List of top Biology Questions asked in CBSE CLASS XII

Assertion (A): A piece of DNA inserted into an alien organism generally does not replicate, if not inserted into a chromosome.
Reason (R): \textit{Chromosomes have specific sequences called ‘ori’ region, where DNA replication is initiated.
Assertion (A): Swiss cheese is characterized by large holes due to CO2 production.
Reason (R): It is ripened by growing a specific fungi.
(a) “The process of evolution of different species in a given geographical area starts from a point and literally radiates to other geographical areas.” Explain it with an example.
(b) Cite an example where more than one adaptive radiation has occurred in an isolated geographical area. Name the type of evolution your example depicts.
Gene therapy can be used to treat an ADA deficient patient. Explain.
Is it a permanent cure? How can ADA be cured permanently?
Student to attempt either option (A) or (B): (A) How is DNA isolated in purified form from a bacterial cell?
OR
(B) Explain how human functional insulin was produced by using recombinant DNA (rDNA) technology.

Construct and label a transcription unit from which the RNA segment given below has been transcribed. Write the complete name of the enzyme that transcribed this RNA.

In a certain population, the frequency of three genotypes is as follows:
Genotypes: PP Pp  pp 
Frequency: 22%  62%  16% 
Choose the option that shows the frequency of P and p alleles correctly:

Assertion (A): Biotechnology produces transgenic microorganisms that function as microfactories for proteins.
Reason (R): Transgenic microorganisms can be developed to produce proteins of human use, like insulin.
Assertion (A): A male individual always inherits haemophilia from his mother.
Reason (R): The gene for haemophilia lies on X-chromosome.
Choose the option that correctly describes the gynoecium of \textit{Michelia:

Study the items of columns I and II where drugs and their effects are given and match them correctly.

Choose the correct answer from the options given below:

Identify the incorrect statement regarding PCR.
Penetration of the sperm in the ovum is followed by:
Which one of the following is not the product of transgenic experiments?
Which of the following conditions correctly describes the manner of determining the sex in the given options?
India has only 2.4% of the world's land area but its share of the global species diversity is:

Answer the following questions:

(a)

  1. What is a test cross? How can we find out the zygosity of a plant by the use of test cross? 
  2. Why are human females rarely haemophilic? Explain with the help of a cross. Under what conditions can a haemophilic female be born? How do haemophilic patients suffer? 

OR 
(b) Name the two events ‘a’ and ‘c’ shown in the diagram below. 

 

  1. Mention where in the cell these events take place. 
  2. Explain the changes taking place during event ‘b’ and mention why these are needed.
Assertion (A): Human male is referred to as heterogametic.
Reason (R): The male produces millions of sperms of the same kind.
Answer the following questions:
  • Write the scientific name of the fruit fly.
  • Why did Morgan prefer to work with fruit flies for his experiments? State two reasons.
Student to attempt either option (A) or (B): (A) Biotechnology has helped farmers to get pest-resistant cotton plants. Explain the technique adopted along with its mode of action.
OR
(B) Explain any two molecular diagnostic techniques that help to detect pathogens from suspected patient.
The base sequence in one of the strands of DNA is: ‘TAGCATGAT’
  • Give the base sequence of its complementary strand.
  • How are these base pairs held together in DNA molecule?
  • Explain the base complementarity rule. Name the scientist who framed this rule.
Name the process involved in the production of nematode-resistant tobacco plants, using genetic engineering. Explain the strategy adopted to develop such plants.
Name the microbe that is used as biocontrol agent for controlling pest butterfly caterpillars:
pBR which is frequently used as a vector for cloning gene in E. coli is a/an:

Study the table given below showing the relationship between organism, its trophic level and kind of food chain it belongs to.