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Classification of
Living Things
Ch. 20 Outline - Classification
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Classification of
Living Things
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Taxonomy
Branch of biology concerned with identifying,
naming, and classifying organisms
Began with the ancient Greeks and Romans
Aristotle classified organisms into groups such as
horses, birds, and oaks
John Ray (1627–1705)
Believed that each organism should have a set
name. Names were given in Latin.
Otherwise, “men…cannot see and record
accurately.”
Classifying Organisms
How would
you name
& classify
these
organisms?
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Taxonomy:
Binomial System
Classification of
Living Things
Mid-eighteenth century, Linnaeus developed the
binomial system of nomenclature
First word is genus name
Second word is specific epithet
- Refers to one species (of potentially many) within
its genus
A species is referred to by the full binomial name
(Genus species)
Genus name can be used alone to refer to a
group of related species
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Taxonomy:
Binomial System
Classification of
Living Things
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Why do organisms need scientific names?
Common names vary from countries because of
different languages
Even in one language area, common names can
differ
- Cougar, mountain lion, puma are all same animal
- Robin in England is different bird than in U.S.
When scientists around the world use the Latin
binomial name, they know they are discussing the
same organism.
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Carolus Linnaeus
Lynx rufus
Lilium
buibiferum
Lilium
canadense
Lynx canadensis
Taxonomy:
Distinguishing Species
Classification of
Living Things
Several ways of distinguishing species:
1. Structural definition rests on distinctive
structural characteristics not shared by
members of a similar species.
- In birds: Shape, size, color, feet, beak,
wings
- Members of same species can also vary
from each other
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Members of a Species - Sexual Dimorphism
Male
Female
Mallards
Male
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Members of a Species - Sexual Dimorphism
Elephant seals - large male
Male
Male
Female
Female
Female Terrapin larger
Rhinoceros
beetles
Male
&
Female
Taxonomy:
Distinguishing Species
Classification of
Living Things
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Several ways of distinguishing species:
2. Biological definition rests on recognition that
distinctive characteristics are passed from
parents to offspring. Based on
interbreeding & sharing the same gene pool.
- Attempts to demonstrate reproductive
isolation is problematic because:
● Some species hybridize, and
● Reproductive isolation is difficult to
observe
Hybridization between species
Zebroids
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Classification of
Living Things
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Classification Categories
Modern taxonomists use the following
classification: (from smallest to largest groups)
Species
Genus – one or more species
Family – one or more genera
Order – one or more families
Class – one or more orders
Phylum – one or more classes
Kingdom – one or more phyla
Domain – one or more kingdoms
Classification of
Living Things
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Classification Categories
Classification of Humans:
Domain -- Eukarya
Kingdom – Animalia
Phylum – Chordata
SubPhylum - Vertebrata
Class – Mammalia
Order – Primates
Family – Hominidae
Genus – Homo
Species – Homo sapiens
Hierarchy of Taxa for
Parthenocissus quinquefolia
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Classification of
Living Things
Classification Categories
The higher the category, the more inclusive
Organisms in the same domain have general
characteristics in common
In most cases, classification categories can be
subdivided into additional categories
Superorder
Order
Suborder
Infraorder
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Classification of
Living Things
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Phylogenetic Trees
Systematics - the diversity of organisms at all
levels
One goal of systematics is to determine
phylogeny (evolutionary history) of a group
Phylogeny often represented as a phylogenetic
tree
A diagram indicating lines of descent
Each branching point:
- Is a divergence from a common ancestor
- Represents an organism that gives rise to two new
groups
Classification and Phylogeny
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Classification of
Living Things
Phylogenetic Trees
Classification categories list the unique
characters of each taxon and is intended to
reflect phylogeny
Ancestral characteristics:
- Present in all members of a group, and
- Present in the common ancestor
Derived characters:
- Own individual characteristics
- Present in some members of a group, but
- Absent in the common ancestor
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Classification and Phylogeny
Derived characters
Derived characters
Common ancestor
(Ancestral characters)
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Classification of
Living Things
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Tracing Phylogeny
Fossil Record
It is often difficult to determine the phylogeny of a
fossil
Are turtles & crocodiles closely related?
Molecular data says yes
Or are turtles ancestors of crocodiles?
•Fossil record is incomplete since soft parts have less
of a chance of becoming fossils.
Ancestral Angiosperm?
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Classification of
Living Things
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Tracing Phylogeny
Homology
Is character similarity that stems from having a
common ancestor
Homologous structures are related to each other
through common descent
Examples:
Vertebrate forelimbs have same bones as in a
common ancestor
Classification of
Living Things
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Tracing Phylogeny
Convergent Evolution
The acquisition of same or similar features in
distantly related lines of descent
The feature is not present in a common ancestor
Such similarities are termed an analogy.
