NEB Class 12 · Past paper
The complete NEB Class 12 2076 exam paper for Biology, all 38 questions with solved model answers.
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What is the major product of C3 cycle?
The first stable product of the $C3$ (Calvin) cycle is the 3-carbon compound 3-phosphoglyceric acid (3-PGA); the cycle ultimately yields carbohydrate (glucose).
What do you mean by master strand?
The master (template) strand is the DNA strand (read $3'\to5'$) that acts as the template for the synthesis of a complementary mRNA/new DNA strand.
Write the name of purine bases.
The purine bases of nucleic acids are Adenine (A) and Guanine (G).
What do you mean by scion and stock?
In grafting, the scion is the short detached shoot or bud of the desired plant that is grafted onto the stock, the rooted lower portion that supplies water and minerals.
Define biofertilizer.
A biofertilizer is a preparation of living microorganisms (e.g. Rhizobium, Azolla-cyanobacteria, mycorrhizae) that enrich soil fertility by fixing nitrogen or mobilising nutrients.
Define tissue.
A tissue is a group of similar or dissimilar cells having a common origin and performing a specific function together.
What is callus culture?
Callus culture is the in vitro culture of an undifferentiated mass of dividing cells (callus) grown from an explant on a nutrient medium in plant tissue culture.
Define megasporogenesis.
Megasporogenesis is the formation of haploid megaspores from a diploid megaspore mother cell by meiosis inside the ovule.
What do you mean by chiropterophily?
Chiropterophily is pollination brought about by bats.
Define turgor pressure.
Turgor pressure is the pressure exerted by the cell contents (water) against the cell wall when the cell absorbs water and becomes turgid.
Significances of respiration.
Respiration releases energy (ATP) from food for all life activities, provides intermediate compounds for the synthesis of proteins, fats and other biomolecules, maintains cellular metabolism, and helps release stored chemical energy in a...
Describe the tunica and corpus theory.
Proposed by Schmidt, this theory describes the shoot apex as having two zones: the tunica, the outer one or more layers dividing only by anticlinal divisions (surface growth, forming epidermis), and the corpus, the inner mass of cells di...
Structure of RNA.
RNA is usually a single-stranded polynucleotide chain. Each nucleotide has the pentose sugar ribose, a phosphate group, and one of the nitrogen bases adenine, guanine, cytosine or uracil (uracil replaces thymine). The three main types ar...
Mechanism of crossing over.
During pachytene of meiosis-I, homologous chromosomes pair (synapsis) forming bivalents. Non-sister chromatids come in contact at points called chiasmata, break at corresponding points, and exchange equal segments with the help of the en...
Application of plant tissue culture.
Plant tissue culture is used for rapid clonal multiplication (micropropagation), production of disease-free (virus-free) plants, raising haploids by anther culture, somatic hybridisation, production of secondary metabolites, and germplas...
Process of male gametogenesis.
In the anther, diploid microspore mother cells undergo meiosis (microsporogenesis) to form haploid microspores (pollen grains). Each microspore nucleus then divides mitotically into a generative cell and a vegetative (tube) cell; the gen...
Describe the co-dominance with suitable example.
Codominance is the phenomenon in which both alleles of a heterozygote express themselves fully and independently, so both phenotypes appear together. Example: in human ABO blood groups, the genotype $I^A I^B$ produces AB blood group, exp...
Describe the anatomical structure of dicot root and compare it with monocot root. (Or) Describe an experiment to demonstrate light is necessary for the process of photosynthesis with clean diagram.
T.S. of a dicot root shows: piliferous (epiblema) layer with root hairs, wide cortex of parenchyma, a single-layered endodermis with Casparian strips, pericycle, radial vascular bundles with 2-4 (di- to tetrarch) xylem groups, a small ce...
What is DNA? Describe the process of semi conservative method of DNA replication with good diagrams.
DNA (Deoxyribonucleic acid) is the hereditary material, a double helix of two antiparallel polynucleotide strands held by hydrogen bonds between complementary bases (A-T, G-C), with a sugar-phosphate backbone (Watson-Crick model).
Semi-conservative replication:
Name the place where actual exchange of gases takes place inside the lung.
The actual exchange of gases takes place in the alveoli (air sacs) of the lungs.
What is double circulation?
Double circulation is the type of circulation in which blood passes through the heart twice in one complete cycle - once as pulmonary circulation (heart-lungs-heart) and once as systemic circulation (heart-body-heart).
Which hormone controls osmoregulation?
Antidiuretic hormone (ADH / vasopressin) from the posterior pituitary controls osmoregulation by regulating water reabsorption in the kidney tubules.
