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Top 10 Important Questions CBSE 12 Biology Exam - 2020

The Class 12 CBSE Board Exam is around the corner and for students who aspire to study Biology in the near future, this is an important subject. This subject is important if you want to be a microbiologist or a doctor. Apart from memorizing the terms, knowing to label diagrams is equally important. So, when the exam is just around the corner and it is peak revision time. Our academic experts have drafter a few important topics for you to focus on.

The Biology paper will have four sections, A, B, C and D and the student will have to attempt all questions.

Important Questions & Answers CBSE Class 12 Board Exam 2020 : Biology


1. How does RNA interference help in developing resistance in tobacco plants against nematode infection?


  • A nematode (Meloidogyne incognita) infects the roots of tobacco plants and affects its yield. So, to prevent this infestation, RNA interference (RNAi) process is adopted.
  • Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant.
  • Introduction of DNA produces sense and antisense RNA in the host cells.
  • These two RNAs, being complementary to each other, form a double-stranded RNA which binds to and prevents the translation of mRNA (silencing) of the nematode.
  • The parasite is unable to survive in a transgenic host expressing specific interfering RNA.
  • The transgenic plant therefore gets itself protected from the attack of parasite.

2. What is IUCN Red List? State its main objective.

3. Bacillus thuringiensis produces insecticidal protein. Why does this toxin not kill Bacillus?

4. In a cross between a black and a white guinea pig, all F1 members are black. But the F2 generation raised by crossing two such F1 progeny consists of approximately ¾ black and ¼ white guinea pigs.
     a. What are the possible genotypes at each level?
     b. What will the offspring be like if two F2 whites are mated?

5. What acts as an inducer in lac operon? How does it switch on the operon?

6. Define the following terms and give one example for each:
     a. Commensalism
     b. Parasitism
     c. Camouflage
     d. Mutualism
     e. Interspecific competition

7. Answer the following questions:
    a. What is inbreeding and inbreeding depression?
    b. Explain how to overcome inbreeding depression in cattle.
    c. List three advantages of inbreeding in cattle.
    d. Name an improved breed of cattle. 

8. Answer the following questions:
     a. Name the stage of Plasmodium which gains entry into the human body.
     b. Trace the stages of Plasmodium in the body of female Anopheles after its entry.
     c. Explain the cause of periodic recurrence of chill and high fever during malarial attack in humans

9. Answer the following questions:
     a. What is global warming? Discuss the causes and effects of global warming.
     b.What measures need to be taken to control global warming?

10. Draw a longitudinal section of a post-pollinated pistil showing the entry of pollen tube into the mature embryo sac. Label the filiform apparatus, chalazal end, hilum, antipodals, male gametes and secondary nucleus.


For reviewing all the important answers and practice material for CBSE Class 12 Chemistry exam 2020 click here:

CBSE Class 12 Biology exam 2020 - Sample Papers

CBSE Class 12 Biology exam 2020 - Previous years papers

CBSE Class 12 Biology exam 2020 – Text book solutions

CBSE Class 12 Biology exam 2020 – Revision notes

Important topics for your reference:

6 Useful subject-specific tips for CBSE Class 12 Science exam preparation - 2020

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