Classification

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  • Created by: portia
  • Created on: 05-08-17 22:30

Taxonomy is the study and practice of classification, which involves placing organisms in a series of taxonomic units, or taxa (singular: taxon)

In biological classificatiom, these taxa form a hierachy

Each kind of organism is assgned to its own species, and similar species are grouped into a genus (plural: genera)

Similar genera are grouped into a family, families into an order, orders into a class, classes into a phylum (plural: phyla) and phyla into a kingdom

The domain is at the top of this hierarchial system

Three domains

Extremophiles which can be described as prokaryotes that share features with both typical bacteria and eukaryotes and fall under the domain Archaea

  • Many Archaea live in extreme environments, such as hot springs, around deep volcanic vents in the oceans and in lakes where there is a very high concentration of salt
  • some of them produce methane, cannot survive where there is oxygen and have many unusual enzymes
  • since they were discovered in extreme environments they have been found in many less extreme environments; for example, they form an important part of the plankton in the oceans
  • the Archea in several ways appear to have more in common with Eukarya than with Bacteria

Domain Bacteria

Bacteria are prokaryotic as their cells have no nucleus. They are all small organisms that vary in size between that of the largest virus and the smallest single-celled eukaryote.

The characteristic features of bacteria are:

  • cells with no nucleus
  • DNA exists as circular 'chromosome' and does not have histone proteins associated with it
  • smaller circular molecules of DNA called plasmids are often present
  • no membrane-bound organelles (such as mitochondria, endoplasmic reticulum, Golgi body, chloroplasts) are present
  • ribosomes (70S) are smaller than in eukaryotic cells
  • cell wall is always present and contains peptidoglycans (not cellulose)
  • cells divide by binary fission, not by mitosis
  • usually exist as single cells or small group of cells

Domain Archaea

Archeans are also prokaryotic as their cells have no nucleus. Their range of size is similar to that of bacteria. Many inhabit extreme environments

The characteristic features of archaeans are:

  • cells with no membrane-bound organelles
  • DNA exists as circular 'chromosome' and does not have histone proteins associated with it
  • smaller circular molecules of DNA called plasmids are often present
  • ribosomes (70S) are smaller than in eukaryotic cells, but they have features that are similar to those in eukaryotic ribosomes, not to bacterial ribosomes
  • cell wall always present, but does ot contain peptidoglycans
  • cells divide…

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