NEB Class 11 · Past paper
The complete NEB Class 11 2074 exam paper for Biology, all 8 questions with solved model answers.
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Answer in short on any seven.
a) What is nuclear membrane?
b) Define cytoplasmic streaming.
c) Mention about mitosis.
d) What does it mean by species?
e) Write positive effects of bacteria.
f) What do you mean by roots?
g) Define corolla.
h) Illustrate food web.
i) What is antibiosis? j) Mention about ammonification.
a) The nuclear membrane, also called the karyotheca, is the double-layered membrane that encloses the nucleoplasm and separates it from the cytoplasm, giving the nucleus a definite, organised shape. b) Cytoplasmic streaming is the contin...
Describe in brief of any five.
a) Functions of lipid.
b) Structure and function of chloroplast.
c) Importance of mitosis.
d) Scope of diversity.
e) Lateral conjugation of spirogyra.
f) Male cone of Pinus.
g) Importance of land management.
a) Lipids are an efficient and concentrated source of energy for the body. They act as heat insulators when deposited in the subcutaneous tissues, and they carry the fat-soluble vitamins A, D, E and K. Vitamin D is synthesised from cholesterol on exposure to sunlight, and complex lipids such as phospholipids form an important structural component of the plasma membrane.
b) The chloroplast is a double-membrane-bound plastid found mainly in the green parts of plants such as leaves. It is bounded by a smooth outer and inner membrane, with a periplastidial space between them, and its matrix, the stroma, contains disc-like grana made of stacked thylakoids where chlorophyll is located. Functionally the chloroplast is the site of photosynthesis, so it is called the kitchen of the cell; it also maintains the balance of oxygen and carbon dioxide in the atmosphere and helps reduce global warming.
c) Mitosis is important because it maintains a constant, fixed number of chromosomes in the somatic cells of an organism from one generation of cells to the next. It brings about the growth and development of new tissues and organs in multicellular organisms, repairs worn-out and damaged tissues, and provides the basis for asexual reproduction in many organisms.
d) The scope of diversity (biodiversity) lies in its many practical uses to humans. It provides a variety of foods, drinks and raw materials, is a source of new medicines, and helps maintain the natural beauty of the environment. It is essential for the conservation of plants, animals and their habitats, helps buffer against natural calamities, and is an important direct source of income and economic development for many communities.
e) Lateral conjugation is the homothallic mode of sexual reproduction in Spirogyra, occurring between two adjacent cells of the same filament. The protoplasts of the two neighbouring cells round off to form gametes, and the common wall between them develops an outgrowth called a papilla. The wall at this point dissolves to form a conjugation tube, through which the male gamete migrates and fuses with the female gamete to form a zygote. The zygote secretes a thick wall around itself to become a resting zygospore, which germinates into a new filament when favourable conditions return.
f) The male cone of Pinus is a small, soft, catkin-like structure produced in clusters at the base of the young shoots of the long branches. Each cone is made up of a central axis bearing numerous spirally arranged microsporophylls, and each microsporophyll carries two microsporangia (pollen sacs) on its lower surface. Inside the microsporangia, microspore mother cells undergo meiosis to form haploid microspores, which develop into winged pollen grains that are later dispersed by wind for pollination.
g) Proper land management is important because it maintains the fertility and productivity of soil for agriculture, prevents soil erosion and land degradation, and helps conserve water resources by managing catchment areas. It also protects natural habitats and biodiversity, reduces the risk of landslides and floods in hilly regions like Nepal, and ensures that land resources remain sustainable for future generations.
Define alternation of generation and discuss the process with special reference to life cycle of Fern. [7.5]
Or,
Describe the family Leguminosae in semitechnical terms with identifying characters, floral diagram and floral formula with examples of economic value.
Alternation of generation is the phenomenon in which a plant completes its life cycle by passing through two distinct, morphologically different phases: a haploid, spore-producing gametophyte generation and a diploid, spore-producing sporophyte generation, which alternate with each other regularly. The haploid gametophytic generation begins with meiosis, that is, the formation of spores, and ends with fertilisation, that is, the formation of the zygote. The diploid sporophytic generation begins with fertilisation and ends with meiosis. This alternation is clearly seen in the life cycle of the fern Dryopteris.
