List of top Questions asked in CBSE CLASS XII- 2026

Choose the incorrect pair of stain and its type.
The purpose of opening a Demat Account with a Depository Participant (DP) is :
Out of Mn\(^{2+}\) and Zn\(^{2+}\), which ion will be more paramagnetic and why? (Atomic numbers: Mn = 25, Zn = 30)

The process of copying genetic information from template strand of DNA into RNA is called transcription. It is mediated by RNA polymerase. Transcription takes place in the nucleus of eukaryotic cells. In transcription, only a segment of DNA and only one of the strands is copied into RNA. 

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow : 

Study the given chart showing evolution of plants. Answer the following questions : 

Arrange the following hormones in sequence of their secretion in a pregnant woman : hCG; LH; FSH; Relaxin.
Mention the source and the functions of the above mentioned hormones.
Briefly explain the events of fertilisation and implantation in an adult human female.
Draw the structure of an antibody molecule and label any four of its parts.
Mention the source and the role of the following in providing defence against infection in the human body : (I) Histamine (II) Interferons
(I) Write the scientific names of the two species of filarial worms causing filariasis.
(II) How do they affect the body of infected persons ?
(III) How does the disease spread ?
How does a chromosomal disorder differ from a Mendelian disorder ? Write one example for each.
Name the phenomenon that leads to situations like ‘XO’ abnormality in humans. Also name this genetic disorder. How are individuals with an XO chromosomal abnormality affected ? Write its symptoms as well as karyotype.
Differentiate between active and passive immunity. Write any three differences.
Work out separate monohybrid crosses up to $F_2$ generation between two pea plants and two Antirrhinum plants, both having contrasting traits with respect to the colour of the flower. Comment on the patterns of inheritance in the crosses carried out in such two cases.
Write the scientific name of the nematode that infects tobacco plants and identify the specific part of the plant that it targets and infects.
Explain how Agrobacterium vectors are used to protect tobacco plants from attacks by the root-knot nematode parasite.
Explain the different organizational levels of biodiversity at the genetic, species, and ecological levels, providing a suitable example for each category.
Explain Gause’s 'Competitive Exclusion Principle' and provide a suitable ecological example that demonstrates this principle in nature.
Mention a product of human welfare obtained with the help of each one of the following:
(a) Saccharomyces cerevisiae
(b) Propionibacterium shermanii
(c) Aspergillus niger
(d) Trichoderma polysporum
(e) Acetobacter aceti
(f) Streptococcus
One of the salient features of the genetic code is that it is nearly universal from bacteria to humans. Mention two exceptions to this rule. Why are some codes said to be degenerates?
Explain the polygenic inheritance pattern with the help of a suitable example.
(a) Draw a sectional view of seminiferous tubule of a human. Label the following cells in the seminiferous tubule: (i) Cells that divide by mitosis to increase their number, (ii) Cells that undergo meiosis I, (iii) Cells that undergo meiosis II, (iv) Cells that help in the process of spermiogenesis.
(b) Mention the role of Leydig cells.
Ecological pyramids are widely accepted but they still have some limitations. Write any two limitations.