Define nerve impulse.
A nerve impulse is the electrochemical signal (wave of depolarisation) that travels along the membrane of a neuron to transmit information.
What is vaccine? Name their types.
A vaccine is a preparation of antigen (weakened, killed or part of a pathogen) that stimulates active immunity. Types: live attenuated, killed/inactivated, toxoid, and subunit/recombinant vaccines.
Give limitations of organ transplantation.
Limitations include immunological rejection of the graft, scarcity of compatible donors, high cost, risk of infection, and the need for lifelong immunosuppressant drugs.
What is a fingerling?
A fingerling is a young juvenile fish about the size of a finger, used to stock ponds in fish culture.
What are pullets?
Pullets are young female domestic hens (below about one year) that are just beginning to lay eggs.
Why do drug addicts suffer from AIDS?
Injecting drug addicts often share contaminated needles and syringes carrying HIV, so the virus is transmitted directly into the blood, causing AIDS.
Hepatitis is more dangerous than AIDS, why?
The Hepatitis B virus is far more infectious than HIV - it is present in higher concentration in body fluids, survives longer outside the body and is more resistant, so it spreads much more easily through the same routes.
Cardiac muscle.
Cardiac muscle forms the wall (myocardium) of the heart. Its fibres are branched, uninucleate, striated and involuntary, joined end to end by intercalated discs that allow rapid conduction of impulses. It contracts rhythmically and tirel...
The process of neurulation.
Neurulation is the formation of the neural tube from ectoderm after gastrulation. The dorsal ectoderm thickens to form the neural plate, its edges rise as neural folds enclosing a neural groove, and the folds meet and fuse into the neura...
The role of vitamins.
Vitamins are organic micronutrients required in small amounts. They act mainly as coenzymes/regulators of metabolism, maintain health and immunity, and prevent deficiency diseases (e.g. vitamin A for vision, C for scurvy prevention, D fo...
The role of bile in the fat digestion.
Bile (from the liver) contains bile salts that emulsify large fat globules into tiny droplets, greatly increasing the surface area for the enzyme lipase to act. Bile is alkaline, neutralises acidic chyme, and its salts also aid absorptio...
Distinguish between endocrine and exocrine glands.
The role of mother in a test tube baby.
In in vitro fertilization (test-tube baby), the mother provides the ova (retrieved after hormonal stimulation) that are fertilised outside the body; she then receives the developing embryo implanted into her uterus, where it is carried t...
Population growth curbs.
Population growth can be curbed by family planning and use of contraceptives, raising the age of marriage, education (especially of women), incentives for small families, women empowerment and employment, and public awareness about the c...
Describe the structure and functions of different parts of human brain. (Or) Give an account of the process of urine formation in human being.
The human brain has three main regions: - Forebrain: the large cerebrum controls thinking, memory, intelligence and voluntary actions; the thalamus relays sensory impulses; the hypothalamus controls temperature, hunger, thirst and links ...
What is addiction? Discuss the symptoms, effects and control measures of alcohol addiction in detail.
Addiction is a compulsive, uncontrollable dependence on a substance despite its harmful effects, marked by tolerance and withdrawal symptoms.
Symptoms of alcohol addiction: strong craving, inability to control drinking, increased tolerance, neglect of work and family, tremors, anxiety and withdrawal symptoms (sweating, nausea) when not drinking.
Effects: liver damage (cirrhosis, fatty liver), gastritis and ulcers, high blood pressure and heart disease, damage to the brain and nerves (memory loss, poor coordination), malnutrition, and social problems such as accidents, violence, broken families and loss of job.
Control measures: counselling and de-addiction/rehabilitation centres, medical treatment and detoxification, family and community support, health education and awareness, legal control on sale, and encouraging healthy alternatives and willpower.
The first stable product of the (Calvin) cycle is the 3-carbon compound 3-phosphoglyceric acid (3-PGA); the cycle ultimately yields carbohydrate (glucose).
The master (template) strand is the DNA strand (read ) that acts as the template for the synthesis of a complementary mRNA/new DNA strand.
Codominance is the phenomenon in which both alleles of a heterozygote express themselves fully and independently, so both phenotypes appear together. Example: in human ABO blood groups, the genotype produces AB blood group, exp...
DNA (Deoxyribonucleic acid) is the hereditary material, a double helix of two antiparallel polynucleotide strands held by hydrogen bonds between complementary bases (A-T, G-C), with a sugar-phosphate backbone (Watson-Crick model).
Semi-conservative replication: