Taxonomy
the branch of biology concerned with identifying and naming organisms
History
1. Naming and identifying organisms began with the Greeks and Romans.
2. In middle ages, organisms were described using long Latin descriptions.
3. Much later, John Ray (1627 – 1705), a British naturalist argued that each organism should have a set name.
4. Carolus Linnaeus (1701-1778) developed binomial system.
The Binomial System
A binomial system of nomenclature names organisms using a two-part Latin name.
The first word is the genus; closely related species are assigned to the same genus.
Second part is the specific epithet; it usually provides something descriptive about an organism.
A scientific name consists of both genus and specific epithet (e.g., Lilium buibiferum and Liliumcanadense).
The genus can be abbreviated when used with a specific epithet if the full name was given before. (E. coli)
Common Names :
Easier
Descriptive
Commonly known
Localized
Repeated for different organisms
1 organism may have several common name.
Scientific Names:
Difficult
Descriptive
Based on Latin
Same all over the world
1 organism – 1 name
1 name – 1 organism
Used by scientists
Not commonly known
The job of naming is unfinished.
We have currently named one million species of animals and a half million plant species. (Estimated: between 3 and 20 million species on Earth.)
Some groups, such as birds, are nearly all known; some insect groups are mostly unknown.
What Is a Species?
Linnaeus considered each species to have a unique structure that made it distinct.
The biological definition of a species states a species can interbreed and share the same gene pool.
When a species has a wide geographic range, variant types may tend to interbreed where they overlap; these populations may be named as subspecies.
a. The rat snakes Elaphe obsoleta obsoleta and Elaphe obsolete bairdi are subspecies of Elaphe obsoleta.
b. Including the subspecies makes this a trinomial, or three-part, name.
Species
Generally, a classification approach is taken to the definition of species.
a. Classification establishes categories to assign species on the basis of their relationship to other species.
b. Species is a taxonomic category below the rank of genus.
c. Species share a more recent common ancestor with species in same genus than with those in other taxa.
d. A taxon is a group of organisms in a classification category; Rosa or Felis are taxa at the genus level.
Classification Categories
Aristotle classified animals into 14 groups (e.g., mammals, birds, etc.), and subdivided them by size. Plants: grasses, shrubs, trees
Ray grouped animals and plants according to how he thought they were related.
Linnaeus grouped plants by flower parts; his categories were published in Systema Naturae.
Groups today
Today, we use a minimum of seven categories of classification: species, genus, family, order, class, phylum (or division for plants), and kingdom.
A higher category, the domain, has been proposed to be added to these seven categories.
The higher the category, the more inclusive it is.
Members of a kingdom share general characters; members of a species share specific characters.
Characters are any structural, chromosomal, or molecular feature that distinguishes groups.
Additional levels of classification can be added by adding super-, sub-, or infra- (e.g., suborder).
Categories
A higher category, the domain, has been proposed to be added to these seven categories.
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).
Classification Systems
1. Early biologists recognized two kingdoms: animals (kingdom Animalia) and plants (kingdom Plantae).
2. The microscope revealed unicellular organisms; in the 1880s, Ernst Haeckel proposed the kingdom Protista
In 1969, R. H. Whittaker suggested a five kingdom system based on cell type, organization, and nutrition: Monera, Protista, Fungi, Plants, Animals
Monera
Members of Monera are prokaryotic bacteria that obtain organic molecules by absorption or photosynthesis.
Protista (Protoctista)
Members of Protista are mainly unicellular eukaryotes that obtain organic molecules by absorption, ingestion, or photosynthesis.
Fungi
Members of the Fungi are multicellular, eukaryotic, heterotrophic saprotrophs that form spores, lack flagella and have cell walls containing chitin.
Plants
The Plantae are multicellular eukaryotes, autotrophic by photosynthesis.
Members of Animalia are multicellular eukaryotes, heterotrophic by ingestion, are generally motile.
Six Kingdoms
Some biologist now recognize 6 Kingdoms, in which the Kingdom Monera is broken into two separate kingdoms: Kingdom Archeabacteria and Kingdom Eubacteria.
B. Three-Domain System
Recent research suggests one group of prokaryotes is so distantly related it should be in separate domain.
Sequencing of rRNA suggests all organisms evolved along three distinct lineages: domains Bacteria, Archaea, and Eukarya.
Bacteria diverged first; archaea and eukarya are more closely related than either is to bacteria.
The archaea live in extreme environments: methanogens in anaerobic swamps, halophiles in salt lakes, and thermoacidophiles in hot acidic environments.
The archaea cell wall is diverse but not the same as the bacterial cell wall.