The conspicuous, familiar fern plant is the sporophyte. It is differentiated into a true root, an underground stem called the rhizome, and leaves known as fronds, which are also called sporophylls because they bear the spore-producing structures. On the lower surface of the pinnae of fertile fronds, clusters of sporangia called sori develop. Each sporangium has a biconvex capsule borne on a stalk, with a ring of thick-walled cells called the annulus running around it, interrupted at one point by the stomium.
Inside the sporangium, the sporogenous cells differentiate into spore mother cells, each of which undergoes meiosis to produce four haploid spores, so that about 32 to 64 spores are formed per sporangium. This meiotic division marks the beginning of the gametophytic generation. At maturity the sporangium wall ruptures along the stomium and the haploid spores are released. On reaching a suitable moist substratum, a spore germinates and develops into a small, green, heart-shaped, independent gametophyte called the prothallus, which anchors itself by rhizoids and photosynthesises for itself.
The prothallus bears the sex organs. Flask-shaped archegonia, each containing a single egg cell, develop near the apical notch at the anterior end, while rounded antheridia, which produce numerous multiflagellate antherozoids (the male gametes), develop towards the posterior end. In the presence of a film of water, the antherozoids swim to the archegonia and one fuses with the egg cell to form a diploid zygote. This fertilisation event ends the gametophytic phase and marks the start of the sporophytic generation.
The zygote divides mitotically to form a two-celled embryo, which continues to divide and grows, while still attached to the prothallus, into a new sporophyte differentiated into root, stem and leaves. This young sporophyte eventually becomes independent of the gametophyte, and on maturity produces sporangia and spores again, thereby completing one full cycle of alternation between the sporophyte and the gametophyte generations.
Or
The family Leguminosae (Fabaceae), commonly called the pea, bean or legume family, is classified under the kingdom Plantae, division Magnoliophyta, class Magnoliopsida, subclass Rosidae and order Fabales, with Pisum sativum as a representative genus and species. It is distributed widely all over the world.
Members of this family are mostly annual herbs with a well-developed taproot system. The stem is herbaceous and erect, though it may be climbing in some species with the help of tendrils. The leaves are simple or, more commonly, compound, and are rarely opposite. The inflorescence is racemose. The flowers are bracteate, bisexual and zygomorphic, with the calyx made up of five sepals showing valvate aestivation. The corolla consists of five petals arranged in the typical papilionaceous form: one large posterior petal called the standard, two lateral petals called wings, and two smaller anterior petals fused together to form the keel, showing descending imbricate aestivation. The androecium usually has ten stamens, which are diadelphous, that is, nine are fused into a tube and one remains free. The gynoecium is monocarpellary with a superior ovary, and the fruit that develops is a legume or pod.
The floral formula of this family is written as: Bracteate, ⊕ (actinomorphic symbol not applicable, zygomorphic) K(5) C1+2+(2) A(9)+1 G1, with the line above G showing a superior ovary.
Diagnostic characters of the family include: mostly herbaceous, mesophytic plants with a taproot; a racemose inflorescence; zygomorphic, bisexual, hypogynous flowers; a papilionaceous corolla; diadelphous stamens; and a fruit that is a legume. Economically the family is highly important: Pisum sativum (pea) and Vigna species (beans, lentils) are major pulse crops and a rich source of dietary protein; Arachis hypogaea (groundnut) yields edible oil; and many legumes, through their root-nodule symbiosis with nitrogen-fixing Rhizobium bacteria, enrich soil fertility and are widely used as green manure and in crop rotation.
What is ecosystem? Discuss in detail about the main components of ecosystem with suitable examples. [8]
An ecosystem is a self-sustaining functional unit of nature in which living organisms of a particular area interact among themselves and with their non-living surroundings, resulting in a flow of energy and a cycling of nutrients between the two. Examples include a pond ecosystem, a forest ecosystem and a grassland ecosystem.
An ecosystem is made up of two main components: the abiotic (non-living) component and the biotic (living) component.
Abiotic component
The abiotic component consists of the physical and chemical factors of the environment that influence the living organisms present. It includes climatic factors such as light, temperature, rainfall, humidity and wind, and edaphic factors such as the soil, water and the mineral nutrients (such as nitrogen, phosphorus and potassium) dissolved in it. These factors determine which organisms can survive and thrive in a given habitat, and they supply the raw materials that producers use to manufacture organic food.
Biotic component
The biotic component consists of all the living organisms of the ecosystem, and on the basis of their nutritional role they are grouped into three categories.
Producers are the autotrophic, chiefly photosynthetic organisms, such as green plants and algae, which trap solar energy and manufacture organic food from simple inorganic substances like carbon dioxide and water. Producers form the base of every food chain, since all other organisms depend directly or indirectly on them for energy.
Consumers are the heterotrophic organisms that cannot manufacture their own food and instead depend on producers or other consumers. Primary consumers or herbivores, such as deer, rabbits and grasshoppers, feed directly on producers. Secondary consumers, or primary carnivores, such as frogs and small fish, feed on the herbivores, while tertiary consumers, or top carnivores, such as hawks and tigers, feed on other carnivores.
Decomposers are saprophytic bacteria and fungi that break down the dead remains and waste products of producers and consumers into simple inorganic substances. This decomposition releases nutrients like nitrogen, phosphorus and carbon back into the soil and atmosphere, making them available again to producers, and it is this constant recycling of matter, driven by decomposers, that keeps an ecosystem functioning.
Through the interaction of these abiotic and biotic components, energy flows in one direction from producers through the various levels of consumers, while nutrients cycle repeatedly between the living organisms and the non-living environment, keeping the ecosystem in a state of dynamic balance.
Answer in short on any seven.
a) Define the term Ornithology.
b) Write the full form of IUCN.
c) How is Zoology related with Chemistry?
d) Differentiate between primary and secondary pollutants.
e) Give the reasons of fish migration.
f) Write two volant features of bat.
g) What do you understand by leadership?
h) What are analogous organ? Give example.
i) Why do frog go under hybernation? j) Give the scientific name of Garden snail and tapeworm.
a) Ornithology is the branch of zoology that deals with the scientific study of birds, their structure, classification, behaviour and distribution.
b) IUCN stands for the International Union for Conservation of Nature. It is an international organisation that works for the conservation of nature and natural resources and publishes the Red List of threatened species.
c) Zoology is closely related to chemistry because the bodies of animals are made up of organic and inorganic chemical compounds, and all physiological activities such as digestion, respiration and excretion occur through biochemical reactions. Genetic materials like DNA and RNA, and energy carriers like ATP, are themselves chemical substances, so an understanding of chemistry is essential to understand animal life processes.
d) Primary pollutants are those pollutants that are released directly into the environment from their source in their original harmful form, such as carbon monoxide, sulphur dioxide and soot from vehicle exhaust and factory chimneys. Secondary pollutants, on the other hand, are not emitted directly but are formed in the atmosphere when primary pollutants react with each other or with other atmospheric constituents; ground-level ozone and smog formed by the reaction of nitrogen oxides and hydrocarbons in sunlight are examples of secondary pollutants.
e) Fish migrate mainly for breeding (to reach suitable spawning grounds with favourable water conditions for their eggs and young), for feeding (to move towards areas rich in food) and to escape unfavourable conditions such as extreme temperature, low oxygen or high salinity in their original habitat.
f) Two volant (flight-related) features of a bat are the presence of a thin, elastic patagium, a wing membrane stretched between its elongated fingers, forelimb and body, which forms the wing surface, and the presence of a light yet strong skeleton with modified, elongated finger bones that support this wing membrane during flight.
g) Leadership, in the context of animal behaviour, refers to the tendency of certain socially living animals to follow a dominant individual of the group, the leader, who guides the group's movement, feeding and defence, thereby maintaining order and cooperation within the social group.
h) Analogous organs are organs that perform the same function but differ in their basic origin and structure. For example, the wings of a butterfly, a bird and a bat all serve the same function of flight, but they have entirely different structural origins in each group.
i) Frogs undergo hibernation during winter because, being cold-blooded (poikilothermic) animals, their body temperature falls with the surrounding temperature, slowing their metabolism to a point where they cannot remain active or find food. To survive the cold and food scarcity, they bury themselves in mud or find sheltered spots and become dormant until favourable warm conditions return.
j) The scientific name of the garden snail is Helix aspersa, and the scientific name of the tapeworm found in humans is Taenia solium.
