List of top Biology Questions asked in CBSE CLASS XII

Observe the schematic representation of assisted reproductive technology given below: 
 


Identify the most appropriate technique depicted in the above diagram. 
 

A phenomenon where a male insect mistakenly identified the patterns of a flower as the female insect partner, and tries to copulate and thereby pollinates the flower is said to be:
Which one of the following statements is correct in the context of observing DNA separation by agarose gel electrophoresis?

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: 
 

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

Which one of the following chromosomal events will not result in genetic variation amongst the offspring?
A person with trisomy of the 21st chromosome shows:
(i) Furrowed tongue
(ii) Characteristic palm crease
(iii) Rudimentary ovaries
(iv) Gynaecomastia
Select the correct option from the choices given below:
(b) In which condition will the pyramid remain always upright?
(b) Name the transgenic animal having the largest number amongst all the existing transgenic animals.
(a) “Mother’s milk is considered very essential for the new born infant.” Justify.
(a) What are transgenic animals?
State why plant breeders are interested in artificial hybridisation programme. How do they carry out this process?
How does latitude influence the species richness of an ecosystem?
(b) Mention what does ‘K’ in the graph represent.
Assertion (A): In molecular diagnosis, single stranded DNA or RNA tagged with radioactive molecule is called a probe.
Reason (R): A probe always searches and hybridises with its complementary DNA in a clone of cells.
(ii) Describe the different steps in the sexual mode of reproduction in the life cycle of a malarial parasite.
Study the following list of bioactive substances and their action:
\[ \begin{array}{|c|c|} \hline \textbf{Bioactive Substance} & \textbf{Role} \\ \hline \text{Statin} & \text{Removal of oil stains} \\ \text{Cyclosporin A} & \text{Removal of clots from blood vessels} \\ \text{Streptokinase} & \text{Lowering of blood cholesterol} \\ \text{Lipase} & \text{Immunosuppressive agent} \\ \hline \end{array} \]
Select the option that gives the correct identification of ovum, morula, and blastocyst in a human female reproduction system as shown in the following diagram:
\begin{figure}[h!] \centering \includegraphics[width=0.5\linewidth]{Screenshot 20250115 135817.png} % Replace with the correct path to your image \caption{Human Female Reproductive System} \label{Human Female Reproductive System} \end{figure}
In a fertilized ovule of an angiosperm, the cells in which n, 2n, and 3n conditions respectively occur are:
Study the table given below:
\[ \begin{array}{|c|c|} \hline \textbf{Contraceptive/Contraceptive Method} & \textbf{Mode of Action} \\ \hline \text{A. The pill} & \text{I. Prevent sperm reaching cervix} \\ \text{B. Condom} & \text{II. Prevent implantation} \\ \text{C. Vasectomy} & \text{III. Inhibits ovulation} \\ \text{D. CopperT} & \text{IV. Semen contains no sperm} \\ \hline \end{array} \] Select the option where contraceptive/contraceptive method are correctly matched with their mode of action.
(b) Write the symptoms of malaria in humans and explain what causes these symptoms.
(iii) Work out a cross to explain how normal parents may have a sicklecell anaemic child.
(iii) Explain the charging of an adaptor molecule. Why this molecule needs to be charged?
(iii) List any two ‘out breeding devices’ in flowering plants. Explain why do plants develop such devices.
(b) Answer the following questions on sicklecell anaemia:
(i) Why is sicklecell anaemia, a human blood disorder, so named?