List of top Questions asked in CBSE CLASS XII

Explain the basis on which gel electrophoresis technique works. Write any two ways the products obtained through this technique can be utilised.
(a) Write the palindromic nucleotide sequence for following sequence of DNA segment:
5' – GAATTC – 3'
(b) Name the restriction endonuclease that recognizes this sequence.
(c) How are sticky ends produced? Mention their role.
Name an alcoholic drink which is produced with the help of microbes:
(1) With distillation
(2) Without distillation
Analyse the following ecosystems and discuss, which will be more productive in terms of primary productivity:
A young forest, a natural old forest, a shallow polluted lake.
Describe in brief any two techniques that can be utilised to transfer recombinant DNA into the host cell directly without using any vector.
A patient with ADA deficiency requires periodic infusion of genetically engineered lymphocytes. Explain why such periodic infusion is required and also suggest a permanent cure for such ADA deficiency.
Differentiate between Net primary productivity and Gross primary productivity in an ecosystem.
Study the cross given below:
abnormalities ‘1’ and ‘2’ in the offsprings of a cross done between a couple
Identify the abnormalities ‘1’ and ‘2’ in the offsprings of a cross done between a couple and distinguish between them.
Explain how cyanobacteria can be used as bio-fertilizer.
How are morphine and heroin related? Mention their effect on the human body.
Assertion (A): When the two genes in a dihybrid cross are situated on the same chromosome, the proportion of parental gene combinations is much higher than non-parental type.
Reason (R): Higher parental gene combinations can be attributed to crossing over between two genes.
How many pollen grains and ovules are likely to be formed in the anther and ovary of an angiosperm bearing 50 microspore mother cells and 50 megaspore mother cells respectively?
RNA interference (RNAi) helps in making tobacco-plant resistant to a nematode (\textit{Meloidogyne incognita}). Choose the correct option that shows how RNAi is achieved:
Assertion (A): A bioreactor provides the optimal conditions for achieving the desired product by providing optimum growth conditions.
Reason (R): The most commonly used bioreactors are of stirring type.
Evolution of modern man involves the following man-like primates. Choose the correct series of human evolution:
Assertion (A): One of the properties of genetic code is degeneracy.
Reason (R): Some amino acids can be coded by more than one codon.
Assertion (A): Saheli is the World’s first non-steroidal oral contraceptive pill.
Reason (R): It has been developed by National Institute of Immunology, New Delhi.
The sequence of nitrogenous bases in a segment of a coding strand of DNA is
5' – AATGCTAGGCAC – 3'.
Choose the option that shows the correct sequence of nitrogenous bases in the mRNA transcribed by the DNA.
The process of mineralization by microorganisms helps in the release of:
Match the items in Column-A with that of Column-B:
Choose the option that matches the items of Column A with that of B correctly:
GEAC stands for
Amplification of gene of interest by using DNA polymerase may go up to:
Transplantation of tissues/organs to some patients often fails due to rejection by the body of the patient. Which type of immune response is responsible for such rejections?
Match the following items of Column-I with that of Column-II:
Column-IColumn-II
(a) Trophoblast(iv) Outer layer of blastocyst
(b) Implantation(i) Embedding of blastocyst in the endometrium
(c) Inner cell mass(ii) Group of cells that would differentiate as embryo
(d) Morula(iii) Embryo with 8–16 blastomeres
Choose the option that matches Column-I with Column-II correctly:
Identify the labelled parts P, Q, R, and S in the stages of a dicot embryo shown in the diagram.
stages of a dicot embryo
Choose the option that indicates correct labelling of 'P', 'Q', 'R', and 'S' of embryo in differenct stages of its development.