Chapter 18
Classification
Pages 448-461
18-1 Finding Order in Diversity
• Why Classify Organisms??
– Biologists use classification systems to name
organisms and group them in a logical order
• Taxonomy: Scientists classify organisms
and assign each organism a universally
accepted name
The History of Organization
Aristotle 384-322 BC
Interested in biological classification.
Patterns in nature.
Carl Linnaeus
1707-1778 ACE
Father of
Biological
Classification!
Aristotle
• Developed the first system of
classification.
• He classified all living things into
plants and animals.
• Animals were grouped depending on
where they lived. (On land, in air or in
water)
• Later scientist became convinced that
his system did not work because of
organisms living in multiple habitats.
Carolus Linnaeus
• Developed the system of
classification that is still used today.
• He selected physical characteristics
that led to classification based on
close relationships of organisms.
• He used characteristics such as
bats having hair and feeding their
young milk to classify the
organisms.
• The system devised by Linnaeus
gives each organism two names
called Binomial Nomenclature.
18-1 Assigning Scientific Names
• For many species, there are often
regional differences in their common
names
– EX: Buzzard in the UK refers to a hawk,
Buzzard in the US refers to a vulture
• To eliminate such confusion, scientists
agreed to use a single name for each
species
18-1 Assigning Scientific Names
• Binomial Nomenclature: Scientists assign each
kind of organism a universally accepted name in
the system
– Two word system using the Genus and Species
– Words are always written in italics
– First word (Genus) is capitalized and second word
(Species) is lowercase
– Second word is a Latinized description of a
particular trait
– Developed by an 18th C. Swedish botanist named
Carolus Linnaeus
• EX: Grizzly Bear = Ursus arctos
18-1 Assigning Scientific Names
• Differences in Binomial Nomenclature:
– 1st part of scientific name is genus to which the
organism belongs
– A genus is composed of a number of closely
related species
– 2nd part of scientific name is unique to the
species within the genus
• EX: Ursus arctos= Grizzly Bear, Ursus maritimus= Polar Bear
• EX: Papio annubis and Papio cynocephalus do NOT
belong to the same species since the species part of the
name is different. However, they do belong to the same
genus
Common name: Robin
• Erithacus rubicula
• Turdus migratorus
Common name: Black and Polar Bear
Ursus americanus
Ursus maritimus
18-1 Assigning Scientific Names
• Linnaeus’s System of Classification:
– Based on Taxonomy naming system
• Taxonomy: a group at any level of an organization is referred
to as a taxon
– Is hierarchical and consists of 7 taxonomic categories
– From largest to smallest:
•
•
•
•
•
•
•
Kingdom (King)= Made up of phylums
Phylum (Phillip) = Made up of several different classes
Class (Came) = Made up of several different orders
Order (Over) = Made up of several different families
Family (For) = Made up of several different genuses
Genus (Grape) = Made up of several different species
Species (Soup)
18-1 Assigning Scientific Names
Examples of Taxonomic Levels:
• The most general and largest of Linnaeus’s
system is the Kingdom
– Linnaeus recognized the kingdoms of plants (Plantae)
and animals (Animalia)
• The class of Mammalia includes mammals
which are organisms that have:
– Are warm-blooded
– Have body hair
– Produce milk for their young
18-2 Modern Evolutionary
Classification
• Traditional classifications like Linnaeus’s tended
to take into account primarily general similarities
in appearance
– However, some organisms that ARE NOT closely
related look alike because of convergent evolution!
• Evolutionary Classification: The procedure of
grouping organisms based on their evolutionary
history
– Species within one genus should be more closely
related to each other than a species in another
genus
– All genera within a family share a common
ancestor. Similar genes
18-2 Modern Evolutionary
Classification
• Derived Characters: An evolutionary innovation
– EX: Free swimming larva, segmented body
• Cladistic Analysis: Analysis that focuses on the
order in which derived characters appear in an
organism
– Looks only at derived characters, or those characteristics that
are evolutionary innovations (EX: body structures, adaptations)
– New characteristics emerge as lineages evolve over time
• Cladogram: a table analyzing derived characters that
shows the evolutionary relationship between
organisms
– Helps scientists understand how lineages branched from one
another in the course of evolution
– Shows the order in which derived characters evolved
18-2 Modern Evolutionary
Classification
Similarities in RNA and DNA:
• Similar genes are evidence of common ancestry
• Similarities in DNA can help determine
classification and evolutionary relationships
– EX: A cow and a yeast’s degree of relationship can
be determined from their genes
– EX: Scientists have found that humans and yeast
have similar genes for the assembly of certain
proteins (Myosin)
• All organisms use DNA and RNA to pass on
information
18-2 Modern Evolutionary
Classification
Similarities in RNA and DNA Cont…:
• DNA evidence can help show the
evolutionary relationship between
organisms and how species have changed
– EX: Presence of similar genes in very
dissimilar organisms implies that the
organisms share a common ancestor like
vultures and storks!
