speciation and classification

• fossils


  preserved remains of once-living organisms
• how do fossils form?

  gradual replacement by minerals, casts and impressions and preservation in places where no decay happens
• fossil formation from mineral replacement

  teeth, shells and bones of animals are resistant to decay and when buried, they are often replaced by minerals as they decompose, or the sediment around them hardens, creating a fossil
• fossil formation from casts and impressions

  organisms can fossilise when buried in soft material like clay, which later hardens around it when the organism decays, leaving a cast of itself. an animals burrow or plant's roots can be preserved as casts and things like footprints can also be pressed into soft materials, leaving an impression when it hardens - these are mould fossil
• fossil formation from preservation with no decay

  in amber and tar pits there's no oxygen or moisture so decay microbes can't survive, in glaciers its too cold for decay microbes to work and peat bogs are too acidic for decay microbes
• what do fossils show?

  provides evidence about the history of life and past environments on Earth and hows how different groups of organisms have evolved over time
• fossil record


  a collection of all discovered fossils that provides information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, the order in which they lived and how they evolved
• why is the fossil record incomplete?

  - fossils that formed millions of years ago may have been destroyed by geological activity

  - conditions needed for organisms to become fossils are not always present

  - many early organisms were soft bodied, and soft tissue tends to decay away completely. so no traces were left behind

  - we haven't found all the fossils yet
• speciation


  the formation of new and distinct species in the course of evolution
• how does speciation occur?

  when populations of the same species become so different that they can no longer successfully interbreed to produce fertile offspring
• what leads to speciation?

  when populations of a species that share the same habitat become reproductively isolated from each other due to a barrier and the conditions of either side of the barrier will be slightly different - because of this, different characteristics will become more common in each population due to natural selection operating differently on the populations and new species, which cannot breed together to produce fertile offspring, would have formed
• reproductive isolation


  condition in which a reproductive barrier separates and keeps two species from interbreeding so that they evolve into two separate species
• how does isolation occur?

  something prevents the two populations from reproducing, such as physical barrier (e.g. floods and earthquakes can cause barriers that geographically isolate some individuals from the main population)
• Alfred Russel Wallace


  - British naturalist who worked on the idea of speciation

  - independently developed a hypothesis of natural selection similar to Darwin's

  - observed that waning colours are used by some species (e.g. butterflies) to deter predators from eating them, which is an example of a beneficial characteristic
• antibiotic resistance


  the evolution of populations of pathogenic bacteria that antibiotics are unable to kill
• How does antibiotic resistance occur?

  - overproduction: bacteria reproduce by binary fission, they can produce two new daughter cells every 20 minutes

  - variation: although bacteria divide by binary fission and produce clones, variation can be introduced through mutations (a random change in DNA)

  - advantage: mutations in DNA may give the bacteria a survival advantage, such as having resistance to antibiotics. If they are exposed to certain antibiotics they will

  survive...

  - reproduction: ... and reproduce (by binary fission)...

  - inheritance: ...and the daughter cells will inherit antibiotic resistance. The population of resistant strains rises.

  - evolution: the resistant strain will then spread because people are not immune to it and there is no effective treatment.

  - speciation: evolution may result in the formation of a new species (e.g. MRSA)
• Why is antibiotic resistance a problem?

  - genetic mutations make some bacteria naturally resistant to an antibiotic

  - if the bacteria can survive, its more likely to reproduce and cause more infection

  - can lead to the antibiotic resistant allele to be passed onto offspring (natural selection)
• why is antibiotic resistance increasing?

  - bacteria have evolved and reproduce rapidly

  - doctors overprescribe antibiotics

  - patients don't finish their course of antibiotics

  - widespread use in animal feeds
• antibiotic resistance prevention


  - antibiotics only used if needed: serious bacterial infections

  - patients take the full course of antibiotics: all bacteria die; can't mutate

  - develop stronger antibiotics (though resistance can develop against these too)
• classification


  the action or process of classifying organisms into groups according to shared qualities or characteristics
• Carl Linnaeus


  "Father of Taxonomy"; established his classification of living things; famous for animal naming system of binomial nomenclature
• Carl Woese


  devised a system of classification based on the cellular organization of organisms - by using evidence gathered from new chemical analysis techniques (e.g. RNA sequence analysis), he found that in some cases, species thought to be closely related in traditional classification systems are in fact not closely related as first thought
• how did new methods of classification come about?

  with knowledge of the biochemical processes taking place inside organisms improving due to the the development of microscopes, allowing scientists to find out more about reg internal structures of organisms
• classification system


  - domain

  - kingdom

  - phylum

  - class

  - order

  - family

  - genus

  - species
• domain


  a taxonomic category above the kingdom level: the three domains are Archaea, Bacteria, and Eukarya.
• Archaea


  domain of unicellular prokaryotes that have cell walls that do not contain peptidoglycan - often found in extreme environments (e.g. hot springs and salt lakes)
• Bacteria


  domain of unicellular prokaryotes that have cell walls containing peptidoglycan - contains true bacteria (e.g. E. coli and Staphylococcus)
• Eukarya


  domain of all organisms whose cells have nuclei, including protists, plants, fungi, and animals
• kingdom


  a taxonomic category below the domain level: the five kingdoms are Animalia (animals), Plantae (plants), Fungi, Protista, and Monera (prokaryotes)
• phylum


  group of closely related classes
• class


  a group of closely related orders
• order


  a a group of closely related families
• family


  a group of closely related genera
• genus


  a group of closely related species
• species


  a group of similar organisms that can breed and produce fertile offspring
• what are organisms named according to?

  binomial system
• binomial system


  an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species that the organism belongs to respectively
• why is the binomial system used?

  to provide succinct, relatively stable and verifiable names that could be used and understood internationally and avoid potential confusion arising from the usage of common names for organisms that may be different depending on area/language
• evolutionary trees


  models used to explain the evolutionary links between groups of organisms, showing common ancestors and relationships between species - the more recent the ancestor, the more closely related, hence the more characteristics they're likely to share
• what is analysed to work out evolutionary relationships?

  current classification data (e.g. DNA analysis and structural similarities) for living organisms and the fossil record for extinct species