List of top Biology Questions asked in CBSE CLASS XII

Mention any four strategies adopted by flowering plants to prevent self-pollination.
(A) Comment upon the mode of pollination in Vallisneria and Zostera. (B)
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.

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): The number of white winged moths decreased after industrialisation in England. Reason (R): Effects of industrialisation were more marked in rural areas of England.
Assertion (A): Corpus luteum secretes the hormone, progesterone. Reason (R): Hormone Progesterone is essential for maintenance of the endometrium.
For commercial and industrial production of citric acid, which one of the following microbes is used?
Select the correct statement from the following biotechnological procedures:
If Meselson and Stahl’s experiment is continued for 80 minutes (till III generation), then what would be the ratio of DNA containing \( N^{15}/N^{15} : N^{15}/N^{14} : N^{14}/N^{14} \) in the medium?
The decrease in the T-Lymphocytes count in human blood will finally result in

A child with blood group A has father with blood group B and the mother with blood group AB. Choose the option that gives the correct genotypes of father, mother, and the child:

A child with blood group A has father with blood group B

Study the items of Column-I and those of Column-II:

Choose the option that correctly matches the items of Column-I with those of Column-II:

Which of the following features correctly show the mechanism of sex-determination in honey-bees?
(i) A zygote formed from the union of a sperm and an egg develops into a male.
(ii) Males have half the number of chromosomes as that of females.
(iii) The females are diploid having 32 chromosomes.
(iv) Males have a father and can produce sons.
Choose the correct option:

Given below is a heterogeneous RNA formed during Eukaryotic transcription:

heterogeneous RNA

How many introns and exons respectively are present in the hnRNA?

In molecular biology, who proposed that genetic information flows in one direction?

Given below is the schematic representation of spermatogenesis in human males:

schematic representation of spermatogenesis in human males

Choose the option that shows the correct labelling of ‘I’, ‘II’, ‘III’ and ‘IV’ in the given diagram.

Some flowers are unisexual, this property of unisexuality of flowers prevents which kind of pollination?
Why are restrictions imposed on MTP in India? Up to how many weeks or trimesters, is MTP considered relatively safe for a female, if necessary to perform, by a medical practitioner?
If a natural population of 60 individuals is in Hardy-Weinberg equilibrium for a gene with two alleles B and b, with the gene frequency of allele B of 0.7, the genotype frequency of Bb will be:
A normal couple produces half the sons as haemophilic and half the daughters as carriers. Choose the option that correctly indicates the chromosome on which the gene for this trait is located.
Name the type of heterogamety observed in most birds.
What is the term used for the milk produced during the initial days of lactation?
Describe the changes in the ovary and the uterus as induced by the changes in the level of pituitary and ovarian hormones during menstrual cycle in a human female.
Explain why the milk produced by the mother during the initial days of lactation is considered to be very essential for the newborn infant.
Explain the structure of a mature embryo sac of a typical flowering plant.