CLASSIFICATION
Chapter 18
Species
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A species is a population of organisms that share
similar characteristics and can breed with one
another and produce fertile offspring.
Biologist have identified approximately 1.5 million
species.
It has been estimated that there are between 2 and
100 additional species that have yet to be
discovered.
Why classify?
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To study to the great diversity of organism, each
organism must be named.
Living things must also be organized into groups
that have biological meaning.
To study the diversity of life, biologists use a
classification system to name organisms and group
them in a logical manner.
Assigning scientific names
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The problem - Common names vary among
languages and even among regions within a single
country.
 What
is a buzzard?
Taxonomy
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In the discipline known as taxonomy, scientists
classify organisms and assign each organism a
universally accepted name.
By using a scientific name, biologists can be certain
that everyone is discussing the same organism.
When taxonomists classify organisms, they organize
them into groups that have biological significance.
Taxonomy
Binomial Nomenclature
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Two-word naming
system.
In binomial
nomenclature, each
species is assigned a
two-part scientific name.
The scientific name is
always written in italics.
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The first word is
capitalized, and the
second word is
lowercased.
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The first part of the
name identifies the
genus to which the
species belongs; the
second part identifies
the species within the
genus.
elk (Cervus canadensis)
mountain lion (Felis
concolor )
cactus (Peromyscus
eremicus)
Linnaeus's System of Classification
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Carolus Linnaeus
Hierarchial system of
classification.
Includes seven taxonomic
categories (smallest to
largest):
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Species
Genus
Family
Order
Class
Phylum
Kingdom
Taxonomic nomenclature
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Each level is called a taxon (plural : taxa), or
taxonomic category.
Organisms belonging to the same kingdom are not
necessarily very similar.
Organisms belonging to the same species are very
similar and can produce offspring.
Genus and species are the smallest categories.
What do the scientific names of the polar and grizzly bears
tell you about their similarity to each other?
Ursus arctos
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Ursus maritimus
They do not belong to the same species. The shared genus Ursus indicates
the two species are closely related
Ailuropoda melanoleuca
Taxonomy categories
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Genera that share the same characteristics are
grouped in a large category, the family.
Similar families are grouped into a larger category, the
order.
Similar orders are grouped into a larger category, the
class.
Several different classes make up a phylum. A phylum
can include many different organisms that share
important characteristics.
The kingdom is the largest and most inclusive taxonomic
category.
18.1 – Key questions
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How are living things
organized for study?
To study the diversity
of life, biologists use a
classification system to
name organisms and
group them in a
logical manner.
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
Why do scientists
avoid using common
names when discussing
organisms?
By using a scientific
name, biologists can
be certain that
everyone is discussing
the same organism.
18.1 – Key questions
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What is binomial nomenclature?
In binomial nomenclature, each species is assigned a
two-part scientific name. The scientific name is
always written in italics. The first word is
capitalized, and the second word is lowercased.
Kingdoms
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Originally, two kingdoms – Animalia and Plantae.
Scientists soon realized that microorganisms were
significantly different from organisms in the two
original kingdoms. Kingdom Protista established.
Then, the mushrooms, yeasts, and molds were
separated from the plants and placed in their own
kingdom, Fungi.
Kingdoms
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Later still, scientists realized that bacteria lack the
nuclei, mitochondria, and chloroplasts found in
other forms of life.
Therefore, they were placed in another new
kingdom, Monera.
This process produced five kingdoms—Monera,
Protista, Fungi, Plantae, and Animalia.
Kingdoms
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Biologists came to recognize that the Monera were
composed of two distinct groups.
Some biologists consider the differences between
these two groups to be as great as those between
animals and plants.
As a result, the Monera have been separated into
two kingdoms, Eubacteria and Archaebacteria,
bringing the total number of kingdoms to six.
Kingdoms
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Five kingdom system
of classification:
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Six-kingdom system of
classification:
 Animalia
 Eubacteria
 Plantae
 Archaebacteria
 Protista
 Protista
 Fungi
 Fungi
 Monera
 Plantae
 Animalia.
Domains
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Molecular analyses have given rise to a new taxonomic
category 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
Domain Eukarya, which is composed of protists, fungi, plants,
and animals;
 Domain Bacteria, which corresponds to the kingdom
Eubacteria;
 Domain Archaea, which corresponds to the kingdom
Archaebacteria.
