List of top Questions asked in CBSE CLASS XII

How does the process of Natural Selection affect Hardy-Weinberg equilibrium? Explain with the help of graphs.
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; it is called specific immunity too. Acquired immunity is characterised by memory. Antibodies are specific to antigens and there are different types of antibodies produced in our body: they are IgA, IgE, IgG, IgC, and IgM. It shows primary response when it encounters the pathogen for the first time and secondary response during the subsequent encounters with the same antigen/pathogen.

Why is the antibody-mediated immunity also called humoral immune response?

Samples of blood and urine of a sports person are collected before any sports event for drug tests. (a) Why is there a need to conduct such tests? (b) Name the drugs the authorities usually look for. (c) Write the generic names of two plants from which these drugs are obtained.

Study the pie chart given below, representing the global biodiversity and proportionate number of species of major taxa.

global biodiversity and proportionate number of species of major taxa


Answer the following questions:
[a] Identify 'X' and 'Y' in the given pie chart.
[b] Which one of the two 'X' or 'Y' is the most species-rich taxonomic group and by what percentage?
[c] Name the level of Biodiversity represented by the following:

  • (i) Estuaries and alpine meadows in India.
  • (ii) The medicinal plant \textit{Rauwolfia vomitoria}.
An application of biotechnology in agriculture involves the production of pest-resistant plants, using "cry" gene from a bacterium, \textit{Bacillus thuringiensis.} (a) Proteins coded by which specific Bt. toxin gene control corn borer? (b) How does Bt. toxin produced by the bacterium kill the insect? Explain.
List two reasons that make copper releasing IUDs as effective contraceptives.
State the conclusions derived by David Tilman’s long-term ecosystem experiments using outdoor plots.
Write the scientific name of the source organism of the thermostable DNA polymerase used in PCR.
Write the composition of intine and exine layers of a pollen grain.
The symptoms of malaria do not appear immediately after the entry of sporozoites into the human body when bitten by female Anopheles mosquito. Explain why it happens.
State the advantage of using thermostable DNA polymerase.
A bilobed dithecous anther has 200 microspore mother cells per microsporangium. How many male gametophytes can be produced by this anther?
Explain how the intake of oral contraceptive pills prevent pregnancy in humans.
Assertion (A): Restriction endonuclease recognises palindromic sequence in DNA and cuts them. Reason (R): Palindromic sequence has two unique recognition sites PstI and PvuI recognised by restriction endonuclease.

Study the given pedigree chart in which neither of the parents shows the trait but the trait is present in both male and female children.

pedigree chart

Write about the trait, also explain the inheritance of such a trait in the progeny on the basis of the given pedigree chart.

(A) Comment upon the mode of pollination in Vallisneria and Zostera. (B)
Describe any two situations where a medical doctor would recommend injection of pre-formed antibodies (antitoxins) into the body of a patient.
Mention any four strategies adopted by flowering plants to prevent self-pollination.

Study the given pedigree chart in which neither of the parents shows the trait but the trait is present in both male and female children.

pedigree chart

Give one example of such a trait in human beings.

Assertion (A): The number of white winged moths decreased after industrialisation in England. Reason (R): Effects of industrialisation were more marked in rural areas of England.
Select the correct statement from the following biotechnological procedures:
For commercial and industrial production of citric acid, which one of the following microbes is used?
Assertion (A): Streptococcus pneumoniae and \textit{Haemophilus influenzae} are responsible for causing infectious disease in human beings. Reason (R): A healthy person acquires the infection by inhaling the aerosols released by an infected person.
Assertion (A): Corpus luteum secretes the hormone, progesterone. Reason (R): Hormone Progesterone is essential for maintenance of the endometrium.
Which of the following features correctly show the mechanism of sex-determination in honey-bees?