b6

• Classes of organisms as determined by Carl Linnaeus


  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Features living creatures are traditionally classified by

  • Structure and characteristics
• Binomial system of naming organisms


  Genus name followed by species name
• The three domains


  • Archaea
  • Eukarya
  • Bacteria
• Organisms in the domain Archaea

  Bacteria, usually living in extreme environments
• Kingdoms in the domain Eukarya

  • Plants
  • Animals
  • Fungi
  • Protists
• How evolutionary trees are created

  Examining the DNA of different species and analysing how similar the sequences are
• Outline the theory of evolution by natural selection


  1. Individuals of a species show a wide range of variation for a characteristic

  2. Those with the characteristic most suited to the environment will survive breed most successfully

  3. The desirable characteristic that has enabled the individuals to survive are passed onto their offspring
• Lamarck's theory of inheritance


  That changes during the lifetime of an organism can be inherited
• Speciation


  The formation of a new species, when two populations become so varied that they cannot interbreed to produce fertile offspring
• Species


  A group of organisms with similar characteristics which are able to interbreed to produce fertile offspring
• Outline the process of speciation through geographic isolation


  1. Two populations of the same species are separated geographically

  2. Geographic isolation prevents interbreeding and mixing of genes between the populations

  3. Due to different selection pressures, different mutations occur producing different phenotypes in each population

  4. Over time, the two populations may evolve so that they are not able to interbreed
• Genetic variation


  Important in speciation as it produces phenotypic variation, some of which are better suited to the environment and are selected for
• Evidence used to show evolution

  • Fossils
  • Antibiotic resistance in bacteria
• How are fossils formed

  1. Parts of organisms that have not decayed due to conditions needed for decay being absent

  2. Parts of organisms that have been replaced by minerals as they decayed eg. bones

  3. Traces of organisms are preserved, covered in sediment and becoming rock
• Why are there few traces of early life-forms left behind

  they are mostly soft bodied
• Variation


  Differences in the characteristics of individuals in a population
• Causes of variation within a species

  • Genetics
  • Environment
  • A mixture of both
• How fossils act as evidence for evolution


  Scientists can identify the ages of the fossils and use them to show how organisms change over time
• Genetic variation


  Variations in the genotypes of organisms of the same species due to the presence of different alleles, creating differences in phenotypes
• Evolutionary trees


  Branches indicate where speciation has occurred
• What creates genetic variation in a species

  • Spontaneous mutations
  • Sexual reproduction
• Extinction


  Where there are no individuals of a species still alive
• Factors that may lead to extinctions

  • New disease
  • Predation
  • Competition
  • Changes to the environment
  • Catastrophic events
• Mutation


  A random change to the base sequence in DNA which results in genetic variants, occurring continuously
• Types of gene mutation

  • Insertion
  • Deletion
  • Substitution
• What enables bacteria to evolve quickly


  The fast rate of their reproduction
• How a gene mutation may affect an organism's phenotype

  • Neutral mutation does not change amino acid sequence, no effect on phenotype
  • Mutation may cause minor change in phenotype e.g. eye colour
  • Mutation may completely change amino acid sequence, resulting in non-functional protein, severe changes to phenotype
• Outline the process of antibiotic resistance bacteria evolving

  1. Mutations occur in bacteria producing genetic variation

  2. Certain strains are resistant to antibiotics and are not killed when the antibiotic is applied

  3. Resistant strains survive and reproduce

  4. Over time, the population of the resistant strains increase
• A new phenotype caused by a mutation being suited to an environmental change


  There will be a rapid change in the species
• Why resistant strains of bacteria are dangerous

  People have no immunity to them and there is no effective treatment
• What can be done to reduce the rate of development of antibiotic resistant bacteria

  • Refrain from inappropriately prescribing antibiotics eg. for viral diseases
  • Patients should complete the prescribed course of antibiotics
  • Restrict agricultural uses of antibiotics
• Evolution


  A gradual change in the inherited traits within a population over time, occurring due to natural selection which may result in the formation of a new species
• Theory of natural selection

  1. Genetic variation exists due to spontaneous mutations

  2. Selection pressures (e.g. competition, disease) exist

  3. Random mutation gives an organism a selective advantage

  4. Organism is better adapted to the environment and survives

  5. Organism reproduces, passing on its beneficial alleles

  6. Frequency of advantageous alleles increase
• Speciation


  When the phenotypes of two populations become different to the extent that they can no longer interbreed to produce fertile offspring
• Selective breeding


  The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes
• Steps in selective breeding

  1. Identify a desired characteristic

  2. Select parent organisms with desired traits and breed them

  3. Select offspring with desired traits and breed them

  4. Repeat process until all offspring have desired traits
• Characteristics selected for in selective breeding

  • Disease resistance in crops
  • Higher milk or meat production in animals
  • Gentle nature in domestic dogs
  • Large flowers
• Sexual reproduction


  • Type of reproduction
  • Involves the production of gametes by meiosis
  • A gamete from each parent fuses to form a zygote
  • Genetic information from each gamete is mixed so the resulting zygote is unique
• Advantage of selective breeding

  Creates organisms with desirable features e.g. higher crop yields, greater milk supply, larger fruit, domesticated animals