Describe in brief of any five.
a) Describe the sporogony phase of life cycle of Plasmodium.
b) Draw a well labeled diagram of internal structure of heart of Frog. (No description required)
c) Describe the causes of wildlife extinction.
d) Enlist the functions of liver of Frog.
e) Describe Miller & Urey's experiment.
f) Explain draw-backs of theory of Natural Selection.
g) Mention the characteristic features of Class-Mammalia.
a) Sporogony is the sexual phase of the life cycle of Plasmodium that takes place in the body of the female Anopheles mosquito. When the mosquito bites an infected human, it takes up microgametocytes and macrogametocytes along with the blood meal. Inside the mosquito's stomach the microgametocyte nucleus divides to form six to eight flagellated microgametes by a process called exflagellation, and one microgamete fuses with the macrogamete through a structure called the cone of reception to form a zygote. The zygote, now called an ookinete, penetrates the stomach wall and forms a cyst called the oocyst on its outer surface. Inside the oocyst the nucleus divides repeatedly to produce thousands of thread-like sporozoites, and when the oocyst ruptures these sporozoites migrate to the salivary glands of the mosquito, from where they are injected into a healthy human during the next bite, thereby continuing the life cycle.
b) The internal structure of the heart of frog consists of a large, funnel-shaped sinus venosus opening into the right auricle, a left auricle receiving oxygenated blood from the lungs and skin, both auricles emptying into a single, thick-walled ventricle, and a conus arteriosus with a spiral valve leading into the truncus arteriosus, which divides into the carotid, systemic and pulmocutaneous arches.
c) Wildlife extinction is mainly caused by the destruction and fragmentation of natural habitats through deforestation, urbanisation and the expansion of agricultural land, which deprives animals of their shelter and food. Excessive hunting and poaching for meat, skin, horns and other body parts, uncontrolled use of pesticides and other pollutants, the introduction of invasive alien species that outcompete native wildlife, and large-scale climatic change all add further pressure that pushes vulnerable species towards extinction.
d) The liver of the frog performs several important functions: it secretes bile, which is stored in the gall bladder and helps in the emulsification and digestion of fats in the small intestine. It also stores glycogen and releases glucose into the blood as required, helping regulate blood sugar levels. The liver detoxifies harmful substances absorbed from the gut, and it also plays a role in the breakdown of old red blood cells and in the metabolism of proteins.
e) Miller and Urey designed an apparatus consisting of two connected glass chambers, one containing water that could be boiled to produce water vapour, and the other containing a mixture of gases, methane, ammonia and hydrogen, in the ratio 2:1:2, meant to simulate the primitive atmosphere of the earth. Electric sparks were continuously passed through this gas mixture to simulate lightning, and the whole apparatus was run continuously for about a week, with the products being condensed and collected in a trap. Chemical analysis of the collected material showed the presence of simple amino acids such as glycine, alanine and aspartic acid. This result led them to conclude that, under the conditions believed to exist on the primitive earth, electric discharges from lightning could bring about the spontaneous formation of amino acids and other simple organic compounds from inorganic gases, supporting the biochemical theory of the origin of life.
f) Darwin's theory of natural selection has several drawbacks. It fails to explain the actual causes of the variations on which natural selection acts, since Darwin was not aware of the mechanism of heredity or the existence of genes and mutations. Darwin also treated all variations, whether inherited or acquired during an individual's lifetime, as equally significant for evolution, whereas it is now known that only germinal (heritable) variations, and not somatic ones, are passed on to offspring. Furthermore, the theory explains only the survival of the fittest organisms once variation already exists, but it does not explain the arrival, that is, the origin, of the fittest variation in the first place.
g) Class Mammalia is characterised by the presence of hair covering the body, and by the presence of mammary glands in females that secrete milk to nourish the young. Mammals are typically warm-blooded (homeothermic) with a four-chambered heart, they have differentiated teeth (heterodont dentition) set in sockets, a muscular diaphragm that separates the thoracic and abdominal cavities and assists breathing, and, in most species, they give birth to live young (viviparous), which are cared for by the parents after birth.
Define conjugation. Describe its process in Paramecium with labeled diagram. [7.5]
Or,
What is digestion? Give an account on the digestive tract of Pheretima with suitable diagram.
Conjugation is a temporary, sexual method of reproduction found in ciliate protozoans such as Paramecium, in which two morphologically similar but physiologically distinct (opposite mating type) individuals unite briefly along their oral surfaces to exchange nuclear material, after which they separate and continue to multiply independently by binary fission.
In Paramecium, when two individuals of compatible mating types come together, they attach to each other along the region of their oral grooves and a cytoplasmic bridge forms between them. Within each conjugant, the diploid micronucleus first undergoes meiotic division to produce four haploid nuclei, of which three degenerate, leaving only one functional haploid nucleus in each partner. This surviving nucleus then divides once more, mitotically, to form two haploid pronuclei of unequal size in each conjugant, a larger, stationary female pronucleus and a smaller, migratory male pronucleus.
The two partners now exchange their migratory male pronuclei through the cytoplasmic bridge connecting them. In each conjugant, the migratory pronucleus received from the partner fuses with the resident stationary pronucleus, an event called karyogamy, to form a diploid synkaryon or zygote nucleus. Once this nuclear fusion is complete, the two individuals separate; they are now called exconjugants rather than conjugants.
Each exconjugant then undergoes further mitotic divisions of the synkaryon nucleus, ultimately regenerating a new macronucleus and micronucleus, and dividing by binary fission to restore the normal double set of nuclei. Because genetic material has been exchanged between two previously separate lineages, the resulting individuals show new combinations of hereditary characters that did not exist in the parents. Conjugation therefore does not, by itself, increase the number of individuals, since the exconjugants are simply rejuvenated versions of the original two cells, but it is highly significant as it brings about genetic recombination and restores the vigour of the cytoplasm and organelles, making the Paramecium population more efficient at future binary fission.
Or
Digestion is the biological process by which complex, insoluble food substances are broken down mechanically and chemically, with the help of digestive enzymes, into simple, soluble molecules that can be absorbed and used by the cells of the body.
The earthworm Pheretima possesses a straight, well-developed alimentary canal that runs from the mouth to the anus and is regionally differentiated to carry out digestion efficiently. The alimentary canal begins with the mouth, a crescentic opening at the anterior end, which leads into a short, muscular buccal cavity occupying the first one or two segments. This is followed by a thick, muscular pharynx, which acts as a pumping organ to suck in food particles and soil.
The pharynx continues as a short, narrow oesophagus occupying about segments 6 and 7. The oesophagus opens into a hard, thick-walled, muscular gizzard, lying in about segment 8, which grinds and crushes the ingested soil and organic matter with the help of swallowed sand particles, functioning much like a mechanical mill; the earthworm Pheretima has no crop. Behind the gizzard lies the stomach, extending through about segments 9 to 14, whose wall bears calciferous glands that secrete calcium carbonate to neutralise the excess humic acid present in the soil and organic matter ingested by the worm.
The ground food then passes into a long, straight intestine, which extends through the greater part of the body up to the last segment and is the main site of chemical digestion and absorption. The dorsal wall of the intestine is folded inward to form a ridge called the typhlosole, which increases the internal surface area available for the secretion of digestive enzymes and for the absorption of digested nutrients. The undigested residue finally passes into a short rectum and is expelled through the anus, a small, vertical, slit-like opening at the posterior end of the body.
Discuss the evolution of modern man from proconsul. [8]
The origin and evolution of modern man, Homo sapiens sapiens, is traced by anthropologists through a chain of fossil ancestors going back some 20 to 24 million years to a common ape-like ancestor of both modern apes and humans, generally...