Chapter 15: Biological Classification

What is this?

These are some of the common names for this animal. Scientists have assigned it a single scientific name: Porcellio scaber

Sow bug

Potato bugRoly-poly Pill bug

Wood louse

The Importance of Scientific Names

• Each kind of organism on Earth is assigned a unique two-word scientific name– Binomial nomenclature

• All biologists, regardless of their native language, use scientific names when speaking or writing about organisms

• Most organisms also have common names• Using scientific names enables scientists to exchange

information about an organism and to be certain that they are referring to the same living thing

What’s in a Scientific Name?• First word describes the organism in a general way• The second word identifies the exact kind of living thing• The first word of a scientific name is the name of the

genus to which the organism belongs– Group of animals that share major characteristics

• The second word in a scientific name identifies one particular kind of organism within the genus

• Scientists call each different kind of organism a species• The correct name for an organism must include BOTH

parts of its scientific name

Comparison of Red Oak and Willow Oak

Red Oak Willow Oak

Genus Name Quercus Quercus

Scientific Name Quercus rubra Quercus phellos

Traits Acorns about 25mm long

Common in open Northeastern forests; tolerant of city soot and cold temperatures

Lobed leaves

Acorns about 15mm long

Popular shade tree found in the South; grows well in rich, moist soil

Unlobed, narrow leaves

Scientific Names Must Conform to a Set of Rules

• All scientific names must consist of Latin words

• Two different organisms cannot be assigned the same name

• Organisms in different genera cannot have the same genus name

• When choosing a name for a species, biologists often pick a name that describes the appearance or distribution of an organism

The second word of a scientific name is often descriptive of an organism or its distribution. The green anole lizard Anolis carolinensis and the chickadee Parus carolinensis are both found in North Carolina and South Carolina.

Tyrannosaurus rex, which means “tyrant-lizard-king,” was named for its enormous teeth and tremendous size. This dinosaur measured about 50 feet in length.

The frog Rhinoderma darwinii was named to honor Charles Darwin.

Why are Scientific Names in Latin?

• In the Middle Ages, when scientists began to name organisms, Latin was used in academic circles

• Scientists and other scholars found it easier to communicate with each other in Latin

• Latin was the language of the scholar and was used for all spoken and written communication

• Easier to still use Latin than to rename all 1.4 million known organisms

• Latin is a universal language

Linnaeus Devised the Two-Name System

• The modern system of naming organisms was developed by Swedish botanist Carl Linnaeus

• In Linnaeus’s day, organisms were given very long Latin names (sometimes more than 15 words), which were often changed according to the whims of particular scientists

• Linnaeus assigned a standard, two-word Latin name to each organism known in his time

Writing a Scientific Name is Simple

• When you write a scientific name, always capitalize the genus name

• Begin the second word with a lowercase letter• Both parts of a scientific name are underlined or written in

italics– Homo sapiens– Homo sapiens

• After the first use of the full scientific name, the genus name can be abbreviated as a single letter if the meaning is clear– H. sapiens

Classification of Living Things

• The Greek philosopher Aristotle grouped animals by their physical similarities

• Today biologists classify organisms based on their physical, genetic, biochemical, and behavioral similarities

• The classification of organisms is based on decisions made by many scientists using available information

Classification of Living Things

• The science of classifying living things is called taxonomy

• Taxonomists are scientists who examine, classify, and argue about where organisms fit in a group

• In a hierarchal system of classification, species are assigned to genera, genera are assigned to families, and families are assigned to groups of increasing size

Organisms are Classified by Similarity

• In biological classification, organisms are assigned to a group because they share distinctive characteristics with other members of that group

• The biological hierarchy of classification has seven different levels

– Kingdom, phylum, class, order, family, genus, and species

Organisms are Classified by Similarity

• The smallest group in biological classification is the species

• Similar species are collected into a genus• Similar genera are united into a family• Families that are alike are combined into an order• Similar orders are collected into a class• Classes are united into a phylum• Finally, similar phyla are collected into a kingdom• The more classification categories two species share,

the more traits they have in common

Kingdom

Phylum

Class

Order

Family

Genus

Species

Biological Classification

• Kristy

• Poured

• Coffee

• On

• Fred’s

• Green

• Shirt

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Classification and Evolution

• The biological hierarchy of classification is based on the fact that different degrees of similarity exist among organisms

• For Darwin, classification provided strong evidence supporting evolution

• Organisms are similar because they descended from a common ancestor

• The more similarities two organisms share, the more recently they shared a common ancestor

• Thus, the more classification categories two organisms share, the more closely related they are

Similarity Does not Guarantee Close Relationship

• Compare the two ocean-dwelling animals seen here

• Both have stream-lined bodies, paddle-like fins, and flattened tails

• Would you say these organisms are closely related?

