WJEC AS Biology Unit 2 Topic 1 - Basic Revision Notes

Classification

• Classification places organisms into discrete, hierarchical groups.  

  • It is hierarchical because it is a system of smaller groups that belong to larger groups.

  • Smaller the group, more they have in common.

  • Discrete as organisms cannot be in more than one group at the same level.

  • Another name for group is taxon.

• The five kingdom system classifies based on physical appearance, into 5 kingdoms.

• The 5 Kingdom system works as follows

  • Kingdom, Phylum, Class, Order, Family, Genus, Species

• The 5 Kingdoms are

• The classification is tentative.

• • Depends on our current knowledge

  • May be altered as our knowledge changes

  • Velvet worms have soft body and jointed limbs, characteristics of two phyla so a new phylum was created for them.

• Phylogenetic classification groups organisms based on evolutionary relationships.

  • Further up, more recent, top row alive now.

  • Branches represent common ancestors.

Why do we need a classification system?

• • Allows you to infer evolutionary relationships and assess how closely related organisms are.

  • If new animal discovered with some characteristics of a taxon, we can predict its other characteristics based on what we know

  • Easier for communication

  • Easier to count families that species when assessing the health of an ecosystem and/or extinction.

• Species - group of organisms that have similar features and can breed to produce fertile offspring.  

  • May show sexual dimorphism - physical difference between males and females e.g. lions.

• Binomial Name - ‘Genus species’

• Recent biochemical evidence has shown that the kingdom prokaryotae should be split into 2 groups based on fundamental biological differences.  This has led to Three Domain System

  • States that all organisms have evolved down three distinct lines

  • Based on organisms in each domain sharing a distinctive unique pattern of Rrna

  • Eubacteria are true bacteria.

  • Archaea are extremophiles prokaryotes existing in extremes of pH, temperature, pressure and salinity and have unusual metabolisms e.g. some produce methane.

  • Eukarya/Eukaryota are organisms with eukaryotic cells.

Assessing Relatedness

• Physical Features

  • More similar features suggests more closely related organisms.

  • Homologous Structures - evolved from same original structure for different functions through divergent evolution.  E.G. Pentadactyl limb.

  • Analogous Features - have evolved from different structures to perform the same function by convergent evolution.  E.G. wings of birds and insects.

• DNA Sequencing

  • More similarities in dna base sequence, more closely related.  

  • Has confirmed evolutionary relationships and corrected mistakes made from physical feature classification (due to convergent evolution)

• DNA Hybridisation

  • Compares dna base sequence of two species

  • DNA from both is extracted, separated and cut into fragments.

  • Fragments are mixed…