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02 BIOLOGICAL CLASSIFICATION
44 BIOLOGICAL CLASSIFICATION SCAN CODE Biological Classification Chapter 02 Biological Classification 1. Need for Classification  Biological classification is the scientific procedure of arranging organisms into groups and sub-groups on the basis of their similarities and dissimilarities and placing the groups in the hierarchy of categories.  Since the dawn of civilization, there have been many attempts to classify living organisms. It was done instinctively, not using criteria that were scientific but borne out of a need to use organisms for our own use – for food, shelter, and clothing.  The purpose of biological classification is to organize the vast number of known plants into categories that could be named, remembered, and studied.  A proper system of classification is a must because of the following reasons:  The study of one or two organisms provides the idea of the entire group.  It helps in the identification of organisms.  The organisms of the past cannot be studied without a proper system of classification.  Classification helps in knowing the relationship between the different groups of organisms.  On the basis of relationship and simplicity or complexity found in members of various taxa, evolutionary tendencies can be known. 2. Kingdoms of Classification 2.1 Earliest System of Classification  Aristotle was the earliest to attempt a more scientific basis for classification.  He is also known as the ‘Father of Biology’.  He used simple morphological characters (that can be observed by the naked eye) to classify plants into herbs, shrubs, and trees.  He also divided animals into two groups, those which had red blood and those that did not. Enaima (with red blood) Anaima (horseshoe crab, without red blood)
BIOLOGICAL CLASSIFICATION 45 SCAN CODE Biological Classification Fig 2.1: Earliest System of Classification 2.2 Two-Kingdom Classification  Proposed by: Carolus Linnaeus.  He grouped plants and animals into Kingdom Plantae and Kingdom Animalia, respectively.  He classified the plant kingdom into 24 classes on the basis of sex organs- stamens and style. Fig 2.2: Two-kingdom classification Merits of Two-kingdom classification:  The morphological characters can be easily studied.  This can help in the quick identification of the organism in the field. Drawbacks of Two-kingdom classification:  This system did not distinguish between the eukaryotes and prokaryotes, unicellular and multicellular organisms.  Photosynthetic (green algae) and non-photosynthetic (fungi) organisms were not distinguished.  A large number of organisms did not fall into either category.  Morphological characters can change with changes in environmental conditions.  This system did not include other characteristics like cell structure, nature of the wall, mode of nutrition, habitat, methods of reproduction, evolutionary relationships, etc. 2.3 Three-Kingdom Classification  Proposed by: Haeckel  He placed all unicellular organisms with a lack of tissue differentiation in Kingdom Protista.  Algae, fungi, and protozoa were all initially placed under Protista.  Fungi and multicellular algae were taken out. Later, Kingdom Protista was reserved only for the unicellular organism. Aristotle’s Classification Plants Herbs Shrubs Trees Animals Enaima Anaima Linnaeus' Classification Kingdom Plantae Kingdom Animalia