NCERT Book Class 11 Biology Chapter 2 Biological Classification

10 BIOLOGY

C HAPTER 2
B IOLOGICAL C LASSIFICATION
2.1 Kingdom Monera Since the dawn of civilisation, there have been many attempts to classify
living organisms. It was done instinctively not using criteria that were
2.2 Kingdom Protista
scientific but borne out of a need to use organisms for our own use – for
2.3 Kingdom Fungi food, shelter and clothing. Aristotle was the earliest to attempt a more
2.4 Kingdom Plantae scientific basis for classification. He used simple morphological characters
to classify plants into trees, shrubs and herbs. He also divided animals
2.5 Kingdom into two groups, those which had red blood and those that did not.
Animalia In Linnaeus' time a Two Kingdom system of classification with
2.6 Viruses, Viroids Plantae and Animalia kingdoms was developed that included all
and Lichens plants and animals respectively. This system did not distinguish between
the eukaryotes and prokaryotes, unicellular and multicellular organisms
and photosynthetic (green algae) and non-photosynthetic (fungi)
organisms. Classification of organisms into plants and animals was easily
done and was easy to understand, but, a large number of organisms
did not fall into either category. Hence the two kingdom classification
used for a long time was found inadequate. Besides, gross morphology
a need was also felt for including other characteristics like cell structure,
nature of wall, mode of nutrition, habitat, methods of reproduction,
evolutionary relationships, etc. Classification systems for the living
organisms have hence, undergone several changes over the time.
Though plant and animal kingdoms have been a constant under all
different systems, the understanding of what groups/organisms be
included under these kingdoms have been changing; the number and
nature of other kingdoms have also been understood differently by
different scientists over the time.