1. Classification of Organisms
1.1 Every organism of the living world, whether it is a plant or animal or bacteria or animal or bacteria or viruses (microbes) is unique, in itself, which is the basis of the diversity that is shown by the living organism. The variety of plants and animals of one locality may be entirely different from the flora (plants) and fauna (animals) present in other localities such as hills, forests or seaside. This indicates that different places in different parts of the world have their own typical flora and fauna and the degree of diversity is endless. About 92% of flora and fauna (biota) of the unapproachable areas of forests, mountain, deserts and deep seq etc., are still unexplored or it is shown that during the past history of organisms, a large number of new species originated and many become extinct. The extinct species are estimated to be 50 times more than the existing species, hence to study the diversity of living organism in an effective way, these organisms will have to be arranged in an orderly or systematic sequence according to their similarities or dissimilarities (differences). The next step would be to arrange these organisms based on their similarities and differences into other categories such as genus, families, order, class etc. Therefore the method of arranging organisms into groups or sets on the basis of similarities and differences is called classification, which also shown the relationship among these organisms. For understanding the living world, study of a few representatives of each group is sufficient which would give an idea of all members of that group.
Importance of classification:
The science of classifying the flora and found is known as taxonomy, which is an important branch of biological science. The advantages of classification of organisms are: (1) classification is the tool by which one can deal with diverse type of organisms and makes the study of organisms easy. (2) classification projects before us a picture of all lite forms at a glance, (3) classification is essential which tells us about the interrelationship among the different group of organisms (4) classification forms a base for the development of other biological sciences, such as biogeography (study of distribution of plants and animals) that is totally depended on the information provided by classification The taxonomy or systematics is the study of not only the diversity and kind of organisms, but the study also includes inter-relationship among the organisms, naming of the organism and the evolutionary sequence amongst them, based on the information’s observed from the museum specimens, cytological, physiological and bio-chemical aspects of the organisms etc.
Early system of classification were artificial i.e., they were based on a few chosen criteria such as size, colour and nature of the organism, their habitat, life-span etc., (Aristotle and Theophrastus). Car von Linnaeus published in 1737, System nature (classification of Nature) based on the sexual characters of the organisms and it was an artificial system of classification. But in the 19th century, the artificial system of classification were replaced by natural system of classification, based on overall similarities and differences between the organisms and their phylogenetic nearness.
Nomenclature:
Nomenclature is to provide a scientific name for every living organism to be followed al over the world. This will avoid, conferring different names to the same organism in different part of the world and in differe4nt languages for e.g., a dog is called 'kutta' in Tamil and these names are not understood elsewhere.
1.2 Binomial nomenclature:
Nomenclature is a system of naming plants and animals and in biology every organism is given two names. The first is the name f the genus (generic name) and second is the name of the species (specific name). The generic name is shared by a number of other closely related organisms. (It is like sharing the surname with other members of thesame family) whereas the second name species is possessed only by one kind of organism in the genus (not shared with any other organism n the genus). It is a convention that generic name is followed by the specific name and have Latin endings. e.g., the scientific name of human being is Homo (generic) sapiens (specific). Thus this type of naming each organism is bionmial nomenclature which was first developed and used by Linnaeus who has been considered as Father of taxonomy. He published his book Species plantarum in 1753. Thus the scientific names are unique, understood and followed all over the world and are not changed easily and they are guided by a set of rules stated in International code of Nomenclature.Hence giving a Latin name to a living organism is not enough, unless it is grouped or placed in a system which relates it to all other living things, which is done by arranging al organisms into groups called tax, which is further split into smaller groups, with each group having certain common features. Living organisms are first grouped into plant and animal kingdom which are further split into smaller group such as phyla, and phyla into classes, classes into order into families, families into genera and genera into species. Thus species is the basic level of all latest classification. (Species is an isolated reproductive unit, group of similar organisms that are able to breed together and produce fertile offspring). (e.g. Human beings, dogs etc.) if two different species inter-breed, the product is sterile (e.g., horse x sterile mule).
Classification of plants and animals:
The differences between plants and animals are distinct, plants are stationary, trap solar energy and synthesize their own food and grow and some grow indefinitely, whereas animals generally move, consume plants or other animals and their body stops growing after attaining certain size. The plants cells have a cell wall and contain chloroplast synthesize starch whereas animal cells neither have cell wall nor chloroplast. Based on these basic differences the plants and animals are grouped into two groups namely Plant kingdom and Animal kingdom. This system of classification was first purposed by Carlus Linnaeus in 1758. But further taxonomic studies indicated that certain organisms could not be placed in ether of the above groups because of certain unique characters. Hence a German Zoologist, E.H. Haeckel (1866) raised a third kingdom Protista for unicicellular organisms. But when significant differences become evident among the protists, an American ecologist Robert H. Whittaker (1969) proposed a fourth kingdom monera for bacteria which are prokaryotes and fifth one, kingdom Fungi, whose members are eukaryotic, lack chlorophyll and obtain their food through obsorption. Thus Classification of organism is a
progressive process and if more data regarding life forms are known, classification becomes more and more refined.
The five major kingdoms are
1. Kingdom Monera - Bacteria,bluegreen algae
2. Kingdom Protista - Protozoa, unicellular angle and slime moulds
3. Kingdom Plantae - Multicellular plants (producersautotrophs)
4. Kingdom Fungi - True fungi
5. Kngdom Animalia - Muticellular animals (consumersheterotrophs)
Even in the five-kingdom classification, viruses could not be suitably placed as they occur at the border line of living and non-living world.
Classification of plants: Eichler (1883) has divided Plant kingdom, into two subkingdom, Cryptogamae and phanerogams (Spermatophyta).
Subkingdom Cryptogamae:
(Crypto-hidden; gamous marriage) Plants included under the subkingdom is/are 'lower plants'. They are 'flowerless' and 'seedless', but have hidden reproductive system. It is further divided into 3 divisions namely: Thallophyta, Bryophyta and Pteridophyta. The subkingdom Phanerogamae or Spermatophyta includes seed plants and the plant body has distinct root, stem and leaves, vasular system (xylem and phloem), multicellular sex organs and formation of embryo from the fertilized egg. On the basis of presence or absence of fruit it is further subdivided into Gymnospermae and Angiospermae. The former include plants with naked seeds and the later with enclosed seeds.
This kingdom constitutes various types of bacteria which are the most ancient and the most numerous living beings. Bacteria are found everywhere, where life can possibly exist. They may occur in hot springs, under icebergs, in the dry deserts, in the deep ocean floors or within many living things, Bacteria was first observed by Anton von Leewenhoek in 1672.
The kingdom Monera consists of two major groups:
(i) The Eubacteria (true bacteria) and (ii) the Archaebacteria (ancient bacteria).
2.1. Size and shape of the bacteria: The bacteria are microscopic in size and their average m. Bacteria may be classified depending on their basic shapes.
(i) Bacilli - (bacillus - singular) rod shaped e.g., Escherichia
(ii) Cocci - (coccus - singular) - spherical or oval shaped e.g., Staphylococcus
(iii) Spirilla - (spirllum - singular) - spiral or cork - screw shaped e.g., Spirillum
(iv) Vibrio - comma shaped e.g., Vibrio cholerae