*gills obtain oxygen from water

*belongs to the class Chondrichthyes

*skin has placoid (toothlike) scales

*skeleton of cartilage

*vertical tail fin

*breathes air through lungs

*belongs to the class Mammalia

*skin has hair

*skeleton of bone

*horizontal tail fin

Similarity Does not Guarantee Close Relationship

• Similar appearance does not guarantee common ancestry

• Because the number of differences between sharks and dolphins far exceeds the number of similarities, it is easy to reject the hypothesis that these animals are close relatives

Methods of Taxonomy

• The example of the shark and dolphin illustrates the difficulty in determining which similarities will be useful when classifying an organism

• There are two alternative methods of choosing which similarities are important

• The first method is cladistics

Taxonomy and Technology

• Biologists have traditionally compared the appearances of organisms in order to discover the relationships among them

• Biologists also consider the behavioral patterns, methods of reproduction, life cycles, and development from fertilization to adulthood

• Technological advances have enabled biologists to study the genes that produce the traits used to classify organisms

Taxonomy and Technology

• Taxonomists use techniques of molecular biology to compare the DNA nucleotide sequences of different organisms

• Comparisons of DNA sequences are especially important for the taxonomist because mutations are random events

• As time passes, more mutations tend to occur in the DNA of a particular species

• Thus, DNA acts as a “molecular clock”

What Is a Species?

• A species is just a level in the classification system to which scientists assign very similar organisms

• Over time, species change and give rise to new species in a process known as speciation

• Biologists have traditionally defined a species as organisms that are able to interbreed with each other to produce fertile offspring and that usually do not reproduce with members of other groups

What Is a Species?

• This definition works well for most animals• For example, the horse and the zebra belong to

different species• Although they can mate, the resulting offspring, the

“zebroid”, is sterile• Reproductive barriers between species are not

always perfect• Hybrids are offspring that result from interbreeding

by individuals of different species– Coyotes, dogs, and wolves

A Species is a Unique Kind of Organism

• A species is basically a unique kind of organism

• Members of a species share at least one inherited characteristic not found in other similar organisms

• In sexually reproducing species, this distinctive characteristic is maintained from generation to generation because members of different species do not interbreed

Six – Kingdom System

• Biologists used to classify every living thing into either kingdom Plantae or kingdom Animalia

• However, numerous living things do not quite fit either description

• For example, where would a mushroom fit?• Since Linnaeus’s time, biologists have learned

a great deal about the structure and function of living things

Six – Kingdom System• This information has enabled them to make increasingly

precise distinctions among the major groups of organisms

• Most biologists now use a six-kingdom system of classification– Archaebacteria– Eubacteria– Protista– Fungi– Plantae– Animalia

Bacteria

• All prokaryotes, also called bacteria, are in the kingdoms Archaebacteria or Eubacteria

• The bacteria represent the most ancient groups on earth

• They have adapted to almost every environment

• All bacteria lack cell nuclei

Kingdom Archaebacteria

• The archaebacteria evolved before oxygen filled our atmosphere and now are found in extreme environments

• Fewer than 100 species have been recognized so far

• Archaebacteria are believed to be the ancestors of the protists

Kingdom Eubacteria

• Contains most of the common bacteria that share our world

• They are an extremely diverse group, containing both autotrophic and heterotrophic forms

• Approximately 5,000 species have been characterized so far, but many more exist

• Eubacteria are believed to be the ancestors of mitochondria and chloroplasts, organelles within eukaryotic cells

Kingdom Protista

• All the multicellular eukaryotes not classified as plants, animals, or fungi are assigned to this kingdom

• Protists include protozoa, such as Amoeba and Paramecium, and algae, such as seaweeds and kelps

• Slime molds and water molds also belong to this kingdom

Kingdom Fungi

• Mushrooms, yeast, and molds are members of this kingdom

• Instead of roots, stems, and leaves, fungi are made of thin filaments that penetrate the soil or decaying organisms, absorbing nutrients from them

• Fungi do not contain chloroplasts and cannot make their own food by photosynthesis

Kingdom Plantae

• This kingdom includes only terrestrial multicellular organisms that use photosynthesis to obtain their nutrients

• Nearly all plants occur on dry land, but a few grow submerged in fresh water, and a very few grow at the edges of the sea

• Plants cells have cell walls• Because some green algae are so similar to plants

they have been identified as the ancestral groups for this kingdom

Kingdom Animalia

• The first members of this kingdom evolved in the ocean

• The largest number of animal phyla are still found only in the sea

• Organisms in kingdom Animalia are multicellular• Animals do not photosynthesize• Their cells do not have cell walls• Nearly all animals have some sort of nervous

system