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In the chapter “The Living World” of Biology Class 11, students will learn about diversity in the living world, taxonomic studies of plants, animals, industry, forestry, and agriculture; biodiversity, binomial nomenclature, what is living, taxonomical aids, taxonomical categories, etc.
Why are living organisms classified ?
The Objectives of Biological Classification
- It is impossible to study all living organisms. It is necessary to devise some means to make it possible. It is called classification.
- To recognise and precisely describe the basic units of classification, i.e., species.
- To devise an appropriate method of assigning the basic unit (species) into an ascending series of groups on the basis of their similarities and relationships.
- Advantages of biological classification are to organise the vast number of plants and animals into categories that could be named, remembered and studied.
Why are classification systems changing every now and then ?
Classification systems are changing from time to time. Right from Aristotle to Linnaeus, every naturalist employed a few traits for classification of organisms. Later on with increased detailed study of various biological domains, more and more characters were taken into consideration for classification. Hence these systems are changing from time to time. The system of classification is subjected to modification.
What different criteria would you choose to classify people that you meet often ?
Classification is the process by which anything is grouped into convenient categories based on observable characters such as shape, colour, hair, behaviour, geographical distribution and even language.
What do we learn from identification of individuals and population ?
Population system strive to bring about evolutionary relationship among organisms. Study of morphological characters and other investigations are carried out to know the variations of trait. These variations are randomly distributed in species populations through sexual reproduction and environmental interaction.
Below is given the scientific name of Mango. Identify the correctly written name.
Give reasons in support of your answer.
The correct scientific name of Mango is Mangifera indica.
Reasons in support of this answer are :
Universal rules of nomenclature :
- Biological names are generally in Latin and written in Italics.
- First word in a biological name represents genus while the second component denotes specific epithet.
- First word denoting genus starts with capital letter while the specific epithet is written starting with small letter. It can be illustrated with example of Mangifera indica.
Define a taxon. Give some examples of taxa as different hierarchial levels.
Taxon. Each category also referred to as unit of classification in fact represents a rank and is commonly termed as taxon (pl. = taxa) : This unit or taxon should be recognisable and must belong to a category. Examples. Insects represent a group of organisms sharing common features like three pairs of jointed legs. It means insects are recognisable concrete objects which can be classified, thus given a rank or category. Other examples are : fishes, birds, plants, animals, what and grasses. Each group represents a category. Category further denotes rank. All categories together constitute a Taxonomic hierarchy. Each rank or Taxon, in fact represents a unit of classification. These taxonomic groups /categories are biological entities and not merely morphological aggregates.
Can you identify the correct sequence of taxonomical categories ?
Species order phylum kingdom Genus species order kingdom Species genus order phylum
The correct sequence of taxonomical categories is :
Species Genus Order Phylum.
Try to collect the currently accepted meaning for the word ‘species’. Discuss with your teacher the currently accepted meaning of species in case of higher plants and animals on one hand and bacteria on the other hand.
Species. It is most important category in taxonomic hierarchy. It is the basic unit in evolution. A species may be defined as a group of individuals which resemble one another in structural and functional characters, interbreed freely and truly among themselves and are thought to have originated from a common ancestor. Because of their common inheritance, members of a species possess similar hereditary or genetic material.
Currently accepted meaning of species
- The purely morphological species definition has been replaced by a biological one; which takes ecology, geography, genetics, cytology, physiology, biochemistry and behaviour into consideration.
- The importance of the species as such is reduced since most of the work is done with subdivisions of species, such as subspecies and population.
- Species are regarded as a dynamic unit as opposed to the static unit of classical systematics.
Define and understand the following terms :
(i) Kingdom (ii) Phylum (iii) Class (iv) Order (v) Family (vi) Genus.
Kingdom. It is highest category of taxonomy with related phyla/divisions. Phylum. A number of classes having common features constitute a phylum. The classes, Pisces, Amphibia, Reptilia, Aves and Mammalia though differ from each other are still placed in the same phylum Chordata because of common features like presence of notochord, dorsal hollow nervous system and pharynx perforated by gill slits.
Class. The class is the basic category. Similar orders are grouped together in the common class. A class is generally a subdivision of a phylum.
Order. A number of families having many common characters are placed in an order. The cat and its relatives like Lion, Tiger and Leopard belong to family Felidae. The bears form the family Ursidae. Since dogs, cats and bears are carnivorous, hence they are placed under order Carnivora.
Family. A number of genera having several common characters constitute a family. The genus Vulpus shares a few characters with genus Canis. Thus both these genera are placed in the same family Canidae.
Genus. It forms the taxonomic higher category than species. It is a group of closely related species e.g. Dog, Jackal and Wolf are placed in the same genus Canis because they are closely related to each other but belong to different species.
How the key is helpful in identification and classification of organisms ?
Key is a taxonomical aid used for identification of unknown plants and animals based on the similarities and dissimilarities. The keys are taxonomic literature based on the contrasting characters generally a pair called couplet. Key represents artificial analytical order arrangement with choice to be applied between two opposite options. This results in acceptance of only one and rejection of other. Each statement in the key is called a lead. The joined leads of a pair are arranged. Separate taxonomic keys are required for each taxonomic category such as family, genus and species for identification purposes. Keys are generally analytical in nature.
Illustrate the taxonomical hierarchy with suitable examples.
Taxonomical hierarchy is the arrangement of organisms in a definite sequence of categories depending upon their relative dimensions.
Taxonomic categories showing hierarchial arrangement in ascending order.
Discuss how classification systems have undergone several changes over period of time.
Since the time of Aristotle, living things have been divided into plant kingdom and animal kingdom. It has been noted that characters assinged to each kingdom are not always present in all cases e.g. fungi, lichens. This system imposes an unnatural division on one celled organisms also. Bacteria, cyanobacteria etc. has also been wrongly placed. In order to meet the shortcomings classification systems have undergone changes. Now a days organisms are classified on the basis of evolution relationship. Such classifications are called phylogenetic classification.