Classification and evolution

• Classification:

  = the process by which organisms are sorted into groups by shared features
• Taxonomic group= group in a hierarchy
• Carl Linnaeus was the first to propose a hierarchical classification system.
• 8 groups of the hierarchy system:

  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Scientists classify organisms to:

  • identify species
  • predict characteristics
  • find evolutionary links
• the three domains are Archaea, Bacteria and Eukarya
• Species= group of organisms that can produce a fertile offspring
• The five kingdoms are:

  • Prokaryotae
  • Protoctista
  • Fungi
  • Plantae
  • Animalia
• Prokaryotae:

  • unicellular
  • no nucleus or other membrane-bound organelles
  • has a ring of DNA and small ribosomes
  • nutrients are absorbed through cell wall or by photosynthesis
• Protoctista:

  • mainly unicellular
  • has a nucleus and other membrane-bound organelles
  • some have chloroplasts
  • nutrients are acquired by photosynthesis and ingestion of other organisms
• Fungi:

  • unicellular or multicellular
  • nucleus and other organelles but no chloroplasts
  • nutrients are acquired by absorption
  • store food as glycogen
• Plantae:

  • multicellular
  • nucleus and other organelles including cell wall
  • nutrients are acquired by photosynthesis
  • store food as starch
• Animalia:

  • multicellular
  • nucelus and other organelles but no chloroplasts or cell walls
  • nutrients are acquired by ingestion
  • food stored as glycogen
• Woese’s Three Domain System:

  • Eukarya: have 80s ribosomes, RNA polymerase contains 12 proteins
  • Archaea: have 70s ribosomes, RNA polymerase contains 8-10 proteins
  • Bacteria: have 70s ribosomes, RNA polymerase contains 5 proteins
• Woese splits the Prokaryotae kingdom into Archaebacteria and Eubacteria (creating 6 kingdoms instead of 5)
• Eubacteria are classified as their own kingdom because they have a different genetic make-up to Archaebacteria.
• Types of variation:

  • Interspecific variation = variation between members of different species
  • Intraspecific variation = variation between organisms within a species
• Genetic causes of variation:

  • alleles
  • mutations
  • meiosis
• Advantages of Phylogenetic Classification:

  • produces a continuous tree (doesn’t force scientists to put organisms into a group they don’t really fit)
  • hierarcha, nature of Linnaean classification can be misleading
• Evidence for evolution:

  • palaeontology- study of fossils
  • comparative anatomy- study of similarities and differences between organisms' anatomy
  • comparative biochemistry- similarities and differences between the chemical makeup of organisms
• The fossil record is not complete. For example, many organisms are soft-bodied and decompose quickly before they have a chance to fossilise. The conditions needed for fossils to form often are not present. Many other fossils have been destroyed by the Earth's movements ,such as volcanoes, or still lie undiscovered.
• Homologous structure= structure that appears superficially different in different organisms but has the same underlying structure
• The presence of homologous structures provides evidence for divergent evolution. This describes how, from a common ancestor, different species have evolved.
• Interspecific variation= variation between members of different species
• Intraspecific variation= differences between organisms within a species
• Genetic causes of variation:

  • alleles
  • mutations
  • meiosis
  • sexual reproduction
  • chance
• Discontinuous variation= characteristic that can only result in certain values (no in-between values). Variation determined purely by genetic factors falls into this category.
• Continuous variation= characteristic that can take any value (controlled by a number of genes and are also often influenced by the environment).
• Adaptions:

  • anatomical
  • behavioural
  • physiological
• Anatomical adaptions= physical features
• Behavioural adaptions= the way an organism acts, these can be inherited or learnt from their parents.
• Physiological adaptions= processes that take place inside an organism.
• Adaptions= characteristics that increase an organism's chance of survival and reproduction in its environment.
• Anatomical adaptions:

  • body covering (scales, hair, feathers)
  • camouflage
  • teeth (shape and type of teeth are related to their diet)
  • mimicry (copying another animal's appearance/sounds to fool predators into thinking it is dangerous)
• Behavioural adaptions:

  • survival behaviours (playing dead)
  • courtship (to attract a mate)
  • seasonal behaviours (migration and hibernation)
• Behavioural adaptions are generally either innate (instinctive) or learnt.
• Physiological adaptations:

  • poison production
  • antibiotic production
  • water holding
• Analogous structures = adapted to perform the same function but have a different genetic origin (the tail fins of a whale and fish perform the same role but when you look at them in detail their structures are very different).
• Convergent evolution= when unrelated species begin to share similar traits
• Natural selection:

  1. organisms within a species show variation caused by their genes
  2. organisms whose characteristics are best adapted to a selection pressure have an increased chance of survival and reproduction
  3. successful organisms pass the allele encoding the advantageous characteristic onto their offspring
  4. over time the proportion of individuals with the advantageous characteristic increases
  5. this can lead to the evolution of a new species