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Domains
Domain Bacteria
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Members of the domain
are unicellular and
prokaryotic.
Their cells have thick, rigid
cell walls that surround a
cell membrane.
The cell walls contain a
substance known as
peptidoglycan.
The domain Bacteria
corresponds to the
kingdom Eubacteria.
Peptidoglycan
Domain Bacteria
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These bacteria are
ecologically diverse,
ranging from free-living
soil organisms to deadly
parasites.
Some photosynthesize,
while others do not.
Some need oxygen to
survive, while others are
killed by oxygen.
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These are "true" bacteria
ubiquitous in nature.
They are found practically
in all the environments, at
all the attitudes and
depths, in extremely low
and high temperature, in
fresh as well as in marine
water and in bodies of
plants and animals both
living and dead.
Domain Bacteria
Domain Archaea
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Most archaeans don't look that different from bacteria
under the microscope, and that the extreme conditions
under which many species live has made them difficult
to culture, so their unique place among living organisms
long went unrecognized.
However, biochemically and genetically, they are as
different from bacteria as you are.
Although many books and articles still refer to them as
"Archaebacteria", that term has been abandoned
because they aren't bacteria -- they're Archaea.
Domain Archaea
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Unicellular and prokaryotic.
Live in some of the most
extreme environments you can
imagine—volcanic hot springs,
brine pools, and black
organic mud totally devoid of
oxygen.
Many of these bacteria can
survive only in the absence of
oxygen.
Cell walls lack peptidoglycan,
and their cell membranes
contain unusual lipids that are
not found in any other
organism.
Domain Eukarya
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The domain Eukarya consists of all organisms that
have a nucleus.
It is organized into the four remaining kingdoms of
the six-kingdom system: Protista, Fungi, Plantae, and
Animalia,
The distinction recognizes the common traits that
eukaryotic organisms share, such as nuclei,
cytoskeletons, and internal membranes.
Domain Eukarya
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Kingdom Protista
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Eukaryotic organisms that cannot be classified as animals, plants, or fungi.
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Of the six kingdoms, Protista is the least satisfying classification, because its
members display the greatest variety.
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Most protists are unicellular organisms, but some, such as the multicellular algae,
are not.
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Some protists are photosynthetic, while others are heterotrophic.
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Some share characteristics with plants, others with fungi, and still others with
animals.
Giardia
Volvox
Paramencium
Diatoms
Domain Eukarya
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Kingdom Fungi
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Members of the kingdom
Fungi are heterotrophs.
Most feed on dead or
decaying organic matter.
Unlike other heterotrophs,
fungi secrete digestive
enzymes into their food
source. They then absorb the
smaller food molecules into
their bodies.
The most recognizable fungi,
including mushrooms, are
multicellular.
Some fungi, such as yeasts,
are unicellular.
Domain Eukarya
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Kingdom Plantae
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Members of the kingdom Plantae
are multicellular organisms that
are photosynthetic autotrophs.
They carry out photosynthesis.
Plants are nonmotile—they
cannot move from place to place.
They also have cell walls that
contain cellulose.
The plant kingdom includes conebearing and flowering plants as
well as mosses and ferns.
Although older classification
systems regard multicellular
algae as plants, in this book we
group algae with the protists.
Domain Eukarya
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Kingdom Animalia
 Members
of the
kingdom Animalia are
multicellular and
heterotrophic.
 The cells of animals do
not have cell walls.
 Most animals can move
about, at least for
some part of their life
cycle.
Key questions
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What are the six kingdoms of life as they are now
identified?
The six-kingdom system of classification includes the
kingdoms Eubacteria, Archae, Protista, Fungi, Plantae,
and Animalia.
Why was the kingdom Monera divided into two
separate kingdoms?
Biologists recognized that the Monera were composed
of two distinct groups of organisms. The two groups are
as different as plants are to animals.
Key questions
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How are members of the kingdom Fungi different from
members of the kingdom Plantae?
Fungi are heterotrophs and secrete digestive enzymes
into their food source. They then absorb the smaller
food molecules into their bodies. Fungi are unicellular.
Plantae are multicellular organisms that are
photosynthetic autotrophs. In other words, they carry out
photosynthesis.
How are members of the kingdom Fungi similar to
members of the kingdom Plantae?
Some fungi are multicellular like plantae organisms.