Classification:

Georgia Performance Standards:

• Compare how structures and functions vary between the six kingdoms (archaebacteria, eubacteria, protests, fungi, plants, and animals).

• Examine the evolutionary basis of modern classification systems

Essential Questions:

1. How does the evidence of evolution contribute to modern classification systems?

2. Why classify?3. On what criteria do Taxonomists base their classification of organisms?4. In what way does scientific discovery lead to the development of a new

classification group?

Why Classify?

• To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.

• In taxonomy, scientists classify organisms and assign each organism a universally accepted name.

• By using a scientific name, biologists can be certain that everyone is discussing the same organism.

Early Efforts at Naming Organisms

• The first attempts at standard scientific names often described the physical characteristics of a species in great detail.

• Results in long names

• Difficult to standardize the names of organisms

• Different scientists described different characteristics.

Binomial Nomenclature

•  Carolus Linnaeus developed a two-word naming system called binomial nomenclature.

• In binomial nomenclature, each species is assigned a two-part scientific name. – The scientific name is always written in italics. – The first word (the genus) is capitalized – The second word (the species) is lowercased.

Linnaeus's System of Classification

• A group or level of organization is called a taxonomic category, or taxon

• The are 7 taxonomic categories. (from smallest to largest)

• species • genus• family• order • class • Phylum• kingdom.

The 7 taxonomic categories• Species - a group of organisms that breed with one another

and produce fertile offspring.

• Genus - a group of closely related species.

• Family - genera that share many characteristics.

• Order - is a broad taxonomic category composed of similar families.

• Class - is composed of similar orders.

• Phylum- several different classes that share important characteristics.

• Kingdom - largest taxonomic group, consisting of closely related phyla

Checkpoint Questions:

1.  How are living things organized for study?

2. Describe the system for naming species that Linnaeus developed.

3. What are the seven taxonomic categories of Linnaeus’s classification system?

4. Why do scientists avoid using common names when discussing organisms?

5.   Which category has more biological meaning—all brown birds or all hawklike birds? Why?

Modern Evolutionary Classification 

• Organisms are grouped into categories that represent lines of evolutionary descent, not just physical similarities

• This strategy of grouping organisms together based on their evolutionary history is called evolutionary classification.

Modern classification systems are based upon biochemical and genetic evidence that indicates evolutionary relationships

Classification Using Cladograms• Cladistic analysis identifies and considers only the

characteristics that arise as lineages evolve over time. – Characteristics that appear in recent parts of a lineage but

not in its older members are called derived characters.– Derived characters can be used to construct a cladogram,

a diagram that shows the evolutionary relationships among a group of organisms.

TRADITIONAL CLASSIFICATION

CLADOGRAM

Appendages Conical Shells

Crab Barnacle Limpet Crab Barnacle Limpet

Crustaceans Gastropod

Molted exoskeleton

Segmentation

Tiny free-swimming larva

Section 18-2Traditional Classification Versus Cladogram

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Modern Evolutionary Classification 

• Similarities in DNA and RNA

– The genes of many organisms show important similarities at the molecular level that can be used as criteria to help determine classification.

Modern Evolutionary Classification

• Molecular Clocks– Comparisons of DNA can

also be used to mark the passage of evolutionary time.

– A model known as a molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently.

• Comparison reveals more DNA in common, the more recent the common ancestor

Checkpoint Questions:

1. How is information about evolutionary relationships useful in classification?

2. How are genes used to help scientists classify organisms?

3. What is the principle behind cladistic analysis?

4. Describe the relationship between evolutionary time and the similarity of genes in two species.

5. How have new discoveries in molecular biology affected the way in which we classify organisms compared with the system used by Linnaeus? Constructing a Chart  

Kingdoms and Domains 

• The six-kingdom system of classification includes the following kingdoms:

– Eubacteria– Archaebacteria – Protista– Fungi– Plantae– Animalia.

The Three-Domain System• The domain is the most inclusive taxonomic

category; larger than a kingdom   

• The three domains are:

– Bacteria : kingdom Eubacteria

– Archaea,: kingdom Archaebacteria;

– Eukarya :Kingdom protists, fungi, plants, and animals.

KingdomsEubacteria

Archaebacteria

Protista

Plantae

Fungi

Animalia

DOMAIN EUKARYA

DOMAIN ARCHAEA

DOMAIN BACTERIA

Section 18-3

Cladogram of Six Kingdoms and Three Domains

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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

EukaryaClassification of Living Things

Key Characteristics of Kingdoms and Domains

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Section 18-3

are characterized by

such as

and differing which place them in

which coincides withwhich coincides with

which place them in which is subdivided into

Living Things

Kingdom Eubacteria

Kingdom Archaebacteria

Eukaryotic cellsProkaryotic cells

Important characteristics

Cell wall structures

Domain Eukarya

Domain Bacteria

Domain Archaea

Kingdom Plantae

Kingdom Protista

Kingdom Fungi

Kingdom Animalia

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Checkpoint Questions:

1. What are the six kingdoms of life as they are now identified?

2.  What are the three domains of life?

3. Why was the kingdom Monera divided into two separate kingdoms?

4. Why might kingdom Protista be thought of as the “odds and ends” kingdom?

5. Which kingdoms include only prokaryotes? Which kingdoms include only heterotrophs?