Classification 11

• classification


  is the way in which living organisms are divided into groups
• taxonomy


  is the scientific practice of grouping organisms based on shared characteristics
• modern classification systems


  they do not just group organisms based on easily observable features but use many different sources of evidence (e.g. fossil records, cell ultrastructure, biochemistry, molecular biology, behaviour)

  also hierarchal- larger groups that are divided into progressively into smaller groups

  phylogenetic- it is based on the evolutionary history of organisms, i.e. their common ancestry
• hierarchal system


  • Domain
  • Kingdom
  • Phylum (pl. =phyla)
  • Class
  • Order
  • Family
  • Genus (pl. = genera)
  • Species

  each group is a called a taxon (pl. taxa)
• Domains are the largest group there are 3 domains and species contain the fewest organisms. Non-overlapping means each organism can only appear in one group at a particular taxonomic level.
• which are the six kingdoms all living organisms are currently classified into?

  Bacteria, Archaea, Protoctista, Fungi, Plants, Animals
• All mammals are classified in the same kingdom, phylum and class. At the next level- order- the mammals begin to diverge until only those organisms with the greatest similarities and the ability to interbreed and produce fertile offspring share the species level
• binomial naming system


  the biological name of each species is derived from its genus and species names

  • the first is the genus name and always has a capital letter
  • the second is the species name and always has a lowercase letter
  • if handwritten, the full name is underlined
• phylogenetic system


  this reflects the evolutionary relationship between organisms, it looks at similarities and differences in structure and function.
• phylogenetic tree


  the oldest species at the base of the tree and the most recent ones represented by the ends of the trees. Each branch represents where a divergence occured ( where a common ancestor evolves to become a new species). the closer the branches, the closer the evolutionary relationship, so the more recently they shared a common ancestor

  
• technologies that have been useful for clarifying evolutionary relationships

  • genome sequencing
  • comparing amino acid sequences
  • immunological comparisons
• define species


  two organisms belong to the same species if they have the potential to breed with each other and their offspring are fertile
• suggest a reason why the cells of a mule which have 63 chromosomes are unable to undergo meiosis and so cannot produce gametes

  during meiosis, chromosomes pair up with their homologous partner. with an odd number of chromosomes this pairing cannot occur so meiosis cannot be completed and so no gametes form
• Problems with classifying organisms as distinct species

  • Life probably evolved 3.5 billion years ago
  • Extinct species greatly outnumber the living ones
  • Most species didn't leave fossils
  • Even when fossils are found, they are often incomplete and not all features can be observed
  • If organisms are only known from fossils, unable to test if they can breed and produce fertile offspring
  • There is considerable variation within any one species
  • Groups isolated from one another e.g. oceans may be classified as different species, however they may be the same species if their ability to interbreed is tested
  • The ability to interbreed can't be tested on organisms that use asexual reproduction
• courtship behaviour


  it is genetically determined. All members of the same species are genetically programmed to show exactly the same courtship behaviour as they share the same genes. Therefore, it can be used to identify individuals as members of the same or different species. it can be a display of breeding colours, a dance or song. birds in woodland may rely heavily on song
• species recognition


  it allows one species to recognise other members of the same species. the chain of actions that occur is same for all members of a species.
• synchronising reproductive behaviour


  in many cases, the behaviour of one individual stimulates a response from the other. this ensures mating only takes place when there is maximum probability of sperm and egg meeting. only respond when fertile
• identify a male capable of breeding

  as both partners need to be sexually mature and receptive to breeding
• formation of a pair bond

  some species keep the male and female together, a strategy that increases the survival chance of the offspring
• becoming able to breed

  bringing a member of the opposite sex into a physiological state that allows breeding to occur e.g. stimulating production of gametes
• how will a courtship song be important in successful breeding?

  different species will produce different songs ensuring they only mate with their own species. song is especially important in nocturnal organisms and in areas like woodland where visual displays will be ineffective
• 4 ways of investigating genetic diversity

  • the frequency of measurable or observable characteristics
  • the base sequence of DNA
  • the base sequence of mRNA
  • the amino acid sequence of the proteins encoded by DNA or mRNA
• 1.the frequency of measurable or observable characteristics


  Before modern gene technology, genetic diversity could only be investigated through careful detailed observations of the anatomy and physiology of different individuals. However, observable characteristics are often coded by more than one gene. In addition the environment can also influence some characteristics so does not directly show differences in an organism's DNA
• Comparing the base sequence of DNA

  Members of the same species will have very similar DNA base sequences. Over time, as populations evolve, random mutations accumulate and cause genetic variation. Species that have closer evolutionary relationships and share a more recent common ancestor will have more similar DNA sequences in a particular gene.
• Comparing the base sequence of mRNA


  Sometimes it's more useful to compare organisms by looking at what part of their genomes are expressed.
• Comparing the amino acid sequence of the proteins encoded by DNA or mRNA

  as DNA base sequences codes for the sequence of amino acids in proteins, organisms that share a recent ancestor and are more closely related will have a similar amino acid sequence when looking at a particular protein
• immunological techniques


  antibodies that are specific to antigens from a particular species (e.g. humans) can be mixed with antigens from a different species (e.g. chimps) to see if they are also complementary. If the antigens of the 2 species are similar there will be large number of antigen-antibody complexes formed suggesting they are closely related and share a recent common ancestor
• Large samples are more representative of the population than small samples and minimise the influence of chance on the results. However the size of the sample is often determined by the time available to collect the sample.
• Ways to ensure a representative sample

  Random sampling- avoids sampling bias
• Standard deviation


  • the measure of the spread of values about the mean and this indicates the extent of variation a population shows (approx 68% of the data)
  • data is more similar if the standard deviation is smaller I.e there is less variation
  • SD can be indicative of the reliability of the data- smaller the SD the more precise the data is
  • SD not same as range. SD more valid as it involves use of all values but will reduce the impact of extreme data points unlike the range.
• Example: if the mean was 32 and SD was 2.5 this can be expressed as 32 ±2.5. So most values lie between 29.5 to 34.5)
• It’s useful to compare two or more sets of data, if the SD overlap then there is no significant difference, if there is no overlap likely to be significant difference
• The SD can be doubled to give a spread about the mean in which approx 95% of the data lies. If this is used to compare data sets, and there is no overlap of 2x SD then much more likely to be significant difference between means . Often done in scientific investigations