NEB Class 11 · Past paper
The complete NEB Class 11 2072 exam paper for Biology, all 8 questions with solved model answers.
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Answer in short any seven. a. Give the meaning of Cytology and Histology. b. Who propounded the Special Creation Theory? c. Mention the functions of contractile vacuole in paramecium. d. At what time copulatory pads are developed and for what? e. What do you mean by pollutant? f. Where the Reflex arc is formed? g. How is primarily aquatic adaptation different from secondarily aquatic adaptation? h. State Biogenetic law. i. What are the life processes? j. In which category do you put Spiny Babbler?
a. Cytology is the branch of biology that deals with the study of the structure and function of the cell, while histology is the branch that deals with the study of the structure of tissues, that is, groups of similar cells performing a ...
Answer in brief on any five: a. Differentiate between cartilaginous and bony fish. b. Discuss Gamogony in plasmodium. c. Write short note on economic importance of earthworm. d. Describe one experiment in favour of Abiogenesis. e. Give the significance of wild life. f. Discuss the working mechanism of Heart in Frog. g. Why do birds migrate?
a. Cartilaginous fish (class Chondrichthyes), such as sharks and rays, have an endoskeleton made entirely of cartilage rather than bone, a mouth situated on the ventral surface, exposed gill slits without a covering operculum, and placoi...
Describe the process of conjugation in paramecium with diagram. [7.5]
OR
Describe the pulmonary respiration and mechanism of breathing in Frog.
Conjugation is a temporary sexual process of reproduction seen in ciliate protozoans such as Paramecium, in which two individuals of compatible but opposite mating types unite briefly to exchange nuclear material, after which they separate and resume independent multiplication by binary fission.
During conjugation, two individuals come together and attach along the region of their oral grooves, forming a temporary cytoplasmic bridge. In each conjugant, the diploid micronucleus undergoes meiosis to produce four haploid nuclei, of which three degenerate, leaving one functional haploid nucleus. This surviving nucleus divides once more by mitosis to produce two unequal haploid pronuclei, a larger, stationary female pronucleus and a smaller, motile male pronucleus. The two conjugants then exchange their migratory male pronuclei through the cytoplasmic bridge, and in each partner the received male pronucleus fuses with the resident female pronucleus, an act of karyogamy, to form a diploid zygote nucleus (synkaryon).
Once this nuclear fusion is completed, the two individuals, now called exconjugants, separate from each other. Each exconjugant undergoes further divisions of the synkaryon to regenerate a functional macronucleus and micronucleus, and subsequently multiplies by ordinary binary fission. Although conjugation does not directly increase the number of individuals, since it involves only an exchange of genetic material between two pre-existing cells, it produces new combinations of hereditary characters in the exconjugants and restores the vigour of the cytoplasm and organelles, making them more efficient at subsequent binary fission.
OR
Pulmonary respiration in the frog is carried out by a pair of thin-walled, elastic, sac-like lungs, which are used mainly when the frog is active on land, since the frog lacks a muscular diaphragm and ribs capable of expanding the chest and must instead rely on movements of the floor of its mouth (buccal cavity) to force air in and out of the lungs.
During inspiration, the external nostrils (nares) open, the mouth remains closed, and the floor of the buccal cavity is lowered, drawing atmospheric air into the buccal cavity through the nostrils. The nostrils are then closed by special valves, and the floor of the buccal cavity is raised again; since the mouth is closed and the nostrils are shut, this increased pressure forces air through the open glottis, down the short windpipe, and into the lungs, where it inflates the thin, sac-like, internally folded lung walls that are richly supplied with blood capillaries, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out into the lung cavity.
During expiration, the muscles of the body wall and the elastic recoil of the lung tissue itself compress the lungs, forcing the carbon-dioxide-rich air back up through the glottis into the buccal cavity; the floor of the buccal cavity is then lowered and raised in a rhythmic pumping action, and with the nostrils open and the mouth closed, this stale air is finally expelled to the outside through the nostrils. This entire cycle of lowering and raising the floor of the buccal cavity, coordinated with the opening and closing of the nostrils and glottis, is repeated rhythmically to keep the lungs supplied with fresh air. Pulmonary respiration in the frog usually works together with cutaneous (skin) respiration, since the frog's thin, moist, vascular skin also continues to exchange gases directly with the surrounding air or water at the same time.
