Define classical taxonomy.

Hint: Classical taxonomy is often regarded as old taxonomy. In this, species is used as a basic element.

Complete Answer:
- The science which deals with classification is taxonomy. Systematic classification is important in biology or in some other areas to put an order into the apparent confusion, such that the various forms in a heterogeneous assemblage may be organised into groups of similar properties.
- In science, taxonomy attempts to group the species into units called taxa on the basis of common similarity. The taxonomic class, taxon, can have differing levels depending on the degree of similarity between the species contained in it. Every level or rank is assigned differently and these ranks create a hierarchical arrangement.
- Classification of any group of species requires use of chosen stable characteristics that differ between taxa. This is also said as taxonomic features.
- Classically, the bacteria are categorized on the basis of similarity in phenotypic characteristics, such as morphological characteristics, Gram stain reaction, cultural features, biochemical physiological properties, pathogenicity, serological relationships, antibiotic susceptibility, etc.
- This taxonomy was studied by few individuals. It began with Plato followed by Aristotle (Father of Zoology), Theophrastus (Father of Botany) and his successors up to Linnaeus (Father of Taxonomy).

Note: Classical taxonomy is based on recognizable morphological characters of normal individuals assumed to be the same expression while their differences are known to be imperfect expressions.