List of top Questions asked in CBSE CLASS XII- 2025

Assertion (A): Streptococcus pneumoniae and 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.
The decrease in the T-Lymphocytes count in human blood will finally result in
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?
Study the items of Column-I and those of Column-II:
Column-I Column-II
(a) RNA polymerase I (i) 18s rRNA
(b) RNA polymerase II (ii) SnRNAs
(c) RNA polymerase III (iii) hnRNA
Choose the option that correctly matches the items of Column-I with those of Column-II:

Given below is a heterogeneous RNA formed during Eukaryotic transcription:
 
How many introns and exons respectively are present in the hnRNA?

The phosphoester linkage in the nucleotides is between
Which one of the following options shows the correct evolutionary order of the plants mentioned below?
(i) Ferns (ii) Ginkgo (iii) Zosterophyllum (iv) Gnetales
Choose the correct option.

In a pedigree chart represents :

A child with blood group A has the 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 :
The number of autosomes present in a human secondary spermatocyte
Explain the process of separation and isolation of DNA fragments by a typical gel electrophoresis.
(a) (i) Give the full form of ‘ELISA’. Write the principle on which ELISA test is based.
(ii) Describe all the methods used to treat or cure Adenosine deaminase deficiency in humans.
Explain the process of formation of placenta in a human female after the implantation of the blastocyst in the endometrium of the uterus.
Thomas Hunt Morgan carried out several dihybrid crosses in Drosophila melanogaster to study genes that were sex linked. (a) Give four major reasons for using the tiny fruit flies by Morgan for his experiments. (b) How did Morgan and his group explain the physical association of the two genes on a chromosome to the frequency of recombination between gene pairs on the same chromosome?
Student to attempt either option (A) or (B):
(A) Write two features of an ideal contraceptive. Explain any one natural contraceptive method that makes the chances of conception almost nil.
(B) Explain GIFT and ICSI.
In a pea plant (Pisum sativum) green pod colour is dominant over yellow pod colour. The expected ratio of phenotypes of the first generation offspring in a cross between both the parents with heterozygous green pod colour will be:
The most widely used transgenic animal for testing the safety of vaccine before they are used in humans is:

Use the given information to select the amino acid attached to the 3′ end of tRNA during the process of translation, if the coding strand of the structural gene being transcribed has the nucleotide sequence ‘TCC’.

The first human-like hominid evolved during human evolution is supposed to be:
Select the statements that are true for outbreeding devices in the flowering plants.
    [(i)]
  • They discourage cross-pollination and ensure self-pollination.
  • They are advantageous as they lead to inbreeding depression.
  • Self-incompatibility prevents self-pollen from fertilising the ovules.
  • To prevent self-pollination in some species pollen release and stigma receptivity are not synchronised.
Choose the correct answer:
Allergy in humans is a result of release of the following chemicals from the mast cells:

A pedigree chart is shown below for a disease that is autosomal dominant. The genetic make-up of the first generation is: