Chap 18- Classification Natural selection and other processes have led to a staggering diversity of...

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


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


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


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


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


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


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


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


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


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


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


Evidence used in Systematic Taxonomy:

• Fossil record• Morphology• Embryological Patterns of Development• Similarities in Macromolecules


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


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


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


Genes of many organisms show important similarities at molecular level

Similarities in DNA can be used to help determine classification & evolutionary relationships


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


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


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


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


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


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


Methanogens, halophiles

Protista

Eukaryote

Cell walls of cellulose in some; some have chloroplasts

Most unicellular; some colonial; some multicellular


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


Domain BacteriaUnicellular and prokaryoticCells have thick, rigid cell walls (contain

peptidoglycan) around cell membrane Ecologically diverseSome photosynthesize, others do notSome are aerobic, some anaerobic


Domain ArchaeaUnicellular and prokaryoticLive in very extreme environmentsMost are anaerobicCell walls lack peptidoglycanCell membranes contain unusual lipids not

found in other organisms


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


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


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

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