NEB Class 12 · Past paper
The complete NEB Class 12 2078 exam paper for Biology, all 38 questions with solved model answers.
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Define apical meristem.
Apical meristem is the meristematic tissue located at the tips of roots and shoots that brings about primary growth (increase in length) of the plant.
What is osmosis?
Osmosis is the movement of solvent (water) molecules through a semipermeable membrane from a region of lower solute concentration (higher water potential) to a region of higher solute concentration.
Write two plant hormone.
Auxin (IAA) and Gibberellin (GA).
State about hybridization.
Hybridization is the crossing of two genetically dissimilar plants (varieties/species) to combine desired characters and produce a hybrid offspring with improved traits.
What is phenotype?
Phenotype is the observable morphological, physiological and behavioural characters of an organism, resulting from the interaction of its genotype with the environment (e.g. tall, red flower).
Define rhizome.
A rhizome is an underground, horizontally growing modified stem with nodes, internodes and scale leaves that stores food and serves in vegetative propagation (e.g. ginger).
What does it mean by pollen grains?
Pollen grains are the microspores / immature male gametophytes of seed plants, produced in the anther and carrying the male gametes.
Mention about entomophilly.
Entomophily is pollination brought about by insects (bees, butterflies); such flowers are usually large, coloured, scented and produce nectar.
Elaborate biotechnology.
Biotechnology is the use of living organisms, cells or their systems/enzymes in controlled processes to produce useful products or services (e.g. genetic engineering, tissue culture, fermentation).
Illustrate biofertilizer.
A biofertilizer is a product containing living microorganisms (e.g. Rhizobium, blue-green algae, Azolla, mycorrhiza) that enrich the soil by fixing nitrogen or making nutrients available to plants.
Structure and function of aerenchyma.
Aerenchyma is a type of parenchyma with large, interconnected air spaces (air chambers) between the cells, found in aquatic and marshy plants. Function: it stores air, provides buoyancy to keep the plant afloat, and facilitates exchange ...
Types of vascular bundles.
Vascular bundles are of the following types: - Radial: xylem and phloem on separate radii (roots). - Conjoint: xylem and phloem on the same radius. It may be collateral (phloem outside xylem), bicollateral (phloem on both sides), open (w...
Reasons for choosing pea plant in Mendel's experiment.
Mendel selected the garden pea because it has clear contrasting traits, is naturally self-pollinating but easily cross-pollinated, has a short life cycle with many seeds, and produces fertile, pure-breeding hybrids, making inheritance ea...
Crossing over and its importance.
Crossing over is the exchange of segments between non-sister chromatids of homologous chromosomes at chiasmata during pachytene of meiosis-I. Importance: it produces new combinations of genes (recombination), increases genetic variation,...
Difference between incomplete dominance and codominance.
Fertilization in angiosperms.
In angiosperms double fertilization occurs. The pollen tube carries two male gametes into the embryo sac: one male gamete fuses with the egg (syngamy) to form the diploid zygote, and the other fuses with the two polar nuclei (triple fusi...
Importance of fermentation technology.
Fermentation technology is important for the industrial production of alcohol and beverages, antibiotics (penicillin), organic acids, enzymes, vitamins, single-cell protein, and dairy products (curd, cheese), and in sewage and waste trea...
Compare the anatomical structure of dicot and monocot leaf with neat and clean diagram. (Or) What is transpiration? Describe an experiment to show the transpiration by bell jar method.
Dicot (dorsiventral) leaf: has differentiated mesophyll into upper palisade and lower spongy parenchyma; stomata mainly on the lower surface; vascular bundles of different sizes. Monocot (isobilateral) leaf: mesophyll is not differentiat...
Define sex-linked inheritance and discuss it with special reference to eye colour of fruit fly (Drosophila melanogaster).
Sex-linked inheritance is the transmission of characters controlled by genes located on the sex chromosomes (mainly X), so their inheritance is associated with the sex of the offspring.
In Drosophila, the gene for eye colour is on the X chromosome; red (W) is dominant over white (w).
Name the muscle present in the dark band of skeletal muscle.
The dark band (A-band / anisotropic band) of a skeletal muscle fibre is formed by the thick myosin protein filaments.
Define Neurulation.
Neurulation is the process of formation of the neural tube from the dorsal ectoderm (neural plate) of the developing embryo, giving rise to the brain and spinal cord.
