SolveItClass 11 · NCERT

NCERT Solutions · Class 11 Biology The Living World

10 questions · 10 still being checked

Exercises 1.1–1.10

  1. Exercise 1.1

    Why are living organisms classified?

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    Living organisms are classified because they are far too many and too varied to be studied one at a time — classification puts them into convenient groups and so makes their study possible.
    The number of known and described species is already about $\displaystyle 1.7$–$\displaystyle 1.8$ million, and new organisms are continuously being identified as we explore new areas and even old ones.
    Classification groups organisms into categories on the basis of some easily observable characters, so the moment a group name is used — 'mammals', 'wheat', 'dogs' — a definite set of characters is at once associated with it.
    It makes identification and correct naming possible, and lets a newly found organism be placed in a group already known.
    It brings out the similarities and the differences between organisms, and hence their relationships — the concern of systematics, which takes evolutionary relationships into account.
    Taxonomic studies of the various species are useful in agriculture, forestry, industry and, in general, for knowing our bio-resources and their diversity.

  2. Exercise 1.2

    Why are the classification systems changing every now and then?

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    Because our knowledge of organisms keeps growing, and a classification has to keep pace with it.
    New organisms are continuously being identified, as we explore new areas and even old ones; every new find has to be accommodated somewhere in the system.
    The characters used have themselves changed. Modern taxonomic studies rest on external and internal structure, the structure of the cell, the development process and ecological information — evidence that earlier workers did not have.
    The earliest classifications were based merely on the 'uses' of organisms; such convenience-based schemes are replaced as sounder criteria become available.
    Systematics takes into account evolutionary relationships between organisms, so as these relationships come to be better understood, the arrangement of groups is revised.
    Taxonomists also keep developing sub-categories within the hierarchy, for a more sound and scientific placement of the various taxa.

  3. Exercise 1.3

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

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    Any set of easily observable, distinguishing characters may be chosen — the chapter's rule is that classification groups things "into convenient categories based on some easily observable characters".
    Criteria one could use for people met often:
    Relationship to oneself — family, relatives, neighbours, classmates, teachers, shopkeepers.
    Place — where they live, or where they are met (home, school, playground, market).
    Sex and age group — children, adults, elderly.
    Occupation or profession.
    Language spoken, or region of origin.
    Physical features such as height, build and complexion.
    Note that one person falls into several of these groups at the same time, just as a single organism belongs to taxa at several different levels at once.

  4. Exercise 1.4

    What do we learn from identification of individuals and populations?

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    Identification tells us exactly what organism we are dealing with, so that the correct scientific name can be attached to it — nomenclature is possible only when the organism has first been described correctly.
    It ensures that a description made anywhere in the world leads everyone to the same name, and that the name has not already been used for some other known organism.
    From it we learn the characters of the individual or of the group, and by comparison the similarities and dissimilarities among individuals of the same kind and of other kinds.
    Those likenesses and differences are what fix the organism's place in the taxonomic hierarchy — its species, genus, family and higher categories.
    At the level of populations it tells us whether a form is already known or is new, since new organisms are continuously being identified; this is how the count of described species ($\displaystyle 1.7$–$\displaystyle 1.8$ million) grows.
    It therefore gives us a measure of biodiversity — the number and types of organisms present on earth.
    Practically, such studies are useful in agriculture, forestry, industry and for knowing our bio-resources and their diversity.

  5. Exercise 1.5

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

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    The correctly written name is *Mangifera indica*.
    The first word denotes the genus and begins with a capital letter — Mangifera.
    The second word is the specific epithet and begins with a small letter — indica. This is why Mangifera Indica is wrong.
    Biological names are in Latin and are printed in italics; when handwritten, the two words are underlined separately.
    If the author is cited, the name is written after the specific epithet in an abbreviated form, e.g. Mangifera indica Linn., showing that Linnaeus first described this species.

  6. Exercise 1.6

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

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    A taxon (pl. taxa) is a unit of classification — any category or rank in the taxonomic hierarchy that stands for a real, recognisable group of organisms sharing definite characters.
    Taxa are distinct biological entities, not merely morphological aggregates, and a taxon can be at any level: 'Plants', 'Animals', 'Mammals', 'Dogs' and 'Wheat' are all taxa, but a dog is a mammal and mammals are animals, so these are taxa at different levels.
    Examples at the different hierarchical levels:
    Kingdom — Animalia, Plantae
    Phylum / Division — Chordata (animals), Angiospermae (plants)
    Class — Mammalia, Insecta, Dicotyledonae
    Order — Carnivora, Primata, Diptera, Polymoniales
    Family — Felidae, Canidae, Solanaceae, Muscidae
    Genus — Panthera, Felis, Solanum, Homo
    Species — Homo sapiens, Panthera leo, Mangifera indica
    As one moves from species upward to kingdom, the number of characters common to the members of the taxon goes on decreasing.

