NCERT Questions & Answers PDF | Class XI | The Living World

The Living World - NCERT Questions & Answers

Q 1: Why are living organisms classified?
✅ It has been described 1.7-1.8 million species of organisms so far. They differ greatly in their form structure and mode of life. All of them cannot be studied individually. So to find out a desired organism from the millions of plants and animals, the organisms must be classified.
Q 2: Why are the classification systems changing every now and then?
✅ Classification is based on characters such as morphology, anatomy, cytology, physiology, ontogeny, phylogeny, reproduction, biochemistry etc. But day by day biologists are learning new about organism and their fossil records. So classification systems may be changed based on new findings.
Q 3: What different criteria would you choose to classify people that you meet often?
✅ Behaviour, language, geographical distribution, morphology etc.
Q 4: What do we learn from identification of individuals and populations?
✅ Identified individuals and population show morphological, anatomical, cytological, physiological, biochemical and behavioural variations. These variations are randomly distributed in species population through sexual reproduction.
Q 5: Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera lndica
Mangifera indica
✅ The correctly written one is Mangifera indica.
Q 6: Define a taxon. Give some examples of taxa at different hierarchical levels.
✅ A taxon is a group of similar, genetically related individuals having some characters distinct from other groups.
Examples of taxa:
Taxonomic category (rank)
Musca domestica
Q 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
✅ (c) Species → Genus → Order → Phylum
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.
✅ Species is a group of populations which resemble one another in all essential morphological and reproductive characters so that they can interbreed freely and produce fertile offspring.

Mayr (l964) defined species as “a group of actually or potentially interbreeding populations that are reproductively isolated from other such groups”.

For example:
Mangifera indica is a species that represents Mango (genus Mangifera, species indica).
Panthera leo is a species that represents Lion (genus Panthera, species leo).
Pseudomonas pyocyanea is a species that represents the bacteria Pseudomonas (genus Pseudomonas, species pyocyanea).

The members of a species can interbreed to produce fertile young ones. In some cases, members of different species may breed but their progeny are sterile. E.g. Mule. It is the offspring of female horse & male donkey.

Q 9: Define and understand the following terms:
(i) Phylum
(ii) Class
(iii) Family
(iv) Order
(v) Genus
(i) Phylum: It is a group of closely related classes. E.g. phylum chordata contains class Mammalia, Aves (birds), Reptilia, Amphibia etc.

(ii) Class: It is a group of related orders. E.g. class Dicotyledonae contains several orders (eg, rosales, sapindales, ranales. etc.). Class Mammalia includes orders such as marsupialia, rodentia, carnivora, primata etc.

(iii) Family: It is group of related genera. They are separable from genera of a related family by important and characteristic differences in both vegetative and reproductive features. E.g. the genera of cats (Felis) and leopard (Panthera) are included in the family felidae. Family Solanaceae contains many genera like Solanum, Datura, Petunia and Nicotiana.

(iv) Order: It is a group of related families. E.g. order polymoniales contains families such as Solanaceae, convolvulaceae etc. Order Carnivora contains families such as Felidae and Canidae.

(v) Genus: It is a group of related species. All the species of a genus are evolved from a common ancestor. E.g. Modern man (Homo sapiens) comes under the genus Homo. Genus Equus has many species, e.g., E. cabalus (horse), E. vulgris (ass), E. zebra (zebra).

Q 10: How is a key helpful in the identification and classification of an organism?
✅ Key is an analytic device having a list of statements with dichotomic table of alternate characteristics which is used for identifying organisms. Usually a couplet or two contrasting characters are used.

The one present in the organism is chosen while the other is rejected. Taxonomic keys are aids for rapid identification of unknown plants and animals based on the similarities and dissimilarities. Separate taxonomic keys are used for each taxonomic category like family, genus and species.

Q 11: Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
✅ Taxonomical hierarchy is the arrangement of organisms in a definite sequence of categories (taxonomic categories).
The hierarchy includes 7 categories – kingdom, division or phylum, class, order, family, genus and species.

Taxonomical hierarchy of plant (e.g., wheat):


Taxonomical hierarchy of animal (e.g., housefly):


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