Principles of Classification

• Biodiversity is a measure of the variety of living organisms and their genetic differences
• Taxonomy is the science of describing, classifying and naming living organisms
• The aim of a classification system is to group organisms to accurately identify them and represent their ancestral relationships
• Previously, during the time of Aristotle, people put organisms in groups based on their physical appearances or morphology. People often used analogous features to classify organism, but some organisms could be placed in inaccurate groups.
• A valid classification system must be based on careful observation and the use of homologous structures - structures that show common ancestry.
• In the 18th century, the Swedish botanist, Carolus Linnaeus developed the first scientifically devised classification system
• The largest taxonomy groups are the domains: Archaea, Bacteria and Eukaryota
• The main taxonomic groups are: domain, kingdom, phylum (division for plants), class, order, family, genus and species
• The Archaea domain contains one kingdom - archaebacteria
• The Bacteria domain contains one kingdom - eubacteria
• The Eukaryota domain contains 4 kingdoms - protista, fungi, plantae and animalia
• Protista are microscopic single celled organisms, some are heterotrophs (they need to eat other organisms), and some are autotrophs (they make their own food by photosynthesis). They mainly reproduce asexually.
• Fungi are all heterotrophs, most are saprophytic (organisms that feed on the dead and decaying organisms), and some are parasitic (an organism that lives on a host, taking what it needs to stay alive while often injuring the host). They have chitin in their cell walls. They can be unicellular (yeast) and multicellular (moulds). They reproduce both sexually and asexually
• Most plantae are multicellular autotrophs (making their own food by photosynthesis). They use light captured by the green pigment chlorophyll
• Animalia are all heterotrophs that move their whole bodies around during at least one stage of their life. They include invertebrates and vertebrates. They can reproduce asexually and sexually
• The binomial system was devised by Linnaeus
• In the binomial system, organisms are given two Latin names. The first name is the genus and the second is the species or specific name which identified the organism precisely.
• There are certain rules to obey when writing binomial names:

  • use italics
  • the genus name has an upper case letter and the species has a lower case letter
• A genus is a group of species that all share common characteristics