Download Section 18 - St. Clair Schools

Section 18.1 Finding Order in Diversity
Natural selection and other processes have led to a staggering
Biologists have identified and named about
They estimate that
Why Classify?
 To study the
them in a logical manner.
additional species have yet to be discovered.
, biologists use a classification system to

In the discipline of taxonomy,

When taxonomists classify organisms, they organize them into groups that have biological significance.
Assigning Scientific Names
 Common names of organisms vary, so scientists assign
 Because 18th century scientists understood
for scientific names.
 This practice is still followed in naming new species.
Early Efforts at Naming Organisms
 The first attempts at standard scientific names
great detail.
 These names
different characteristics.
Binomial NomenclatureWhat is binomial nomenclature?
 Carolus Linneaus developed a naming system called
each species is assigned a

The first part of the name is
. The genus name is

The second part of the name is
often describes
Linnaeus's System of Classification
Linnaeus not only named species, he also
What is Linneaus’s system of classification?
Linnaeus's seven levels of classification are—from
1. Kingdom
2. Phylum
3. Class
4. Order
5. Family
6. Genus
7. Species
, they used those languages
of a species in
because different scientists described
. In binomial nomenclature,
. The scientific name is
to which the organism belongs. A genus is a group of
within the genus. This part of the name
. The species name is
.

Each level is called a






The
is the largest and most inclusive of Linnaeus's taxonomic categories.
Several different classes make up a
The next larger category, the
is composed of similar orders.
An
is a broad category composed of similar families.
Genera that share many characteristics are grouped in a larger category, the
are the two smallest categories.
Section 18.2 Modern Evolutionary Classification
Which Similarities Are Most Important?
Linnaeus grouped species into larger
How are evolutionary relationships important in classification?
Evolutionary Classification
 Phylogeny is the study of

Biologists currently group organisms into categories that represent

The strategy of grouping organisms is based on evolutionary history and is called

The higher the level of the taxon, the further
the taxon.

Organisms that appear very similar may not share a recent

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.

of all the organisms in
Classification Using Cladograms
 Many biologists now use a method called

Cladistic analysis identifies and considers only

Characteristics that appear in recent parts of a lineage but not in its older members are called

Derived characters can be used to construct a cladogram (also known as a branching diagram), a
diagram that

Cladograms help scientists understand how one lineage branched from another
Similarities in DNA and RNA
How can DNA and RNA help scientists determine evolutionary relationships?
 The genes of many organisms show important

Similarities in DNA can be used to help determine
DNA Evidence
 DNA evidence shows

The more similar the
, and the more closely they are related in evolutionary terms.

The more two species have diverged from each other, the
Molecular Clocks
 Comparisons of DNA are used to mark the

A molecular clock uses DNA comparisons to estimate the

A molecular clock relies on

Simple mutations in

Neutral mutations accumulate in different species

Comparing sequences in two species shows how
to mark time.
Section 18.3 Kingdoms & Domains
The Tree of Life Evolves
 Systems of classification
 Linnaeus classified organisms into
 The only known differences among living things were the fundamental traits that separated animals from
plants.
Five Kingdoms
Scientists realized there were enough differences among organisms to make 5 kingdoms:
Six Kingdoms
Recently, biologists recognized that Monera were composed of two distinct groups:
The six-kingdom system of classification includes:
The Three-Domain System
 Molecular analyses have given rise to a
many scientists.
 The
that is now recognized by
—larger than a kingdom.
The three domains are:
 Eukarya, which is composed of
 Bacteria, which corresponds to the
 Archaea, which corresponds to the
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
 Their cells have thick, rigid
 Their cell walls contain
The domain Bacteria corresponds to the kingdom
Domain Archaea
 Members of the domain Archaea are
 They live in
 Their cell walls lack
The domain Archaea corresponds to the kingdom
Domain Eukarya
 The domain Eukarya consists of organisms that
 This domain is organized into four kingdoms:
1. Protista
 The kingdom Protista is composed of eukaryotic organisms that

Its members display the greatest

They can be
with plants, fungi, or animals.
2. Fungi
 Members of the kingdom Fungi are

Most fungi feed on

They can be either
3. Plantae
 Members of the kingdom Plantae are

Plants are

Plants have

The plant kingdom includes
as well as mosses and ferns.
4. Animalia
 Members of the kingdom Animalia are

The cells of animals

Most animals can

There is great
of the planet.
within the animal kingdom, and many species exist in nearly every part