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The Vault
RowQ
The Vault
CBSE Class 9 Biology · 12 questions · 29 marks
Roughly two million kinds of organisms have been described so far, and biologists suspect that is only a fraction of what actually exists. Rather than memorising them one by one, this chapter shows how scientists sort living things into nested groups based on shared, fundamental characteristics — cell type, body organisation, tissue plan and mode of nutrition. The same logic that separates a bacterium from a mango tree also explains why a whale belongs with the cow rather than with the shark.
Which characteristic is regarded as the most basic and is therefore used first when classifying organisms?
Answer
Presence or absence of a true nucleus is correct — whether a cell is prokaryotic or eukaryotic is the most fundamental difference in body design and affects every other feature of the organism, so it is applied first. Mode of nutrition and body symmetry are used at later levels, and the number of limbs is far too narrow a feature to begin with.
Bryophytes such as mosses are often called the amphibians of the plant kingdom because they:
Answer
Live on land but need water for reproduction is correct — mosses grow in damp soil and on rocks, yet their male gametes must swim through a film of water to reach the female gametes, so they depend on both habitats. They cannot swim freely, they have no gills or lungs at all, and they are not restricted to submerged conditions.
A small animal has a soft, unsegmented body, a muscular foot, and a hard external shell. To which phylum does it most likely belong?
Answer
Mollusca is correct — snails, mussels and similar animals have soft unsegmented bodies, a muscular foot for movement, and usually a calcareous shell. Annelids are segmented worms, arthropods have jointed legs and a chitinous exoskeleton, and echinoderms have spiny skin and a water vascular system.
In the scientific name Panthera tigris, the word Panthera represents the:
Answer
Genus is correct — in binomial nomenclature the first word, written with a capital letter, is the genus and the second word, written in small letters, is the species. So tigris is the species name, while family and order are higher categories that are not part of the two-word name.
Assertion (A): A whale is classified as a mammal even though it lives its whole life in the sea and looks broadly like a large fish. Reason (R): Classification is based on fundamental characteristics such as being warm-blooded, breathing through lungs and feeding young on milk, rather than on outward appearance or habitat.
Answer
Both A and R are true and R is the correct explanation of A — a whale breathes air through lungs, maintains a constant body temperature, bears live young and nourishes them with milk from mammary glands, all of which are defining mammalian features. Its streamlined, fish-like shape is only an adaptation to swimming and reflects its habitat, not its ancestry, so classification correctly places it with mammals.
Give three differences between monocotyledonous and dicotyledonous plants, with one example of each.
Answer
First, a monocot seed has a single cotyledon, while a dicot seed has two cotyledons. Second, monocot leaves usually show parallel venation, whereas dicot leaves show reticulate or net-like venation. Third, monocots typically have a fibrous root system in which many roots of similar size arise from the base of the stem, while dicots have a tap root system with one main root and smaller lateral branches. Maize or wheat is an example of a monocot, and mustard or gram is an example of a dicot.
State the features that place an organism in the kingdom Fungi rather than Plantae.
Answer
Fungi are eukaryotic and often multicellular like plants, but they have no chlorophyll, so they cannot make their own food; instead they obtain nutrition heterotrophically, mostly as saprophytes feeding on dead and decaying organic matter, and sometimes as parasites. Their cell walls are made of chitin rather than cellulose, and their body is usually a network of thread-like hyphae rather than being organised into roots, stems and leaves. These features together separate them from members of the kingdom Plantae.
What is binomial nomenclature? State the conventions followed while writing a scientific name and explain why a universal naming system is necessary.
Answer
Binomial nomenclature, introduced by Carolus Linnaeus, is the system of giving every species a scientific name made of two Latin words: the first is the genus, and the second is the species. The conventions are that the genus name begins with a capital letter and the species name with a small letter, the whole name is printed in italics or underlined separately when handwritten, and the name of the scientist who described it may follow in ordinary type — for example, Mangifera indica for the mango. Such a universal system is necessary because a single organism may carry many different local names in different languages and regions, which causes confusion when scientists from different countries communicate. A single agreed scientific name identifies exactly one species everywhere in the world.
Why are Pteridophytes considered more advanced than Bryophytes?
Answer
Pteridophytes such as ferns possess well-differentiated plant bodies with true roots, stems and leaves, whereas the bryophyte body is only thallus-like with root-like rhizoids and no true organs. More importantly, pteridophytes are the first plants to have specialised vascular tissue, xylem and phloem, for conducting water and food over distances within the body. This conducting system supports a larger, taller body and better adaptation to land, which makes pteridophytes structurally more advanced.
Explain the hierarchy of characteristics used in classification, and describe the five kingdoms of Whittaker's system with one example each.
