QUESTION PAPER
2025 BOARD EXAM
CBSE CLASS 12-PCB BIOLOGY Board Paper 2025 — Set 6
2025
BIOLOGY
CLASS 12-PCB
CBSE EXAMINATION PAPER-2025
BIOLOGY
(Solved)
General Instructions :
Read the following instructions carefully and follow them :
- This question paper contains 38 questions. All questions are compulsory.
- This question paper is divided into 5 sections.
- Section A – questions number 1 to 3 are case based questions
- Section B – questions number 4 to 17 are multiple choice questions
- Section C – questions number 18 to 25 are very short answer
- Section D – questions number 26 to 32 are short answer
- Section E – questions number 33 to 38 are long answer
- There is no overall choice given in the question paper. However, an internal choice has been provided in few questions.
- Use of calculator is NOT allowed.
Section A
Study the figure given below and answer the questions that follow
(1) (a) Identify the figure and state its importance.
(2) Why is air diffused into the aerator tank ? Explain.
(3) How is BOD related to organic matter present in the water ?
(4) What changes take place in the settling tank ?
The following question is based on pollination. Study the figures carefully and answer the questions that follow.
(1) Give the scientific terms for the processes taking place in Figures A and B respectively.
(2) Mention two conditions necessary for the process occurring in Figure B.
(3) State one advantage and one disadvantage of the process occurring in Figure B.
(4) Name the plant where , in some flower only the flower in progress in figure B takes place and give the reason responsible for it.
Section B
What are minisatellites ?
Identify the incorrect statement regarding PCR.
The following information is about drugs and tobacco. Select the correct statement from the options given below.
Given below are the events that are observed in an artificial hybridisation programme. Arrange them in the correct sequential order and select the correct option.
(i) Re-bagging
(ii) Selection of parents
(iii) Bagging
(iv) Dusting the pollens on stigma
(v) Emasculation
(vi) Collection of pollens from male parent
Which of the following conditions correctly describes the manner of determining the sex in the given options?
Choose the option that correctly describes the gynoecium of Michelia :
The given graph shows the range of variation among population members, for a trait determined by multiple genes. If this population is subjected to disruptive selection for several generations, which of the following distributions is most likely to result?
Which one of the following immune system components does not correctly match with its respective role?
Which one of the following is not the product of transgenic experiments?
A biologist studied the population of rats in a granary. He found the average natality was 280, average mortality was 200, immigration was 40 and emigration was 50. The net increase in population is :
India has only 2.4% of the world's land area but its share of the global species diversity is :
Out of the following, select the correct match :
Assertion (A) : Swiss cheese is characterized by large holes due to CO2 production. Reason (R) : It is ripened by growing a specific fungi.
Assertion (A) : A male individual always inherits haemophilia from his mother. Reason (R) : The gene for haemophilia lies on X-chromosome.
Section C
Name the Indian crop variety for which, in 1997, an American company got patent rights through the US Patent and Trademark Office. This is considered a case of Biopiracy.Justify.
How does a human body respond when vaccine is introduced into it? It is said that vaccinations are a must for a healthy society. Justify.
Give reasons for the following :
(i) Why can a woman generally not conceive a child after 50 years of age ?
(ii) Polar bodies are formed during oogenesis and not during spermatogenesis.
A few stages and their respective time period in the evolutionary history of human beings are mentioned in the flowchart given below :
Based on the above information, answer the following questions :
(a) Name one primate about 15 mya.
(b) Name one place where fossils of primates were discovered in Eastern Africa.
(c) Name the ancestor that lived in the East African grasslands about 2 mya.
(d) Name the hominid that was found around 1·5 mya
A karyotype of a human suffering from a certain disorder is given below :
(a) Identify the disorder.
(b) Write the symptoms of the disorder.
(c) Give reason for such a disorder.
"A fully developed foetus initiates its delivery from the mothers womb" Explain.
Section D
A village health worker was taking a session with women. She tells them that one has to be careful while using oral pills as a method of birth control. Wrong usage can actually promote conception.
(a) Analyse the above statement and compare the merits and demerits of using oral pills and surgical methods of birth control.
(b) Village women are confused as to how a thin metallic copper loop can provide protection against pregnancy. Explain the mode of action of IUDs. Give two points.
(a) " The process of evolution of different species in a given geographical area starts from a point and literally radiates to other
(b) Cite an example where more than one adaptive radiation has occurred in an isolated geographical area. Name the type of evolution your example depicts.
A segment of DNA, 'TTG AGG GGG ATG' was translated into an oligopeptide with the amino acids, Lysine Serine Proline Tyrosine.
(a) Write the codons in correct sequence for the four amino acids.
(b) If first adenine in DNA is substituted by guanine, what will be the sequence of amino acids in the new oligopeptide ?
(c) Write the anticodons for these amino acids.
A person is suffering from high grade fever. Which symptoms will help to identify if he/she is suffering from Typhoid, Pneumonia or Malaria ?
(a) Why are transgenic animals so called ?
(b) With the help of an example each, explain the role of transgenic animals in the following : (i) Vaccine safety (ii) Biological products
(a) Mention any two advantages of micropropagation techniques.
(b) Write in brief how the process is carried out in the laboratory.
(c) Name any two important food plants grown commercially by this method.
Name the type of food chains responsible for the flow of larger fraction of energy in an aquatic ecosystem and a terrestrial ecosystem, respectively. Mention any two differences between the two food chains.
Section E
Study the given diagram showing the sectional view of a seminiferous tubule.
Answer the following questions:
(i) Label A, B, C and D in the figure.
(ii) What will be the number of chromosomes in secondary spermatocyte and spermatid respectively?
(iii) Explain the terms Spermiogenesis and Spermiation.
How does alien species invasion cause a decline in biodiversity? Explain. How have the following contributed to biodiversity loss?
I. Nile Perch
II. Lantana and Eichhornia
III. Clarias gariepinus
(ii) Why have certain regions been declared as biodiversity hotspots by environmentalists of the world ? Name any two such regions in India.
(b) Differentiate between the following :
(i) Polygenic Inheritance and Pleiotropy
(ii) Dominance, Codominance and Incomplete dominance
Study the figures given below showing initial stages in the formation of female gametophyte and answer the questions that follow.
(i) Identify (P) and (Q).
(ii) I. What kind of division does cell (P) undergo to form (Q) ?
II. How many (Q) cells form the embryo sac ? What is the name given to such kind of development ?
III. How many free nuclear mitotic divisions will the functional megaspore undergo to form the embryo sac ?
IV. Describe the structure of a mature female gametophyte.
(i) Write an equation for Verhulst-Pearl Logistic Growth Curve where : N = Population density at t r = Intrinsic rate of natural increase (ii) Draw a graph for a population whose population density has reached carrying capacity. (iii) Draw a growth curve where resources are non-limiting to growth of population. (iv) Which growth curve is considered more realistic and why ? Explain
Other Years — BIOLOGY