Classification - Binomial System

CLASSIFICATIOn Binomial Nomenclature Domains of Life The binomial system of naming is a globally recognised classification scheme developed at a series of congresses • It was first proposed by Carl Linnaeus in 1735 All living organisms are classified into one of three domains: • Eukarya (all eukaryotic organisms) • Archaea (prokaryotic extremophiles) • Eubacteria (common pathogenic bacteria) According to the binomial system, every organism has a two-part scientific name: • Genus is written first and is capitalised (e.g. Homo) • Species follows in lower case (e.g. Homo sapiens) Originally, the two prokaryotic domains (Archaea and Eubacteria) were considered part of a single kingdom (Monera) • However, biochemical differences prompted a reclassification Eukarya Archaea Eubacteria Histones Present Present Absent Introns Present Present Absent Nucleus Present Absent Absent Ribosome 80S 70S 70S Hierarchy of Taxa Taxonomy is the science of classifying organisms based on shared characteristics (or taxa) • More taxa shared = more closely related organisms Taxa Animal Plant Kingdom Animalia Plantae Katy Phylum Chordata Angiosperm Perry Class Mammalia Eudicotidae Comes Order Primate Ranunculales Over Family Hominidae Ranunculacae For Genus Homo Ranunculus Grape Species sapiens acris Soda Common Human Buttercup Hint: Natural Classification Natural classification involves grouping organisms according to common ancestry rather than by common characteristics • This allows for species to be identified by their evolutionary pathways and enables the prediction of traits within a group A disadvantage of natural classification is that taxonomists may need to reclassify groups if new phylogenetic evidence emerges • Gorillas and chimps were included in a Homininae sub-family • The figwort family was reclassified based on cladistics data Dichotomous Keys A dichotomous key involves sequentially dividing organisms into two categories until every organism is individually identified Example of a Dichotomous Key: Diagrammatic Representation: 1. Organism is asymmetrical .................................... Porifera Organism is symmetrical ................................... Go to Q2 2. Has radial symmetry ............................................ Cnidaria Has bilateral symmetry ...................................... Go to Q3 3. Has no separate anus ................................. Platyhelmintha Has a separate anus ........................................... Go to Q4 4. Has visible body segmentation .......................... Go to Q5 Segmentation not clearly visible .......................... Mollusca 5. Has an exoskeleton ........................................ Arthropoda Has no exoskeleton ............................................ Annelida Invertebrate Phyla Asymmetrical Symmetrical Bilateral Radial Porifera Anus No anus Cnidaria Not visible Segmentation Platyhelmintha Mollusca None Annelida Exoskeleton Arthropoda