These essential MCQ questions are selected from the most important topics in CBSE Class 12 Biology 2026 as per the latest NCERT syllabus. Sections include Reproduction in Organisms, Genetics & Evolution, Human Health & Disease, Biotechnology & its Applications, and Ecology & Environment. For truly unlimited daily MCQ practice, visit Vooo AI Education.
🧬 CBSE Class 12 Biology
1The term used for transfer of pollen from anther to stigma of another flower of the same plant is:
Answer: B — Geitonogamy
Geitonogamy is transfer of pollen from the anther to the stigma of a different flower on the same plant. It is functionally equivalent to self-pollination genetically. Autogamy is transfer of pollen to the stigma of the same flower. Xenogamy (cross-pollination) is transfer of pollen to a flower on a different plant of the same species — it brings genetic variation. Geitonogamy requires a pollinating agent.
Geitonogamy is transfer of pollen from the anther to the stigma of a different flower on the same plant. It is functionally equivalent to self-pollination genetically. Autogamy is transfer of pollen to the stigma of the same flower. Xenogamy (cross-pollination) is transfer of pollen to a flower on a different plant of the same species — it brings genetic variation. Geitonogamy requires a pollinating agent.
2In a dihybrid cross between RRYY and rryy, the phenotypic ratio in F₂ generation is:
Answer: A — 9:3:3:1
In a dihybrid cross (RRYY × rryy), the F1 is RrYy. F2 phenotypic ratio = 9 (R_Y_) : 3 (R_yy) : 3 (rrY_) : 1 (rryy) = 9:3:3:1. This demonstrates Mendel's Law of Independent Assortment — genes for different traits assort independently during gamete formation. This ratio only holds when genes are on different (non-homologous) chromosomes and show complete dominance.
In a dihybrid cross (RRYY × rryy), the F1 is RrYy. F2 phenotypic ratio = 9 (R_Y_) : 3 (R_yy) : 3 (rrY_) : 1 (rryy) = 9:3:3:1. This demonstrates Mendel's Law of Independent Assortment — genes for different traits assort independently during gamete formation. This ratio only holds when genes are on different (non-homologous) chromosomes and show complete dominance.
3Which enzyme is used to cut DNA at specific sequences in recombinant DNA technology?
Answer: C — Restriction endonuclease
Restriction endonucleases (restriction enzymes) are the molecular scissors of genetic engineering. They recognise specific palindromic sequences in DNA and cut both strands, producing either blunt ends or sticky ends. EcoRI, HindIII, and BamHI are common examples. DNA ligase acts as the molecular glue to join DNA fragments. These enzymes were first discovered in bacteria where they help defend against viral DNA.
Restriction endonucleases (restriction enzymes) are the molecular scissors of genetic engineering. They recognise specific palindromic sequences in DNA and cut both strands, producing either blunt ends or sticky ends. EcoRI, HindIII, and BamHI are common examples. DNA ligase acts as the molecular glue to join DNA fragments. These enzymes were first discovered in bacteria where they help defend against viral DNA.
4Which of the following is a vector-borne disease?
Answer: B — Malaria
Malaria is caused by Plasmodium (a protozoan) and transmitted by the bite of infected female Anopheles mosquito — making it vector-borne. Tuberculosis is caused by Mycobacterium tuberculosis (airborne). Cholera is caused by Vibrio cholerae (waterborne). Typhoid is caused by Salmonella typhi (food/waterborne). The female Anopheles is the vector; Plasmodium vivax, P. falciparum cause different types of malaria. P. falciparum causes the most severe form.
Malaria is caused by Plasmodium (a protozoan) and transmitted by the bite of infected female Anopheles mosquito — making it vector-borne. Tuberculosis is caused by Mycobacterium tuberculosis (airborne). Cholera is caused by Vibrio cholerae (waterborne). Typhoid is caused by Salmonella typhi (food/waterborne). The female Anopheles is the vector; Plasmodium vivax, P. falciparum cause different types of malaria. P. falciparum causes the most severe form.
5The full form of PCR used in biotechnology is:
Answer: B — Polymerase Chain Reaction
PCR (Polymerase Chain Reaction) is a technique to amplify (make many copies of) a specific DNA sequence in vitro. It uses a thermostable DNA polymerase (Taq polymerase), primers, dNTPs, and template DNA. Three steps: denaturation (94°C), annealing (50-65°C), and extension (72°C). PCR is used in forensics, disease diagnosis, research, and paternity testing. It can amplify DNA from a single cell to millions of copies.
PCR (Polymerase Chain Reaction) is a technique to amplify (make many copies of) a specific DNA sequence in vitro. It uses a thermostable DNA polymerase (Taq polymerase), primers, dNTPs, and template DNA. Three steps: denaturation (94°C), annealing (50-65°C), and extension (72°C). PCR is used in forensics, disease diagnosis, research, and paternity testing. It can amplify DNA from a single cell to millions of copies.
