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CHAPTER 18
Natural selection has led to great diversity.
• 1.5 million species so far
• 2–100 million yet to be discovered
Classification is a way to group species in a logical manner.
Taxonomy, a system to classify organisms. Each organism is given a biologically significant name (that deals with their characteristics).
Why Assign Scientific Names?
Common names vary
The cougar is also known as the puma, mountain lion, mountain cat, catamount and panther.
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.
Linnaeus's not only named species, he also grouped them into categories (taxa).
Latin and Greek, are used
for scientific names.
The first part = genus name (Capitalized).
A genus is a group of closely related species.
The second part = species name (lowercase).
The species name often describes an important trait or where the organism lives.
Linnaeus’s seven levels of classification are—from largest to smallest—•Kingdom - largest •Phylum•Class•Order•Family•Genus•Species – most specific
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King Phillip Could Only Find Green Socks
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Species = smallest, most specific category. It includes organisms that can breed together and produce fertile offspring.
A genus contains closely related species that cannot breed successfully.
Grizzly bear
Black bear
Grizzly bear
Black bear
Giant panda
Genera that share many characteristics are grouped in a larger category, the family.
Red fox
Grizzly bear
Black bear
Giant panda
An order is a broad category composed of similar families.
Abert squirrel
Class Mammalia
Black bear
Giant panda
Grizzly bear
Red fox
The next larger category, the class, is composed of similar orders.
PHYLUM Chordata
Black bear
Giant panda
Grizzly bear
Red fox
Abert squirrel
Coral snake
Several different classes make up a phylum.
KINGDOM Animalia
Black bear
Giant panda
Grizzly bear
Red fox
Sea star
Abert squirrel
Coral snake
The kingdom is the largest and most inclusive of Linnaeus's taxonomic categories.
Red fox
Grizzly bear
Black bear
Giant panda
Sea star
Coral snake
Abert squirrel
Linnaeus grouped species into larger taxa according to visible similarities and differences.
Now we group organisms based on evolutionary descent (or phylogeny) not just physical similarities.
Grouping organisms based on evolutionary history is called evolutionary classification.
Phylogeny is the study of evolutionary relationships among organisms.
18-2 Modern Evolutionary Classification
•Cladistic analysis considers only new characteristics that arise (called derived characters).
•Characteristics that appear in recent parts of a lineage (line) 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.
Barnacles and crabs share an evolutionary ancestor that is more recent than the ancestor that barnacles and limpets share.
Crustaceans Mollusk
Crab Barnacle Limpet
Tiny free-swimming larva
Molted external skeleton
Segmentation
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
•A molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently.
Molecular Clocks
new mutation
new mutation
2 mutations
A
B
C
A gene in an ancestral species
Species
Species
Species
new mutation
2 mutations
A molecular clock relies on mutations to mark time.
Comparing sequences in two species shows how dissimilar the genes are, and shows when they shared a common ancestor.
The Tree of Life Evolves
•Classification systems change with new discoveries.
•Linnaeus classified organisms into two kingdoms—animals and plants.
Then new differences called for a 5 kingdom system:
•Monera
•Protista
•Fungi
•Plantae
•Animalia
Now we have a Six Kingdom System
•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
Introduced Names of Kingdoms
1700’s
Late 1800’s
1950’s
1990’s
Plantae Animalia
Protista Plantae
Monera Protista Fungi Plantae
Eubacteria Archae-bacteria
Animalia
Animalia
AnimaliaProtista Fungi Plantae
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.
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Size Comparison of Select Organisms
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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.
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Bacteria
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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.
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Common Protista
Fungi
•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).
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FUNGI
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Domain EukaryaPlantae
•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 cone-bearing and flowering plants as well as mosses and ferns.
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Plant Kingdom
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Domain EukaryaAnimalia
•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.
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Animal Kingdom
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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
