order in Diversity
18-1 Finding Order in Diversity
Natural selection and other processes have
led to a staggering diversity of organisms.
Biologists have identified and named about
1.5 million species so far.
They estimate that 2–100 million additional
species have yet to be discovered.
To study the diversity of life,
biologists use a classification
system to name organisms and
group them in a logical manner.
In the discipline of taxonomy,
scientists classify organisms and
assign each organism a universally
accepted name.
When taxonomists classify
organisms, they organize them into
groups that have biological
significance.
Assigning Scientific Names
Common names of organisms vary,
so scientists assign one name for
each species.
18th century scientists understood
Latin and Greek, so they used those
languages for scientific names.
This practice is still followed in
naming new species.
Early Efforts at Naming Organisms
The first attempts at standard
scientific names described the
physical characteristics of a species
in great detail.
These names were not standardized
because different scientists described
different characteristics.
Carolus Linneaus developed a
naming system called
binomial nomenclature.
In binomial nomenclature, each
species is assigned a two-part
scientific name.
The scientific name is italicized.
The first part of the name is the Genus
name (Capitalized).
A Genus is a group of closely related
species.
The second part of the name is the
species name (lowercase).
The species name describes important
trait or where the organism lives.
Linnaeus's System of Classification
Linnaeus not only named species, he
also grouped them into categories.
Linnaeus’s seven levels of
classification are
(from smallest to largest)
species
genus
family
order
class
phylum
kingdom
Each level is called a taxon, or
taxonomic category.
Species and genus are the two
smallest categories.
Grizzly
bear
Black
bear
Genera that share many
characteristics are grouped in a larger
category, the family.
Grizzly
bear
Black
bear
FAMILY Ursidae
Giant
panda
An order is a broad category
composed of similar families.
Grizzly
bear
Black
bear
Giant
panda
ORDER Carnivora
Red
fox
The next larger category, the class, is
composed of similar orders.
Grizzly
bear
Black
bear
Giant
panda
CLASS Mammalia
Red
fox
Abert
squirrel
Several different classes make up a
phylum.
Grizzly
bear
Black
bear
Giant
panda
PHYLUM
Red
fox
Chordata
Abert
squirrel
Coral
snake
The kingdom is the largest and most
inclusive of Linnaeus's taxonomic
categories.
Grizzly
bear
Black
bear
Giant
panda
Red
fox
Abert
squirrel
KINGDOM Animalia
Coral
snake
Sea
star
Grizzly Black Giant
bear
bear panda
Coral Sea
Red Abert
fox squirrel snake star
18-2 Modern Evolutionary Classification
Linnaeus grouped species into larger
taxa mainly according to visible
similarities and differences.
Evolutionary Classification
• Phylogeny is the study of
evolutionary relationships among
organisms.
Biologists currently group organisms
into categories that represent lines of
evolutionary descent, or phylogeny,
not just physical similarities.
Grouping organisms based on
evolutionary history is called
evolutionary classification.
The higher the level of the taxon, the
further back in time is the common
ancestor of the organisms in the taxon.
Organisms that appear very similar may
not share a recent common ancestor.
• Different Methods of Classification
Appendages
Crab
Conical Shells
Barnacle
Limpet
Crustaceans
Crab
Barnacle
Molted external
skeleton
Segmentation
CLASSIFICATION BASED ON
VISIBLE SIMILARITY
Mollusks
Limpet
Tiny freeswimming larva
CLADOGRAM
Superficial similarities led barnacles
and limpets to be grouped together.
Appendages
Crab
Conical Shells
Barnacle
Limpet
However, barnacles and crabs share
an evolutionary ancestor that is more
recent than the ancestor that
barnacles and limpets share.
Barnacles and crabs are classified as
crustaceans, and limpets are
mollusks.
Many biologists now use a method
called cladistic analysis
• Cladistic analysis considers only new
characteristics that arise as lineages
evolve ( called derived characters).
• Characteristics that appear in recent parts
of a lineage but not in its older members
are called derived characters.
