4.6.4 Classification of living organisms

Classification Definition

• Living organisms must be classified, in order to compare between them and see the differences between different types of organisms
  • Carl Linnaeus devised this system in the 1700s.

Organisms are split into the following system:

Kingdom

Phylum

Class

Order

Family

Genus

Species

Kingdom

• Organisms are split into five kingdoms.

Phylum

• Phylum lies in between Kingdom and Class.
  • The phylum of an organism is a generalisation based on the body plan of an organism.
  • It is a classification that lies in between Kingdom and Class. The class of humans is Chordata.

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Class

• Class is another division in organisms.
  • You may be familiar with some of the divisions of class.

Order

• Order comes after class.
  • Orders of organisms can be defined.
  • They are formed after class.

Family

• Families are made from classes.
  • Families are a subdivision of class.
  • Birds for example can be divided into families of pigeons and doves and ducks along with many more

Genus

• The genus is a subdivision of families.
  • Families can be further divided into the genus.
  • An example of a genus is Felix, that of domestic cats.

Species

• The species is the final division.
  • We generally know what an organism is through its species.
  • It is the final division of an organism.

No Overlap

• An organism can only be in one group at each level.

Higher Groups have more Organisms

• There are more organisms in the early groups, and less and less as you move down the classification system

Lower Organisms Closer Related

• Organisms in the same lower groups are more closely related.
  • For example, organisms in the same species are more closely related than organisms in the same domain.

The System is Continuously Updated

• The classification system is continually evolving and changing as new types of analysis are discovered.
  • One example is gene sequencing.

The Importance of Microscopes

• As microscopes have developed over time, they have allowed us to improve our understanding.
  • Using microscopes has improved our understanding of different organisms and the distinctions between them.

The Importance of Microscopes

• We can use this understanding to learn more and more about different sorts of organisms, pertaining to their biochemical processes and other such processes.
  • Linnaeus for example, struggled to see the differences between lichens and mosses.

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Carl Woese

• As time went by, chemical analysis has led to the advent of Carl Woese’s ‘three-domain system.’
  • This model was only introduced in the 1970s after RNA analysis.
  • It involves dividing organisms into three categories:
  • Archaea
  • Bacteria
  • Eukaryota

Archaea

• These are more primitive bacteria that have become accustomed to living in extreme environments.
  • They have no nucleus.
  • Examples include the halobacteriales.

Bacteria

• These cells are the true bacterial cells.
  • They are again prokaryotic and examples include the Spirochates.

Eukaryota

• This is the rest of the organisms.
  • It includes fungi, plants, animals and protists.
  • Anything with a membrane bound nucleus fits into this section.

Evolutionary Trees

• Evolutionary trees show the relationships between species.
  • Living organisms are mapped using current data, however fossils are used to map extinct organisms.
  • These trees therefore span generations upon generations and show how extinct organisms are linked to living organisms.