CBSE Class 12 Board Exam Biology Flashcards

24 sample cards from the Biology deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. From which microorganisms are the antibiotic penicillin and the cholesterol-lowering statins obtained?

   Penicillin is obtained from the fungus Penicillium notatum (chrysogenum); statins are produced by the yeast Monascus purpureus.

2. What are biofertilizers, and name examples of nitrogen-fixing organisms used as biofertilizers.

   Biofertilizers are organisms that enrich soil nutrients. Examples: Rhizobium (symbiotic with legumes), Azospirillum and Azotobacter (free-living), and cyanobacteria (e.g., Anabaena, Nostoc); also mycorrhizal fungi (Glomus).

3. What is the role of methanogens (e.g., Methanobacterium) in biogas production?

   Methanogens are anaerobic bacteria (found in cattle dung/rumen and sludge) that produce methane (biogas) by breaking down organic matter/cellulose.

4. Define a food chain and distinguish grazing food chain from detritus food chain.

   A food chain is the transfer of energy through successive trophic levels. A grazing food chain (GFC) starts with producers (green plants). A detritus food chain (DFC) starts with dead organic matter (detritus) consumed by detritivores/decomposers.

5. State the 10 percent law of energy transfer in ecosystems.

   Only about 10% of the energy stored at one trophic level is transferred to the next trophic level; the rest is lost mainly as heat (Lindeman's 10% law).

6. Why is an ecological pyramid of energy always upright?

   Because energy decreases at each successive trophic level (only ~10% passes on), so producers always have the most energy and top consumers the least—it can never be inverted.

7. What is ecological succession, and differentiate primary from secondary succession.

   Ecological succession is the gradual, orderly change in community composition over time toward a climax. Primary succession begins on bare/lifeless areas (e.g., bare rock). Secondary succession occurs where a community was destroyed but soil remains (faster).

8. According to the species-area relationship, what does the slope (z value) typically range for small areas?

   For relatively small areas, the slope of the regression (z value) of the species-area relationship is remarkably similar, ranging between 0.1 and 0.2 (regardless of taxonomic group or region).

9. What is biodiversity, and name its three levels.

   Biodiversity is the variety of life forms. Its three levels are genetic diversity, species diversity, and ecological (ecosystem) diversity.

10. Differentiate in-situ from ex-situ conservation of biodiversity with examples.

    In-situ conservation protects species in their natural habitat (e.g., national parks, biosphere reserves, sanctuaries). Ex-situ conservation protects species outside their habitat (e.g., zoos, botanical gardens, seed banks, cryopreservation).

11. What are the two core techniques on which modern biotechnology is based?

    Genetic engineering (recombinant DNA technology, gene cloning, gene transfer) and maintenance of sterile/aseptic microbial/cell culture conditions for large-scale production of biotech products.

12. What is the function of restriction endonucleases in genetic engineering?

    Restriction endonucleases are 'molecular scissors' that cut DNA at specific recognition sequences (palindromic sites), producing fragments often with sticky ends used in recombinant DNA technology.

13. What is the role of DNA ligase in recombinant DNA technology?

    DNA ligase is 'molecular glue' that joins DNA fragments by forming phosphodiester bonds, e.g., sealing the foreign DNA into the vector.

14. What are the three basic requirements (features) of a good cloning vector?

    An origin of replication (ori), a selectable marker (e.g., antibiotic resistance gene), and recognition/cloning sites (unique restriction sites); ideally a small size and high copy number.

15. Why is calcium chloride (and heat shock) used in transformation of bacteria?

    Treating bacterial cells with divalent cations like CaCl2 makes the cell membrane more permeable ('competent'), and a brief heat shock (42°C) allows recombinant DNA to enter the host cell.

16. What are the three main steps of one cycle of the Polymerase Chain Reaction (PCR)?

    Denaturation (separating DNA strands by heat ~94°C), annealing (primers bind to template), and extension (Taq polymerase synthesizes new strands at ~72°C).

17. Why is Taq polymerase used in PCR?

    Taq polymerase, isolated from the thermophilic bacterium Thermus aquaticus, is heat-stable and remains active at the high temperatures used during denaturation, so it need not be added each cycle.

18. What is gel electrophoresis used for, and in which direction does DNA move?

    Gel electrophoresis separates DNA/RNA fragments by size. Since DNA is negatively charged, it moves toward the positive electrode (anode); smaller fragments move faster/farther through the agarose gel.

19. What is Bt cotton, and which gene gives it insect resistance?

    Bt cotton is a transgenic crop carrying cry genes (e.g., cryIAc, cryIIAb) from Bacillus thuringiensis; these produce Bt toxin that kills bollworm/insect pests.

20. How does RNA interference (RNAi) protect tobacco plants from nematode (Meloidogyne incognita) infestation?

    By introducing nematode-specific genes using Agrobacterium vectors, the plant produces both sense and antisense RNA that form double-stranded RNA; this silences the nematode's specific mRNA (RNAi), so the parasite cannot survive.

21. What is the significance of humanized/recombinant insulin (Humulin), and why was earlier animal insulin problematic?

    Recombinant human insulin (made by inserting A and B chain genes into E. coli, then joining the chains) avoids allergic reactions; insulin from slaughtered animals sometimes caused allergy or immune reactions in patients.

22. What is gene therapy, and give the first example of its clinical use.

    Gene therapy is the correction of a genetic defect by inserting a normal/functional gene into a patient's cells. The first clinical use (1990) treated a girl with ADA (adenosine deaminase) deficiency.

23. What is molecular diagnosis using PCR/ELISA used for in biotechnology applications?

    PCR detects very low amounts of pathogen DNA/RNA for early diagnosis (e.g., HIV, mutations). ELISA detects infection by detecting antigens or antibodies, enabling early disease diagnosis before symptoms appear.

24. What is biopiracy, and why was the Indian patent on basmati rice / turmeric significant?

    Biopiracy is the unauthorized use and patenting of bio-resources or traditional knowledge by organizations/companies without proper authorization or compensation. The basmati and turmeric cases highlighted the need to protect indigenous traditional knowledge.

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