Describe the Theory of Natural Selection with its draw backs. [8]
The Theory of Natural Selection, also called Darwinism, was published by Charles Darwin in 1859 in his book On the Origin of Species, and it remains one of the most influential explanations of how organic evolution takes place. Darwin built his theory upon a set of careful observations and logical deductions.
The first observation is over-production: Darwin noted that every organism has the capacity to produce far more offspring than can possibly survive to maturity, a fern plant may release fifty million spores, and a house fly may lay several thousand eggs in its lifetime, yet the population of most species remains fairly constant over time. This over-production inevitably leads to the second element, the struggle for existence, in which the excess individuals are forced into constant competition, both among members of their own species (intraspecific) and with members of other species (interspecific), for limited resources such as food, water, space and mates, as well as a struggle against the harsh physical conditions of the environment.
Darwin's third observation was that individuals of a species are not identical but show heritable variation, differing from one another and from their parents in size, colour, strength and other characters, some of which are more favourable than others under the existing environmental conditions. From this follows the central concept of the theory, natural selection or the survival of the fittest: in the ongoing struggle for existence, individuals possessing variations favourable to their particular environment are more likely to survive and successfully reproduce, while those with unfavourable variations are eliminated, so that nature itself acts as a selecting agent, favouring the fittest individuals.
Finally, Darwin proposed that these favourable variations, being heritable, accumulate gradually over many successive generations, and that the continued action of natural selection on such accumulated variations over long periods of time eventually produces populations so different from the original ancestral stock that they come to constitute distinct new species, thereby explaining the origin of species through the gradual process of natural selection.
Drawbacks of Darwinism
Despite its enormous influence, Darwin's theory of natural selection has certain drawbacks. Darwin was unable to explain the actual causes underlying the origin of variations, since the science of genetics and the concept of mutation were unknown in his time. He also treated all variations, whether inherited (germinal) or acquired during an individual's own lifetime (somatic), as being of equal importance for evolution, whereas we now know that only germinal variations are transmitted to offspring, while acquired somatic changes are not inherited at all. Most fundamentally, Darwinism successfully explains the survival of the fittest, that is, why favourable variations persist once they already exist in a population, but it does not explain the arrival of the fittest, that is, how such favourable variations originate in the first place; this gap was only later filled by the discovery of mutation and by the modern synthetic theory of evolution.
Answer in short any seven: a. Define true nucleus. b. What is the function of golgi body? c. Give the meaning of amitosis. d. What do you mean by algae? e. Write the two names of bacteria on the basis of its shape. f. What is rhizome? g. What does it mean by sporophytic generation? h. Define homeostatis. i. Point out about parasitism. j. Mention about green house effect.
a. A true nucleus is a membrane-bound structure found in eukaryotic cells, enclosing the genetic material (chromatin) within a well-defined nuclear membrane, along with nucleoplasm and one or more nucleoli, and it controls and regulates ...
Answer in brief on any five: [5 X 3 = 15] a. Biological role of water. b. Structure and function of endoplasmic reticulum. c. Significances of mitosis. d. Structure of Nostoc and its importance. e. Structure of Pinus. f. Concept of mountain-ecosystem. g. Importance of afforestation.
a. Water is the most abundant inorganic component of the protoplasm, making up about 60 to 90% of it, and it performs several vital biological roles: it acts as a universal solvent in which most biochemical substances dissolve and react,...
Define alternation of generation and describe it in the reference of Moss with necessary diagram. [7.5]
OR
Describe the family solanaceae in semitechnical terms with distinguishing characters, floral diagram and floral formula with two examples of the economic importance.
Alternation of generation is the phenomenon seen in the life cycle of plants such as bryophytes, in which a haploid, gamete-producing gametophyte generation regularly alternates with a diploid, spore-producing sporophyte generation. The gametophytic generation begins with meiosis, that is, the formation of haploid spores, and ends with fertilisation, that is, the formation of the diploid zygote, while the sporophytic generation begins with this fertilisation and ends with the meiotic formation of spores once again. This alternation is clearly demonstrated in the life cycle of the moss-relative Marchantia, a representative bryophyte.
