List of top Questions asked in CBSE CLASS XII

Choose the correct statements :

(i) Polycistronic mRNA is generally found in eukaryotes.

(ii) The RNA polymerase II transcribes precursor of mRNA, the hnRNA.

(iii) The process of translation of mRNA begins when the mRNA encounters the large subunit of ribosomes.

(iv) Stop codons do not have any tRNAs.

A man is found to have a sperm count of less than 20 million/mL and his wife is diagnosed with blockage in the oviduct. This couple would be advised to go for which of the following techniques ?

(i) ZIFT

(ii) AI

(iii) IUT

(iv) ICSI

(v) GIFT

Elution means :

Some cyanobacteria in aquatic and terrestrial environment that enrich the soil by fixing nitrogen are :

Which of the following amino acid substitutions is responsible for causing sickle cell anemia ?

Which of the following groups of cells in the male gonad represent haploid cells ?

Filiform apparatus in the embryo sac of an angiosperm is present at the micropylar tip of :

(i) Insertional inactivation is a method to detect the recombinant DNA. Explain this method.

(ii) Name the commonly used vector for transferring genes in plants from bacteria.

(iii) How is this able to transform a normal plant cell into a tumour ?

Write the types and locations of the genes causing thalassemia in humans. State the cause and symptoms of the disease. How is sickle-cell anemia different from this disease ?

Immunity in our body is of two types (i) Innate immunity, and (ii) Acquired immunity. Innate immunity is a non-specific defence mechanism, whereas Acquired immunity is pathogen specific. Acquired immunity is characterised by memory. Antibodies are specific to antigens and there are four types of antibodies produced in our body - IgA, IgE, IgG and IgM. It shows primary response where it encounters the pathogen for the first time and secondary response during the subsequent encounters with the same antigen/pathogen. These immune responses are carried out with the help of two special types of lymphocytes present in the blood.

(b) (ii) The organ transplants (grafts) are often rejected if not taken from suitable compatible persons. Mention the characteristic of our immune system that is responsible for the rejection.

(i) Draw a diagram of L.S. of maize grain and label its any six parts.

(ii) Differentiate between perisperm and endosperm giving one example of each.

Immunity in our body is of two types (i) Innate immunity, and (ii) Acquired immunity. Innate immunity is a non-specific defence mechanism, whereas Acquired immunity is pathogen specific. Acquired immunity is characterised by memory. Antibodies are specific to antigens and there are four types of antibodies produced in our body - IgA, IgE, IgG and IgM. It shows primary response where it encounters the pathogen for the first time and secondary response during the subsequent encounters with the same antigen/pathogen. These immune responses are carried out with the help of two special types of lymphocytes present in the blood.

(c) How is active immunity different from passive immunity ? Write any two differences.

(i) EcoR I has played a very important role in rDNA technology.

(I) Explain the convention for naming EcoR I.

(II) Write the recognition site of this endonuclease restriction enzyme.

(ii) Name the overhanging stretches of DNA produced by these restriction enzymes. Describe their role in the formation of rDNA.

(i) Enlist any four prime goals of the Human Genome Project (HGP).

(ii) List the two methodologies which were involved in the human genome project. Mention how they were used.

(iii) Expand "YAC" and mention what it was used for.

Gene expresses itself in a cell system as a protein/enzyme. How an expression of gene occurs in a cell system, when it needs to occur and how the gene expression is regulated in prokaryotic cell system was studied by the combined efforts of Francois Jacob, a geneticist and Jacques Monod, a biochemist. For their work on lactose metabolism in E. coli and introducing the concept of "lac operon", they were awarded the Nobel Prize in 1965.

(c) Why is lac operon said to be a transcriptionally regulated system ?

Gene expresses itself in a cell system as a protein/enzyme. How an expression of gene occurs in a cell system, when it needs to occur and how the gene expression is regulated in prokaryotic cell system was studied by the combined efforts of Francois Jacob, a geneticist and Jacques Monod, a biochemist. For their work on lactose metabolism in E. coli and introducing the concept of "lac operon", they were awarded the Nobel Prize in 1965.

(b) (ii) Why is the regulation of operon called negative regulation ?

Gene expresses itself in a cell system as a protein/enzyme. How an expression of gene occurs in a cell system, when it needs to occur and how the gene expression is regulated in prokaryotic cell system was studied by the combined efforts of Francois Jacob, a geneticist and Jacques Monod, a biochemist. For their work on lactose metabolism in E. coli and introducing the concept of "lac operon", they were awarded the Nobel Prize in 1965.

(b) (i) How are the structural genes activated in the lac operon in E. coli ?

Immunity in our body is of two types (i) Innate immunity, and (ii) Acquired immunity. Innate immunity is a non-specific defence mechanism, whereas Acquired immunity is pathogen specific. Acquired immunity is characterised by memory. Antibodies are specific to antigens and there are four types of antibodies produced in our body - IgA, IgE, IgG and IgM. It shows primary response where it encounters the pathogen for the first time and secondary response during the subsequent encounters with the same antigen/pathogen. These immune responses are carried out with the help of two special types of lymphocytes present in the blood.

(a) Name the two types of specialised cells which carry out the primary and secondary responses.

Gene expresses itself in a cell system as a protein/enzyme. How an expression of gene occurs in a cell system, when it needs to occur and how the gene expression is regulated in prokaryotic cell system was studied by the combined efforts of Francois Jacob, a geneticist and Jacques Monod, a biochemist. For their work on lactose metabolism in E. coli and introducing the concept of "lac operon", they were awarded the Nobel Prize in 1965.

(a) It is said that 'lac operon' has to be operational at a very low level in the bacterial cell all the time. Justify.

Immunity in our body is of two types (i) Innate immunity, and (ii) Acquired immunity. Innate immunity is a non-specific defence mechanism, whereas Acquired immunity is pathogen specific. Acquired immunity is characterised by memory. Antibodies are specific to antigens and there are four types of antibodies produced in our body - IgA, IgE, IgG and IgM. It shows primary response where it encounters the pathogen for the first time and secondary response during the subsequent encounters with the same antigen/pathogen. These immune responses are carried out with the help of two special types of lymphocytes present in the blood.

(b) (i) Name any two barriers present in our body that provide innate immunity.

There are many animals, which have become extinct in the wild, but continue to be maintained in zoological parks. Answer the questions that follow :

(a) What type of bio-diversity conservation is observed in this case ?

(b) Explain any other two ways which help in this type of conservation.

(c) Besides zoological parks, mention one place that serves this purpose.

Answer the following questions :

(i) Define 'predation'.

(ii) Why is predation required in a community of different organisms ? Give any two points.

(iii) Why are predators 'prudent' in nature ?

Explain the three different ways in which natural selection operates. Explain with the help of graphs.

(a) Construct a complete transcription unit with promoter and terminator on the basis of the hypothetical coding strand given below :

A T G C A T G C A T A G

(The strand is drawn on a line with arrow heads at both ends and short vertical ticks under each base, for you to complete.)

(b) Write the RNA strand transcribed from the above transcription unit along with its polarity.

Study the graph given below and answer the questions that follow :

(i) Write the status of food and space in the curves a and b.

(ii) In the absence of predators, which one of the two curves would appropriately depict the prey population ?

(iii) 'Time' has been shown on x-axis and there is a parallel dotted line above it. Give the significance of this dotted line.