Biology [[Classification, Selection and Evolution]] Classification

Taxonomy: the study of the classification of organisms

Organisms can be classified accroding to their evolutionary relationships. To do this, taxonomists look for shared homologous features between different organisms.

Homologous Features: features which appear to have similar underlying designs, and so have evolved from the same original design which exsited in a particular organism at one stages.

For example: limb bone of veterbrates
Single bone in upper limb, two bones in the lower limb.
This is the same for all vertabrates

All organisms are grouped into Species. Species which share homologous features are grouped into a Genus.
Every species is given a two word latin name called a binomal, the use of which is global and precises. The binomal is made up of the name of the organisms Genus, followed by that of its species. The first name has a capital letter, the second does not. Both are written in italics, and when italics cannot be used (eg hand writing) the binomal should be underlines.
Genera(Genus) are grouped into Families, which are grouped into Orders, which are grouped into Classes, which are grouped in to Phyla and which are, in turn, grouped into Kingdoms.

For Example: Zebra

Kingdom: Animalia (non-photosynthetic multicellular organisms)
Phylum: Chordata (animals with stiffening rod along back)
Class: Mammalia (chordates with hair and mammary glands)
Order: Perissodactyla (mammals with hooves made up of an odd number of toes)
Family: Equidae (horse-like perissodactyla)
Genus: Equus (horses, zebras and asses)
Species: burchelli (common zebra)

Classification represents evolutionary history of an organism and its relationship with other organisms. The evolutionary history of an organism is known as they phylogeny.

The higher up the classification system we go, we are less certain about relationships between the groups.

[[The Five Kingdoms]]
Traditionally all livings things were divided into plants and animals. Plants = anything that was not an animal, so included fungi and bacteria. As microscopy allows us to see more detail of cell structre, it became clear that the 'plant' group actually contained several groups.

1988 - Margulis and Schwartz proposed that the living world should be divided into 5 Kingdoms
Prokaryotae
Protoctista
Fungi
Plantaw
Animalia

Prokaryotes
Organisms made up of the prokarytic cells.
* no membrane bound organelles
* small ribosomes
* single loop of DNA

Protoctists
Simple Eukaryotic organisms
* many are unicellular
* can be filamentous, colonial or thalloid
* can be auutotrophic or heterotrophic
* most are aquatic or live in moist conditions such as the soil

Fungi
Eukaryotic organisms that feed heterotrophically
* Cells have cell walls
* Unlike plant cells they contain materials such as Chitin
* Cell walls are never made from cellulose
* Considered saprotrophs or parasites
* Can be unicellular

Plants
Multicellular eukaryotic organisms that feed by photosynthesis.
* Cells have cell walls made of cellulose
* Some cells contain chloroplasts
* Cells contain large, sap filled Vacuoles

Animals
Multicelular eukaryotic organisms that feed heterotrophically
* cells do not have cell walls
* cells never contain chloroplasts or vacuoles

This system is widley used but some biologists have reservations about it
Protocists are not related to each other, and are put in that group because they do not fit anywhere else