What is the role of Sodium in body?
Sodium ions ($Na^+$) help in the generation and conduction of nerve impulses, muscle contraction, maintenance of osmotic balance and fluid volume, and acid-base balance of the body.
What do you mean by cardiac output?
Cardiac output is the volume of blood pumped out by each ventricle of the heart per minute; it equals stroke volume × heart rate (about 5 litres/min at rest).
What is meant by sensory nerves?
Sensory (afferent) nerves are nerves that carry impulses from receptors/sense organs towards the central nervous system (brain and spinal cord).
What is meant by faeco-oral disease?
A faeco-oral disease is one transmitted when pathogens from the faeces of an infected person contaminate food or water and are then ingested by another person (e.g. cholera, typhoid).
Write the Zoological name of sand fly that transmits Kalazar.
Phlebotomus argentipes is the sand fly that transmits Kalazar (visceral leishmaniasis).
What is Heterograft used for?
A heterograft (xenograft) is a graft between two different species and is used mainly as a temporary covering, e.g. skin grafts for burns and pig heart valves for humans.
Give two examples of second generation vaccines.
Recombinant Hepatitis B vaccine and acellular (subunit) pertussis vaccine are examples of second-generation (subunit/recombinant) vaccines.
What is meant by layers and broilers in poultry farming?
Layers are hens reared specially for egg production, whereas broilers are fast-growing birds reared for meat production.
Write short note on cartilage.
Cartilage is a firm but flexible skeletal (connective) tissue whose cells, called chondrocytes, lie in fluid-filled spaces (lacunae) embedded in a tough matrix of chondrin. It supports and cushions structures, reduces friction at joints, and is found in the pinna, nose tip, larynx, trachea and between vertebrae.
Discuss the process of coelom formation in frog.
In the frog the coelom (body cavity) forms by schizocoely. During gastrulation the mesoderm forms between the ectoderm and endoderm; this mesoderm then splits into two layers - an outer somatic (parietal) layer and an inner splanchnic (v...
Discuss role of Rhesus factor during pregnancy.
If an Rh-negative mother carries an Rh-positive foetus, foetal Rh antigens entering the mother's blood (usually at first delivery) make her produce anti-Rh antibodies. In a subsequent Rh-positive pregnancy these antibodies cross the plac...
Write down the mechanism of hearing in human beings.
Sound waves collected by the pinna pass through the auditory canal and vibrate the tympanic membrane. The vibrations are amplified by the ear ossicles (malleus, incus, stapes) and transmitted through the oval window to the fluid (perilym...
Discuss mode of transmission of Tuberculosis.
Tuberculosis, caused by Mycobacterium tuberculosis, spreads mainly through the air (droplet infection) - when an infected person coughs, sneezes or spits, bacteria-laden droplets are inhaled by others. It may also spread through contamin...
Illustrate the advantages of organ and tissue transplantation.
Transplantation replaces a diseased, damaged or non-functional organ/tissue with a healthy one, thereby saving or prolonging life (kidney, heart, liver), restoring lost function (cornea for sight), reducing dependence on treatments like ...
Discuss consequences of over population.
Overpopulation leads to shortage of food, water, housing and jobs, overexploitation and depletion of natural resources, environmental pollution and deforestation, poverty, unemployment, poor health and sanitation, and increased social pr...
Describe the structure of uriniferous tubule with labeled diagram. (Or) Describe physiology of digestion in human being.
The uriniferous tubule (nephron) is the structural and functional unit of the kidney. It consists of:
(Or) Physiology of digestion: starch is digested by amylase (mouth, pancreas), proteins by pepsin (stomach) and trypsin (pancreas), and fats emulsified by bile and digested by lipase, giving amino acids, glucose and fatty acids that are absorbed by intestinal villi.
Describe various aspects of any one non communicable disease you have studied.
Diabetes mellitus is a non-communicable metabolic disorder.
(Other acceptable examples: hypertension, cancer, coronary heart disease.)
Sex-linked inheritance is the transmission of characters controlled by genes located on the sex chromosomes (mainly X), so their inheritance is associated with the sex of the offspring.
In Drosophila, the gene for eye colour is on the X chromosome; red (W) is dominant over white (w).
Sodium ions () help in the generation and conduction of nerve impulses, muscle contraction, maintenance of osmotic balance and fluid volume, and acid-base balance of the body.