List of top Biology Questions asked in CBSE CLASS XII

In which of the following chromosomal disorders do the individuals have short stature, small head, furrowed tongue, and partially open mouth?
Embryo formation without fertilization is observed in some species of:
Biodiversity hotspots cover less than 2% of Earth's land area. Strict protection of these areas can reduce the rate of ongoing extinctions. Explain.
Mention the difference in the site of transcription in a prokaryote and eukaryote cell.

Explain the following phases in the menstrual cycle of a human female: 
(1) Menstruation 
(2) Follicular phase 
(3) Luteal phase

Study the table given below:

\[ \begin{array}{|l|l|} \hline \textbf{Contraceptive/Contraceptive Method} & \textbf{Mode of Action} \\ \hline \text{A. The pill} & \text{III. Inhibits ovulation} \\ \text{B. Condom} & \text{I. Prevent sperm reaching cervix} \\ \text{C. Vasectomy} & \text{IV. Semen contains no sperm} \\ \text{D. Copper-T} & \text{II. Prevent implantation} \\ \hline \end{array} \]

Select the option where contraceptive/contraceptive method are correctly matched with their mode of action.

Given below is a list of some commercially important products in column A, whereas in column B are names of source organisms:
\[ \begin{array}{|l|l|} \hline \textbf{Column A (Bioactive Products)} & \textbf{Column B (Source Organisms)} \\ \hline A. \text{Cyclosporin – A} & i. \text{Streptococcus} \\ B. \text{Statins} & ii. \text{Trichoderma polysporum} \\ C. \text{Streptokinase} & iii. \text{Penicillium notatum} \\ D. \text{Penicillin} & iv. \text{Monascus purpureus} \\ \hline \end{array} \]

Select the option where the product and their source organisms are correctly matched.
How do the following organisms act as bio-fertilizers? Explain.
(a) Mycorrhiza
(b) Anabaena
(c) Rhizobium
Explain the charging of an adaptor molecule. Why does this molecule need to be charged?
Explain the genetic basis that results in the expression of this disorder.
Identify the polarity from ‘X’ to ‘Y’ in the mRNA segment shown. Mention how many more amino acids can be added to the polypeptide that is being translated and why.
Why is sickle-cell anaemia, a human blood disorder, so named?
Work out a cross to explain how normal parents may have a sickle-cell anaemic child.
Write the initiating codon for translation, its anticodon, and the amino acid it codes for.
Describe the different steps in the sexual mode of reproduction in the life cycle of a malarial parasite from the time of its initiation till where it is completed and ready to start a fresh cycle.}
‘A proper understanding of the menstrual cycle can help immensely in family planning.’ Do you agree with the statement? Provide reasons for your answer.
Describe the life cycle of HIV from the time of its entry into the human body till full-blown AIDS sets in.
Write the symptoms of malaria in humans and explain what causes these symptoms.
Which one of the two curves is more “realistic” and why?
Which of the two curves is relevant in present days with respect to human population in our country and why?
Draw a labelled diagram showing the different embryonic stages of a dicot plant, up to a fully mature embryo.
Growth curve ‘B’ shows a different pattern from that of growth curve ‘A’. Justify giving one reason.
Why does endosperm development precede embryo development in angiosperm seeds? State the role of endosperm in mature albuminous seeds.
Name this RNA product transcribed from the DNA that subsequently translates into a polypeptide of 400 amino acids. Mention the enzyme responsible for transcribing this type of RNA from the DNA.
Name and explain the process the RNA molecule transcribed from 8000 nucleotide-long DNA undergoes to be able to translate a polypeptide of 400 amino acids.