Chapter 18

Classification

18 – 1 Finding Order in Diversity

• Evolution has lead to a staggering variety or organisms

• Biologists have identified and named about 1.5 million species so far

• They estimate anywhere between 2 and 100 million additional species have yet to be discovered

Taxonomy

• The science of classifying and naming organisms

Assigning Scientific Names

• By the 18th century, European scientists recognized that referring to organisms by common names was confusing

• Common names vary among regions within a country

Mountain Lion

Cougar

Puma

Panther

Early Efforts at Naming Organisms

• First attempts at standard scientific names often described physical characteristics

• As a result, these names could be 20 words long!

• Ex.) The English translation of the scientific name of a particular tree might be “Oak with deeply divided leaves that have no hairs on their undersides and no teeth around their edges.”

Binomial Nomenclature• Carolus Linnaeus (18th Century)

• Swedish Botanist

• Developed a system for naming organisms

Binomial Nomenclature

• Two word naming system

Rules for Binomial Nomenclature

• Written in italics• First word is capitalized• Second word is lowercased

Ex.)

Genus species

Genus species

G. species

• The name often tells you something about the species

• Ex.) Tyranosaurus Rex

• Tyrant Lizard King

Taxon (taxonomic category)

• A group or level of organization

Linnaeus’s system of classification uses seven taxonomic categories

Kingdom

Phylum

Class

Order

Family

Genus

species

Largest / Least Specific

Smallest / Most Specific

Mnemonic DeviceKingdom

Phylum

Class

Order

Family

Genus

species

• King

• Phillip

• Came

• Over

• For

• Good

• Soup

18 -2 Modern Evolutionary Classification

Problems with Traditional Classification

• Sometimes, due to convergent Evolution organisms that are quite different from each other evolve similar body structures

• Ex.) Crab, limpet, barnacle

Evolutionary Classification • Darwin’s theory of evolution

changed the entire way that biologists thought about classification

• Biologists now group organisms into categories that represent lines of evolutionary descent, not just physical similarities

Classification Using Cladograms

• Many biologists now prefer a method called cladistic analysis

• This method of classification identifies and considers only those characteristics that arise as lineages evolve over time

Derived characteristics

• Characteristics that appear in recent parts of a lineage but not in its older members

Cladograms• Diagram that shows the

evolutionary relationships among a group of organisms

Similarities in DNA and RNA• Suppose you were trying to compare

diverse organisms such as yeast and humans

• It wouldn’t make sense to try to classify anatomical similarities

• The genes of many organisms show important similarities at the molecular level

• These similarities can be used as criteria to help determine classification

• Ex.) Myosin in humans & yeast

Molecular Clocks• Use DNA comparison to estimate

the length of time that two species have been evolving independently

Molecular Clocks• Mutations happen all the time at about

the same rate• A comparison of DNA sequences in

two species can reveal how dissimilar the genes are

• The degree of dissimilarity is an indication of how long ago the two species shared a common ancestor

18 -3 Kingdoms and Domains

• In taxonomy, as in all areas of science, ideas and models change as new information arises, some explanations have been discarded altogether, whereas others such as Darwin’s theory of evolution by natural selection, have been upheld

• So it should not be surprising that since the 1800’s, the tree of life has been revised and edited since the discovery of all this new information

The Tree of Life Evolves

• Before Linnaeus’s time, the only two Kingdoms that existed were Plants and Animals

• As scientists discovered new organisms that didn’t fit into the plant or animal category, they made a new category

The Old 5 Kingdom System

1. Animals

2. Plants

3. Fungi

4. Protist

5. Bacteria

• In recent years, as evidence about microorganisms continued to accumulate, biologists come to recognize that the Monera were composed of two distinct groups

The New 6 Kingdom System

1. Animals

2. Plants

3. Fungi

4. Protist

5. Eubacteria

6. Archaebacteria

The Three Domain System

• Molecular analysis has given rise to a new taxonomic category that is now recognized by many scientists

Domain

• Larger than a kingdom

3 Domains1. Bacteria• Eubacteria

2. Archaea• Archaebacteria

3. Eukarya• Protists, fungi, plants, animals

(Everything with a nucleus)

Domain Bacteria• Unicellular• Prokaryotic - no nucleus, no membrane

bound organelles• Thick walls (containing peptigoglycan)• Free living and parasitic• Important decomposers• Some photosynthesize• Some don’t need oxygen

– Anerobic

• Some need oxygen– Aerobic

Petri dish

Agar

Bacteria Colonies

What is this used for?

Domain Archaea

• Unicellular• Small• Prokaryotic• Live in extreme environments

Ex.) volcanic hotsprings, brine pools, black organic mud without oxygen

• Acidophiles – live in acidic environments

• Thermophiles – can tolerate hot temperatures 50 – 110 degrees

• Halophiles – can stand extreme concentrations of NaCl

• Methanogens – Produce methane CO2 + H CH4

Acidophiles

Thermophile

Halophile

Domain Eukarya• Consists of all organisms that

have a nucleus

Protista• Small

• Mostly unicellular

• Eukaryotic – has a nucleus, and membrane bound organelles

• Cannot be classified as animals, plants or fungi, but share many characteristics with plants, animals and fungi

Plant like Protists• Algae

• Photosynthetic – can make their own food

Euglenas

Flagella

Diatoms

Dinoflagellates

Dinoflagellates• Red tide

Green Algae

Red Algae

Brown Algae

Animal like Protists• Protozoans

• Heterotrophic – can’t make their own food

Fungus like Protists• Slime molds, water molds

• Decompose their food

Fungi• Mostly multicellular

Ex.) Mushroom, yeast

• Cell walls

Fungi• Heterotrophs

• Feed on decaying organic matter

• Secrete digestive enzymes into food source then

• Spread and reproduce by spores

Spores• Reproductive cells that form new

organisms without fertilization

Many are used in medicine

• Antibiotics

• Anti rejection

• Anti viral

Penicillium

Plantae• Multicellular

• Photosynthetic autotrophs – make their own food by photosynthesis

• Non-motile

• Cell walls (cellulose)

Animalia• Multicellular

• Heterotrophic

• No cell walls

• Most move

• Incredible diversity