NCERT Solutions Class 11 Biology Chapter 1

Q.1 Why are living organisms classified?

Ans-

Classification is a process of grouping things based on easily observable characters. Classification of organisms is done for various scientific reasons. Some of the main reasons are listed below.

• Classification helps in the identification of specific organisms from the groups of organisms.
• It makes the study of organisms convenient.
• It helps in spotting the similarities and differences among the different groups of organisms.
• It helps in the study of fossils and evolutionary relationships of organisms.

Q.2 Why are the classification systems changing every now and then?

Ans-

Millions of living forms exist on the earth that include plants, animals and microorganisms. Out of them, many are known and have been classified by the scientists under suitable groups, but on the other side, many new species are continuously being discovered. Many of these newly discovered species have a new set of characters and to classify them, either a new system of classification should be developed or an older one should be revised. This brings changes in the existing system of classification every now and then.

Q.3 What different criteria would you choose to classify people that you meet often?

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We can classify the people we meet often on a various basis such as gender, age range, profession, education, hobbies and common interests.

Q.4 What do we learn from the identification of individuals and populations?

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In a diverse country like India, we can learn from the identification of individuals and populations about their native places, tribes, food habits, languages and dialects, clothing, religions, castes, customs, etc.

Q.5 Given below is the scientific name of Mango. Identify the correct written name.
Magnifera Indica
Magnifera indica

Ans-

Magnifera indica is the correct scientific name of Mango. It is because in the binomial system of nomenclature, the generic name of the species starts with the capital letter and the specific name starts with a small letter.

Q.6 Define a taxon. Give some examples of taxa at different hierarchical levels.

Ans-

The specific level in the hierarchy of the system of classification of living organisms is called taxon. The following table states the different taxa with an example at different hierarchical levels.

Q.7 Can you identify the correct sequence of taxonomical categories?

Ans-

(a) Species → Order → Phylum → Kingdom

(b) Genus → Species → Order → Kingdom

(c) Species → Genus → Order → Phylum

Both (a) and (c) are the correct sequence of taxonomical categories. The correct sequence of taxonomical categories is Species, Genus, Family, Order, Class, Phylum/Division, and Kingdom.

Q.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-

The various definition of species are:

(i) Species is the group of individual organisms with fundamental similarities such as in their morphology, anatomy and physiology.

(ii) Species is the basic unit of classification where individuals share common characteristics.

(iii) Species is the group of individuals who can interbreed among themselves and are capable of producing fertile offspring. They are reproductively isolated from the other members of the different species.

Since higher plants and animals perform sexual reproduction, their species can interbreed freely among themselves to produce the fertile offspring.

On the other hand, bacteria with common genetic material belong to the same species since they perform asexual reproduction.

Q.9 Define and understand the following terms:
(i) Phylum
(ii) Class
(iii) Family
(iv) Order
(v) Genus

Ans-

(i) Phylum: Phylum is a taxon consisting of one or more classes that possess correlated characters. It comes just below the kingdom. In plants, classes with similar characters are assigned under division rather than phylum.

(ii) Class: Class is a group of closely related orders. Class lies above order and below phylum. One example of a class is all members of class Mammalia have mammary glands to feed their offspring and have hair on their bodies.

(iii) Family: Family is composed of different genera with less number of similarities as compared to the genus and species level. It lies above the genus and below order. Example: All tiger, lion and leopard belong to the cat family.

(iv) Order: An order is the taxa with the one or more families of organisms that possess some specifically correlated characters that are different from the members of the different orders. It lies above family and below the class. The similar characters in an order are lesser in number as compared to different genera in the included family.

(v) Genus: Genus is a group of related species which has more common characters in comparison to species of other genera. It lies above species and below family. Example: Lion, leopard and tiger belong to the same genus Panthera.

Q.10 How is a key helpful in the identification and classification of an organism?

Ans-

Key is a taxonomical tool that is made in use for the identification of plants and animals based on the similarities and differences. It is developed on the basis of contrasting characters usually presented in a pair, called couplet, that represents the choice between two opposite characters. The selection of one character in a key leads to the rejection of another character when family, species or genera is identified. For example, the presence or absence of hair is a couplet to identify if the animal is a mammal or not.

Once the family is known, a set of identification key can be used for finding its species and then genus. If the organism is not already recorded, the efforts are made to find its details before giving it a new name.

Q. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.

Ans-

The taxonomical hierarchy of a plant and an animal is given in the following table.