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.
Because 18th century scientists
understood Latin and Greek, 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 often describes an
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
Giant
panda
An order is a broad category composed of
similar families.
Grizzly
bear
Black
bear
Giant
panda
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 all 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
Crab
Barnacle
Molted external
skeleton
Segmentation
CLASSIFICATION BASED ON
VISIBLE SIMILARITY
Active Art
Mollusk
Crustaceans
Limpet
Tiny freeswimming larva
CLADOGRAM
Superficial similarities once 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
Tiny 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.
• The 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
The Three-Domain System
•Molecular analyses have given
rise to the three-domain system
of taxonomy that is 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
• 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.
Fungi
Domain Eukarya
•Members of the kingdom Fungi
are heterotrophs with cell walls
that contain 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 that contain
cellulose.
• The plant kingdom includes conebearing and flowering plants as well as
mosses and ferns.
Domain Eukarya
Animalia
• Members of the kingdom Animalia are
multicellular and heterotrophic.
• The 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