Classification

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Classification is the process of organizing living organisms into groups based on their physical structure and characteristics, allowing scientists to identify, name, and understand relationships between different species.

The Linnaean System

Carl Linnaeus developed the Linnaean system of classification in the 1700s.
In this system, living organisms are categorized into a hierarchical structure with the following levels: kingdom, phylum, class, order, family, genus, and species.
This system allows for a systematic and universal approach to naming and classifying organisms.

The Binomial System

The binomial system is a method of naming species using two Latin names: the first part represents the genus, and the second part represents the species.
This naming convention is used globally, overcoming language barriers and ensuring consistency in the identification of organisms.
Example: The scientific name of the ladybug is Harmonia axyridis, where Harmonia is the genus, and axyridis is the species.

The Three-Domain System

Advances in science, including improved microscopy and biochemical analysis (e.g., RNA sequencing), revealed that some organisms are more distantly related than previously believed.
Carl Woese introduced the three-domain system in the late 20th century, adding a higher classification level above kingdoms:
- Archaea: Primitive bacteria-like organisms that thrive in extreme environments, such as hot springs and salt lakes.
- Bacteria: True bacteria, which are distinct from archaea despite some similarities in appearance.
- Eukaryota: Organisms with cells that have a nucleus enclosed within membranes, including the kingdoms of protists, fungi, plants, and animals.

Evolutionary Trees

Evolutionary trees are diagrams used to illustrate the evolutionary relationships between different species, showing how closely related they are.
These trees are constructed using data from classification systems and fossil records, helping to trace the ancestry and divergence of species over time.

Traditionally…

Organisms classified according to similarities/differences in observable characteristics (eg how many legs something has).
...As technology improved you can see with microscopes (eg. cell structure)…

These characteristics classify organisms in 6 kingdoms

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animals – fish, mammals
plants - grass, trees
fungi - mushrooms, toadstools
prokaryote - all single celled organisms without nucleus
protists - eukaryotic singled celled organisms e. algae

Kingdoms then subdivided into smaller and smaller groups that have common features. –phylum, class, order, family, gene, species

Classification Simplified Revision Notes for GCSE Edexcel Biology