Sunday 23 October 2016

CBSE Class – XI - Biology - NCERT Chapter 1 - The Living World (NCERT Chapter Solutions)

The Living World

Class – XI - Biology - NCERT Chapter 1 Solutions

CBSE Class – XI - Biology - NCERT Chapter 1 - The Living World (NCERT Chapter Solutions)

Question 1: Why are living organisms classified?


Classification helps us understand biodiversity better way. Biodiversity have direct and indirect economic benefits to humans as well as to our ecosystem. Systematic study of such biodiversity is essential to better understand the inter-relationships in our ecosystems. Following are the needs to classify them:

Plants and animals have valuable genetic variation information. It will help us understand the ways evolution take place.

Humans often benefits from plants and animals in different ways. Systematic study will help exploring other potential benefits.

Certain species warn us of imbalances in our ecosystem. e.g. white-rumped vultures became almost extinct because of use of drug brufen (diclofenac) in domestic animals. When vultures ate these dead animals, it led to their kidney failures. Systematic study of the organisms would help in restoring the balance in their ecosystems.

Plants and animals have been the inspiration for technology and engineering design. e.g. SONARS and RADARS work on the same acoustics principles as used by bats. Classification will help us revealing such more inspirations.

It is estimated that the Earth has almost 8.8 million animal, plant, and fungi species, but we’ve only discovered less than a one fourth of this. A large variety of plants, animals, and microbes are found on earth. All these living organisms differ in size, shape, colour, habitat, and many other characteristics. Classification gives a system for identification of known and unknown organisms.

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

Answer: In the last few hundred million years, plants and animals have undertaken an epic evolutionary journey that has altered the very make-up of the planet. Millions of plants, animals, and microorganisms are found on earth. Many of these have been identified by the scientists. While many new species are still being discovered around the world.

Another reason is that scientists started classifying organisms on the basis of evolutionary relationships rather than solely on the basis of similarities in physical traits.

Therefore, to classify these newly discovered species and finding new basis of classification, new systems of classification have to be devised every now and then. This creates the requirement to change the existing systems of classification.

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

Answer: To classify people we often meet, we try to categorise in an ordered fashion.

To begin with we classify them based on gender. It results in the formation of two major groups- boys and girls.

Each of these two groups can be further classified on the basis of the blood relatives, distant relatives, friends, knowns and strangers.

Finally each individual be identified by its name (first name and sir name)

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

① It helps in studying characteristics of an individual or its entire population.
② It helps in identifying similarities and dissimilarities among the individuals of same kind or between different types of organisms.
③ It helps the scientists find basis to classify organisms in various categories.
④ It helps us finding the relation between the individuals (or its population) with the ecosystem (Biotic and Abiotic factors).

Question 5: Given below is the scientific name of Mango. Identify the correctly written name.
              Mangifera Indica
              Mangifera indica

In binomial system of nomenclature, the generic name of a species always starts with a capital letter whereas the specific name starts with a small letter.

Therefore, the correct scientific name of Mango is Mangifera indica.

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

Answer: Each unit or category of classification is called as a taxon. It represents a rank  in this hierarchical classification. For example, the basic level of classification is species, followed by genus, family, order, class, phylum or division, in ascending order. The highest level of classification is known as kingdom.

Question 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

The correct hierarchical arrangement of taxonomic categories in ascending order is:
               Species → Genus → Family → Order → Class → Phylum → Kingdom

 Options (a) and (c) represent correct sequences of taxonomic categories.
 Option (b) is an incorrect sequence.

Question 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.

Answer: In biological terms, species is the basic taxonomical unit. It is is a group of organisms that are similar enough to mate and produce fertile offspring together. Species can also be defined as group of individuals that share the same gene pool.

Question 9: Define and understand the following terms:

    (i) Phylum
    (ii) Class
    (iii) Family
    (iv) Order
     (v) Genus

(i) Phylum
Phylum is the primary division of kingdom. It includes one or more related classes of animals. In plants, instead of phylum, the term ‘division’ is used.

(ii) Class
Class is a taxonomic group consisting of one or more related orders. For example, the class, Mammalia, includes many orders.

(iii) Family
Family is a taxonomic group containing one or more related genera. In plants, families are categorized on the basis of vegetative and reproductive features. For example in animals, families in the primate order include hominids (apes and humans) and hylobatids (gibbons).

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

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

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

⒜ Key is another taxonomic way used to identify 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. Thus, it 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.

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

Answer: The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy. In this hierarchy, species is represented at the lowest level whereas kingdom takes the highest level.

Classification of a plant
As an example, let us classify Solanum melongena (Brinjal).
Kingdom   – Plantae
Division  – Angiospermae
Class     – Dicotyledonae
Order     – Solanales
Family    – Solanaceae
Genus     – Solanum
Species   – melongena

Classification of an animal
As an example, let us classify Columba livia (Blue rock Dove).
Kingdom – Animalia
Phylum  – Chordata
Class   – Aves
Order   – Columbiformes
Family  – Columbidae
Genus   – Columba
Species – livia

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