Binomial system – a system that uses the genus name and the species name to avoid confusion when naming organism

Classification – the process of placing living things into groups

Reasons for classification:

• For convenience
• To make the study of living things easier
• For easier identification
• To show the relationships between species

Species – the basic unit of classification. All members show variation but are essentially the same

Genus – a group of closely related species

Family – a group of closely related genera

Order – a subdivision of class using additional information about organisms such as meat eating (Carnivora) or vegetation eating (Herbivora)

Class – a group of organisms with the same general traits e.g. number of legs

Phylum – major subdivision of the kingdom, contains all organisms with the same body plan e.g. chordata (possessing backbone)

Kingdom – Five main kingdoms

Domain – highest taxonomic rank

As you descend the taxonomic ranks from Domain 👉 Species it becomes harder to distinguish and separate closely related organisms from each other and to place them accurately.

• The same organism may have a completely different common name in different parts of a country
• Different common names are used in different countries
• Translation of languages and dialects may give different names
• The same common name may be used for a different species in a different part of the world

Species – a group of organisms that can freely interbreed to produce fertile offspring

Phylogenetic definition of species – a group of individual organisms that are very similar in appearance, anatomy, physiology, biochemistry and genetics

Early classification systems by Linnaeus and Aristotle were based solely on appearance and features which limited the classification to observable features only.

• Biological Molecules

Some biological molecules, such as those for DNA replication and respiration are essential for life and therefore all living things have a variant that can be compared to show how closely related they are.

If we assume that the earliest living common ancestors to living things had the same version of these molecules then any changes are a direct result of evolution.

1. Cytochrome C

The protein cytochrome C is essential in respiration but is not identical in all species due to evolution. The sequences of amino acids in the protein can help draw conclusions about how closely related they are. If the sequences are the same then the two species must be closely related and if they are different they are not so closely related. The more differences found between the sequences, the less closely related the two species.

 2. RNA Polymerase

RNA Polymerase is also used as an indicator of evolution because of its essential role in protein synthesis

• DNA

1. Genome Sequencing

Advances in genome sequencing have meant that the entire base sequence of an organism’s DNA can be determined. The DNA sequence of one organism can then be compared to the DNA sequence of another organism. This will show you how closely related they are to each other.

2. Comparing amino acid sequences

Proteins are made of amino acids. The sequence of amino acids in a protein is coded for by a base sequence in the DNA. Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.

• Immunological Comparisons

Similar proteins will bind to the same antibodies. So, if antibodies to a human version of a protein were added to isolated samples from other species, then any protein similar to the human version will be recognized and bind to the antibody.

Artificial Classification

• classification for convenience, e.g. in plant identification books, sorting by flower colour

Natural Classification

• Biological classification involving a detailed study of the individuals in a species, it uses many characteristics, reflects evolutionary relationships and may change with advancing knowledge

Phylogeny

• The study of the evolutionary relationships between organisms

This is the end of this topic

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Drafted by Eva (Biology)

Photo references:

1. https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/8%3A_Microbial_Evolution_Phylogeny_and_Diversity/8.03%3A_Microbial_Phylogeny/8.3C%3A_The_Levels_of_Classification
2. https://www.toppr.com/ask/content/story/amp/three-domains-of-life-86033/
3. https://www.brainkart.com/article/Whittaker---s-System-of-Classification_35254/
4. https://en.wikipedia.org/wiki/Cytochrome_c_oxidase
5. https://www.yourgenome.org/facts/how-do-you-find-out-the-significance-of-a-genome-after-sequencing
6. https://ruo.mbl.co.jp/bio/e/support/method/antibody.html
7. https://sciencemusicvideos.com/ap-biology/evolution-natural-selection-unit-7-menu/phylogeny-and-classification/