6Which level of biodiversity is measured by counting the number of species in a given area?
Answer: B — Species diversity
Biodiversity is measured at three levels: genetic diversity (variation within a species), species diversity (variety of species in an area — measured by species richness), and ecosystem diversity (variety of ecosystems/habitats). The term 'biodiversity' was popularised by sociobiologist Edward Wilson. India is a mega-diversity country. Hotspots of biodiversity are areas with high species richness and high levels of endemism facing habitat loss.
Biodiversity is measured at three levels: genetic diversity (variation within a species), species diversity (variety of species in an area — measured by species richness), and ecosystem diversity (variety of ecosystems/habitats). The term 'biodiversity' was popularised by sociobiologist Edward Wilson. India is a mega-diversity country. Hotspots of biodiversity are areas with high species richness and high levels of endemism facing habitat loss.
7Ozone (O₃) in the stratosphere absorbs which harmful radiation from the Sun?
Answer: B — Ultraviolet radiation
The ozone layer in the stratosphere (15–35 km altitude) absorbs harmful UV-B and UV-C radiation from the Sun. Depletion of ozone is caused by CFCs (chlorofluorocarbons). UV radiation causes skin cancer (melanoma), cataracts, and damage to DNA. The Antarctic ozone hole was discovered in 1985. The Montreal Protocol (1987) is the international agreement to phase out ozone-depleting substances. UV-A is less harmful and reaches the Earth's surface.
The ozone layer in the stratosphere (15–35 km altitude) absorbs harmful UV-B and UV-C radiation from the Sun. Depletion of ozone is caused by CFCs (chlorofluorocarbons). UV radiation causes skin cancer (melanoma), cataracts, and damage to DNA. The Antarctic ozone hole was discovered in 1985. The Montreal Protocol (1987) is the international agreement to phase out ozone-depleting substances. UV-A is less harmful and reaches the Earth's surface.
8The chromosomal theory of inheritance was proposed by:
Answer: C — Sutton and Boveri
Walter Sutton and Theodor Boveri independently proposed the chromosomal theory of inheritance in 1902, suggesting that Mendel's factors (genes) are located on chromosomes. This explained how genes behave during meiosis. Watson and Crick proposed the double-helix structure of DNA (1953). Mendel discovered the laws of inheritance. Darwin proposed the theory of evolution by natural selection. Thomas Hunt Morgan provided experimental evidence using Drosophila.
Walter Sutton and Theodor Boveri independently proposed the chromosomal theory of inheritance in 1902, suggesting that Mendel's factors (genes) are located on chromosomes. This explained how genes behave during meiosis. Watson and Crick proposed the double-helix structure of DNA (1953). Mendel discovered the laws of inheritance. Darwin proposed the theory of evolution by natural selection. Thomas Hunt Morgan provided experimental evidence using Drosophila.
9Which antibiotic is produced by the fungus Penicillium notatum?
Answer: A — Penicillin
Penicillin was the first antibiotic discovered by Alexander Fleming in 1928 from the mould Penicillium notatum. It inhibits bacterial cell wall synthesis. Streptomycin is produced by Streptomyces griseus (used for TB). Tetracycline and erythromycin are produced by other Streptomyces species. Antibiotics are chemical substances produced by microorganisms that kill or inhibit the growth of other microorganisms. Antibiotics are ineffective against viruses.
Penicillin was the first antibiotic discovered by Alexander Fleming in 1928 from the mould Penicillium notatum. It inhibits bacterial cell wall synthesis. Streptomycin is produced by Streptomyces griseus (used for TB). Tetracycline and erythromycin are produced by other Streptomyces species. Antibiotics are chemical substances produced by microorganisms that kill or inhibit the growth of other microorganisms. Antibiotics are ineffective against viruses.
10In a food chain, the energy available to the next trophic level is approximately:
Answer: C — 10%
According to Lindeman's Ten Percent Law (1942), only about 10% of the energy at one trophic level is transferred to the next. The remaining 90% is lost as heat during metabolism and respiration. For example, if producers have 1000 J, primary consumers get 100 J, secondary consumers get 10 J, and tertiary consumers get only 1 J. This is why food chains rarely have more than 4–5 trophic levels — there is insufficient energy to sustain higher levels.
According to Lindeman's Ten Percent Law (1942), only about 10% of the energy at one trophic level is transferred to the next. The remaining 90% is lost as heat during metabolism and respiration. For example, if producers have 1000 J, primary consumers get 100 J, secondary consumers get 10 J, and tertiary consumers get only 1 J. This is why food chains rarely have more than 4–5 trophic levels — there is insufficient energy to sustain higher levels.
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