List of top Biology Questions asked in CBSE CLASS XII

Assertion (A): Swiss cheese is characterized by large holes due to CO2 production.
Reason (R): It is ripened by growing a specific fungi.
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): 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.
Identify the incorrect statement regarding PCR.

Read the passage given below and answer the question. 
Food chains ‘P’ and ‘Q’ form an interconnection. ‘P’ initiates with wheat grass whose population supports a few grasshoppers, frogs and snakes. 
‘Q’ starts with dead decaying leaves of wheat grass which are eaten by earthworms and then food chain is continued with frog of food chain ‘P’. 
Identify the types of food chains ‘P’ and ‘Q’:

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:

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:

India has only 2.4% of the world's land area but its share of the global species diversity is:
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?
The RNA triplet UAG acts as a stop codon which terminates the synthesis of a polypeptide. Below is given a strand of DNA which codes for four amino acids.
In which position will an insertion of a thymine nucleotide result in the termination of translation?
DNA strand:
3′ T C C A C C C G A T G C 5′

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.
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.
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.
Assertion (A): Human male is referred to as heterogametic.
Reason (R): The male produces millions of sperms of the same kind.

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

Name the microbe that is used as biocontrol agent for controlling pest butterfly caterpillars:
A dwarf pea plant was treated with gibberellic acid and it becomes as tall as a tall pea plant. If these treated pea plants are crossed with pure tall pea plants, the phenotypic ratio in $F_1$ generation will be:
During the process of oogenesis in human female, the primary oocyte results in the formation of which of the following?
Choose the correct option.
pBR which is frequently used as a vector for cloning gene in E. coli is a/an: