Identification of organisms, classification and nomenclature.

  Need for classification and nomenclature

                   From the dawn of human civilization people must have begun to identify plants and animals

                   and named them, because their survival was dependent on the use of plants and animals.

                   Species were identified separately by their specific characters.

                   Major groups of plants and animals (like grasses, fishes, snakes, birds)were also identified

                   separately.

                   The names used were however varied depending on the language of the people and the place.

                   Biological study of organisms needs a unified system of classification and nomenclature.

                   Aristotle was the first person who classified organisms systematically.

Binomial nomenclature

                    With the advance of science and knowledge of biology, different scientists, Botanists and

                   zoologists used different methods of naming and classification of organisms. Most often a

                                                      

                   polynomial system was used, until 18th  century.

                    Carolous Linnaeus (1707-1778) proposed a binomial system of nomenclature of species,

                   which was accepted world wide.

                    The name of an organism has two parts

                     First is  the generic name and the second is specific epithet

                    Generic name is usually a noun and specific epithet an adjective describing a particular

                     feature. Example  Homo  means man,  sapiens  means intelligent

                     Related species have the same generic name with different specific epithets.  Dipterocarpus

                   means fruit with two wings,  zeylanicus  means endemic to Sri Lanka.

                 

 International codes of  Binominal nomenclature

                   Biologists have adopted sets of rules or Codes of nomenclature. These codes are slightly

                   different for plants, animals, bacteria and viruses. Some of the important rules for naming

                   plants, fungi and animals are as follows.

                   1. Two species of organisms cannot have the same name.

                   2. Each species has a generic name and a specific name, both together forming the species

                         name or scientific name.

                   3.  Name should be made up of  Latinized words written in the Roman script.

                   4. It should be underlined when hand written and italicized when printed.

                   5. The first letter of the generic name must be capitalized and specific epithet must be in

                         simple letter.

                   6. A third word can be used to represent a subspecies or a variety, example  Panthera pardus

                          kotiya  (Sri lankan leopard).

                   7. In scientific work name of the author who gave the name is indicated by a capital letter,

                      an abbreviation or full word at the end of the name, which is not latinised. example  Cocos

                      nucifera  L., ( L for Linnaeus).

                

Methods of natural & artificial classification

                    Arrangement of organisms into groups on the basis of the common characteristics is called

                    classification. Taxonomy is the science of classification. This includes placing groups of

                    organisms in a hierarchical order.

                    Two methods of classification

                    (1) Artificial classification - grouping is based on a few pre selected unifying characters.

                        •   The characters are selected first according to convenience and organisms are grouped

                          based on the selected criteria.

                        •   Natural relationships are ignored.

                                                    th

                        •   Only system used before 18  century.

                        •   Easy to use, easy to expand by adding more groups.

                          Examples. Plants can be classified as cereals, ornamental plants, medicinal plants,

                          poisonous plants etc. Animals can be classified as two legged, four legged, six

                          legged, eight legged etc. Linneaus classified plants according to number of stamens.

                    (2) Natural classification - grouping based on evolutionary relationships.

                        •   Represent true (natural) relationships, based on phylogeny.

                        •   Systems developed after study of evolution.

                        •   Based on many characters.

                          Characters used can be morphological, anatomical, cytological or molecular.

                          Most recently DNA and RNA sequences (molecular) are being used

                          Examples- Plants can be classified into Bryophyta, Lycophyta, Pterophyta,

                          Cycadophyta, Coniferophyta and Anthophyta etc. Arthropods can be classified into

                          Crustacea, Insecta, Chilopoda, Diplopoda and Arachnida.

                 •   Discuss the advantages and disadvantages of the two systems of classification

                 •   Use of keys

                   Used to group organisms and to identify

                   Common key is the dichotomous key

                   Do not show the evolutionary relationships

   Example1 :   Ant, Butterfly, honey bee, Beetle

               1. Posses wings …………………………………………………. (2)

                   Do not posses wings ………………………………………….. Ant

               2. Having transparent wings ……………………………………   (3)

                   Do not have transparent wings………………………………….Beetle

               3. Posses hairs on appendages ……...……………………………. Honey Bee

                   Do not posses hairs on appendages……………………………...Butterfly

  Example 2:  Snake, Earthworm, Frog, Sea anemone, Butterfly

               1. Radially symmetrical body ……………………………………..Sea anemone

                   Not having radially symmetrical body …………………………..(2)

               2. Possess legs………………………………………………………(3)

                   Do not possess legs ……………………………………………...(4)

               3. Having wings……………………………………….....................Butterfly

                   Do not have wings………………………………….....................Frog

               4   .Body covered by scales …………………………………………Snake

                   Body do not covered by scales.………………………………….Earthworm