3.4.5 Species and taxonomy

• A species is a group of similar organisms that are able to breed to produce fertile offspring.
• Members of the same species have the...

  1. same number of homologous chromosomes (diploid number)
  2. similar genes = similar proteins = similar characteristics
• Species is the basic unit of classfication.
• The greater the similarities of physical features, courtship behaviour, genome sequencing, amino acid sequences and immune response, the greater the likelihood of a a recent common ancestor.
• Carl Linnaeus developed the binomial classification system and it's rules include:

  • Use of latin/greek names (universal)
  • Each species is given two names: Genus species
  • Genus is capitalised
  • species is lower case
  • Printed in italics, or underlined if handwritten
• Classification is the process of sorting organisms into groups based on shared characteristics.
• Taxonomy is the study of classification.
• Binomial classification system:

  Contains 7 taxonomic groups arranged into a hierarchy - each taxonomic group is called a taxon

  7 taxa are:

  1. KIngdom
  2. Phylum
  3. Class
  4. Order
  5. Family
  6. Genus
  7. Species
• As you progress down the hierarchy for binomial classification, the similarity between species increases as they share more of the same characteristics.
• A hierarchy is a system where smaller groups are placed within larger groups, with no overlap between groups.
• Carl Woese discovered a new group of organisms, called Archae. Following the discovery, he proposed that all organisms are grouped into three domains: Archae, Bacteria, and Eukarya.
• Domain is the highest taxonomic rank.
• Archaea and bacteria are the domains that contain prokaryotic organisms.
• The DNA of Archaea and Bacteria are similar because they are both circular.
• What is different about the DNA between Archaea and Bacteria?

  • Bacteria do not have histones, archaea do.
  • Archaea have more introns than bacteria.
• Compare the cell membrane composition of the 3 domains.

  • Eukarya and Bacteria have the same composition with glycerol-ester linkages.
  • Archaea have glycerol-ether linkages.
• Compare the cell wall composition of the 3 domains.

  • Archaea and Bacteria always have a cell wall but Archaea doesn’t contain murein (peptidoglycan).
  • Eukarya sometimes have a cell wall, which also doesn’t contain murein (peptidoglycan) (plants – cellulose, fungi – chitin).
• A phylogenetic classification arranges species into groups based on their evolutionary origins and relationships. It uses a hierarchy of taxa: domain, kingdom, phylum, class, order, family, genus, species.
• A phylogenetic group is a group of organisms that have similar evolutionary history/share common ancestors.
• Phylogenetic classification focuses on homologous characteristics which are characteristics that have different function, but similar evolutionary origins so the structure is similar.
• Artifical classification is based on useful observable characteristics. It is focused on analogous characteristics, which are characteristics that have the same function, but different evolutionary origins so the structure is different.
• Courtship is behaviour shown by a species when selecting partners for reproduction. It is a necessary precursor to successful mating.
• Courtship behaviour enables...

  • members of the same species to recognise each other
  • identify mate of opposite gender
  • indicates readiness to mate
  • stimulates mating and release of gametes
  • pair bond
• Biodiversity is the variety of different species in an ecosystem or on Earth.
• Species diversity is the number of different species and the number of individuals in each species in a particular area at any one time. It is also known as the index of diversity.
• Formula to calculate species diversity (index of diversity):

  d = N(N-1)/Σn(n-1)

  • d = index of diversity
  • N = total number of organisms of all species
  • n = total number of organisms of each species
  • Σ = the sum of
• Higher index of diversity = greater species diversity

  • more species and more individuals within each
  • larger plant populations = more food/shelter for insects/birds etc.
  • indicates community is more stable and more likely to cope with environmental changes
• Natural selection

  • random mutation can result in new alleles of a gene
  • in certain environments, the new allele is advantageous, so the possessor is more likely to survive and reproduce.
  • advantageous allele inherited by offspring
  • over many generations, the new allele increases in frequency in the population

  *This leads to the evolution of populations.
• Genetic diversity is the number of different alleles for a gene in a species or population. It is important because it protects against environmental change.
• Genetic diversity within a population is increased by:

  • mutations
  • migration bringing different alleles into population and reproduce - known as gene flow
• Genetic diversity allows natural selection to occur when there is competition or selection pressure.
• Evolution is the change in allele frequency over time.
• Allele frequency is how common an allele is in a population.
• Gene pool is all the alleles in a population.
• Differential reproductive success is when some genotypes give an advantage or a disadvantage to an individual's ability to reproduce and pass on an allele.
• Intraspecific variation is when members of the same species differ from each other.
• Interspecific variation is when one species differs from another species.