Classification and Evolution 4.3

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Biological Classification
The reason we have classification and the reason we record species is…
-For our own evidence
-To make the study of life more manageable
-To make it easier to identify species and organisms
-To help see species relationships

The modern classification hierarchy
Organisms are classified into eight categories. The categories are…
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

but an easier way to remember all that is to remember the food mantra ‘Delicious King Prawn Curry Or Fat Greasy Sausages’.

Domain- The domain is the highest taxonomic rank. There are only three taxonomic ranks, archae, eubacteria and eukaryote.
Kingdom- There are five kingdoms; Animalia, plantae, fungi, protoctista, prokaryote. All single celled organisms are in the kingdom prokaryote.
Phylum- A subdivision of the kingdoms. The phylum splits the kingdoms into structure type, e.g vertebrate and invertebrate.
Class- Organisms that possess the same features are put into the same class e.g arachnids have 8 legs so spider and tarantulas are put in that category.
Order- A subdivision of the classes using additional information such as mammals split into carnivore and herbivore
Family- Closely related organisms in the order e.g four legged mammals such as felines and dogs are in different families.
Genus- Closely related family members
Species- Basic and most precise classification

Classifying species
At the top of the classification hierarchy the differences between the animals are much easier to see and consequently are classified and recognised easily. As the hierarchy progresses the differences become much smaller and less easy to differentiate between. As you descend down the taxonomic groups the difficulty to separate species increases.

The binomial naming system
The binomial naming system is the system by which all organisms are named. The organisms are given two latin names which are their genus and their species. The reason the names are latin is so that they are internationally understood. The reason the common name is not used is because they are not used in all countries and some common names in one country could mean a different thing in another country.

Features used in Classification
The biological definition of a species is ‘a group of organisms that van freely interbreed to produce fertile offspring’. This definition is not entirely accurate as some organisms such as bacteria can reproduce asexually. Therefore the phylogenetic definition of a species is more widely accepted as it is ‘a group of organisms that are similar in appearance, anatomy, biochemistry, genetics and physiology’.

Aristotle’s research was incorrect when he hypothesised about classification as he stated that there were only two kingdoms and they were plant and animal. However by the 17th century the microscope had been developed and therefore more kingdoms were discovered.

As technology advanced the two classification systems developed into the five kingdom classification system.

Features of the kingdoms

Prokaryotes
-No nucleus
-Loops of DNA
-No membrane bound organelles
-Small ribosome
-Free living (parasitic)

Protoctista
-Eukaryotic
-Mainly single celled
-Wide variety of forms

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