- A clean, no-nonsense summary for Edexcel AS/A level Biology B Topic 3
Classification and Biodiversity
- Written using specification and contains everything needed for an A/A*
- Linked set of flashcards also available
Classification
Taxonomy
Taxonomy is the science of classification. A taxon is a category in a classification system such
as genus or species.
Humans have been classifying organisms from the start of human life. Original classification
systems were based on edibility, where they live, dangerous or not, and size. However,
organisms are continuously reclassified as technology and how organisms are classified have
improved.
Classification is essential as it allows an internationally recognised method to identify
organisms and organise existing organisms. Classification involves giving every organism a
name and organising organisms into categories.
Artificial Classification
Uses analogous features to classify organisms. Analogous features are features that look
morphologically similar and have the same function but are not from the same biological
origin such as wings on birds and bats. Artificial classification groups organisms based on
non-evolutionary features and morphological characteristics therefore do not show
evolutionary history (phylogeny). This was used in early methods of classification.
Natural Classification
Uses homologous features to classify organisms. Homologous features are features that
share a common ancestor and have a similar bone structure but through natural selection
have become modified for different purposes such as flippers on a whale and arm of a
human. Natural classification groups organism based on evolutionary similarities and
common ancestors. This is used in modern classification.
Linnaeus introduced classification rules in the 18 th century. He proposed a binomial
nomenclature and a hierarchical structure for classification
Binomial nomenclature: Every species is given a binomial name based on its genus and
species. The genus is written with a capital letter, species is lowercase. The whole name
must be italicised or underlined when handwritten. After a mention of the whole name, the
genus can be abbreviated to the first letter of the name.
The hierarchy Linnaeus set up:
Kingdom Phylum Class Order Family Genus Species
This was replaced by the 3-domain system
3-Domain Model
Whittaker proposed the 5-kingdom model in 1966. The 5 kingdoms were Monera,
Protoctista, Fungi, Plantae, Animalia. Whittaker had classified most of the prokaryotes under
the bacteria kingdom. As technology improved and RNA and DNA sequencing became
available, it shows a lot of variation in genetics.
Woese proposed the 3-domain model in 1990 which separated the prokaryotes into 2
domains.
Domain Kingdom Phylum Class Order Family Genus Species
This produces 6 kingdoms:
Archaebacteria – Prokaryotic cells that are extremophiles and can survive extreme
conditions. Normally reproduce asexually
Eubacteria – Prokaryotic cells that include typical bacteria. Normally reproduce
asexually
Protoctista – Eukaryotic cells. Normally reproduce asexually
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