List of top Questions asked in CBSE CLASS XII

ELISA technique is based on the principle of:
The ‘molecular scissors’ fall in the category of:
Assertion (A): Plasmids are autonomously replicating circular extra-chromosomal DNA.
Reason (R): Plasmids are usually present in eukaryotic cells.
Study the following diagram of Transverse Section of a young anther of an angiosperm:
\textit{(Refer to the provided diagram)}
Select the option where parts ‘A’, ‘B’, and ‘C’ are correctly identified.
Identify the category of genetic disorder depicted in the pedigree chart given below:
Which of the options has correct identification of ‘P’, ‘Q’, and ‘R’ in the illustration of ‘Central Dogma’ given below?
Hugo de Vries proposed the mutation theory of organic evolution after his experiments on:
A list of organisms is given in column ‘R’, whereas in column ‘S’ a list of products produced by them: \begin{center} \begin{tabular}{|c|c|} \hline Column ‘R’ (Organisms) & Column ‘S’ (Products)
\hline \textit{Lactobacillus} & Cheese
\hline \textit{Saccharomyces cerevisiae} & Curd
\hline \textit{Aspergillus niger} & Citric acid
\hline \textit{Acetobacter aceti} & Acetic acid
\hline \end{tabular} \end{center} Select the option where the organisms are correctly matched with the product:
Study the table given below: \begin{center} \begin{tabular}{|c|l|l|} \hline Contraceptive & Mode of Action
\hline A. The pill & I. Prevent sperm reaching cervix
B. Condom & II. Prevent implantation
C. Vasectomy & III. Inhibits ovulation
D. Copper-T & IV. Semen contains no sperm
\hline \end{tabular} \end{center} Select the option where contraceptive/contraceptive method are correctly matched with their mode of action:
In a fertilized ovule of an angiosperm, the cells in which \(n\), \(2n\), and \(3n\) conditions respectively occur are:
Give the scientific name of the bacteria widely used in biotechnology to create a GM cotton crop resistant to bollworm attacks.
Explain any three roles of ‘predation’ in an ecosystem with the help of suitable examples.
Specific site at which meiosis II is completed.

Three crosses were carried out in pea plants with respect to flower colour violet/white (V/v) and flower position axial/terminal (A/a). Study in the table the crosses ‘a’, ‘b’ and ‘c’ where parental phenotypes and their $F_1$ progeny phenotypes are given. 
Find the genotypes of each of the parental pairs of crosses ‘a’, ‘b’ and ‘c’. 

Explain how GM cotton crop is able to resist insect attacks.

Explain the mechanism of switching ‘on’ of the structural genes of lac operon.
 

“Regulation of lac operon is referred to be negatively regulated.” Justify giving a reason.
 

Describe the life cycle of Plasmodium from the time it enters the human body till a female Anopheles mosquito bites an infected person.
Mention the two events of Plasmodium life cycle that occur within the female Anopheles body.
A patient is suffering from the infection of the alveoli of lungs and is showing the symptoms of fever, chills, cough, headache, and bluish-colored lips and fingernails. The patient was diagnosed to be suffering from the infection of:

The linking of the antibiotic resistance gene with the plasmid vector of Salmonella typhimurium by Stanley Cohen and Herbert Boyer was made possible by the enzyme:
 

In an experiment, {E. coli is grown in a medium containing \({}^{14}NH_4Cl\) (\({}^{14}N\) is the light isotope of Nitrogen) followed by growing it for six generations in a medium having the heavy isotope of nitrogen (\({}^{15}N\)). After six generations, their DNA was extracted and subjected to CsCl density gradient centrifugation. Identify the correct density (Light/Hybrid/Heavy) and ratio of the bands of DNA in CsCl density gradient centrifugation:}
The population growth curve applicable for a population of beetles growing in nature under unlimited resource conditions available to them will be:

Which one of the following represents the correct annealing of primers to the DNA to be amplified in the PCR? 

Assertion (A): The stirrer facilitates the even mixing of oxygen availability in a bioreactor. 
Reason (R): Stirred-tank bioreactors generally have a flat base.}