CLASSIFICATION

Because there are millions of organisms on earth, we need some sort of ordered system for keeping track of them and communicating about them. Without a name the information about an organism is lost.

I. Taxonomy

A. Taxonomy =  the science of naming and classifying organisms

B. Polynomial - During medieval times Latin was the language of scholars and most western scientific writing was done in Latin. Organisms were identified by long descriptive Latin phrases called polynomials

C. Binomials -  Linnaeus (mid 18th century) developed binomial naming system:

1. Each species has a two part name, e.g. the scientific name for humans is Homo sapiens

2. The first part of a binomial is the genus, e.g. Quercus is the genus of oak trees

3. The second part of a binomial is the specific epithet, usually a latinized descriptive. E.g. Quercus alba, Q. nigra and Q. rubra are the white, black and red oaks, respectively

4. Note that a specific epithet is meaningless without the genus name

5. Scientific names are always latinized and either italicized or underlined, and the first letter of only the genus name is capitalized

6. Why use scientific names rather than common names?

a. the same organism may have more than one name in different languages or different regions

b. the same common name is often applied to more than one organism, e.g. daisy

c. many common names are confusing, e.g. a pineapple tree is neither a pine nor apple

d. there are no rules for using common names, with millions of named species there must be some rules

II. The taxonomic hierarchy - Species are grouped into an ordered hierarchical system of classification, i.e. more inclusive groups:

A. Kingdom

Phylum

Class

Order

Family

Genus

Species = genus + specific epithet

B. The higher the category, the more inclusive it is

C. Members of a kingdom share general characters; members of a species share quite specific characters

D. Characters are any structural, chromosomal, or molecular feature that distinguishes groups

E. Additional levels of classification can be added by adding super-, sub-, or infra- (e.g., suborder, subspecies).

III. Development of classification

A. Until relatively recently organisms were classified as either plants or animals and two kingdoms were recognized:

1. Non-motile autotrophs were placed in the plant kingdom

2. Motile heterotrophs were placed in the animal kingdom

B. However, as more organisms were discovered and studied it became apparent that many organisms did not fit into this system:

1. Euglena is a unicellular, motile autotroph

2. Fungi (mushrooms and molds), traditionally classified as plants, are non-motile heterotrophs

C. Development of better microscopes led to the discovery that there are two fundamental types of organisms, defined by their cell types:

1. Prokaryotes (bacteria) - they lack: nuclei, organelles, 9+2 flagella, chromosomes, multicellularity and sexuality

2. Eukaryotes (nearly all other organisms) - they have: nuclei, organelles, 9+2 flagella, DNA associated with histone proteins to form chromatin/chromosomes, sexual reproduction and most are multicellular

D. Whitaker proposed a five kingdom system, all Prokaryotes were placed into a single kingdom and the Eukaryotes were placed into four kingdoms

IV. Five kingdoms

A. Kingdom Monera - all Prokaryotes, they lack: nuclei, organelles, 9+2 flagella, chromosomes, multicellularity and sexuality.

1. Includes all bacteria and "blue green algae" (now called cyanobacteria)

B. Kingdom Animalia (Animals) - Eukaryotes, motile, multicellular, lack plastids and cell walls, heterotrophic via ingestion, sexual reproduction

C. Kingdom Plantae (Plants) - Eukaryotes, nonmotile, multicellular, plastids and autotrophic via photosynthesis, cell walls made of cellulose, adapted for life on land, mostly sexual reproduction

1. "Algae" are not included in this kingdom

D. Kingdom Fungi (Mushrooms and Molds) - Eukaryotes, nonmotile, filamentous, lack plastids, cell walls are made of chitin, heterotrophic via absorption of nutrients from dead (saprophytic) or living (parasitic) matter. Virtually all are multicellular except yeast. Both sexual and asexual reproduction

E. Kingdom Protista - Eukaryotes. Heterogeneous assemblage of unicellular, colonial and multicellular Eukaryotes that do not have the distinctive characters of plants, animals or fungi

1. They have various types of reproduction from simple cell division through sexual, and various types of nutrition

2. Includes all groups previously called protozoa as well as all the algae except blue greens. Also includes some organisms previously called fungi

V. Three domains

A. Recent genetic and molecular investigations have demonstrated that there are two major groups of prokaryotes. They differ radically in the composition of their cell walls, membrane lipids, ribosomal RNA, and a variety of other biochemical features

B. Therefore, our text recognizes three domains above the rank of kingdom, and a total of six kingdoms

1. Domain Eubacteria - prokaryotes with muramic acid in cell walls. Majority of bacteria plus cyanobacteria ("blue green algae") - one kingdom Eubacteria 

2. Domain Archaebacteria (ancient bacteria) - prokaryotes that lack muramic acid in cell walls. Many inhabit "harsh" environments. Includes methane producers, extreme halophiles, extreme thermophiles, acidophiles and one group which lacks cell walls - one kingdom Archaebacteria 

3. Domain Eukaryotes - all eukaryotes - four kingdoms as defined above:

a. Kingdom Animalia (Animals) - Eukaryotes, motile, multicellular, lack plastids and cell walls, heterotrophic via ingestion, sexual reproduction

b. Kingdom Plantae (Plants) - Eukaryotes, nonmotile, multicellular, plastids and autotrophic via photosynthesis, cell walls made of cellulose, adapted for life on land, mostly sexual reproduction

c. Kingdom Fungi (Mushrooms and Molds) - Eukaryotes, nonmotile, filamentous, lack plastids, cell walls are made of chitin, heterotrophic via absorption of nutrients from dead (saprophytic) or living (parasitic) matter. Virtually all are multicellular except yeast. Both sexual and asexual reproduction

c. Kingdom Protista - Eukaryotes. Heterogeneous assemblage of unicellular, colonial and multicellular Eukaryotes that do not have the distinctive characters of plants, animals or fungi

VI. Classifying organisms

A. There are two ways to classify organisms:

1. Phenetic - based on overall similarity of form and structure. Must be based on homologous, not analogous features

2. Phylogenetic - based on common evolutionary descent

 a. Phylogeny = the evolutionary history of a group of organisms

b. Now the preferred method because it has predictive value