Analogous structures have same function in
different groups of organisms but don’t have a
common ancestor
Examples: wings of birds and insects
American cacti and African spurges
Convergent Evolution
North America
Africa
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Classification of
Living Things
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Tracing Phylogeny
Parallel Evolution
The acquisition of a same or similar feature in two
or more related lineages
The feature is not present in a common ancestor
Sometimes difficult to tell parallel evolution from
convergent evolution.
Classification of
Living Things
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Molecular Data
Protein Comparisons
Amino acid sequencing
- Cytochrome c is found in all aerobic organisms
- Compare a.a. sequence in different species to infer
relationships:
3 differences between chickens & ducks
13 differences between chickens & humans
- Thus chickens & ducks are more closely related
than chickens & humans.
Classification of
Living Things
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Molecular Data
RNA and DNA Comparisons
All cells have ribosomes
Genes that code for rRNA have changed very slowly during
evolution
This can provide a reliable indicator of similarities between
organisms.
rRNA information led to the division of life into three
domains.
Classification of
Living Things
Molecular Data
DNA-DNA hybridization
- Separate DNA into single strands & then
combine with different species.
- The better the strands stick together the more
closely related the organisms.
- This has been used to resolve ancestry of
giant pandas.
Are giant pandas more closely related to bears or
raccoons?
DNA hybridization says “bears”.
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Ancestry of Giant Pandas
Have raccoon features
Feeds on bamboo but
lacks false thumb
DNA of raccoons & red pandas
more similar
Eat bamboo with
help of false thumb
but look more
like a bear
DNA of giant pandas & bears
more similar
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Molecular Data
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Classification of
Living Things
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Classification Systems
Until the middle of the twentieth century,
biologists recognized only two kingdoms
Plantae (plants)
Animalia (animals)
Protista (protists) were proposed as an additional
third kingdom in the 1880s but wasn’t accepted
until 1950s.
Whittaker expanded to five kingdoms in 1969 by
adding Fungi and Monera
Classification of
Living Things
Three-Domain System
The Bacteria and Archaea are so different they
have been assigned to separate domains
Similar in that both are asexually reproducing
unicellular prokaryotes
Distinguishable by:
Difference in rRNA base sequences
Plasma membrane chemistry
Cell wall chemistry
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Classification of
Living Things
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Three-Domain System
Characteristics
Of Domain
Unicellularity
Membrane
lipids
Cell Wall
Nuclear
envelope
Membranebound
organelles
Ribosomes
Introns
Bacteria
Archaea
Eukarya
Yes
Yes
No
No
Yes
Yes
Yes
Yes
No
Some
Yes
Some, most
multicellular
Phospholipids
Varied
Phospholipids
unbranched branched lipids unbranched
Yes (has
Yes (no
Yes; some (no
Peptidoglycan) Peptidoglycan) Peptidoglycan)
No
No
Yes
Classification of
Living Things
Three-Domain System
Domain Bacteria
Unicellular asexually reproducing organisms
Very diversified and plentiful group.
Found everywhere on Earth.
Most are heterotrophic; some photosynthetic
Domain Archaea
Unicellular asexually reproducing organisms
Most live under extreme conditions
Cell membrane & wall chemistry is different
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Classification of
Living Things
Three-Domain System
Domain Eukarya
Unicellular and multicellular organisms
Cells with a membrane-bounded nucleus
Sexual reproduction common
Contains four kingdoms
- Kingdom Protista
- Kingdom Fungi
- Kingdom Plantae
- Kingdom Animalia
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The Three-Domain
System of Classification
1. Ancestor of ALL life
split into the two
Domains of Bacteria
& Archaea
2. Archaea split to
produce Eukarya
3. First Eukarya were
Protists
4. Protists split in three
directions to produce:
- Plants
- Fungi
- Animals
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The Three Domains of Life
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Classification of
Living Things
Eukarya Kingdoms
Protists
Diverse group of eukaryotes
Mainly unicellular
Lack true tissues
Some heterotrophic; some autotrophic
Some texts put protists into several kingdoms
Examples:
Green algae, paramecia, slime molds
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Classification of
Living Things
Eukarya Kingdoms
Fungi
Eukaryotes that form spores
Have cell walls containing chitin
Most multicellular
Heterotrophic by absorption – secrete digestive
enzymes onto food and then absorb nutrients
Examples: Mushrooms, molds, yeast
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Classification of
Living Things
Eukarya Kingdoms
Plants
Eukaryotes that are multicellular
Have cell walls containing cellulose
Nonmotile (don’t move on own)
Autotrophic via photosynthesis
Have true tissues and organs
Examples: Trees, cacti, flowers, ferns
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Classification of
Living Things
Eukarya Kingdoms
Animals
Eukaryotes that are multicellular
Motile (do move on own)
Heterotrophic by ingestion (eat food)
Have true tissues and organs
Examples: Birds, fish, reptiles, amphibians,
mammals, worms, snails, etc.
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