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Chap 18- Classification Why Classify? For study purposes, biologists must give each organism a name Must also attempt to organize living things into groups that have biological meaning Biologists use classification system to name organisms & group them in a logical manner
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Chap 18- Classification
Natural selection and other processes have led to a staggering diversity of organisms
Biologists have identified and named about 1.5 million species so far
Estimate that anywhere between 2 and 100 million additional species have yet to be discovered
Chap 18- Classification
Why Classify?For study purposes, biologists must give
each organism a nameMust also attempt to organize living things
into groups that have biological meaningBiologists use classification system to name
organisms & group them in a logical manner
Chap 18- Classification
In taxonomy, scientists classify organisms and assign each organism a universally accepted name
Using scientific name reduces confusion about which organism is being discussed
When taxonomists classify organisms, place them into biologically significant groups
Chap 18- Classification
Science often requires smaller categories as well as larger, more general categories
Good system of classification – organisms placed into particular group more similar to each other than to organisms in another group
Chap 18- Classification
Assigning Scientific NamesBy 18th century, scientists recognized that
referring to organisms by common names was confusing
To eliminate confusion, scientists agreed to a single name for each species
Latin & Greek were used for scientific names
Chap 18- Classification
Early Efforts1st attempts often described physical
characteristics in great detailSome names twenty words longAlso difficult to standardize names of
organisms since different scientists described different characteristics
Chap 18- Classification
Binomial NomenclatureCarolus Linnaeus- Swedish botanist, 18th
centuryDeveloped two-word naming system called
binomial nomenclatureEach species assigned a two-part scientific
nameAlways written in italics; 1st word capitalized
Homo sapiens
Chap 18- Classification
Linnaeus’ System of ClassificationHierarchical; consists of levelsSeven levels (smallest to largest): species,
genus, family, order, class, phylum, and kingdom
Each level called a taxon, or taxonomic category
Chap 18- Classification
Species- group of similar organisms that can breed and produce fertile offspring
Genus- group of closely related speciesFamily- group of genera that share many
characteristicsOrder- broad taxonomic category composed
of similar families
Chap 18- ClassificationClass- composed of similar ordersEx.- Order Carnivora placed in class
Mammalia (animals that are warm-blooded, have body hair, and produce milk for offspring)
Phylum- Several different classes; members may be different from one another, but share important characteristics
Kingdom- most inclusive of all taxons
Grizzly bear Black bear Giant panda Red fox Albert squirrel Coral snake Sea star
KINGDOM Animalia
PHYLUM Chordata
CLASS Mammalia
ORDER Carnivora
FAMILY Ursidae
GENUS Ursus
SPECIES Ursus arctos
Chap 18- ClassificationOrganisms determine who belongs to their
species by choosing who to mate withTaxons above the species level are
“invented” by taxonomists who decide how to distinguish between one genus, family, or phylum
Always tried to group according to biologically important characteristics
Chapter 18- ClassificationLinnaean system has limitations & problemsSystem uses homologies to group species
into larger and more general categories Since Darwin, classification is a way of
describing evolutionary relationships
Chap 18- Classification
Which Similarities Are Most Important?Linnaeus grouped species into larger taxa
mainly according to visible similarities & differences
Which are most important?Ex.- DolphinsFish due to fin-like limbs and live in water?Mammals due to milk and breathe air?
Chap 18- ClassificationEvolutionary ClassificationDarwin’s ideas gave rise to study of
phylogeny (evolutionary relationships between organisms)
Now group organisms into categories that represent lines of evolutionary descent, not just physical similarities
Systematics- classification based on evolutionary relationships, not just physical similarities
Chap 18- Classification
Species within a genus more closely related to each other than to species within another genus
Because all members of a genus share a recent common ancestor
So, all genera in a family share a common ancestor; much farther in past
Higher the taxon level, further back the RCA of all organisms in the taxon
Chap 18- Classification
Evidence used in Systematic Taxonomy:
• Fossil record• Morphology• Embryological Patterns of Development• Similarities in Macromolecules
Chap 18- Classification
Organisms that appear very similar (like barnacles and limpets) may not share a RCA
Natural selection has often caused convergent evolution
Barnacles & limpets used to be classified together based on superficial similarities
Evolutionary classification now shows barnacles more closely related to crabs than limpets
CLASSIFICATION BASED ON VISIBLE SIMILARITIES
Evolutionary Classification
Appendages Conical Shells
Crab Barnacle Limpet Crab Barnacle Limpet
Crustaceans Gastropod
Chap 18- Classification
Classification Using CladogramsRefining the process, many biologists now
prefer a method called cladistic analysis Identifies and considers only those
