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Chapter 20
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20-1
The Classification of Organisms
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The problem with common names
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Different in every language
Different names can be used to identify the same organism.
Organisms must have names that all scientists can
identify.
Naming organisms involves two different activities.
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Taxonomy
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Phylogeny
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The naming of organisms
Demonstrating how organisms are related evolutionarily
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Garden Snake or Gardner
Snake?
20-3
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Taxonomy
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The science of naming organisms and
grouping them into logical categories
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20-4
Taxis = arrangement
Scientific names of organisms are in Latin.
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Taxonomy
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Organism names follow the binomial system
of nomenclature.
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Introduced by Linnaeus
Uses two Latin names
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The genus and the specific epithet
A genus is a group of closely related organisms.
A specific epithet identifies the particular species to
which the organism belongs.
Binomial names are italicized or underlined.
The first letter of the genus is capitalized; the specific
epithet is not.
Thamnophis sirtalis
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Taxonomy
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Three sets of rules determine how organisms
are named.
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Organisms are organized into logical groups.
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International Rules for Botanical Nomenclature
International Rules for Zoological Nomenclature
International Bacteriological Code of
Nomenclature
These groups are hierarchical.
Domain, kingdom, phylum, class, order, family,
genus, species
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The Three Domains of Life
20-7
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Classification of Humans
20-8
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Phylogeny
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The science that explores the evolutionary
relationships among organisms
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Taxonomists use phylogeny to classify organisms
whenever possible.
Phylogenists use a variety of data to establish
evolutionary relationships.
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Seeks to reconstruct evolutionary history
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Fossils
Comparative anatomy studies
Life cycle information
Biochemical and molecular studies
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Fossils
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Different types of fossils
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Some organisms fossilize more easily than others.
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Whole organisms that have been preserved intact
Bones embedded in rock
Impressions left in rock
Found in sedimentary rock, not igneous or metamorphic
Those with hard parts vs. those with soft bodies
Those that live in water and can be buried in sediment
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Fossils
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Fossils can be placed
in a time sequence.
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Established by the order
that the organisms
appear in the layers of
sediment
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Rocks can be aged by
analyzing radioactive
isotopes.
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Deeper layers were laid
down first.
Older rocks have fewer
radioactive isotopes.
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Comparative Anatomy Studies
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The anatomy of fossilized organisms can be
compared to that of living organisms.
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Allows for the classification of fossils
Those organisms that have similar structures are
presumed to be related.
Examples
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Plants with flowers are related.
Animals with hair and mammary glands are related.
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Life Cycle Information
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Larval stages can provide clues about the
relatedness of organisms.
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The anatomy of eggs also provides clues.
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Birds and reptiles
The anatomy of seeds can be used as well.
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20-13
Barnacles and shrimp
Peas, peanuts and lima beans
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Biochemical and Molecular
Studies
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New DNA technologies have allowed
phylogenists to use DNA sequence
comparisons to determine relatedness.
These analyses have clarified phylogenetic
relationships that previously could not be
confirmed.
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Storks, flamingoes and geese
Green algae and plants
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A Current Phylogenetic Tree
20-15
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A Brief Survey of the Domains
of Life
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Eubacteria, Archaea and Eucarya
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Order of appearance
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Eubacteria and Archaea are prokaryotic.
Eucarya is eukaryotic.
Eubacteria evolved first.
Gave rise to Archaea
Eucarya evolved most recently.
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Domain Eubacteria
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“True bacteria”
Unicellular
Small (1-10 mm)
Prokaryotic (no nucleus)
– Contain a single,
circular chromosome
– Reproduce asexually
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Domain Eubacteria
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Cell walls made of peptidoglycan
– One component, muramic acid, is only found in
bacteria.
Can be rods, spheres or spirals
Move via slime or flagella
Varied metabolic requirements
– Some are aerobic, some are anaerobic.
– Some are decomposers, others are parasites;
some are commensals.
– Some are autotrophs, others are chemosynthetic.
