Classification - Unit 2 OCR

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  • Created by: Amy
  • Created on: 31-05-13 18:17
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  • Classification
    • Basics
      • What is it? - Act of arranging organisms into groups based on their similarities and differences, easier for scientists to identify and study : Taxonomy is study of classification, few different systems in use but all involve placing organisms in groups in taxonomic hierarchy
        • In hierarchy  there are 8 levels of groups (taxonomic groups), similar organisms first sorted in one of 3 large groups called domains (animals, plants, fungi are in Eukarya domain), then sorted into slightly smaller groups called kingdoms (all animals are in Animalia), similar in that kingdom are grouped into phylum then class order family genus and species
          • As you move down hierarchy, there are more groups but less organisms in each
      • Naming Species
        • Nomenclature used is called the binomial system, all organisms are given one internationally accepted specific name in Latin that has two parts
          • First part is the genus name with capital letter, second part is the species name with lower case letter - names are always in italics or underlined
            • E.g. Humans are Homo sapiens - genus is Homo, species is sapiens
            • E.g. Dogs are Canis familiaris - genus is Canis, species is familliaris
        • Binomial system helps avoid confusion of using common names - Americans call a type of bird a cockatoo whereas Australians call them flaming galahs, its the same bird with the scientific name Eolophus roseicapillus
      • The Five Kingdoms
        • Prokaryotae (Monera) - features : prokaryotic, unicellular, no nucleus, less than 5 micrometers (e.g. bacteria)
        • Protoctista - eukaryotic, usually live in water, single celled of simple multicellular organisms (e.g. algae, protozoa)
        • Fungi - eukaryotic, chitin cell wall, saprotrophic, use spores to reproduce (e.g. moulds, yeast, mushrooms)
        • Plantae - eukaryotic, multicellular, cellulose cell wall, can photosynthesise, contain chlorophyll, autotrophic (e.g. mosses, ferns, flowering plants)
        • Animalia - eukaryotic, multicellular, no cell wall, heterotrophic (e.g. nematodes, molluscs, insects, fish, reptiles, birds, mammals)
      • Phylogeny - study of the evolutionary history of groups of organisms, tells us who's related and how closely, all organisms have evolved from shared common ancestors and closely related species diverged away from each other most recently
    • Evolution of Systems
      • Evidence - early systems used observable features to place organisms in groups, these can be anatomical or behavioural, however scientists don't always agree on relative importance of different features and groups based on physical feature may not show how related organisms are
        • Classifications are now based on observable features along with other evidence, evidence says how similar and related they are
          • 1. Molecular Evidence - analysing similarities in proteins and DNA, more closely related will have more similar molecules, can compare how DNA is sorted or the sequence of DNA bases or amino acid sequence
          • 2. Embryological Evidence - looking at similarities in the early stages of organism development
          • 3. The Fossil Record - study fossils provides evidence of how organisms evolved from one another so how closely related : part of phylogeny
      • Changing the Classification of Organisms
        • New technology can result in new discoveries, scientists can share their new discoveries in meetings and scientific journals, how organisms are classified is continually revised to take into account any new findings
      • Five Kingdoms vs Three Domains
        • Three domain system is relatively new, suggested because of new evidence
        • Older system contained larger groups of five kingdoms, all organisms were placed in one of groups, in 1900 three domains were proposed
        • New system has three domains, large superkingdoms, are above kingdoms in taxonomic hierarchy
        • In three domains, organisms with cells and nucleus placed in Eukarya (includes four of five kingdoms) whereas Prokaryotae are separated in two domains of Archaea and Bacteria
        • Lower hierarchy stays the same with Kingdom Phylum Class Order Family Genus Species : three domains proposed due to mainly molecular evidence
    • Dichotomous Keys
      • What Are They?
        • Used to identify organisms and provides a way to identify them based on observable features
          • Consist of series of questions each with only two possible answers, each answer leads to the name of an organism or another question and so on until the organism is identified
      • Using a Key
        • Gives pictures of organisms with a table of questions
          • Observe the picture and answer questions yes or no in relation to the organism


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