Answer
Classification uses a hierarchy of characteristics, beginning with those that are most fundamental and affect the widest range of other features. The first is the nature of the cell — whether the organism is prokaryotic, with no membrane-bound nucleus, or eukaryotic, with a true nucleus and organelles. The second is whether the body is unicellular or multicellular, since multicellularity allows division of labour among cells. The third is the mode of nutrition, autotrophic or heterotrophic. Only after these are settled do biologists consider finer features such as body symmetry, presence of a coelom, segmentation and the complexity of organ systems. Applying this hierarchy, Whittaker proposed five kingdoms. Monera includes prokaryotic organisms with no true nucleus and no membrane-bound organelles; they may have a cell wall and may be autotrophic or heterotrophic — for example, bacteria. Protista includes unicellular eukaryotes, some of which move using cilia, flagella or pseudopodia, and which may be autotrophic or heterotrophic — for example, Amoeba or Paramecium. Fungi are eukaryotic, mostly multicellular heterotrophs with chitinous cell walls that feed saprophytically on decaying matter — for example, Rhizopus. Plantae comprises multicellular eukaryotes with cellulose cell walls and chlorophyll, which prepare their own food by photosynthesis — for example, a mango tree. Animalia comprises multicellular eukaryotes without cell walls and without chlorophyll, which obtain food heterotrophically and are usually capable of movement — for example, an earthworm.
Compare the five classes of vertebrates, mentioning body covering, respiration, temperature regulation and mode of reproduction, and give one example of each.
Answer
All vertebrates possess a notochord that is replaced by a vertebral column, a dorsal hollow nerve cord, a segmented body and paired gill pouches at some stage of life, but the five classes differ sharply in other features. Pisces are covered with scales and a slimy skin, breathe through gills using dissolved oxygen in water, are cold-blooded, and most lay eggs that are fertilised externally in water. Their bodies are streamlined and they swim using fins — for example, Rohu. Amphibia have moist, glandular skin without scales, respire through gills as larvae and through lungs and skin as adults, are cold-blooded, and lay eggs in water where the young pass through a tadpole stage — for example, the frog. Reptilia have dry, horny scales on the skin, breathe through lungs throughout life, are cold-blooded, and lay eggs with tough protective shells that can be laid on dry land — for example, the lizard. Aves are covered with feathers, have forelimbs modified into wings and hollow lightweight bones, breathe through lungs assisted by air sacs, are warm-blooded, and lay hard-shelled eggs which they usually incubate — for example, the pigeon. Mammalia have skin bearing hair and sweat and oil glands, breathe through lungs, are warm-blooded, and possess mammary glands that produce milk for their young. Most give birth to live young, though a few, such as the platypus, lay eggs — for example, the cow. Across these classes the trend is towards greater independence from water: from external fertilisation in water, to shelled eggs on land, to internal development and parental care of the young.
A field-biology club surveying a coastal wetland records four unfamiliar organisms. Organism P is a green, thread-like growth floating in shallow water with no roots, stems or leaves. Organism Q is a soft-bodied crawler with a single coiled shell and a muscular foot. Organism R has a hard jointed outer covering, three pairs of legs and compound eyes. Organism S has moist skin, swims as a legless tadpole in the pond but hops on land as an adult. Answer the following: (a) Assign P and Q to their groups, with reasons. (b) Assign R and S to their groups, with reasons. (c) Which of these four is warm-blooded, and what does that term mean? (d) The wetland is now threatened by construction. State one reason why protecting such a habitat matters for biodiversity.
Answer
(a) Organism P belongs to Thallophyta, the algae, because its body is a simple undifferentiated thallus with no true roots, stems or leaves, and it is green, indicating chlorophyll and autotrophic nutrition. Organism Q belongs to the phylum Mollusca, since a soft unsegmented body with a muscular foot and a calcareous shell is characteristic of snails and their relatives. (b) Organism R belongs to the phylum Arthropoda, because a hard jointed exoskeleton, jointed legs and compound eyes are defining arthropod features, and three pairs of legs specifically indicate an insect. Organism S belongs to the class Amphibia, since it passes a larval tadpole stage in water, respiring through gills, and lives on land as an adult with moist skin, breathing through lungs and skin. (c) None of the four organisms is warm-blooded. Warm-blooded, or homeothermic, means that an animal keeps its internal body temperature nearly constant regardless of the temperature of its surroundings; only birds and mammals do this, whereas the amphibian S and the invertebrates Q and R are cold-blooded and P is not an animal at all. (d) Wetlands support a large number of species, including many that are found nowhere else and many that depend on the site for breeding. Destroying the habitat removes the shelter, breeding grounds and food chains that these species rely on, so local populations may disappear permanently. Because extinction is irreversible, protecting the habitat is the only practical way to conserve the biodiversity it holds.
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