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.
Assertion (A): Saheli is the World’s first non-steroidal oral contraceptive pill.
Reason (R): It has been developed by National Institute of Immunology, New Delhi.
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:
Evolution of modern man involves the following man-like primates. Choose the correct series of human evolution:
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?
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.
Amplification of gene of interest by using DNA polymerase may go up to:
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.
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:
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?
The process of mineralization by microorganisms helps in the release of:
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:
GEAC stands for
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?
Describe ‘Ex situ’ approach for conserving biodiversity. Give any two examples.
The world is facing the accelerated rate of species extinctions due to human activities. Explain any three major causes of biodiversity losses.
Draw a graph showing species-area relationship. Name the naturalist who studied such relationship. Write the observation made by him.
Explain giving three reasons why tropics show greatest levels of species diversity.
Why are Transgenic animals being produced? Explain any four reasons.
What are transgenic animals?
Explain the steps of amplification of gene of interest using PCR technique.
Explain how is a bacterial cell made ’competent’ to take up recombinant DNA from the medium.
Draw the diagram of a mature pollen grain released at the two-celled stage and label four parts in it.
Describe the three types of pollination that can occur in a chasmogamous bisexual flower.
Mention the number of chromosomes at each stage. Correlate the life phases of the individual with the stages of the process.