  7. Exercise 1.7

    Can you identify the correct sequence of taxonomical categories?
    (a)
    Species Order Phylum Kingdom
    (b)
    Genus Species Order Kingdom
    (c)
    Species Genus Order Phylum

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    The correct sequence is (c) Species → Genus → Order → Phylum.
    The accepted hierarchy in ascending order is species, genus, family, order, class, phylum (division in plants) and kingdom, with species as the lowest category. Sequence (c) follows this order without disturbing it.
    (b) Genus → Species → Order → Kingdom is wrong because genus is placed below species, whereas genus is an aggregate of closely related species and therefore stands above it.
    (a) Species → Order → Phylum → Kingdom does run from lower to higher, but it leaves out three successive categories (genus, family and class); (c) is the sequence taken as correct because it follows the hierarchy with the fewest categories omitted.

  8. Exercise 1.8

    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.

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    In this chapter, a species is a group of individual organisms with fundamental similarities, which can be told apart from other, closely related species on the basis of distinct morphological differences.
    It is the lowest taxonomic category, and all organisms — plants and animals alike — have species as the lowest category.
    In a binomial name the species is the second word, the specific epithet: indica in Mangifera indica, tuberosum in Solanum tuberosum, leo in Panthera leo.
    One genus may contain several species that are morphologically similar: Panthera leo, P. pardus and P. tigris; Solanum tuberosum, S. nigrum and S. melongena.
    The chapter notes that Ernst Mayr "pioneered the currently accepted definition of a biological species", but it does not print that definition, and it says nothing about how species is understood in bacteria. Collect those meanings and discuss them with your teacher, as the exercise asks.

  9. Exercise 1.9

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

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    NCERT publishes no answers for this textbook, so there is nothing in the book to check this working against. It has also not yet been read through by hand.

    (i) Phylum — the category above class; classes with a few common features are grouped into a phylum. Classes of fishes, amphibians, reptiles, birds and mammals are put together in phylum Chordata on common features such as the presence of a notochord and a dorsal hollow neural system. In plants the corresponding category is called Division.
    (ii) Class — a category that includes related orders. For example, order Primata (monkey, gorilla, gibbon) is placed in class Mammalia along with order Carnivora (tiger, cat, dog); class Mammalia has other orders as well.
    (iii) Family — a group of related genera, with still fewer similarities than are shown within a genus or species. Plant families are characterised on both vegetative and reproductive features: Solanum, Petunia and Datura are placed in Solanaceae. Among animals, Panthera and Felis are placed in Felidae, while the dog goes into a separate family, Canidae.
    (iv) Order — an assemblage of families that show a few similar characters; these are fewer than the characters shared by the genera of one family. Order and higher categories are identified on aggregates of characters. Convolvulaceae and Solanaceae are placed in the order Polymoniales, mainly on floral characters; Felidae and Canidae are placed in the animal order Carnivora.
    (v) Genus — a group of related species having more characters in common than they share with species of other genera; genera are aggregates of closely related species. Potato and brinjal are different species of the genus *Solanum*; lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) belong to the genus *Panthera*, which differs from Felis, the genus of cats.

  10. Exercise 1.10

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

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    The taxonomic hierarchy runs, in ascending order, from the lowest category to the highest: species → genus → family → order → class → phylum (division in plants) → kingdom.
    As one goes up from species to kingdom the number of common characteristics goes on decreasing; the lower the taxon, the more the characters its members share.
    CategoryAnimal — ManPlant — Mango
    Speciessapiens (Homo sapiens)indica (Mangifera indica)
    GenusHomoMangifera
    FamilyHominidaeAnacardiaceae
    OrderPrimataSapindales
    ClassMammaliaDicotyledonae
    Phylum / DivisionChordataAngiospermae
    KingdomAnimaliaPlantae
    Two more examples worked the same way: housefly — Musca domestica, genus Musca, family Muscidae, order Diptera, class Insecta, phylum Arthropoda; wheat — Triticum aestivum, genus Triticum, family Poaceae, order Poales, class Monocotyledonae, division Angiospermae.
    Diagram to draw: a vertical ladder of seven boxes, one above the other, with an upward arrow along the side to show ascending order. Label the bottom box Species, then upwards Genus, Family, Order, Class, Phylum, and Kingdom at the top. Beside the ladder draw two parallel columns headed 'Mango (plant)' and 'Man (animal)' and write the entries of the table above against each rung. In the plant column mark the sixth rung as Division instead of Phylum.
    NCERT_Solution_Class11_Biology_Ch1_Q1-10