NCERT Solutions for Class 11 Biology Chapter 2: Biological Classification

1. Discuss how classification systems have undergone several changes over a period of time?

Ans. Biological classification systems have undergone several changes over time. The sequential discussion is listed below:

(a) Aristotle first of all 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.

(b) 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.

(c) After that, Ernst Haeckel, then, separated unicellular eukaryotic organisms into separate kingdom named Protista and hence, gave three kingdom classification.

(d) Copeland, then separated all prokaryotic organisms into a separate kingdom named Monera and hence, Four-Kingdom systems of classification came into existence.

(e) Finally, R.H. Whittaker proposed a five kingdom system of classification in 1969. He separated achlorophyllous, decomposer organisms into a separate kingdom named Fungi. According to this system, there are following five kingdoms: