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The Vault
RowQ
The Vault
CBSE Class 11 Biology · 10 questions · 24 marks
Ask ten people what makes something alive and you will get ten answers — this chapter replaces guesswork with defining criteria that biologists actually use. It then tackles a practical problem: with millions of species already described and more found every year, how do we name and file them so that a researcher in Pune and one in Peru mean the same organism? You will meet binomial nomenclature, the taxonomic hierarchy, and the herbaria and museums that store the physical evidence behind every name.
In the scientific name Panthera tigris, the word 'Panthera' represents the:
Answer
Generic name is correct — in binomial nomenclature the first word is the genus and is written with a capital initial letter, while the second word 'tigris' is the specific epithet written entirely in lower case.
Which of the following is arranged correctly from the most inclusive category to the least inclusive?
Answer
Order, Family, Genus, Species is correct — an order contains several families, a family contains several genera, and a genus contains several species, so the number of organisms falls steadily as you descend the hierarchy.
A taxonomic aid consisting of dried, pressed plant specimens mounted on labelled sheets is called a:
Answer
Herbarium is correct — it stores preserved, dead plant material on sheets bearing collection details, whereas a botanical garden keeps living plants and a monograph is a written account of one taxon.
Which property is considered a defining feature of life even though many living organisms cannot reproduce?
Answer
Metabolism is correct — sterile organisms such as worker bees or a mule cannot reproduce, but no living thing is without the sum of chemical reactions that make up metabolism, and no non-living object shows it.
Assertion (A): Growth cannot by itself be taken as a defining property of living organisms. Reason (R): Non-living objects such as a heap of sand or a salt crystal also increase in size.
Answer
Both A and R are true and R is the correct explanation of A — non-living things grow extrinsically by the addition of material to their surface, so growth alone cannot separate the living from the non-living; only intrinsic growth from within by cell division is characteristic of life.
State two differences between growth in a living organism and the increase in size seen in a non-living object.
Answer
Growth in a living organism is intrinsic — new material is added from inside the body through cell division, so the organism increases in cell number and in mass. Increase in size in a non-living object such as a sand mound or a crystal is extrinsic — material simply piles up or is deposited on the outer surface. In addition, growth in living organisms is a controlled, self-directed process linked to metabolism, whereas the enlargement of a non-living object depends entirely on external supply of material.
Why was binomial nomenclature introduced, and what are the main rules governing the writing of a scientific name?
Answer
Local or common names differ from region to region and language to language, so the same plant may carry a dozen names and the same name may refer to different organisms; binomial nomenclature was introduced to give every species one universally accepted, unambiguous name. The rules are: the name has two components, the generic name followed by the specific epithet; both are Latinised and printed in italics; the generic name begins with a capital letter while the specific epithet begins with a small letter; when handwritten, the two words are underlined separately; and the name of the author who first described the species is added in abbreviated form after the specific epithet.
Explain the taxonomic hierarchy with a suitable example, and describe how the number of shared characters changes as one moves up the hierarchy.
Answer
The taxonomic hierarchy is a ladder of ranks in which every organism is placed, running from Kingdom at the top through Phylum (Division in plants), Class, Order, Family, Genus and finally Species at the base. Taking the domestic cat as an example, it belongs to the species catus, genus Felis, family Felidae, order Carnivora, class Mammalia, phylum Chordata and kingdom Animalia. At the species level, individuals share the greatest number of characters — they resemble each other in fundamental structure and can interbreed to produce fertile offspring. Moving up to the genus, only closely related species are grouped and some characters begin to differ, for example the size and habits of different Felis species. At the family level still fewer characters are common, being mainly features of the skull, claws and dentition shared by all cat-like carnivores. By the level of class and phylum, only very broad features such as the presence of hair and mammary glands, or a notochord and dorsal hollow nerve cord, are held in common. Therefore, as one ascends the hierarchy the number of organisms included in a taxon increases steadily while the number of characters they share decreases; as one descends, the taxa become smaller but their members become progressively more similar.
Describe the major taxonomic aids used by biologists and explain the specific purpose each one serves.
Answer
Taxonomic aids are the tools, collections and publications that make identification and classification possible. A herbarium is a store of plant specimens that have been collected, dried, pressed and mounted on stiff sheets; each sheet carries a label recording the date and place of collection, the collector's name and the family, and the collection acts as a quick referral system and a repository of type specimens. A botanical garden maintains living plants grown and labelled with their scientific names and families, allowing direct study of habit, flowering and identification features. A museum preserves dead specimens of animals and plants — insects pinned in boxes, larger animals stuffed after preservation, and soft-bodied forms kept in jars of formalin — along with skeletons and fossils, providing reference material for comparison. Zoological parks keep wild animals alive under conditions resembling their natural habitat, enabling the study of food habits and behaviour and supporting conservation and captive breeding. Keys are analytical written aids built from couplets, each offering two contrasting statements of which one is accepted and the other rejected, leading the user step by step to a name; separate keys are made for families, genera and species. Finally, publications such as floras (accounts of the plants of an area), manuals (guides to identifying species of an area), monographs (complete accounts of one taxon) and catalogues supply the descriptive detail that supports every identification.
A college team surveying a coastal scrub forest collects a small flowering shrub they cannot name. They press and mount several specimens, note the site and date, and later work through a printed identification key. The key eventually places the shrub in the same genus as two other shrubs already known from the region, but with a leaf margin and fruit type unlike either. (a) Name the taxonomic aid the team created by pressing and mounting the plants, and state two details their label must carry. (b) What is the structural unit of an identification key called, and how does it work? (c) If the shrub shares a genus with the two known shrubs, what does that tell you about how closely related they are? (d) Suggest one further taxonomic aid the team should consult before claiming the shrub is a new species.
Answer
(a) They created a herbarium sheet, part of a herbarium collection. The label must carry the date and place of collection along with the collector's name; the family and scientific name are also recorded once identification is complete. (b) The unit of a key is a couplet — a pair of contrasting statements. The user compares the specimen with both statements, accepts the one that fits (called a lead) and rejects the other, and is directed to the next couplet, repeating the process until only one name remains. (c) Sharing a genus means the three shrubs are closely related and possess several common features of vegetative and reproductive structure; they differ only in the specific characters, here the leaf margin and fruit type, that separate one species from another within the genus. (d) They should consult a monograph on that genus, which gives a complete account of every known species in it, or the regional flora, so that they can be sure the shrub does not match a species already described.
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