characteristics of organisms that are evolutionary innovations
Characteristics that appear in recent parts of a lineage but not in older members- derived characters
Chap 18- Classification
Derived characters used to construct a cladogram
Diagram that shows evolutionary relationships among a group of organisms
Useful tools that help to show how one lineage branched from another in the course of evolution
Cladogram represents a type of evolutionary tree
CLASSIFICATION BASED ON VISIBLE SIMILARITIES
CLADOGRAM
Appendages Conical Shells
Crab Barnacle Limpet Crab Barnacle Limpet
Crustaceans Gastropod
Molted exoskeleton
Segmentation
Tiny free-swimming larva
Chap 18- ClassificationSimilarities in DNA & RNAAll classification methods discussed so far
based primarily on physical similarities & differences
Organisms with very different anatomies can have common traits
Since DNA & RNA so similar across all forms of life, provide method of comparing organisms at genetic level
Chap 18- Classification
Genes of many organisms show important similarities at molecular level
Similarities in DNA can be used to help determine classification & evolutionary relationships
Chap 18- Classification
Even genes of diverse organisms such as humans and yeasts show many similarities
Humans have gene for muscle protein myosin
Yeasts also have gene for protein myosinIndicator that humans and yeasts share a
common ancestry
Chap 18- Classification
Can also help show evolutionary relationships of species and how species have changed
More similar DNA sequences of two species, more recently they shared a common ancestor
More two species have diverged, less similar their DNA will be
Chap 18- Classification
Tree of Life EvolvesIn Linnaeus’ time, scientific view of life was
simplerOnly known differences among living things
were traits that separated animals & plantsAs biologists learned more about natural
world, realized Linnaeus’ two kingdoms did not represent full diversity of life
Chap 18- Classification
Microorganisms were first given a new kingdom based on significant differences from animals & plants (Protista)
Next, mushrooms, yeasts, & molds were separated from the plants & placed into own kingdom (Fungi)
Later on, bacteria were realized to be missing membrane-bound organelles and placed into own kingdom (Monera)
Chap 18- ClassificationRecently, as new data about bacteria
accumulated, Monera were recognized as being two separate groups
As a result, Monera has been split into two new kingdoms: Eubacteria & Archaebacteria
Gives us six kingdom system: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, & Animalia
Chap 18- Classification
Three-Domain SystemSome most recent evolutionary trees have
been produced using comparative studies of rRNA found in all living things
These molecular analyses given rise to a new taxonomic category, the domain
The domain is more inclusive category- larger than a kingdom
Chap 18- Classification
Three domains:-Eukarya: composed of protists, fungi,
plants, & animals-Bacteria: corresponds to kingdom
Eubacteria-Archaea: corresponds to kingdom
Archaebacteria
DOMAIN
KINGDOM
CELL TYPE
CELL STRUCTURES
NUMBER OF CELLS
MODE OF NUTRITION
EXAMPLES
Bacteria
Eubacteria
Prokaryote
Cell walls with peptidoglycan
Unicellular
Autotroph or heterotroph
Streptococcus, Escherichia coli
Archaea
Archaebacteria
Prokaryote
Cell walls without peptidoglycan
Unicellular
Autotroph or heterotroph
Methanogens, halophiles
Protista
Eukaryote
Cell walls of cellulose in some; some have chloroplasts
Most unicellular; some colonial; some multicellular
Autotroph or heterotroph
Amoeba, Paramecium, slime molds, giant kelp
Fungi
Eukaryote
Cell walls of chitin
Most multicellular; some unicellular
Heterotroph
Mushrooms, yeasts
Plantae
Eukaryote
Cell walls of cellulose; chloroplasts
Multicellular
Autotroph
Mosses, ferns, flowering plants
Animalia
Eukaryote
No cell walls or chloroplasts
Multicellular
Heterotroph
Sponges, worms, insects, fishes, mammals
Eukarya
Classification of Living Things
Chap 18- Classification
Domain BacteriaUnicellular and prokaryoticCells have thick, rigid cell walls (contain
peptidoglycan) around cell membrane Ecologically diverseSome photosynthesize, others do notSome are aerobic, some anaerobic
Chap 18- Classification
Domain ArchaeaUnicellular and prokaryoticLive in very extreme environmentsMost are anaerobicCell walls lack peptidoglycanCell membranes contain unusual lipids not
found in other organisms
Chap 18- Classification
Domain EukaryaConsists of all organisms that have a
nucleusProtistaComposed of eukaryotic organisms that
cannot be classified as plants, animals, or fungi
Members display great variety
Chap 18- Classification
Most are single-celled, some are multi-cellularSome are photosynthetic, some are
heterotrophicSome share characteristics with fungi, some
with plants, others with animalsFungiHeterotrophsFeed on dead or decaying organic matter
Chap 18- Classification
Secrete digestive enzymes into their food source (unlike other heterotrophs)
Most are multicellular, some (yeasts) are unicellular
PlantaeMulticellular, photosynthetic autotrophsNonmotileHave cell walls that contain cellulose
Chap 18- ClassificationIncludes cone-bearing & flowering plants as
well as mosses and fernsMulticellular algae are found in Protista, not
PlantaeAnimaliaMulticellular & heterotrophicNo cell wallsMost animals are motile, for at least part of
life cycle
KingdomsEubacteriaArchaebacteriaProtistaPlantaeFungiAnimalia
DOMAIN EUKARYA
DOMAIN ARCHAEA
DOMAIN BACTERIA