Derived characters can be used to
construct a cladogram, a diagram that
shows the evolutionary relationships
among a group of organisms.
Cladograms help scientists
understand how one lineage branched
from another in the course of
evolution.
A cladogram shows the evolutionary
relationships between crabs,
barnacles, and limpets.
Crustaceans
Crab
Mollusk
Barnacle
Limpet
Molted external skeleton
Segmentation
Free-swimming larva
The genes of many organisms show
important similarities at the molecular
level.
Similarities in DNA can be used to help
determine classification and
evolutionary relationships.
DNA Evidence
• DNA evidence shows evolutionary
relationships of species.
• The more similar the DNA of two species,
the more recently they shared a common
ancestor, and the more closely they are
related in evolutionary terms.
• The more two species have diverged from
each other, the less similar their DNA is.
Molecular Clocks
• Comparisons of DNA are used to
mark the passage of evolutionary
time.
• A molecular clock uses DNA
comparisons to estimate the length
of time that two species have been
evolving independently.
Molecular Clocks
A gene in an
ancestral species
2 mutations
new
mutation
Species A
2 mutations
new
new
mutation mutation
Species B
Species C
A molecular clock relies on mutations to
mark time.
Simple mutations in DNA structure occur
often.
Neutral mutations accumulate in different
species at about the same rate.
Comparing sequences in two species
shows how dissimilar the genes are, and
shows when they shared a common
ancestor.
18-3 Kingdoms and Domains
The Tree of Life Evolves
• Systems of classification adapt to new
discoveries.
• Linnaeus classified organisms into two
kingdoms—animals and plants.
• Only known differences among living
things were the fundamental traits that
separated animals from plants.
There are enough differences among
organisms to make 5 kingdoms:
Monera
Protista
Fungi
Plantae
Animalia
Six Kingdoms
• Recently, biologists recognized
that Monera were composed of two
distinct groups:
• Eubacteria and Archaebacteria.
The six-kingdom system of
classification includes:
• Eubacteria
• Archaebacteria
• Protista
• Fungi
• Plantae
• Animalia
Changing Number of Kingdoms
Names of Kingdoms
Introduced
1700’s
Late 1800’s
1950’s
1990’s
Plantae
Plantae
Protista
Monera
Eubacteria
Archaebacteria
Animalia
Animalia
Protista
Fungi
Plantae
Animalia
Protista
Fungi
Plantae
Animalia
Six Kingdoms
Bacteria
Archaea
Eubacteria
Archaebacteria
Prokaryote
Prokaryote
E.coli
halophiles
Eukarya
Protista
Fungi
Plantae
Animalia
Eukaryote
Amoeba
Mushroom,
yeast
Moss,
ferns,
flowering
plants
Sponges,
worms,
insects,
fishes,
mammals
The Three-Domain System
• Molecular analyses have given rise to
the three-domain system of taxonomy
now recognized by many scientists.
• The domain is a more inclusive category
than any other—larger than a kingdom.
The three domains are:
• Eukarya, which is composed of
protists, fungi, plants, and animals.
• Bacteria, which corresponds to the
kingdom Eubacteria (true bacteria).
• Archaea, which corresponds to the
kingdom Archaebacteria.
Modern classification is a rapidly
changing science.
As new information is gained about
organisms in the domains Bacteria
and Archaea, they may be subdivided
into additional kingdoms.
Domain Bacteria
Domain Bacteria
• Members of the domain Bacteria are
unicellular prokaryotes.
• Their cells have thick, rigid cell walls
that surround a cell membrane.
• Their cell walls contain peptidoglycan.
Domain Bacteria
The domain
Bacteria
corresponds to
the kingdom
Eubacteria.
Domain Archaea
Domain Archaea
• Members of the domain Archaea are
unicellular prokaryotes.
• Archaea live in extreme environments.
• Their cell walls lack peptidoglycan, and
their cell membranes contain unusual
lipids not found in any other organism.
Domain Archaea
The domain
Archaea
corresponds to
the kingdom
Archaebacteria.
Domain Eukarya
•The domain Eukarya consists of
organisms that have a nucleus.
•Eukarya includes the kingdoms:
Protista
Fungi
Plantae
Animalia
Domain Eukarya
Domain Eukarya
Protista
• The kingdom Protista is composed of
eukaryotic organisms that cannot be
classified as animals, plants, or fungi.
• Its members display the greatest variety.
• They can be unicellular or multicellular;
photosynthetic or heterotrophic; and can
share characteristics with plants, fungi,
or animals.
Domain Eukarya
Fungi
• Members of the kingdom Fungi are
heterotrophs with cell walls of chitin.
• Most fungi feed on dead or decaying
organic matter by secreting digestive
enzymes into it and absorbing small
food molecules into their bodies.
• They can be either multicellular
(mushrooms) or unicellular (yeasts).
Domain Eukarya
Plantae
• Members of the kingdom Plantae are
multicellular, photosynthetic autotrophs.
• Plants are nonmotile—they cannot move
from place to place.
• Plants have cell walls of cellulose.
• The plant kingdom includes cone-bearing
and flowering plants, mosses and ferns.
Domain Eukarya
Animalia
• Members of the kingdom Animalia are
multicellular and heterotrophic.
• Cells of animals do not have cell walls.
• Most animals can move about.
• There is great diversity within the animal
kingdom, and many species exist in nearly
every part of the planet.
Which statement about classification is true?
a. Biologists use regional names for organisms.
b. Biologists use a common classification system
based on similarities that have scientific
significance.
c. Biologists have identified and named most
species found on Earth
d. Taxonomy uses a combination of common and
scientific names to make the system more
useful.
Linnaeus's two-word naming system is
called
a. binomial nomenclature.
b. taxonomy.
c. trinomial nomenclature.
d. classification.
Several different classes make up a(an)
a. family.
b. species.
c. kingdom.
d. phylum.
A group of closely related species is
a(an)
a. class.
b. genus.
c. family.
d. order.
Which of the following lists the terms in
order from the group with the most
species to the group with the least?
a. order, phylum, family, genus
b. family, genus, order, phylum
c. phylum, class, order, family
d. genus, family, order, phylum
Grouping organisms together based on
their evolutionary history is called
a. evolutionary classification.
b. traditional classification.
c. cladogram classification.
d. taxonomic classification.
Traditional classification groups
organisms together based on
a. derived characters.
b. similarities in appearance.
c. DNA and RNA similarities.
d. molecular clocks.
In an evolutionary classification system, the
higher the taxon level,
a. the more similar the members of the
taxon become.
b. the more common ancestors would be
found in recent time.
c. the fewer the number of species in the
taxon.
d. the farther back in time the common
ancestors would be.
Classifying organisms using a cladogram
depends on identifying
a. external and internal structural
similarities.
b. new characteristics that have appeared
most recently as lineages evolve.
c. characteristics that have been present in
the group for the longest time.
d. individual variations within the group.
To compare traits of very different
organisms, you would use
a. anatomical similarities.
b. anatomical differences.
c. DNA and RNA.
d. proteins and carbohydrates.
Organisms whose cell walls contain
peptidoglycan belong in the kingdom
a. Fungi.
b. Eubacteria.
c. Plantae.
d. Archaebacteria.
Multicellular organisms with no cell
walls or chloroplasts are members of
the kingdom
a. Animalia.
b. Protista.
c. Plantae.
d. Fungi.
Organisms that have cell walls
containing cellulose are found in
a. Eubacteria and Plantae.
b. Fungi and Plantae.
c. Plantae and Protista.
d. Plantae only.
Molecular analyses have given rise to a
new taxonomic classification that
includes
a. three domains.
b. seven kingdoms.
c. two domains.
d. five kingdoms.
Which of the following contain more
than one kingdom?
a. only Archaea
b. only Bacteria
c. only Eukarya
d. both Eukarya and Archaea