List of top Questions asked in CBSE CLASS XII

A person with trisomy of 21\textsuperscript{st chromosome shows:}
(i) Furrowed tongue
(ii) Characteristic palm crease
(iii) Rudimentary ovaries
(iv) Gynaecomastia
Select the correct option from the choices given below:
If the sequence of nitrogen bases of the coding strand in a transcription unit is 5'–ATGAATG–3', the sequence of bases in its RNA transcript would be:
During biological treatment of sewage, the masses of bacteria held together by fungal filaments to form mesh-like structures are called:
Which one of the following is not a characteristic feature of “humus” that is formed during decomposition of detritus?
Which one of the following enzymes a fungal cell should be treated with to get the DNA along with other macromolecules released from it?
Match the following genes of the lac operon listed in column 'A' with their respective products listed in column 'B':
\[ \begin{array}{|c|c|} \hline \textbf{A: Gene} & \textbf{B: Products} \\ \hline \text{a. 'i' gene} & \text{(i) β-galactosidase} \\ \text{b. 'z' gene} & \text{(ii) lac permease} \\ \text{c. 'a' gene} & \text{(iii) repressor} \\ \text{d. 'y' gene} & \text{(iv) transacetylase} \\ \hline \end{array} \] Select the correct option:

Identify the most appropriate technique depicted in the above diagram: 

Identify the structural feature marked ‘A’ of Sanchi Stupa and choose the correct option from the following:

Identify the correct labellings in the figure of a fertilised embryo sac of an angiosperm given below: 

Explain the events which occur within a female Anopheles mosquito after it has sucked blood from a malaria patient.

(c) Name a species of mosquito other than female Anopheles and the disease, for which it carries the pathogen.

Natural selection operates in different ways in nature. 
(a) (i) Identify the type of natural selection depicted in the graph above. 
 

(i) Draw a schematic diagram of the cloning vector pBR322 and label:
(1) BamHI site 
(2) Gene for ampicillin resistance 
(3) Ori 
(4) Rop gene 

(iv) Why could parasite not survive in a transgenic tobacco plant?
(iii) How do sense and anti-sense RNAs function?
(iii) Name the type of flowers that are invariably autogamous.
(ii) How does geitonogamy differ from xenogamy?
(i) Name the nematode (scientific name) that infects the roots of tobacco plant and reduces its yield.
(iv) Why is insertional inactivation preferred over the use of selectable markers in cloning vectors?
(ii) Name the vector that is used to introduce nematode-specific genes into the host plant (tobacco).
(ii) State the role of ‘rop’ gene.
(iii) A cloning vector does not have a selectable marker. How will it affect the process of cloning?
(ii) Explain the role of hormones in spermatogenesis.
(iii) Write the conclusion they arrived at the end of their experiment.
(iii) Anthropogenic action can enhance the rate of evolution. Explain with the help of an example.