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Domain Archaea
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Unicellular
Prokaryotic
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Single circular chromosomes
Have several genes that are different from
eubacteria and eucarya
No peptidoglycan in their cell walls
Have unique cell membranes
Can be spheres, spirals, filaments or flat
plates
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Domain Archaea
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Metabolically labeled as extremophiles
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Methanogens
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Halobacteria
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Live in extremely salty environments
Photosynthetic
Thermophiles
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Produce methane
Found in sewage, guts of ruminants, intestines of
humans
Live in high temperatures or areas with high sulfur
concentrations
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Habitat for Thermophilic Archaea
20-21
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Domain Eucarya
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Eukaryotic
Appear to have evolved through
endosymbiosis of prokaryotic cells
Larger than prokaryotes
Contain specialized membranous organelles
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Kingdom Protista
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Diverse
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Live in freshwater, marine, terrestrial
Some are parasitic, commensalistic or mutualistic.
Some reproduce asexually via mitosis.
Some are autotrophic, others are heterotrophic.
May not be a cohesive phylogenetic unit
Include algae, protozoa and slime molds
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60,000 species
Amoeba, Paramecium
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A Diversity of Protista
20-24
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Kingdom Fungi
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Most are non-motile
Have a thin, rigid cell wall composed of chitin
Heterotrophic
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Most are saprophytes that secrete enzymes that
break down the material they live on.
Decomposers
Some are parasitic, others are mutualistic.
Can form lichens
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Kingdom Fungi
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Most are multicellular.
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A few are unicellular.
 Yeast
Made up of filaments
 Include
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Athlete’s foot
Plant pathogens
Ringworm
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Examples of Fungi
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Kingdom Plantae
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Photosynthetic
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Green because of chlorophyll
Non-motile
Terrestrial
Likely evolved from green algae
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Non-vascular plants first
Then vascular
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Cone-bearing
Flowering
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Kingdom Plantae
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Multicellular
Contain a cellulose cell wall
Exhibit alternation of generations
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Multicellular gametophyte stage produces
gametes via mitosis.
Multicellular sprorophyte stage produces spores
via meiosis.
Able to reproduce sexually and asexually
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Plant Evolution
20-30
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Kingdom Animalia
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Are thought to have evolved from protozoa
Over a million species identified
Range from microscopic to very large
Common traits
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Heterotrophs
Multicellular
Motile
Can reproduce sexually
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Animal Diversity
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Acellular Infectious Particles
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Living organisms are made of cells.
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Particles that show some of these characteristics,
but not all, are called acellular.
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Have cell membranes
Use nucleic acids as genetic material
Have cytoplasm
Contain enzymes
Contain ribosomes
Use ATP as their source of energy
Most of these cause disease.
Viruses, viroids and prions
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Viruses
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An infectious particle consisting of a nucleic
acid core surrounded by a coat of protein.
Are obligate intracellular parasites
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Not technically “living”
Some cause disease, some do not
Vary in size and shape
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Because they cannot live outside of a living cell
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Rod-shaped, spherical, coil, helix
Most are extremely small.
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Typical Viruses
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Viral Disease
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How Viruses Cause Disease
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Viruses are host-specific.
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Only infect one type of cell that has specific
receptor sites on the cell membrane
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Viruses must get their nucleic acids into the
cell.
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This is where the virus attaches.
Is usually a glycoprotein
Once attached, viruses either enter the cell whole,
or inject their nucleic acid into the cytoplasm.
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How Viruses Cause Disease
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Viruses don’t have many enzymes.
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After viruses are replicated they leave the
cell.
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They depend on their hosts to replicate their DNA
and make their proteins.
Frequently, this process kills the cell.
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Viral Invasion of a Bacterial Cell
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Viroids: Infectious RNA
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Infectious particles
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Simply single strands of RNA
Only found to infect plants
Viroid infections cause stunted growth
May cause plant death
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Prions: Infectious Proteins
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Infectious proteins
All prion diseases cause brain tissue to
become “spongy”.
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Cause spongiform encephalitis
Mad cow (BSE), scrapie (sheep), CreutzfeldJakob and Kuru (human)
Can be transmitted from one animal to
another
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How Prions Cause Disease
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How do prions form and how do they multiply?
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Normal prion proteins exist in the brain.
Infectious prions come in contact with normal prions and
cause them to change shape.
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The infectious proteins aggregate and form plaques.
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Called conversion
Makes the normal prions infectious
These plaques disrupt brain function and kill brain cells.
Where cells die, a hole is formed.
Causes infected brain tissue to look “spongy”
Some people are more resistant to prion disease
than others.
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