List of top Questions asked in CBSE CLASS XII

Assertion (A) : Male contraceptive ‘Nirodh’ works on the principle of avoiding chances of ovum and sperm meeting.
Reason (R) : It is made of thin rubber/latex sheath and is used to cover the penis before coitus.

Assertion (A) : Isolated single cells can be fused to produce somatic hybrids.
Reason (R) : Cells selected for somatic hybridisation have desirable characters.

Certain viruses used as biological control agents belong to the genus :

Land reptiles which went back into water about 200 mya to evolve into fish-like reptiles were :

The lymphoid organ located within the lining of respiratory, digestive and urogenital tract is :

If the sequence of bases in DNA is ATTCGATG, then the sequence of bases in the transcript will be :

In a translational unit UTRs are present at :

Given below are a few statements with reference to the human sperm.
1. Sperm head contains a large nucleus and a lot of cytoplasm.
2. Mitochondria in the middle piece of a sperm provides ATP for the sperm motility.
3. Posterior part of the sperm head is covered by acrosome.
4. Spermatids undergo maturation into spermatozoa by the process of spermiogenesis.
5. Acrosomal secretions help in the entry of the sperm into the ovum at the time of fertilization.
Choose the option with all true statements from the given options :

In a pedigree chart, if two unaffected individuals have a child with the trait, what is the most likely mode of inheritance for this trait ?

How is triple fusion achieved in these plants ?

If a natural population with 200 individuals is in Hardy-Weinberg equilibrium for a gene with two alleles A and a, and with the gene frequency of allele A of 0.8, the genotype frequency of Aa will be :

Cistron is a segment of DNA coding for a :

Select the statements that are true for a typical monocotyledonous embryo from the given options.
1. Scutellum is present towards the centre of the embryonal axis.
2. Embryonal axis of the lower end has radicle and root cap covered by coleoptile.
3. The portion of embryonal axis above the level of attachment of scutellum is epicotyl.
4. Shoot apex and few leaf primordia of embryo are enclosed in a hollow foliar structure.
Choose the correct answer from the following :

State any two criteria for determining biodiversity hotspots.

Describe the Species-Area relationship as observed by Alexander von Humboldt, for a wide variety of taxa in nature.

Explain how human pro-insulin is processed in the cell to become a fully mature functional insulin.

Describe how human insulin is produced using the techniques of genetic engineering.

Explain the working of a simple stirred-tank bioreactor.

Describe what is meant by downstream processing.

Name and explain the role of inner and middle walls of the human female uterus.

Write the location and function of fimbriae in human female.

Explain the beneficial role of the following, produced as a result of the processes of biotechnology, to mankind:
Cow named Rosie

Explain the beneficial role of the following, produced as a result of the processes of biotechnology, to mankind:
(α) −1−antitrypsin

State any two criteria for determining biodiversity hotspots

If the birds have 18 pairs of autosomal chromosomes and a pair of sex chromosomes, fill in the blanks (i), (ii), (iii) and (iv) in the table given below. (Use symbols Z and W for sex chromosomes).