List of top Biology Questions asked in CBSE CLASS XII

What are transgenic animals?
If the cells in the leaves of a maize plant contain 10 chromosomes each, write the number of chromosomes in its endosperm and zygote. Name and explain the process by which an endosperm and a zygote are formed in maize.
Why does DNA replication occur within a replication fork and not in its entire length simultaneously?
The ecological pyramids may have an ‘upright’ or an ‘inverted’ shape. Justify with the help of suitable examples.
Explain how are plants benefitted by their association with “Glomus species.”
What does an ecological pyramid represent?
5\(\prime\)–G\(^\downarrow\)AATTC–3\(\prime\)
3\(\prime\)–CTTAA\(^\uparrow\)G–5\(\prime\)
(a) Name the restriction enzyme that recognises the given specific sequence of bases. What are such sequences of bases referred to as?
(b) What are the arrows in the given figure indicating? Write the result obtained thereafter.
Tropical regions harbour more species than the temperate regions. How have biologists tried to explain this in their own ways? Explain.
Mention one advantage and one disadvantage of amniocentesis.
“Farmers prefer apomictic seeds to hybrid seeds.” Justify giving two reasons.
The question consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
The question consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
The question consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
The question consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Match the following genes of the lac operon listed in column ‘A’ with their respective products listed in column ‘B’: \begin{center} \begin{tabular}{|c|c|} \hline Column A (Gene) & Column B (Product)
\hline a. ‘i’ gene & (i) \(\beta\)-galactosidase
b. ‘z’ gene & (ii) Lac permease
c. ‘a’ gene & (iii) Repressor
d. ‘y’ gene & (iv) Transacetylase
\hline \end{tabular} \end{center} Select the correct option:
A phenomenon where a male insect mistakenly identified the patterns of an orchid flower as the female insect partner, and tries to copulate and thereby pollinates the flower is said to be:
Identify the correct labellings in the figure of a fertilised embryo sac of an angiosperm given below:
If both the parents are carriers for thalassaemia, the chances of an afflicted child to be born to them is:
Study the pedigree chart of a family showing the inheritance pattern of a certain disorder. Select the option that correctly identifies the nature of the trait depicted in the pedigree chart.
If the sequence of nitrogen bases of the coding strand in a transcription unit is 5\(\prime\)–ATGAATG–3\(\prime\), 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:
Observe the schematic representation of assisted reproductive technology given below:
Identify the most appropriate technique depicted in the above diagram.
Which one of the following statements is correct in the context of observing DNA separation by agarose gel electrophoresis?
Interferons are proteins secreted by:
A single gene that controls the expression of more than one trait is said to show: