Ques 1: Why are living organisms classified?
Ans: Organisms are classified because of following reasons:
Although the organisms belonging to a particular group have similarities, they also have dissimilarities. Scientists are always reluctant to find new methods of classification that ensures organisms with most similar characteristics are placed in a particular taxon.
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Ques 6: Define a taxon. Give some examples of taxa at different hierarchical levels.
Ans: Taxon is a group of organisms of any level in the hierarchical classification, which is based on some common characteristics.
Example insects represent a class of phylum-Arthropoda.
All the insects possess common characters of three pairs of jointed legs.
Examples of taxa are kingdom, phylum or division, class, order, family, genus and species. These taxa form taxonomic hierarchy.
Example of taxa for human: Phylum — Chordata Class — Mammalia Order — Primata Family — Hominidae Genus — Homo Species — sapiens
Ques 7: Can you identify the correct sequence of taxonomical categories?
(a) Species → Order → Phylum → Kingdom
(b) Genus → Species → Order → Kingdom
(c) Species → Genus → Order → Phylum
Ans: The correct hierarchical arrangement of taxonomic categories in ascending order is:
Species → Genus → Family → Order → Class → Phylum → Kingdom
Therefore, both (a) and (c) represent correct sequences of taxonomic categories. In sequence (b), species should be followed by genus. Therefore, it does not represent the correct sequence.
Ques 8: 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 and animals on one hand and bacteria on the other hand.
Ans: In biological terms, species is the basic taxonomical rank. It can be defined as a group of similar organisms that are capable of interbreeding under natural conditions to produce fertile offspring.
Therefore, a group of similar individuals that are respectively isolated form a species. Species can also be defined as a group of individuals that share the same gene pool.
Ques 9: Define and understand the following terms:
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
(i) Phylum: It is a principal taxonomic category that comes above class and below kingdom. It is a group or taxon of one or several related classes. In botany, the term Division is used for phylum instead of phylum.
For example, Chordata is a phylum. It contains all those organisms that have or at some point during their development had a notochord.
(ii) Class: It is a taxonomical rank that ranks above Order and below phylum. Class is a group or taxon of one or more related orders.
For example, Mammalia is a class. It contains all those chordate organisms that have characteristic features of mammals like fur, mammary glands, glands, and warm- bloodedness.
(iii) Family: This taxonomical rank contains a group of related genera. It is classified between order and genus.
For example, cat belongs to the family, felidae. This means that all animals that are chordates, mammals and carnivorous having characteristic cat like features would belong to this family. So cats, lions, tigers, leopard all belong to the family felidae.
(iv) Order: It is a taxonomic rank used for classifying organisms below the rank class, and is made up of families sharing a set of similar nature or characters.
For example, Primata is an order which contains all the primates.
(v) Genus: A genus is a taxonomic rank that ranks above species and below family, and is denoted by a capitalized Latin name, e.g. Mangifera. Genus is also known as generic name. It is a group or taxon of one or several related species.
Ques 10: How is a key helpful in the identification and classification of an organism?
Ans: Keys are based on similarities and dissimilarities in characters, generally in a pair called couplet. For example, animals with or without organs. It represents the choice made between two opposite options. This results in acceptance of only one and rejection of the other.
Each statement in the key is called a lead. Separate taxonomic keys are required for each taxonomic category such as family, genus and species for identification purposes. Keys are generally analytical in nature.
Flora, manuals, monographs and catalogues are some other means of recording descriptions. They also help in correct identification. Flora contains the actual account of habitat and distribution of plants of a given area.
These provide the index to the plant species found in a particular area. Manuals are useful in providing information for identification of names of species found in an area. Monographs contain information on any one taxon.
Ques 11: Illustrate the Taxonomical hierarchy with suitable examples of a plant and an animal.
Ans: The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy.
In this hierarchy, species is present at the lowest level whereas kingdom is present at the highest level.
A Taxonomic hierarchy
Classification of a plant:
As an example, let us classify Solanum melongena (Brinjal).
1. Kingdom – Plantae
2. Division – Angiospermae
3. Class – Dicotyledonae
4. Order – Solanales
5. Family – Solanaceae
6. Genus – Solanum
7. Species – Melongena
Classification of an animal:
As an example, let us classify Columba livia (Blue rock Dove).
1. Kingdom – Animalia
2. Phylum – Chordata
3. Class – Aves
4. Order – Columbiformes
5. Family – Columbidae
6.Genus – Columba
7. Species – Livia