List of top Questions asked in CBSE CLASS XII

The world is facing accelerated rates of species extinction largely due to human activities. Explain any three human activities responsible for accelerated rates of species extinction.
In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow: \begin{figure}[h!] \centering \includegraphics[width=0.8\textwidth]{Screenshot 2025-01-17 101211.png} % Replace 'path_to_your_image.png' with the actual path to your graph image \caption{Graph showing the hormonal regulation and events during the menstrual cycle.} \label{fig:menstrual_cycle} \end{figure} Name the hormones and their source organ, which are responsible for menstrual cycle at puberty.
In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow: \begin{figure}[h!] \centering \includegraphics[width=0.8\textwidth]{Screenshot 2025-01-17 101211.png} % Replace 'path_to_your_image.png' with the actual path to your graph image \caption{Graph showing the hormonal regulation and events during the menstrual cycle.} \label{fig:menstrual_cycle} \end{figure} For successful pregnancy, at what phase of the menstrual cycle can an early embryo (up to 3 blastomeres) be implanted in the uterus (IUT) of a human female who has opted for Assisted Reproductive Technology (ART)? Support your answer with a reason.
In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow: \begin{figure}[h!] \centering \includegraphics[width=0.8\textwidth]{Screenshot 2025-01-17 101211.png} % Replace 'path_to_your_image.png' with the actual path to your graph image \caption{Graph showing the hormonal regulation and events during the menstrual cycle.} \label{fig:menstrual_cycle} \end{figure} Name the hormone and its source organ responsible for the events occurring during proliferative phase of menstrual cycle. Explain the event.}
In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow: \begin{figure}[h!] \centering \includegraphics[width=0.8\textwidth]{Screenshot 2025-01-17 101211.png} % Replace 'path_to_your_image.png' with the actual path to your graph image \caption{Graph showing the hormonal regulation and events during the menstrual cycle.} \label{fig:menstrual_cycle} \end{figure} In a normal human female, why does menstruation only occur if the released ovum is not fertilised? Explain.}
Read the following passage and answer the questions that follow: {“Mosquitoes are drastically affecting the human health in almost all the developing tropical countries. Different species of mosquitoes cause very fatal diseases so much so that many humans lose their life and if they survive, are unable to put in productive hours to sustain their life. With the result, the health index of the country goes down.” Name the form in which {Plasmodium} gains entry into
(i) human body
(ii) the female {Anopheles} body.
Read the following passage and answer the questions that follow: “Mosquitoes are drastically affecting the human health in almost all the developing tropical countries. Different species of mosquitoes cause very fatal diseases so much so that many humans lose their life and if they survive, are unable to put in productive hours to sustain their life. With the result, the health index of the country goes down.” Why do the symptoms of malaria not appear in a person immediately after being bitten by an infected female {Anopheles}? Give one reason. Explain when and how the symptoms of the disease would appear.
“DNA replication is continuous and discontinuous on the two strands within the replication fork.” Explain with the help of a schematic representation.
What are transgenic animals?
Name the transgenic animal having the largest number amongst all the existing transgenic animals.
State any 3 reasons for which these types of animals are being produced.
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?
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.
Explain how are plants benefitted by their association with “Glomus species.”
Tropical regions harbour more species than the temperate regions. How have biologists tried to explain this in their own ways? Explain.
What does an ecological pyramid represent?
The ecological pyramids may have an ‘upright’ or an ‘inverted’ shape. Justify with the help of suitable examples.
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:
“Farmers prefer apomictic seeds to hybrid seeds.” Justify giving two reasons.
Mention one advantage and one disadvantage of amniocentesis.
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: