2.1 Evolution

• The term phylogenetic means evolutionary relatedness.
• A phylogenetic method of

  classification (grouping organisms) reflects an organism’s evolutionary history; closely

  related organisms are grouped together. Organisms in the same group have a more recent

  common ancestor. If they are closely related they may show physical similarities.
• Phylogenetic tree - branch points represent common ancestors

  of the organisms in the branches above. Living organisms are shown at the tips of

  branches. Ancestral species (now extinct) would be shown in the trunk.
• Taxa are levels of classification. Large taxa contain smaller taxonomic groups.
• Organisms become more closely related as you move down the taxonomic groups. The largest taxonomic groups are called Domains. The smallest taxonomic group is called Species.
• Order of classification

   Domain

   Kingdom

   Phylum

   Class

   Order

   Family

   Genus

   Species
• A phylogenetic classification system is useful to:

   To infer evolutionary relationships.

   If a new animal is discovered we can predict some of its other characteristics

   When we communicate, it is quicker to say ‘bird’ than to say the ‘vertebrate, egg laying biped with a beak and feathers’.

   When describing the health of an ecosystem or the rate of extinction in the geological record, conservationists often find it more useful to count families than species.
• A Domain is the largest taxon and all living thing belong to one of three Domains. Modern methods of

  analysis consider similarities in the DNA base sequence.
• The 3 domains are

  • eubacteria
  • archaea
  • eukaryota
• Eubacteria

  • These are familiar bacteria such as E. coli and Salmonella.
  • They are prokaryotes.
• Archaea

  • These are bacteria, and often have unusual metabolism
  • They live in marginal habitats (are extremophiles) and are also prokaryotes.
• Eukaryota

  • This domain includes Plantae, Animalia, Fungi and Protoctista. They are all eukaryotic organisms.
• Domains contain Kingdoms. There are 5 main kingdoms largely based on morphological

  similarities between organisms not on DNA analysis.
• The 5 kingdoms are:

  • Prokaryota
  • Protoctista
  • Fungi
  • Planta
  • Animalia
• Prokaryota

  • Includes all bacteria and cyanobacteria.
  • Microscopic, single celled, organisms with no membrane bound organelles
  • The cell wall is made out of peptidoglycan or murein
• Protoctista

  • Eukaryotic organisms.
  • Single celled.
  • No tissue differentiation.
• Fungi

  • Heterotrophic eukaryotes with cell wall made up of chitin.
  • They reproduce by spores.
• Planta

  • Multicellular eukaryotes.
  • Photosynthetic.
  • Cellulose cell walls.
• Animalia

  • Multi cellular eukaryotes.
  • Heterotrophic.
  • No cell wall.
  • Nervous coordination.
• Heterotrophic: consumers who depend on other sources for their food (eat food)
• Autotrophs:  producers who prepare their own food. (e.g plants)
• Saprophytes: a plant, fungus, or microorganism that lives on dead or decaying organic matter.
• Homologous structures – Have a

  similar arrangement of component

  parts and a similar developmental

  origin but different functions.
• Analogous structures – Have a

  corresponding function, but

  different developmental origins.
• Sterile hybrids - Closely related organisms may be able to interbreed, but will not

  produce fertile offspring. A common example is the mule; the mule is a sterile hybrid of a

  male horse and a female donkey.
• Species: a group of organisms that are able to reproduce successfully, that is that their offspring are fertile (fertilized eggs have paired chromosomes)
• The Genus and species form the scientific name, or binomial, of an organism. The name is in latin and must be underlined or in bold
• Extremophiles are able to exist in a wide variety of environmental conditions e.g high/low temperatures, pH and pressure.
• The 3 main animal phyla are:

  • annelids (e.g worms)
  • arthropods (e.g insects)
  • chordates (vertabrates)
• Annelids:

  • segmented worms with a closed circulatory system
  • hydrostatic skeleton
  • permeable skin for gas exchange
  • e.g earthworm, lugworm
• Arthropods

  • jointed legs
  • protective waterproof exoskeleton
  • fluid filled body cavity
  • e.g arachnids, crustaceans
• Insects are a form of arthropod and are characterized by:

  • 2 pairs of wings
  • 6 legs in adult stage
  • 3 main body parts
  • open circulation and tracheal system for gas exchange
  • some insect groups have lost these features e.g no wings on fleas
• Chordates

  • known as vertebrates possessing a vertebral column or backbone (stiffened notochord)
• The main groups of chordates are:

  • fish (single circulation and gills)
  • amphibians
  • reptiles
  • birds
  • mammals (lungs and double circulation)
• Evidence for classification

  • vestigial structures
  • homologous structures
  • analogous structures
  • molecular studies
• Vestigial structures

  • e.g appendix and coccyx in humans
  • indicate common ancestry/ underlying relationship
  • the structures are no longer useful to the organism but was at some time in its evolution
• Adaptive radiation

  • when homologous structures have adapted to carry out different functions but indicate an underlying relationship
• Molecular studies

  • show that the structure of proteins, e.g haemoglobin, reflect patterns of evolution
• Convergent evolution occurs when species independently evolve similar traits. This can create analogous structures
• During the course of evolution, species undergo changes in

  their DNA base sequences, which accumulate until the

  organisms are so different that they are considered to be a

  different species. More closely related species show more

  similarity in their DNA base sequence than those more

  distantly related. DNA analysis has confirmed evolutionary

  relationships, and corrected mistakes made in classification

  based on physical characteristics.