Allergy involves:
- A. IgA
- B. IgECorrect
- C. IgM
- D. IgG
Explanation. In allergy, IgE antibodies bind to mast cells and basophils; on re-exposure to the allergen they trigger release of histamine and other mediators.
12th Standard Zoology: Most Repeated Board Exam Questions
Worked out from the 105 one-mark questions of the 2020–2026 public exams. The table shows how many board questions came from each chapter; below it are the questions the board asked more than once, with the answer.
Board questions from each chapter
Questions asked in more than one year
The most common substrate used in distilleries for the production of ethanol is ________.
- A. MolassesCorrect
- B. Soya meal
- C. Corn meal
- D. Groundgram
Explanation. Molasses, the by-product of sugarcane factories, is rich in sugars and is the most common substrate fermented by yeast in distilleries to produce ethanol.
The mode of sexual reproduction in bacteria is by :
- A. ConjugationCorrect
- B. Formation of gametes
- C. Zoospore formation
- D. Endospore formation
Explanation. Bacteria do not form gametes; genetic material is exchanged between two cells through conjugation, which is regarded as their sexual mode of reproduction.
The wings of birds and butterflies is an example of:
- A. Divergent evolution
- B. Adaptive radiation
- C. Variation
- D. Convergent evolutionCorrect
Explanation. Wings of birds and butterflies have different origins and structure but perform the same function (flight). Such analogous organs are an example of convergent evolution.
Which one of the following are at higher risk of extinction due to habitat destruction?
- A. AmphibiansCorrect
- B. Mammals
- C. Echinoderms
- D. Birds
Explanation. Amphibians depend on both water and land, have moist permeable skin and limited dispersal, so habitat loss affects them most; they are the most threatened vertebrate group.
________ is/are an ideal disinfectant for waste water.
- A. Boiling
- B. U-V Rays
- C. OzonisationCorrect
- D. Chlorination
Explanation. Ozone is a powerful oxidant that kills pathogens, including chlorine-resistant ones, and breaks down to oxygen without leaving harmful residues, so ozonisation is the ideal disinfectant for waste water.
Haemozoin is :
- A. A toxin from Plasmodium speciesCorrect
- B. A precursor of haemoglobin
- C. A toxin from Haemophilus species
- D. A toxin from Streptococcus
Explanation. When RBCs infected by Plasmodium rupture, the toxin haemozoin is released, causing the chill and high fever of malaria.
ABO blood group in man is controlled by :
- A. Sex linked genes
- B. Multiple allelesCorrect
- C. Holandric genes
- D. Lethal genes
Explanation. The ABO blood group is governed by one gene (I) with three alleles, IA, IB and i, so it is an example of multiple alleles.
In which mode of reproduction variations are seen ?
- A. SexualCorrect
- B. Asexual
- C. Parthenogenesis
- D. Both (a) and (b)
Explanation. In sexual reproduction, crossing over during meiosis and fusion of gametes from two parents create new gene combinations, so offspring show variations. Asexual reproduction and parthenogenesis give offspring like the single parent.
________ is used to lower blood cholesterol level.
- A. StatinsCorrect
- B. Clot buster
- C. Tetracycline
- D. Cyclosporin A
Explanation. Statins, produced by the yeast Monascus purpureus, inhibit the enzyme that synthesises cholesterol and so lower blood cholesterol.
The golden age of reptiles was :
- A. Paleozoic era
- B. Mesozoic eraCorrect
- C. Proterozoic era
- D. Cenozoic era
Explanation. Reptiles, including the dinosaurs, dominated the Earth during the Mesozoic era, which is therefore called the golden age of reptiles.
A population will not exist in Hardy Weinberg equilibrium, if:
- A. There is no migration
- B. Individuals mate selectivelyCorrect
- C. The population is large
- D. There are no mutations
Explanation. Hardy-Weinberg equilibrium requires random mating, a large population, and no migration, mutation or selection; selective (non-random) mating disturbs it.