NEB Class 12 · Past paper
The complete NEB Class 12 2079 exam paper for Biology, all 23 questions with solved model answers.
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In a monohybrid cross of two heterozygous parents (Rr), what would the expected genotypes of the offsprings be? A) 1 RR : 2 Rr : 1 rr B) 1 rr : 3 RR C) 3 Rr : 1 rr D) All Rr
Correct option: A) 1 RR : 2 Rr : 1 rr. A cross $Rr \times Rr$ gives the genotypic ratio $1,RR : 2,Rr : 1,rr$ (and the phenotypic ratio $3:1$).
Which of the following cells in an embryo sac degenerate after fertilization? A) Synergids and primary endosperm cell B) Synergids and antipodal cells C) Antipodal cells and primary endosperm cell D) Eggs and antipodal cells
Correct option: B) Synergids and antipodal cells. After fertilization the egg forms the zygote and the polar nuclei form the endosperm, while the synergids and antipodal cells degenerate as they have no further role.
Two cells P and Q are in contact but separated by a semi-permeable membrane. The osmotic pressure of cell P is 15 atm and that of Q 12 atm; the turgor pressure of cell P is 10 atm and that of Q is 6 atm. In which direction will water move more? A) From cell P to cell Q B) From cell Q to cell P C) There will be no movement of water D) Water can move either from P to Q or Q to P
Correct option: A) From cell P to cell Q. Water moves towards the cell with higher DPD (Diffusion Pressure Deficit = OP - TP). $$ \begin{aligned} DPDP &= 15 - 10 \ &= 5\ \text{atm} \ DPDQ &= 12 - 6 \ &= 6\ \text{atm} \end{aligned} $$ ...
Which one of the following parenchyma cells makes the aquatic plants light and helps in buoyancy? A) Prosenchyma B) Assimilatory parenchyma C) Aerenchyma D) Stellate parenchyma
Correct option: C) Aerenchyma. Aerenchyma has large air spaces that store air, making aquatic plants light and giving them buoyancy to float.
In an economically important plant species, embryo mortality is very high. What method do you suggest to check the mortality? A) Micropropagation B) Polyploid mutation C) Embryo culture D) Meristem culture
Correct option: C) Embryo culture. Excising the embryo and growing it in vitro on a nutrient medium (embryo culture / embryo rescue) prevents embryo abortion and raises viable plants.
'Meristem is also known as Juvenile tissue'. Justify. Explain the types of meristem on the basis of position. [1+3]
Justification: Meristem is called juvenile tissue because it is made of young, thin-walled, actively dividing cells that remain permanently youthful and undifferentiated, continuously producing new cells for growth. Types on the basis of...
What are the differences between transpiration and guttation? [4] (Or) Explain in brief about significance of polyploidy with examples.
Write the salient features of dicot embryo in reference to its development pattern with labelled diagrams. [2+2]
The dicot embryo develops from the zygote by the Onagrad (Crucifer) type pattern. The zygote divides transversely into a basal cell (towards micropyle) and a terminal cell. The basal cell forms the suspensor (pushes embryo into endosperm...
'Hybridisation is a modern breeding method for the development of crop plants with desired characters as well as hybrid vigour'. Justify this statement by describing various steps of hybridisation procedure in plants. [1+3]
Justification: Hybridisation crosses two genetically different parents so that desirable characters from both combine in the offspring, often producing hybrid vigour (heterosis) - superior yield, disease resistance and quality. Steps of ...
Mutation is important from the evolutionary point of view. Give reasons. How does gene mutation occur? Explain its types. [2+2+4] (Or) Why is Drosophila melanogaster selected for genetical study? 'The inheritance of sex-linked trait follows criss-cross pattern of inheritance'. Justify with special reference to eye colour of Drosophila. [3+5]
Importance in evolution: mutation is the ultimate source of new heritable variations and new alleles/genes; these variations, acted upon by natural selection, provide the raw material for evolution and the origin of new species.
How gene (point) mutation occurs: it results from a change in the base sequence of DNA - through substitution, addition or deletion of nucleotides - caused by mutagens (radiation, chemicals) or errors in replication, altering the codon and hence the protein.
Types of gene mutation:
(Or) Drosophila is selected because of its short life cycle, many offspring, easy culture, few (4 pairs) large chromosomes and clear mutant traits. For eye colour (X-linked), a red female × white male gives red F1 and a $3:1$ F2 with white only in males; the reciprocal cross passes the father's trait to daughters and the mother's to sons - criss-cross inheritance.
The source of oxygen in photosynthesis is the water but not the carbon dioxide. Explain with reasons. Briefly describe the Hill reaction. [2+6]
Source of $O2$: The oxygen released in photosynthesis comes from water, not carbon dioxide. This was proved by using water labelled with the heavy isotope $^{18}O$; the released oxygen was $^{18}O2$, showing it originated from the photol...
Which of the following tissues possess fat globules? A) Areolar tissue B) Adipose tissue C) Blood plasma D) Striped muscle
Correct option: B) Adipose tissue. Adipose tissue is a connective tissue whose cells (adipocytes) are filled with large fat globules, serving as a store of fat and an insulator.
