Discuss how classification systems have undergone several changes over a period of time?
Answers
Biological classification is the scientific procedure of arranging organisms in a hierarchical series of groups and sub-groups on the basis of their similarities and dissimilarities. Scientists have proposed different systems of classification which have undergone several changes from time to time.
Earlier Aristotle proposed artificial system of classification, which divided animals and plants on basis of habitat. E.g., Aquatic (fish, whale), terrestrial (e.g., reptiles, cattle) and aerial (e.g., bat, birds). Then, natural system of classification was based on morphology^ anatomy, physiology, reproduction, ontogeny, cytochemistry, etc. After natural system, organisms were classified on basis of evolutionary relationships called phyloge¬netic system. It is based on cytotaxonomy, chemotaxOnomy, numerical taxonomy and cladistic taxonomy.
Answer:
Aristotle was the first to classify organisms based on morphological characters to differentiate plants and animals. He classified plants into trees, shrubs and herbs and animals based on the presence or absence of red-coloured blood.
Later, Linnaeus proposed two kingdoms-Plant Kingdom and Animal Kingdom. This system did not distinguish between eukaryotes and prokaryotes, unicellular and multicellular organisms and photosynthetic and non-photosynthetic organisms. Plants and animals could easily be classified under this system, but a large number of organisms did not fall under either category. So, a need was felt to include more number of characteristics such as mode of reproduction, evolutionary relationship etc. to facilitate better categorisation.
Thus, R. H. Whittaker proposed a 'Five Kingdom Classification'.
The five kingdoms of the Five Kingdom Classification system are
i. Monera
ii. Protista
iii. Fungi
iv. Plantae
v. Animalia
The main criteria for the classification of organisms in the Five Kingdom Classification include cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.
Explanation: