Chapter 1 The living world NCERT QUESTION SOLUTION CLASS 11 (BIOLOGY) ,UNIT 1(DIVERSITY IN THE LIVING WORLD)
Chapter 1
THE LIVING WOLRD
NCERT QUESTION SOLUTION
Q1. Why are living organisms classified ?
Ans. A huge variety of plants, animals, and microbes are found on earth. All these living organisms differ in size, shape, colour, habitat, and many other characteristics. As there are large number of living organisms on earth, studying each of them is impossible. Therefore, scientists have devised mechanisms to classify all living organisms. These methods of classification are based on rules and principles that allow identification, nomenclature, and finally classification of an organism.
Q2.Why are the classification systems changing every now and then?
Ans. Huge numbers 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. Therefore, to classify these newly discovered species, new systems of classification have to be derived every now and then. This creates the requirement to change the existing systems of classification.
Q3. What are different criteria would you choose to classify people that you meet often?
Ans. The various criteria that may be chosen to classify people whom we meet often include behaviour, geographical location, morphology, family members, relatives, friends etc.
Q4. 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 similar kind or between different types of organisms. It helps us to classify the organisms in various categories depending upon these similarities and dissimilarities.
Q5. Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera Indica
Mangifera indica
Ans.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.
Q6. Define a taxon.Give some example of texa at different hierarchical levels.
Ans. Taxon can be defined as the taxonomic unit in the biological system of classification of organism. For example a phylum, order, family, genus or species represents taxon. It represents a rank. For example, all the insects form a taxon. Taxon of class category for birds is Aves and taxon of Phylum category for birds is Chordata. The degree of relationship and degree of similarity varies with the rank of the taxon. Individuals of a higher rank, say Order or Family, are less closely related than those of a lower rank, such as Genus or Species.
Q7. 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.
Q8.. 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. Species occupies a key position in classification. It is the lowest taxonomic category. It is a natural population of individuals or group of populations which resemble one another in all essential morphological and reproductive characters so that they are able to interbreed freely and produce fertile offsprings. Each species is also called genetically distinct and reproductively isolated natural population. Mayr (1964) has defined species as “a group of actually or potentially interbreeding populations that are reproductively isolated from other such groups”.
In higher plants and animals the term ‘species’ refers to a group of individuals that are able to interbreed freely and produce fertile offsprings. But, in case of bacteria interbreeding cannot serve as the best criteria for delimiting species because bacteria usually reproduce asexually. Conjugation, transformation and transduction, which are termed as sexual reproduction methods in bacteria, also do not correspond to true interbreeding. Thus, for bacteria many other characters such as molecular homology, biochemical, physiological, ecological and morphological characters are taken into consideration while classifying them.
9. Define and understand the following terms:
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Ans. Explanation:
(i) Phylum- Phylum is a level of taxonomic rank that exists below the kingdom and above the class.
e.g. phylum chordata.
Equivalent of phylum is division in plant kingdom.
(ii) Class- A class is a taxonomic rank that exists below the phylum and above the order.
e.g. class mammalia, class aves.
(iii) Family- Family is a taxonomic rank in biological classification that exists below order and above genus.
e.g. family hominidae
(iv) Order- Order is a taxonomic rank that exists below class and above family. e.g. order primates.
(v) Genus- Genus is a taxonomic rank in the biological classification that exists below family and above species.
e.g. homo
Q10. Illustrate the taxnomical hierarchy with suitable examples of plant and an animal.
Ans. Key is a taxonomical aid that helps in the identification of plant and animal species. These keys are based on similarities and dissimilarities in characters, generally in a pair called a couplet.
Each statement in a taxonomic key is referred to as a lead. For categorizing each taxonomic rank, such as family, genus, species, etc., different keys are used. It is also useful in the identification of unknown organisms.
Keys are of two types - indented and bracketed keys. Indented key provides a sequence of choices between two or more statements while in bracketed key, a pair of contrasting characters is used.
(i) Indented key to identify different species of Rhododendron.
1. Leaves evergreen
2. leaves densely hairy below, orange or white hair; flower
appears to have separate petals Rhododendron groenlandicum
3. Hair absent on leaves, flower has five petals fused in a shallow
tube Rhododendron maximus
4. Leaves deciduous
5. pink flowers with two free petals and three fused petals Rhododendron canadense
6. white to pink flowers with all petals fused together
(ii) Bracketed key to identify different species of Rhododendron.
1. Leaves evergreen - 2
2. Leaves deciduous - 3
3. Leaves densely hairy below, orange or white hair; flower
appears to have separate petals Rhododendron groenlandicum
4. Hair absent on leaves, flower has five petals fused in shallow
tube Rhododendron maximus
5. Pink flowers with two free petals and three fused petals Rhododendron canadense
6. White to pink flowers with all petals fused together - 4
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