NCERT Solutions for Class 11 Biology Chapter 1: The Living World

1. Why are living organisms classified?

Ans. There are different varieties of living organisms on earth. They vary in size, shape, colour, habitat, and many other characteristics. So, it is a tedious or impossible task to study them properly. Therefore, scientists have devised mechanisms to classify all living organisms on certain rules and principles that allow identification,
nomenclature, and finally classification of an organism. Classification is the process by which anything can be grouped in convenient categories based on some easily observable characters. Classification of organisms is important because:

(a) It helps in identifying and grouping of new
species easily.

(b) It helps out in knowing similarities and dissimilarities which help in knowing relationships among different groups.

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

Ans. Evolution of species is responsible for the change in classification systems. It is a continuous process and due to this so many different species of plants and animals are added in the already existed biodiversity. The newly discovered plant and animal species are then identified, classified and named according to the already
existing classification systems. Thus, as the species keep on changing, so necessary changes in the already existed classification systems are necessary to place every newly discovered plant and animal in their respective ranks correctly.

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

Ans. The different scientific criteria to classify people that we meet often would be:

(a) The different criteria that may be chosen to classify the people that we meet often include behaviour, geographical location, morphology, gender, family members, etc.

(b) Geographical location of the individuals defines their ability to adapt to the surrounding environment.

(c) The morphology or phenotype (physical appearance) of the person and his/ her behaviour is also responsible for differentiating humans.

(d) Gender also helps in the major classification of humans that helps in the population studies.

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

Ans. The knowledge of characteristic of an individual or its whole population helps in identification of similarities and dissimilarities among the individuals of same kind or of different kinds. It helps us to classify the organisms in various categories depending upon the identified similarities and dissimilarities.

5. Given below is the scientific name of Mango. Identify the correctly written name.

Mangifera Indica
Mangifera indica

Ans. In Binomial system of nomenclature, the genus name is always starts with capital letter and rest letter will be small case and species name should be completely in small letters. Both names should be in italics or underlined separately. Therefore, the correct scientific name of Mango is Mangifera indica.

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

Ans. Taxon: A taxon is generally referred to as a group of organisms classified as a unit.
For example, the basic level of classification is species, followed by genus, family, order, class, phylum or division, and kingdom in ascending order.

Kingdom Phylum/Division Class Class Family Genus Species
Animalia Chordata Mammalia Primata Hominidae Homo sapiens
Animalia Arthropoda Insecta Diptera Muscidae Musca domestica
Plantae Angiospermae Dicotyledonae Sapindales Anacardiaceae Mangifera indica
Plantae Angiospermae Monocotyledonae Poales Poaceae Triticum aestivum

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. Both (a) and (c) represent correct sequences of taxonomic categories as the correct hierarchical arrangement of taxonomic categories in ascending order is as follows:

Species → Genus → Family → Order → Class → Phylum → Kingdom

In sequence (b), species should have been followed by genus. Therefore, it does not represent the correct sequence.

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.
(a) Species is a group of individuals that are similar in their fundamental characteristics and can interbreed among themselves.
(b) Species is the basic unit of classification which assembles individuals which share common genetic set-up.
(c) Species refers to a natural group of individuals similar in morphology, physiology, anatomy, cytology etc.
Higher plants and animals show sexual reproduction; hence, in their case first definition of species is applicable. According to it, species refers to a group of individuals similar in their fundamental characteristics and can interbreed within their population. On the other hand, in case of bacteria, the second and third definitions are applicable.

9. Define and understand the following terms:

(a) Phylum

(b) Class

(c) Family

(d) Order

(e) Genus

Ans. (a) Phylum is the second highest unit of classification after Kingdom. It includes one or more related classes of animals. In plants, instead of phylum, the term ‘division’ is used.

(b) Class is a taxonomic group consisting of one or more related orders. For example, the class, Mammalia, includes many orders like Primata (Man), Carnivora (Lion, Tiger) etc.

(c) Family is a taxonomic group containing one or more related genera e.g., Family hominidae contains Apes, Monkeys and Man. In plants, families are categorized on the basis of vegetative and reproductive features.

(d) Order is a taxonomic group containing one or more families. For example, the order, carnivora, includes many families.

(e) Genus  is a taxonomic group including closely related species. For example, the genus, Solanum, includes many species such as nigrum, tuberosum, etc.

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

Ans. Key is a taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities. The keys are based on the contrasting characters generally in a pair called couplet. 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.

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

Ans. Taxonomical hierarchy refers to the classification of organisms into a definite sequence of taxonomic categories starting from the kingdom and going up to species. The examples of the taxonomic hierarchy is given below:

Taxonomic categories Animal-Human Plant-Rose
Kingdom Animalia Plantae
Phylum/Division Chordata Angiospermae
Class Mammalia Dicotyledonae
Order Primata Rosales
Family Hominidae Rosaceae
Genus Homo Rosa
Species sapiens indica