What are the sequential steps involved in the process of gametogenesis? A) Multiplication, growth, maturation B) Multiplication, maturation, growth C) Growth, multiplication, maturation D) Maturation, growth, multiplication
Correct option: A) Multiplication, growth, maturation. Gametogenesis proceeds through the multiplication phase (mitosis of germ cells), the growth phase (enlargement), and the maturation phase (meiosis to form gametes).
When an organ transplantation occurs between two genetically identical individuals, what will be the type of transplantation? A) Autograft B) Allograft C) Heterograft D) Isograft
Correct option: D) Isograft. A graft between two genetically identical individuals (e.g. identical twins) is an isograft (syngeneic graft), which is not rejected.
Over population causes adverse consequences in the society. Highlight which of the following can control over population? A) Early marriage B) Polygamy C) Family planning D) Food supply
Correct option: C) Family planning. Family planning (spacing and limiting births using contraceptives) directly controls the birth rate and hence checks overpopulation.
In the middle ear of a human being there are three ear ossicles. Identify and select which of the following ear ossicles are arranged in correct sequence. A) Malleus, Incus, Stapes B) Malleus, Stapes, Incus C) Cochlea, Incus, Malleus D) Malleus, Incus, Saccule
Correct option: A) Malleus, Incus, Stapes. From the tympanic membrane inward the ear ossicles are arranged as malleus (hammer) → incus (anvil) → stapes (stirrup).
Pancreas is a gland having exocrine and endocrine functions. Its exocrine part is the pancreatic acini. What would be the endocrine part? A) Zona glomerulosa B) Islet of Langerhans C) Zona reticularis D) Adenohypophysis
Correct option: B) Islet of Langerhans. The islets of Langerhans are the endocrine part of the pancreas, secreting insulin and glucagon.
How would you elaborate the different types of simple epithelial tissues in animals? Support with diagrams. [3+1]
Simple epithelium is a single layer of cells resting on a basement membrane. Types: - Squamous (pavement) epithelium: flat, plate-like cells; for diffusion and filtration (alveoli, Bowman's capsule, blood vessels). - Cuboidal epithelium:...
Describe the process of oogenesis in animals with diagram. [3+1] (Or) Define the term in-vitro fertilization. Describe its process.
Oogenesis is the formation of the mature ovum in the ovary through three phases: - Multiplication phase: primordial germ cells divide by mitosis to form oogonia. - Growth phase: an oogonium enlarges by storing food (yolk) to become a pri...
Study the given diagram of V.S. of human eye and answer the following: a) Label A, B, C and D. b) Write one function each of the parts labelled. [2+2]
Based on the standard V.S. of the human eye, the labelled parts and their functions are: - Cornea: transparent front layer that refracts and admits light. - Lens: biconvex, focuses light rays onto the retina (accommodation). - Retina: in...
Kidneys are the organs which filter the blood to remove the wastes and keep the electrolyte in balance. If the kidneys do not function normally, various renal disorders are observed. Highlight any two common renal disorders in human beings. [4]
Two common renal disorders: - Kidney (renal) stones (renal calculi): hard crystals of calcium oxalate/phosphate or uric acid that form in the kidney or urinary tract, causing severe pain, blood in urine and obstruction of urine flow. - R...
Explain cholera as an acute diarrhoeal disease. Discuss its causative agent, mode of transmission and symptoms. Mention its control measures. [1+1+2+2+2]
Cholera is an acute diarrhoeal (waterborne) bacterial disease of the small intestine that can cause severe dehydration and death within hours if untreated.
Draw a labelled diagram of the alimentary canal of a human being. How would you explain the digestion of proteins in gut? Justify the relationship between amylase and lipase enzymes in digestion of food. [3+4+1] (Or) Justify the statement 'sino-auricular node is a natural pacemaker'. What would you suggest if the natural pacemaker does not function normally? How do you test blood grouping in human beings? [3+2+3]
Digestion of proteins in the gut: Protein digestion begins in the stomach, where HCl activates pepsinogen to pepsin, which breaks proteins into peptones and proteoses. In the small intestine (duodenum), pancreatic trypsin and chymotrypsi...
Correct option: A) 1 RR : 2 Rr : 1 rr. A cross gives the genotypic ratio (and the phenotypic ratio ).
Correct option: A) From cell P to cell Q. Water moves towards the cell with higher DPD (Diffusion Pressure Deficit = OP - TP). ...
Importance in evolution: mutation is the ultimate source of new heritable variations and new alleles/genes; these variations, acted upon by natural selection, provide the raw material for evolution and the origin of new species.
How gene (point) mutation occurs: it results from a change in the base sequence of DNA - through substitution, addition or deletion of nucleotides - caused by mutagens (radiation, chemicals) or errors in replication, altering the codon and hence the protein.
Types of gene mutation:
(Or) Drosophila is selected because of its short life cycle, many offspring, easy culture, few (4 pairs) large chromosomes and clear mutant traits. For eye colour (X-linked), a red female × white male gives red F1 and a F2 with white only in males; the reciprocal cross passes the father's trait to daughters and the mother's to sons - criss-cross inheritance.
Source of : The oxygen released in photosynthesis comes from water, not carbon dioxide. This was proved by using water labelled with the heavy isotope ; the released oxygen was , showing it originated from the photol...