1. Why are living organisms classified? [NCERT]
Ans: Living organisms are classified due to
(i) There are millions of organisms on the earth, which need a proper system of classification for their easy identification and methodical studies.
(ii) A number of new organisms discovered each year. They require a particular system to be identified and to find out their correct position in the group.
2. Given below is the scientific name of mango. Identify the correctly written name.
(i) Mangifera Indica (ii) Mangifera indica [NCERT]
Ans: (ii) Mangifera indica
3. Why are classification systems changing every now and then? [NCERT]
Ans: Now a days, biologists use several principles and criteria to classify the organisms. These are based on morphology, anatomy, cytology, physiology, phylogeny, reproduction, evolution, biochemistry and genetics. Thus, there are several characteristic differences which help in classification. This is the reason of change in classification systems every now and then.
4. What different criteria would you choose to classify people that you meet often? [NCERT]
Ans: We can recognise and classify the people we often meet on the basis of their
(i) language (ii) behaviour (iii) geographical distribution (iv) sex (v) weight (vi) height, etc.
5. Can you identify the correct sequence of taxonomical categories?
(a) Species -» Order -> Phylum -> Kingdom
(b) Genus -> Species -> Order -> Kingdom
(c) Species-> Genus ->• Order -» Phylum [NCERT]
Ans: The correct sequence is –
(c) Species —> Genus—» Order —» Phylum.
6. What do we learn from identification of individual and populations? [NCERT]
Ans: Identification of individuals and populations categorise it
into a specific species. Each species has unique
characteristic features. On the basis of these features, it
can be distinguished from other closely related species,
e.g.,
Genus Species
Solanum tuberosum
Solanum nigrum (Both are two different species included in genus Solanum)
7. Define a taxon. Give some examples of taxa at different hierarchical levels. [NCERT]
Ans: The different taxonomical categories are-species, genus, family, order, class, phyla/division and kingdom. Some examples of taxa at different hierarchical levels are (i) Mangifera indica is a taxon and species is its category.
(ii) The taxon of all the bacteria is Monera and the category is kingdom,
(iii) The taxon of fishes is Pisces and the category is class.
8. Illustrate the taxonomical hierarchy with suitable example of a plant and an animal. [NCERT]
Ans: Some Organisms with their Taxonomic Categories
Common Name Human Dog
Scientific Name Homo sapiens Canis familiaris
Species sapiens familiaris
Genus Homo Canis
Family Hominidae Canidae
Order Primata Carnivora
Class Mammalia Mammalia
Phylum/Division Chordata Chordata
Kingdom Animalia Animalia
9. Define the following terms
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus [NCERT]
Ans: (i) Phylum – It is a taxonomic category higher than class and lower than kingdom, which consists of more than one class having some similar correlated characters.
e.g., classes-Aves, Amphibia, Pisces, Reptilia and Mammalia belong to the phylum-Chordata. Members of this phylum have notochord in their body plan.
(ii) Class – The category class includes related orders. It is higher than order and lower than phylum, e.g., class-Mammalia has orders-Carnivora, Primata, etc.
(iii) Family – It is the category higher than genus and lower than order, which has one or more related genera having some common features, e.g., Felidae, Canidae, etc. (iv) Order – It is a taxonomic category lower than class and higher than family. It consists of one or more related families possessing some similar correlated characters that differentiate them from families belonging to other orders, e.g., Carnivora, Primata, etc.
(v) Genus – It comprises of a group of related species which has more characters common in comparison to species other genera. In other words, genera are aggregates of closely related species, e.g., genus- Panthera has lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris).
10. Try to collect all the currently accepted meanings for the word ‘species’. Discuss with your teacher the meaning of species in case of higher plants an animals on one hand and bacteria on the other hand. [NCERT]
Ans: (i) Species is a basic unit of classification, where individual share common characteristics.
(ii) It is a natural population or group of natural population of individuals having similar morphology, anatomy physiology and cytology.
(iii) Species is an assemblage of structurally similar individuals, which can interbreed freely, but are reproductively isolated from members of other species.
Higher plants and animals – These are sexually reproducing organisms.
Bacteria – Bacteria do not reproduce sexually. Therefore, the criterion of free interbreeding and reproductive isolation cannot be applied to them.