Transcript Document 7450318

CHAPTER 23
CLASSIFICATION OF ORGANISMS
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CLASSIFICATION
OF ORGANISMS
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30 million species are estimated to live
on Earth
 Only 1.5 million have been named
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Taxonomy – science of naming
organisms and grouping them into
categories
First developed by Aristotle
Modern method developed by Carolus
Linnaeus (1758)
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CLASSIFICATION
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Linnaeus introduced the system of binomial
nomenclature.
 Each organism gets two Latin names (genus and
species)
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Species – organisms that can interbreed
Genus - many closely related organisms
Scientific names must be written in italics or must be
underlined:
 genus name is capitalized
 species name is written in lower case
 Homo sapiens or Homo sapiens (humans)
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CLASSIFICATION OF
ORGANISMS
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Linnaeus also placed organisms into taxonomic
categories, the largest of which is the kingdom.
 Were originally two kingdoms – animals & plants
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Recently a grouping above kingdom, called
domain, was introduced.
Organisms are now placed into 3 domains:
Eubacteria
Archaea
Eucarya
Each domain is subdivided into kingdoms
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CLASSIFICATION OF
ORGANISMS
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Domain Eucarya has 4 kingdoms:
 Plantae
 Animalia
 Fungi
 Protista
A kingdom is further subdivided into a phylum
(known as a division in Plantae)
Further subdivisions are class, order, family,
genus, and species
Hierarchy of classification: domain, kingdom,
phylum (division), class, order, family, genus,
and species.
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DOMAINS EUBACTERIA AND
ARCHAEA
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Members are commonly known as bacteria
Though similar, the two domains have
significant differences in metabolic
activities.
Some are disease-causing, most are not
Differences between the two are based on
DNA and RNA sequences
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EUBACTERIA
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Three common shapes:
spherical
rod
spiral
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Classified as prokaryotes, characterized by:
 no nucleus
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single, circular strand of DNA
reproduce by binary fission
move by flagella or slime they produce
some are aerobic and others anaerobic
some are parasites
some are saprophytes (decomposers)
BINARY FISSION IN BACTERIA
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ARCHAEA
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Ancient prokaryotic bacteria, but differ from
“regular” bacteria in that:
 Found in extreme environments such as:
hot springs at 113º C (above boiling
point)
high salt
acidic places
 Some have special kinds of chlorophyll
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EUCARYA
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Eukaryotic cells are larger than those of
prokaryotes (1000 times more volume)
Cells have membrane-bound organelles
(mitochondria, ER, Golgi, lysosomes, etc.)
Eucarya are divided into:
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Protista
Fungi
Plantae
Animalia
PROTISTA
All are single celled
 Approximately 60,000 different species
 Found in fresh water, marine, and
terrestrial habitats
 Many have chlorophyll and are
autotrophs
 Some reproduce sexually
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FUNGI
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Have a rigid, thin cell wall composed of
chitin; over 70,000 species
Do not have chlorophyll; Nonmotile
Include molds and mushrooms; most are
multicellular
Some are single-celled (yeasts)
Function mainly as decomposers
(saprophytes)
Some are parasitic
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PLANTAE
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All are nonmotile, terrestrial, multicellular
organisms capable of producing their own food
Have cellulose in their cell walls
300,000 species have been identified and of
these, 85% are flowering plants
Members of this group can be vascular or
nonvascular.
Some are seed producing, some (ferns) lack
seeds
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PLANTAE
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Have unique lifecycles:
Haploid gametophyte stage – produces
haploid sex cells by mitosis
Diploid sporophyte stage – produces
haploid spores by meiosis.
Capable of both sexual and asexual
reproduction
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ANIMALIA
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All are heterotrophic and multicellular
All are motile (at least during some part
of their life)
All are capable of reproducing sexually,
but some can reproduce asexually
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VIRUSES
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Consist of a nucleic acid core surrounded
by a coat of protein (capsid)
Obligate intracellular parasites
Are not members of any domain or
kingdom
Not considered living things
Reproduce only when they are in their host
cell
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VIRUSES
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Once inside a cell, viral nucleic acids take over
the cell and direct it to make more viral particles
Viruses are host-specific
 Only infect certain hosts
 Only infect certain cells
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Have either DNA or RNA as their nucleic acid
(not both)
Smallest infectious agents known to humans
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VIRUSES
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Viruses bind to the host and either
Inject its nucleic acid, or
Are engulfed through endocytosis
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In either case, the protein coat is released
and the nucleic acid will replicate using
the machinery of the host cell.
Once new viral particles are assembled,
the host cell is destroyed and new viruses
are released to infect other cells.
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TYPICAL VIRUSES
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VIRUSES
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One of the most recent infectious viruses
is HIV.
Only infects humans
Causes AIDS
claimed 22 million lives so far
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HIV is a spherical virus containing RNA, a
protein shell, and an outer envelope
Estimated to be over 42,500,000 people
infected with the AIDS virus
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VIROIDS
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Similar to viruses, but consist only of a single
strand of RNA
None infect animals
Mainly infect cultivated crops
 Potatoes
 Tomatoes
 Cucumbers
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Hard to detect
Stunted or distorted growth, may or may not
cause plant death
Spread very easily
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PRIONS
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These are infectious proteins that can be
passed from one individual to another
Not species-specific – can be passed
between species
Examples include
scrapie in sheep and goats
mad cow disease in cattle (BSE)
chronic wasting disease in deer and elk
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PRIONS
Epidemic of mad cow disease in Great
Britain was apparently caused by the
spread of prions from sheep to cattle
 Prion-caused diseases in humans include:
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Kuru – occurred in Papua New Guinea and
spread by eating the brains of their dead
Creutzfeldt-Jakob disease – transmitted by
surgical instruments and tissue transplants
Similar to mad cow disease
Causes holes in brain matter
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PRIONS
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Do not reproduce or replicate as do viruses
and viroids
May cause a normal protein to change
shape to that of a dangerous protein
Proteins may stack up and interlock forming
plaques
Finally results in death
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CHAPTER 23
CLASSIFICATION OF ORGANISMS
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