In Marchantia, the dominant, conspicuous, dorsiventrally flattened, dichotomously branched thallus that we commonly see growing on moist soil and rocks is the haploid gametophyte. Marchantia is dioecious, meaning separate male and female thalli are produced. The female thallus bears an umbrella-shaped aerial outgrowth called the archegoniophore, on the underside of which develop numerous flask-shaped archegonia, each containing a single egg cell in its swollen basal venter. The male thallus bears a disc-shaped aerial outgrowth called the antheridiophore, on the upper surface of which develop rounded antheridia that produce numerous biflagellate antherozoids (the male gametes).
In the presence of a film of water, which is essential since these plants are still tied to a moist habitat for reproduction, the antherozoids swim towards the archegonia, drawn by chemical attraction, and one antherozoid fuses with the egg cell inside the venter of an archegonium to form a diploid zygote. This act of fertilisation marks the end of the gametophytic generation and the beginning of the sporophytic generation.
The zygote divides mitotically and develops, while remaining attached to and nutritionally dependent on the female gametophyte, into a sporophyte, which in Marchantia is a much-reduced structure called a sporogonium, differentiated into a foot, a short seta and a terminal capsule. Inside the capsule, sporogenous tissue differentiates into spore mother cells, which undergo meiosis to produce numerous haploid spores; this meiotic division marks the end of the sporophytic generation and the beginning of a new gametophytic generation. On maturity the capsule ruptures and releases the haploid spores, which, on reaching a suitable moist substratum, germinate to produce a new haploid gametophyte thallus, thereby completing one full cycle of alternation of generation.
OR
The family Solanaceae, commonly known as the nightshade or potato family, is classified under the kingdom Plantae, division Magnoliophyta, class Magnoliopsida, order Solanales, with Solanum nigrum as a representative species. Members of this family are distributed widely from tropical to temperate regions and are usually annual or perennial herbs or shrubs.
Plants of this family have a taproot system, and the stem is erect, cylindrical, solid or sometimes hollow (fistular), and branched. The leaves are exstipulate, arranged alternately in the vegetative region of the plant but appearing opposite near the inflorescence. The inflorescence is usually cymose. The flowers are ebracteate, pedicellate, bisexual and actinomorphic (regular). The calyx is made up of five sepals fused together (gamosepalous), showing valvate or imbricate aestivation, and is often persistent, sometimes enlarging around the fruit. The corolla consists of five petals fused together (gamopetalous, often funnel- or wheel-shaped), with valvate or twisted aestivation. The androecium has five stamens, which are epipetalous, that is, attached to the corolla tube and alternating with its lobes. The gynoecium is bicarpellary and syncarpous, with the two carpels placed obliquely rather than in line with the median plane, forming a bilocular, superior ovary containing numerous ovules on a swollen axile placenta, and the fruit is usually a berry or a capsule.
The floral formula of the family may be written as: Ebracteate, ⊕ K(5) C(5) A5 G(2), with the line above G indicating a superior ovary.
Diagnostic characters of the family include: exstipulate leaves, alternate below and opposite near the inflorescence; a cymose inflorescence; ebracteate, actinomorphic, pentamerous flowers; a gamosepalous, persistent calyx; a gamopetalous corolla; epipetalous, alternipetalous stamens; and a syncarpous, bilocular, oblique ovary with axile placentation. Economically the family is highly valuable: Solanum tuberosum (potato) is a major staple food crop grown widely across the world including in the hills of Nepal, and Solanum melongena (brinjal/eggplant) is a widely cultivated vegetable, while other members such as Solanum lycopersicum (tomato) and Capsicum (chilli) are also economically important food crops.
Define ecosystem, describe in detail abut grassland ecosystem with suitable examples. [8]
An ecosystem is a self-sustaining functional unit of nature in which the living organisms of a particular area interact among themselves and with the non-living components of their surroundings, resulting in a continuous flow of energy a...