List of top Biology Questions asked in CBSE CLASS XII

Assertion (A): One of the properties of genetic code is degeneracy.
Reason (R): Some amino acids can be coded by more than one codon.
RNA interference (RNAi) helps in making tobacco-plant resistant to a nematode (\textit{Meloidogyne incognita}). Choose the correct option that shows how RNAi is achieved:
The sequence of nitrogenous bases in a segment of a coding strand of DNA is
5' – AATGCTAGGCAC – 3'.
Choose the option that shows the correct sequence of nitrogenous bases in the mRNA transcribed by the DNA.
Assertion (A): A bioreactor provides the optimal conditions for achieving the desired product by providing optimum growth conditions.
Reason (R): The most commonly used bioreactors are of stirring type.
How many pollen grains and ovules are likely to be formed in the anther and ovary of an angiosperm bearing 50 microspore mother cells and 50 megaspore mother cells respectively?
Match the items in Column-A with that of Column-B:
Choose the option that matches the items of Column A with that of B correctly:
Transplantation of tissues/organs to some patients often fails due to rejection by the body of the patient. Which type of immune response is responsible for such rejections?
Amplification of gene of interest by using DNA polymerase may go up to:
GEAC stands for
Identify the labelled parts P, Q, R, and S in the stages of a dicot embryo shown in the diagram.
stages of a dicot embryo
Choose the option that indicates correct labelling of 'P', 'Q', 'R', and 'S' of embryo in differenct stages of its development.
The process of mineralization by microorganisms helps in the release of:
Match the following items of Column-I with that of Column-II:
Column-IColumn-II
(a) Trophoblast(iv) Outer layer of blastocyst
(b) Implantation(i) Embedding of blastocyst in the endometrium
(c) Inner cell mass(ii) Group of cells that would differentiate as embryo
(d) Morula(iii) Embryo with 8–16 blastomeres
Choose the option that matches Column-I with Column-II correctly:
A man whose father was colour-blind marries a woman who had a colour-blind mother and normal father. What percentage of male children of this couple will be colour-blind?

A child with blood group A has father with blood group B and the mother with blood group AB. Choose the option that gives the correct genotypes of father, mother, and the child:

A child with blood group A has father with blood group B
List two reasons that make copper releasing IUDs as effective contraceptives.

Given below is the schematic representation of spermatogenesis in human males:

schematic representation of spermatogenesis in human males

Choose the option that shows the correct labelling of ‘I’, ‘II’, ‘III’ and ‘IV’ in the given diagram.

Explain the structure of a mature embryo sac of a typical flowering plant.
A bilobed dithecous anther has 200 microspore mother cells per microsporangium. How many male gametophytes can be produced by this anther?

The process of copying the genetic information from one strand of DNA into RNA is termed as transcription. The principle of complementarity of bases governs the process of transcription, also except that uracil comes in place of thymine. Study the complete transcription unit given below and answer the following questions:

The process of copying the genetic information

Describe the location of (C) and (D) in the transcription unit.

Choose the correct option that indicates the enzyme, ribozyme in bacteria that acts as a catalyst.
Assertion (A): Corpus luteum secretes the hormone, progesterone. Reason (R): Hormone Progesterone is essential for maintenance of the endometrium.

The cloning site present in the \( \textit{rop}\) site of \(\textit{E. coli}\) cloning vector pBR322 is:

Assertion (A): In dihybrid crosses involving sex-linked genes in \(\textit{Drosophila}\), generation of non-parental gene combinations are observed 
Reason (R): Two genes present on different chromosomes show linkage and recombination in \(\textit{Drosophila.}\)

Study the given molecular structure of a double-stranded polynucleotide chain of DNA and answer the questions that follow.
molecular structure of a double-stranded polynucleotide

How is the interaction between \(\textit{Ophrys}\) and its specific bee pollinator one of the best examples of co-evolution? Explain.