CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type


Write the scientific names of the causal organisms of elephantiasis and ringworm in humans. Mention the body parts affected by them.


Casual organism: Wuchereria bancrofti

Body part affected: Lymphatic vessels of lower limbs


Casual organism: Belong to the genus MicrosporumTrichophyton, and Epidermophyton

Body part affected: Skin



Study the graph given below. Explain how oxygen concentration is affected in the river when sewage is discharged into it.

The introduction of sewage caused a sudden and sharp drop in the amount of dissolved oxygen in the river. This is caused due to an increase in the biological oxygen demand (BOD). This in turn leads to the death of fishes and other aquatic life. As the sewage gets diluted due the flow of the water, the river slowly regains some of its oxygen concentration.



13. Name the two types of immune systems in a human body. Why are cell-mediated and humoral immunities so called?

The two types of immunity found in humans are Humoral and Cell-mediated immunity. Humoral immunity is called so because its products (antibodies) are found in the blood. Cell-mediated immunity is called so because it is brought about by specialized cells in the body known as T-lymphocytes.


Differentiate between albuminous and non-albuminous seeds, giving one example of each.

The differences between albuminous and non-albuminous seeds are as under:

Albuminous seeds

Non-albuminous seeds

These seeds have endosperm.

These seeds do not have endosperm because it is consumed by the growing embryo.

Examples: wheat and maize

Examples: pea and beans


15. Explain how a hereditary disease can be corrected. Give an example of first successful attempt made towards correction of such diseases.

Gene therapy can be used to correct hereditary diseases. It involves delivery of a normal gene into the individual or embryo to take over the function of and compensate for the non-functional gene.

The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. In this disease, the gene coding for enzyme ADA gets deleted leading to deficiency of ADA and problems in immune system. Gene therapy for ADA deficiency includes isolation of lymphocytes from patient’s blood, culturing them in-vitro, introduction of functional ADA cDNA and returning the cells to the patient’s body.


16. List the key tools used in recombinant DNA technology.

The key tools used in recombinant DNA technology are restriction enzymes, ligases, polymerase enzymes, Polymerase Chain Reaction (PCR), competent host and vectors.

17. Draw a diagram of a male gametophyte of an angiosperm. Label any four parts. Why sporopollenin is considered the most resistant organic material?

Following is the labelled diagram of a male gametophyte of an angiosperm.

Sporopollenin is considered to be the most resistant organic material because it is chemically very stable and it can withstand high temperatures, acidic and alkaline conditions, and enzymes. No enzyme that degrades sporopollenin is so far known.


18. Justify with the help of an example where a deliberate attempt by humans has led to the extinction of a particular species.

Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake is an example where a deliberate attempt by humans led to the extinction of a particular species.


19. Explain the process of RNA interference.

In RNA interference (RNAi), a complementary RNA binds to the mRNA to form a double stranded RNA that cannot translate. Hence, its expression is blocked, this phenomenon is also known as Silencing. RNAi is a method adopted to prevent infestation of roots of tobacco plants by a nematode Meloidogyne incognita.


20. Identify A, D, E and F in the diagram of an antibody molecule given below.