List of top Questions asked in CBSE CLASS XII

(i) Where do the signals for parturition originate from, in humans ?

(ii) Why is it important to feed newborn babies on colostrum ?

Assertion (A) : Endosperm in angiosperm is a triploid tissue.
Reason (R) : Endosperm is formed after triple fusion i.e. fusion, of a diploid secondary nucleus with a haploid male gamete.

(a) Draw a schematic representation of the structure of a transcription unit and show the following in it :

(i) Direction in which transcription occurs

(ii) Polarity of the two strands involved

(iii) Template strand

(iv) Terminator

(b) Mention the function of promoter in transcription.

Which of the following groups of animals has a large number of endemic species in the western ghats ?

Assertion (A) : Chemically synthesised oligonucleotides are used during annealing in PCR technique.
Reason (R) : The primers bind to the double stranded DNA at their complementary regions.

Significance of heat shock method in bacterial transformation is to facilitate which one of the following steps ?

Assertion (A) : Innate immunity is a non-specific type of defence.
Reason (R) : Skin in our body is the main physical barrier which prevents entry of microorganisms.

In spite of interspecific competition in nature, which of the following mechanisms might competing species have evolved to coexist and survive ?

A person admitted to hospital as he had myocardial infarction. A cardiologist injected him 'streptokinase'. Select the option that indicates the correct reason for using streptokinase.

Miller's experiment included some gases in his experiment. Which of the following gas was not part of his experiment ?

When an amino acid is coded by more than one codon, the genetic code is said to be :

Polio vaccine provides which kind of immunity in children ? Select the correct option.

Polyembryony commonly occurs in which one of the following plants ?

Choose the right option that indicates the safe period for medical termination of pregnancy.

Failure of segregation of chromatids during cell division results in gain or loss of chromosomes. Select the correct option.

(I) (i) State the role of selectable markers in rDNA technology.

(ii) Name two such selectable markers which are considered to be useful for E. coli cloning vector.

(iii) State two significances of "Ori" in E. coli cloning vector.

(II) How have biotechnologists effectively used Agrobacterium tumefaciens in plants and retroviruses in animals ? Explain.

Name and describe the technique that helps in separation and isolation of DNA fragments after cutting of DNA by restriction endonucleases.

(i) How and why is charging of tRNA essential in the process of translation ?

(ii) State the function of ribosome as a catalyst in translation in bacteria.

(iii) Explain the process of binding of ribosomal units to mRNA during protein synthesis.

(iv) Where are untranslated regions located in mRNA ? Mention their role.

(i) State the arrangement of different genes, that in bacteria is referred to as "operon".

(ii) Draw a schematic labelled illustration of lac operon in a switched on state.

(iii) Describe the role of lactose in lac operon.

(b) Explain the changes that the primary oocyte undergoes while in different follicular stages before ovulation.

(a) Draw a flow chart to show hormonal control of the human male reproductive system.