classification

• classification is the act of arranging organisms into groups based on their similarities and differences
• taxonomy is the study of classification
• in a taxonomic hierarchy, there are eight taxonomic groups
• similar organisms are first sorted into one of three domains ~ bacteria, archaea and eukarya
• domain kingfom phylum class order family genus species
• the binomial system ~ genus name with capital letter - species name underlined (or italics)
• the five kingdoms ~ prokaryotes, protoctists, fungi, plants, animals
• prokaryotes kingdom features ~ prokaryotic, unicellular, no nucleus, < 500 nm
• protoctists kingdom features ~ eukaryotic cells, live in water, single celled / simple multicellular
• fungi kingdom features ~ eukaryotic, chitin cell wall, saprotrophic
• plants kingdom features ~ autotrophic, photosynthesise, cellulose cell walls, eukaryotic, multicellular
• animals kingdom features ~ eukaryotic, heterotrophic, multicellular
• phylogeny is the study of the evolutionary history of groups of organisms
• the first branch point of a phylogenetic tree represents a common ancestor of all the family members
• a species is the smallest group that shares a common ancestor
• phylogeny is the basis of classification
• early classification systems of just using observable features is problematic as scientists often dont agree on the relative importance of different features and groups based solely on physical features may not show how related organisms are
• molecular evidence involves analysing the similarities in proteins and DNA
• you can compare: how DNA is stored, the sequence of DNA bases, the sequence of amino acids
• the three domain system was proposed because of new molecular evidence
• the three domain system has the previously ‘prokaryota’ system split into two domains - archaea and bacteria
• evidence that led to the prokaryota kingdom being split into bacteria and archaea:

  • molecular evidence ~ the enzyme RNA polymerase is different in bacteria and archaea. archaea have similar histones to eukarya
  • cellular evidence ~ the bonds of the lipids in the cell membranes of bacteria and archaea are different
• intraspecific variation ~ variation within species
• interspecific variation ~ variation between different species
• continuous variation ~ when individuals in a population vary within a range
• discontinuous variation ~ two or more distinct categories
• variation can be caused by: genetics, environmental factors or both
• genetic variation ~ alleles in an organism make up its genotype

  the differences in genotype result in variation in phenotype
• environmental factors for variation ~ caused by differences in lifestyle, food, climate
• most samples will include values either side of the mean, so you end up with a bell shaped graph - normal distribution
• normal distribution is symmetrical about the mean
• standard deviation is a measure of the spread of values about the mean
• standard deviation is more useful than the range, as it takes into account all the values in the data set
• spearmans rank correlation coefficient tells you:

  • whether two variables are related
  • how strongly theyre related
• the spearmans rank coefficient results in a number between -1 and 1

  if the figure is -1, there’s a perfect negative correlation

  +1 indicates a perfect positive correlation

  the closer the figure is to 0, the weaker the correlation
• a null hypothesis states that there is no correlation between factors being investigated
• highest value is given a rank of 1
• if spearmans rank correlation coefficient is higher than critical value, you reject the null hypothesis
• prokaryotes divide by binary fission
• a species is a group of organisms that can reproduce to produce fertile offspring