List of top Questions asked in CBSE CLASS XII

Select the option that has only termination codons.

Morgan hybridised Drosophila white-eyed and yellow-bodied female with red-eyed and brown-bodied male (wild type) and intercrossed their F1 progeny. He observed that the two genes :

The undifferentiated sheath that encloses the radicle and root cap in a monocot embryo, is known as :

An organic compound (X) has the molecular formula \(C_5H_{10}O\). Draw structures for (X) if it:
(I) does not give Tollen's test but gives a positive iodoform test.
(II) does not give Tollen's test and iodoform test but undergoes Aldol condensation.
(III) undergoes Cannizzaro's reaction.

Explain how the following microbes act as biocontrol agents :

(a) Bacillus thuringiensis

(b) Nucleopolyhedrovirus

Given below is an equation describing the growth pattern of a population :

\( \dfrac{dN}{dt} = rN \)

(a) Mention the type of growth model or growth pattern of the population described by the given equation.

(b) What does r in the equation signify ?

(c) Mention the type of growth curve that will be obtained if the population density (N) is plotted against time (t).

(d) According to you, will the resource availability be limited or unlimited for this type of growth in the given population ?

Explain the mutually rewarding relationship between Yucca plant and species of moth.

Assertion (A) : Besides curdling of milk, LAB also improves its nutritional quality by increasing Vitamin B12.

Reason (R) : LAB, when present in the stomach checks disease-causing microbes.

Name the most commonly used bioreactor. List the advantages of the bioreactor. Also write the importance of sampling ports.

Pollination success will be reduced unless the orchid flower co-evolves with the pollinator. Explain.

State the role of thymus as a lymphoid organ. Name the cells that are released from it and mention their functions.

Explain any two methods of vectorless gene transfer.

If a genetic disease is transferred from a phenotypically normal but carrier female to only some of the male progeny, the disease is :

Cattle or goats are never seen browsing on the weed, Calotropis. Select the correct option for the reason.

A doctor identifies symptoms of nasal congestion, headache, sore throat, hoarseness and cough in a patient. The conclusion is that the patient is infected by a pathogen :

Which type of selection is industrial melanism observed in moth, Biston betularia ?

C-peptide of human insulin is :

Match the IUDs in Column I with suitable example in Column II.

Column IColumn II
a. Non-medicatedi. Lippes loop
b. Copper releasingii. LNG-20
c. Hormone releasingiii. Multiload 375

Mention the source and the functions of the following hormones :

hCG; LH; FSH; Relaxin.

Read the following passage and answer the questions that follow :

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :

(c) Name the two restriction sites each in the two genes you have identified as selectable markers.



Read the following passage and answer the questions that follow :

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :

(a) Why are plasmids and bacteriophages used as cloning vectors ?



Read the following passage and answer the questions that follow :

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :

(b) (i) Identify :

(I) The gene in the cloning vector that controls the copy number of the vector.

(II) The restriction site - C in the rop gene.



Read the following passage and answer the questions that follow :

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :

(b) (ii) Identify and name two selectable markers shown in the diagram.



(a) (i) Draw the structure of an antibody molecule and label any four of its parts.

(ii) Differentiate between active and passive immunity. Write any three differences.

Read the following passage and answer the questions that follow :

The process of copying genetic information from template strand of DNA into RNA is called transcription. It is mediated by RNA polymerase. Transcription takes place in the nucleus of eukaryotic cells. In transcription, only a segment of DNA and only one of the strands is copied into RNA.

(b) (ii) Mention the two additional processes which hnRNA needs to undergo after splicing to become functional.