NEB Class 11 · Past paper
The complete NEB Class 11 2073 exam paper for Biology, all 8 questions with solved model answers.
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Answer in short on any seven.
a) Define prokaryotic cell.
b) How do you identify cell plate?
c) What does it mean by cell inclusions?
d) Define mycota.
e) What is heterocyst?
f) Mention about sori.
g) State about cruciform corolla.
h) What do you mean by grazing food chain?
i) Define scavenging. j) Illustrate nitrogen assimilation.
a) A prokaryotic cell is a cell in which the genetic material is not enclosed by a definite nuclear membrane and true, organised nucleus, and which also lacks membrane-bound cell organelles. Bacteria and cyanobacteria are examples of org...
Describe in brief on any five.
a) Biological role of protein.
b) Structure and function of mitochondria.
c) Process of crossing over.
d) Economic importance of bacteria.
e) Male cone of Pinus.
f) Structure and economic importance of virus.
g) Importance of mountain ecosystem.
a) Proteins play a central biological role in living organisms: they act as the building blocks of protoplasm and are needed for the growth, repair and maintenance of body tissues. Many proteins function as enzymes, catalysing almost all...
Describe the structure and reproduction of Spirogyra with necessary diagrams. [7.5]
OR
Describe the family Gramineae in semitechnical terms with identifying characters, floral diagram and floral formula with two examples of economic value.
Spirogyra, commonly known as pond silk or water silk, is a filamentous green alga belonging to the class Chlorophyceae, found floating in fresh water bodies such as ponds, lakes and slow streams. The plant body is an unbranched filament ...
What is ecosystem? Describe in detail about the pond ecosystem. [8]
An ecosystem is a self-sustaining functional unit of nature in which the living organisms of a given area interact among themselves and with the non-living components of their environment, resulting in a continuous flow of energy and cycling of nutrients between them. A pond is a small, self-contained, freshwater ecosystem and provides a convenient example to study the interaction between abiotic and biotic components in nature.
Abiotic component of a pond
The abiotic component of a pond ecosystem includes the water itself along with the dissolved gases such as oxygen and carbon dioxide, dissolved mineral nutrients like nitrates and phosphates, the soil or mud at the bottom, and physical factors such as light, temperature and the depth of water, all of which influence the distribution and activity of the pond organisms.
Biotic component of a pond
The biotic component consists of producers, consumers and decomposers. The producers are the floating and submerged algae, phytoplankton, and aquatic plants such as Hydrilla and water lily, which use sunlight to photosynthesise and form the base of the food chain. Primary consumers are the herbivorous zooplankton, small crustaceans and tadpoles that feed directly on the producers. Secondary consumers are small carnivorous fish, frogs and aquatic insects that feed on the primary consumers, while tertiary consumers include larger fish and water birds that feed on the secondary consumers. Decomposers, mainly bacteria and fungi present in the mud at the bottom of the pond, break down the dead remains of plants and animals and the excretory wastes into simple inorganic substances, releasing nutrients back into the water for reuse by the producers.
Functioning of the pond ecosystem
In a pond, solar energy captured by the producers flows in one direction through the successive trophic levels of consumers, being lost as heat at each step, while nutrients such as nitrogen and phosphorus are continuously recycled between the biotic and abiotic components through the activity of decomposers. This constant flow of energy and cycling of matter, along with the checks provided by predator-prey relationships, keeps the pond ecosystem in a state of dynamic equilibrium as long as it is not overly disturbed by pollution or other external stress.
Answer in short on any seven.
a) Write the meaning of Anatomy and Morphology.
b) Mention one important scope of zoology.
c) Who is the pioneer of Biogenesis?
d) What are fossils?
e) What is the common name of Paramecium?
f) What are homologous organs?
g) When are copulatory pads developed in Frog?
h) What is anadromous migration? Give example.
i) What do you mean by pollution? j) Give two examples of endangered species of Nepal.
a) Anatomy is the branch of biology that deals with the study of the internal structure of an organism revealed through dissection, while morphology is the branch that deals with the study of the external form, shape and structure of an ...
Answer in brief on any five.
a) Describe Miller Urey experiment on origin of life.
b) Give general characters of Phylum Porifera.
c) Describe liver schizogony of Plasmodium.
d) Discuss cocoon formation and structure in Earthworm.
e) Describe mechanism of breathing in Frog.
f) Explain the control of air pollution.
g) Discuss the importance of wild life.
a) Miller and Urey built an apparatus with two connected glass chambers, one holding water that could be boiled to produce vapour and the other containing a mixture of methane, ammonia and hydrogen gas in the ratio 2:1:2, intended to sim...
Describe typical nephridia of Earthworm with labeled diagram. [7.5]
OR
Describe the structure and working mechanism of heart of frog with labeled diagram.
Nephridia are the excretory organs of the earthworm Pheretima, coiled tubular structures found in large numbers throughout the length of the body, which remove nitrogenous metabolic wastes from the coelomic fluid and blood and expel them to the exterior. On the basis of their position and structure, nephridia in the earthworm are of three main types: septal nephridia, integumentary nephridia and pharyngeal nephridia; the septal nephridia, attached in rows to the septa (partitions) from about the fifteenth segment onward, are considered the typical nephridia.
A typical (septal) nephridium is a highly coiled tube divisible into three parts. It begins with a ciliated, funnel-shaped opening called the nephrostome, which projects into the coelomic cavity of the segment in front of the septum on which the nephridium is attached and collects coelomic fluid by the beating of its cilia. The nephrostome leads into a narrow, ciliated tube that passes through the septum and becomes greatly coiled, forming three successive coiled loops of differing diameter, through which the fluid is conducted and useful substances such as water, salts and glucose are gradually reabsorbed back into the surrounding blood capillaries, while nitrogenous wastes remain concentrated in the fluid.
The nephridial tube is closely accompanied by a fine network of blood capillaries, allowing an exchange of substances between the blood and the fluid inside the nephridium as it passes along the coiled loops. The coiled tube finally straightens out into a short, wider terminal duct that opens to the exterior through a minute pore called the nephridiopore, situated on the ventro-lateral surface of the body, through which the concentrated waste fluid is discharged. In this way, each typical nephridium filters coelomic fluid, reabsorbs useful materials, and eliminates only the nitrogenous excretory wastes, functioning much like an individual excretory unit analogous to the nephron of a vertebrate kidney.
OR
The heart of the frog is a three-chambered organ, lying in the pericardial cavity within the anterior part of the body, and consists of two thin-walled auricles (atria) and a single, thick-walled, muscular ventricle. Blood enters the heart through a large, funnel-shaped sinus venosus, which opens into the right auricle, while the left auricle receives oxygenated blood returning from the lungs and skin. Both auricles open into the single ventricle through a common auriculo-ventricular opening, and leading away from the ventricle is a curved, muscular tube called the conus arteriosus, which further continues into the truncus arteriosus; this in turn divides into two aortic trunks, each of which branches into three arches, the carotid arch (supplying the head), the systemic arch (supplying the rest of the body) and the pulmocutaneous arch (supplying the lungs and skin).
In its working mechanism, deoxygenated blood collected from the body through the sinus venosus enters the right auricle, while oxygenated blood from the lungs and skin enters the left auricle through the pulmonary veins. Both auricles contract almost simultaneously and empty their blood into the single ventricle; because the ventricle is undivided, some mixing of oxygenated and deoxygenated blood does occur inside it, though spiral folds (a spiral valve) within the conus arteriosus help to direct the more deoxygenated blood preferentially towards the pulmocutaneous arch (to the lungs and skin for oxygenation) and the more oxygenated blood preferentially towards the carotid and systemic arches (to the head and body). The ventricle then contracts forcefully, driving blood out through the conus and truncus arteriosus into the three pairs of arches, completing the circulation. This arrangement, though it permits some mixing of oxygenated and deoxygenated blood, is well suited to the frog's amphibious life and its dependence on cutaneous respiration in addition to its lungs.
Describe the Theory of Inheritance of Acquired characters with its draw back. [8]
The Theory of Inheritance of Acquired Characters, also known as Lamarckism, was put forward by the French naturalist Jean Baptiste Lamarck in 1809 in his book Zoological Philosophy. Lamarck based his theory on the observation that changing environmental conditions bring about corresponding changes in the structure and habits of organisms, and he explained the mechanism of evolution through four main conclusions.
His first conclusion was the tendency to grow: Lamarck believed that an internal vital force within every organism tends to increase the size of the body and its various parts, up to a certain limit fixed by the organism itself. His second conclusion concerned the formation of new organs: according to Lamarck, whenever an animal feels a new need or want because of a change in its environment, an internal effort towards satisfying that need leads to the production of a new organ suited to that purpose.
The third and most well-known part of the theory is the principle of use and disuse of organs. Lamarck proposed that an organ that is used continuously and vigorously becomes more developed, stronger and better adapted to its function over time, while an organ that remains unused for a long period gradually becomes weaker, reduced and may eventually disappear altogether. He illustrated this with the classic example of the giraffe: he suggested that ancestral giraffes with short necks had to stretch their necks continuously to reach leaves on tall trees, and that this constant stretching, generation after generation, gradually lengthened the neck to its present long form.
The fourth and central conclusion, from which the theory takes its name, is the inheritance of acquired characters. Lamarck held that characteristics acquired by an organism during its own lifetime, as a direct or indirect result of its interaction with the environment, such as the lengthened neck of the giraffe brought about by use, are passed on and inherited by its offspring, so that such changes accumulate over successive generations and eventually give rise to a new species.
Drawbacks of Lamarckism
Lamarckism suffers from several serious objections. Modern genetics has established that only heritable changes in the genetic material, such as mutations, are passed on to offspring, and that characters acquired by an organism during its lifetime through use, disuse or environmental influence do not alter the germ cells and are therefore not inherited at all. In fact, the continuous and excessive use of an organ, such as the eyes, often leads to strain and defects rather than to improvement, which directly contradicts the theory's principle of use and disuse. The strongest opposition to Lamarckism came from August Weismann, who through his experiments on the inheritance of the germplasm (notably by cutting off the tails of mice for many successive generations without any corresponding shortening appearing in their offspring) showed that changes to the body (somatoplasm) cannot influence the hereditary material (germplasm). Furthermore, Lamarckism may account for how an existing character becomes more pronounced or modified through use, but it fails to explain how a completely new character or organ could have originated in the first place.