18-3 Kingdoms and Domains
In the 1800’s scientists used a 3 kingdom classification
system:
– Animals, Plants, Protista
– Scientists grouped organisms according to how long they
have been evolving independently
• Biologists knowledge of diversity of life continued to grow
• We now know there are 6 Kingdoms:
–
–
–
–
–
–
Protista (used to be grouped with Plants)
Fungi
Plantae
Animalia
Eubcteria (used to be grouped as the Monera category)
Archaebacteria (used to be grouped as the Monera
category)
18-3 Kingdoms and Domains
The Three Domain System:
• Modern analysis of evolutionary trees have given rise to
a new taxonomic category– Domain
• A domain is more inclusive and larger than a kingdom
• There are 3 Domains:
– Eukarya: includes kingdoms protist, fungi, plants, &
animals
– Archaea: includes kingdom Archaebacteria
– Bacteria: Includes kingdom Eubacteria
• The 3 domains are thought to have diverged from a
common ancestor before the evolution of the main
groups of eukaryotes
• Recognizes fundamental differences between 2
groups of prokaryotes- Bacteria & Archaea
18-3 Kingdoms and Domains
• Domain Archaea:
– Unicellular
– Found in extreme environments– deep sea
bacteria, make their own food (autotroph) using
energy derived from minerals coming form; without
oxygen
– Cell membranes contain unusual lipids
– Corresponds to the kingdom Archaebacteria
Halophiles (like salt)
Thermophiles (like heat)
• 18-3 Kingdoms and Domains
•Domain Bacteria:
•Unicellular
•Heterotroph
•Cell walls are thick & rigid & contain peptidoglycan
•Corresponds to the kingdom Eubacteria
•Come in 3 basic shapes --- cocci (spheres), bacilli
(rod shaped), spirilla (corkscrew shape)
Some need oxygen to survive & others do not
Eubacteria
• Staphylococcus
aureus
• Bacillus anthracis
• E. coli
18-3 Kingdoms and Domains
• Domain Eukarya:
– Consists of all eukaryotes (cells with a nucleus)
– Consists of the 4 kingdoms:
• Protista:
– organisms that cannot be classified as plants,
animals, or fungi
– Usually unicellular
– Have chloroplasts
– Membrane-bound organelles
– Move by flagellum, cillia, or pseudopods
– EX: Algae
Amoeba
Rotifer
Euglena
Algae
18-3 Kingdoms and Domains
• Kingdom Fungi:
– Heterotrophs that feed on dead or decaying
matter. Do not contain chlorophyll
– decomposers & recyclers
– Can be single or multicelled
– Cell walls contain chitin
– Non-motile
– Lack true roots, stems, & leaves
– EX: Mushrooms & yeast
Mushrooms
Mold
Ringworm
Yeast
18-3 Kingdoms and Domains
•
•
•
•
•
•
•
•
Kingdom Plantae:
Photosynthetic autotrophs
Multicellular
Contain chlorophyll inside of chloroplasts
Undergo photosynthesis
Cell walls contain cellulose
All plants that reproduce sexually
EX: mosses, ferns, flowering plants, conebearing plants, etc…
18-3 Kingdoms and Domains
• Animalia:
– Multicellular & heterotrophic
– Cells contain a nucleus and membrane bound
organelles
– Show levels of organization including cell, tissue,
organ, & system
– Cells are specialized for particular functions
– No cell walls
– Can move about
– EX: animals
What are Dichotomous Keys?
• a method for determining the identity of
something (like the name of a butterfly, a
plant, a lichen, or a rock) by going through
a series of choices that leads the user to
the correct name of the item.
• Dichotomous means "divided in two parts".
Using a dichotomous key
At each step of the process of using the key, the user is
given two choices; each alternative leads to another
question until the item is identified.
1a. If the leaves are flat….go to question 4.
1b. If the leaves are needle-like….go to question 2.
2a. Are the needles in a bunch? Go to question 5
2b. Are they spread along the branch?“…pine tree
Eventually, when enough questions have been
answered, the identity of the tree is revealed.
Why is Taxonomy Important?
Unknown species discovered.
New Discoveries
Questions
New fossil Uncovered.
How can you answer these questions?