8.1 - Classification and Naming of Organisms

Taxonomy

Taxonomy: a field in biology involving the classification, identification and naming of organisms in an organised manner.
Taxonomy manages information and data systematically and methodically for the scientific community.
A scientific classification and naming system based on defining features facilitates studies and discussions among scientists internationally.

Classification: organisms are categorised by physical features in a taxonomic hierarchy system.
Identification: organisms are identified using dichotomous keys.
Naming: organisms are named using a binomial nomenclature system.

Organisms are classified by type of cell, number of cells and type of nutrition.
The six kingdoms are Archaebacteria, Eubacteria, Protista, Fungi, Plantae and Animalia.
Prokaryote: cell without a membrane-bound nucleus and membrane-enclosed organelles.
Eukaryote: cell with a nucleus and membrane-enclosed organelles.
Unicellular: single-celled.
Multicellular: more than one cell.
Heterotroph: cannot synthesise its own food; obtains food molecules by eating other organisms.
Autotroph: synthesises its own food from inorganic raw materials using light energy or chemical energy.

Prokaryotic and unicellular; primitive bacteria.
Cell wall does not contain peptidoglycan.
Lives in very hot, acidic, salty or anaerobic environments.
Methanogen: obligate anaerobe in swamps and the digestive tracts of ruminants and humans; produces methane as a metabolic by-product.
Halophile: lives in extremely high salt concentrations, such as the Dead Sea.
Thermophile: withstands high temperatures; flourishes at an optimum temperature of $60^{\circ} C$ to $80^{\circ} C$ in hot springs and highly acidic locations.
Examples: Sulfolobus sp. and Halobacterium salinarum.

Prokaryotic and unicellular; usually forms colonies; known as “true” bacteria.
Cell wall contains peptidoglycan or murein, a polymer of sugars and amino acids.
Cytoplasm contains ribosomes and plasmids but no membrane-enclosed organelles.
Classified according to shape.
Examples: Streptococcus pneumoniae and Vibrio cholerae.

Eukaryotic; unicellular or multicellular.
Heterotroph, autotroph or both.
Simple cell organisation without specialised tissues.
Cells contain a membrane-bound nucleus and other membrane-bound organelles.
Three groups:
- Protozoa: Euglena sp., Amoeba sp. and Paramecium sp.
- Algae: Chlamydomonas sp. and Spirogyra sp.
- Slime mould: Physarum polycephalum.

Eukaryotic and multicellular.
Photoautotrophic; has chlorophyll and synthesises food by photosynthesis.
Reproduces sexually or asexually.
Includes seedless plants such as ferns and plants with seeds such as flowering plants.

Eukaryotic and multicellular.
Heterotrophic.
Most animals can move and reproduce sexually.
Includes invertebrates such as Asterias sp. and vertebrates such as Elephas maximus.

The Linnaeus hierarchy system classifies organisms from species to domain.
Order from the highest to the lowest rank: domain → kingdom → phylum → class → order → family → genus → species.
Domain is the highest taxonomic rank; species is the smallest group.
Each rank is divided into the next smaller rank: kingdom into phyla, phylum into classes, class into orders, order into families, family into genera and genus into species.
Organisms in the same phylum share characteristics and differ from organisms in other phyla.
Organisms of the same species can interbreed to produce viable, fertile offspring.
From domain towards species:
- the number of organisms in each group decreases;
- genetic links among organisms become closer.

A scientific name has two words: genus name + species name.
The genus name begins with a capital letter; the species name begins with a lowercase letter.
Printed scientific names are italicised, for example Oryza sativa.
When handwritten, the genus and species names are underlined separately.

A dichotomous key is used by taxonomists to identify organisms based on similarities and differences.
It consists of a series of couplets; each couplet contains two statements about traits or groupings.

Each key is specific to one identification process; different organisms require a different key.
Use obvious, observable features.
Avoid overlapping traits.
A key may be presented as numbered couplets or a spider dichotomous key.