Science - Taxonomy (Grade 8)

• Every year, thousands of new species are discovered and subsequently named and classified. Currently, there are around two million species of living organisms that have been named and classified.
• Taxonomy


  The field of biology that deals with the process of identifying, naming, and classifying organisms
• Taxis


  Means "arrangement"
• Nomos


  Means "laws"
• Systematics


  The study of biological diversity and its evolution
• Around 300 BC, Greek philosopher Aristotle, the father of biology, classified organisms into those with red blood cells and those without. He likewise classified organisms as either plants or animals.
• Aristotle subdivided plants by physical characteristics such as size and features. This crude system was used for over 2000 years.
• Typological Species Concept


  Modern taxonomy began with the work of Swedish botanist Carolus Linnaeus. In 1735, Linnaeus published his influential book Systema Naturae, in which he outlined his scheme classifying all known and unknown organisms based on their similarities.
• Linnaean system of classification

  • Hierarchical categories based on each organism's morphological (physical form) and behavioral characteristics
  • Widely accepted during the nineteenth century
• Kingdom


  The highest level in the Linnaean system
• Phyla


  Further division of organisms within each kingdom (for animals) or division (for plants)
• Classes


  Further division of each phylum or division
• Orders


  Further division of each class
• Families


  Further division of each order, grouping organisms with close resemblance
• Genera


  Further division of each family
• Species


  The most specific unit of classification and the basic unit of identification. Organisms within this category are capable to interbreed with one another to produce offspring.
• Biological Species Concept


  A definition of the term 'species' as a group of organisms that can interbreed and produce offspring in the natural environment
• The biological species concept has limitations and does not account for extinct species.</b>
• Phylogenetic Species Concept


  Classifying organisms by showing their relationships based on physical similarities and differences as well as ancestry and descent
• Phylogeny


  The evolutionary history of a certain species
• Phylogenetic systematics


  The field of taxonomy that deals with identifying the evolutionary relationships among the many different kinds of life on Earth, both living (extant) and dead (extinct)
• Molecular phylogenetics


  A branch of biology that studies the relationships of organisms based on their DNA and protein sequences using a computer algorithm
• Phylogenetic tree


  An illustration or diagram used to visually present the evolutionary relationships among groups of organisms
• Binomial nomenclature


  The present system of naming organisms, with the first name being the genus and the second name being the species or specific epithet
• Scientific names are always either italicized (if written in a printed material) or underlined (if written by hand). Note that sometimes genus in a scientific name is abbreviated to its capital first letter followed by a period, such as in the case of E. coli.
• Prokaryotes


  Organisms that lack a true nucleus in their cells
• Prokaryotic organisms


  • Have an irregularly shaped region called a nucleoid that contains the DNA and they lack membrane-bound organelles
• Eukaryotes


  Organisms that have a true nucleus with DNA arranged into chromosomes, and their organelles are surrounded by membrane
• In 1977, American microbiologist Carl Woese, in collaboration with Ralph S. Wolfe from the University of Illinois, proposed a third domain of life that led to the development of a new six kingdom.
• Three domains of life

  • Eukarya (animals, fungi, plants, and protists)
  • Archaea (bacteria-like organisms living in extreme environments)
  • Bacteria (true bacteria)
• Kingdom Eubacteria


  The most diverse and widespread among the prokaryotes. Typically microscopic, single-celled organisms that reproduce asexually through binary fission.
• Ruminants


  • Mammals that have unique digestive systems, such as cows, horses, and goats, and rely on bacteria in their digestive tracks to break down the cellulose in the plants that they eat
• Bacterial pathogens


  Bacteria that can cause diseases due to the toxins they secrete, which attack white blood cells
• Modes of nutrition for bacteria

  • Photoautotrophs (cyanobacteria that harness sunlight, use carbon dioxide, and release oxygen)
  • Chemoautotrophs (able to use chemicals in their environment to survive)
• Bioremediation


  The use of microorganisms to remove pollutants from water, soil, and air
• Archaea


  Believed to be the oldest forms of life on Earth, known as extremophiles that mostly live in the absence of oxygen
• Types of Archaea


  • Extreme halophiles (salt-loving)
  • Methanogens (anaerobic archaeans that release methane)
  • Extreme thermophiles (heat-loving)
• Protists


  Mostly unicellular organisms, but a few are colonial and multicellular. They have a wide array of locomotory organs and can be categorized as plant-like, animal-like, or fungus-like.
• Protists


  • Some perform photosynthesis (autotrophs), while others absorb and ingest food (heterotrophs). Some reproduce asexually, while others reproduce through sexual reproduction.
• Kingdom Plantae


  Multicellular eukaryotic organisms that are all autotrophic, capable of manufacturing their own food through photosynthesis.