discuss how classification system have undergone several changes over a period of time?

The classification systems have undergone several changes with time. The first attempt of classification was made by Aristotle. He classified plants as herbs, shrubs, and trees. Animals, on the other hand, were classified on the basis of presence or absence of red blood cells. This system of classification failed to classify all the known organisms.

Therefore, Linnaeus gave a two kingdom system of classification. It consists of kingdom Plantae and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms and between eukaryotes and prokaryotes. Therefore, there were large numbers of organisms that could not be classified under the two kingdoms.

To solve these problems, a five kingdom system of classification was proposed by R.H Whittaker in 1969. On the basis of characteristics, such as cell structure, mode of nutrition, presence of cell wall, etc., five kingdoms, Monera, Protista, Fungi, Plantae, and Animalia were formed.

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In ancient time, the systems of classification of organisms were simple and were based on one or two characters. The basis of grouping was also very simple. Aristotle and others grouped plants into trees,shrubs and herbson the basis of their habits. Aristotle also divided animals into two groups, one having red blood(Enaima)and others without red blood(Anaima). During the period of greeks to the middle of the century, the crude methodsclassification was habit/habitat and a few structural features. Sometimes the resemblance among the organism observed were very superficial and found unreliable. Due to the the above facts the classification of this period was unreliable and arbitrary.

Later Linnaeus proposed two kingdoms- 1. The plant kingdom i.e., plantae and 2. Animal kingdom i.e.,animalia that included all plants and animals respectively. The kingdom plantae included all those organismswhich were fixed in place, had a spread about appearance, prepared their own food and had cellulose cell wall. The kingdom animalia included all organismswhich could move about,had a comact body, which are hetrotrophs, and lacked cell wall.

R.H.Whittaker an american taxonomist divided all organism into five kingdoms. Viruses were left out. The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia.

These changes were made because the criteria for classificationchanged.Over time, an attempt has been made to evolve a classification  systems which reflects evolutionary relationships.

Hence classification has gone through many changes over time.

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