QUESTION PAPER
2025 BOARD EXAM
CBSE CLASS 12-PCB BIOLOGY Board Paper 2025 — Set 5
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 37 questions. All questions are compulsory.
- This question paper is divided into 5 sections.
- Section A – questions number 1 to 4 are case based questions
- Section B – questions number 5 to 18 are multiple choice questions
- Section C – questions number 19 to 26 are very short answer
- Section D – questions number 27 to 33 are short answer
- Section E – questions number 34 to 37 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
Read the following passage and answer the questions that follow
According to evolutionary theory, every evolutionary change involves the substitution of a new gene for the old one and the new allele arises from
the old one. Continuous accumulation of changes in the DNA coding for proteins leads to evolutionary differences. The chemical composition of
DNA is basically the same in all living beings, except for differences in the sequence of nitrogenous bases. Given below are percentage relative similarities between human DNA and DNA of other vertebrates :
Read the following passage and answer the questions that follow
According to evolutionary theory, every evolutionary change involves the substitution of a new gene for the old one and the new allele arises from
the old one. Continuous accumulation of changes in the DNA coding for proteins leads to evolutionary differences. The chemical composition of
DNA is basically the same in all living beings, except for differences in the sequence of nitrogenous bases. Given below are percentage relative similarities between human DNA and DNA of other vertebrates :
(1) What is the term used for the substitution of a new gene for the old one and the new allele arising from the old one during evolutionary process ?
(2) Greater the evolutionary distance, greater are the differencesin the nitrogenous bases
(3) Greater the evolutionary distance, lesser are the differencesin the nitrogenous bases.
(4) Lesser the evolutionary distance, lesser are the differences in the nitrogenous bases.
(5) (i) To which category of evolution (divergent or convergent) doesthe following relationship belong to ? Justify your answer.Human and Rhesus Monkey
(6) Lesser the evolutionary distance, greater are the differencesin the nitrogenous bases.
(7) Differentiate between Convergent and Divergent evolution.
Read the following passage and answer the questions that follow.
Prevention is the frontline response to drug use. Effective interventions address the underlying conditions contributing to drug use, such as a lack of connection to family or community, instability, insecurity, trauma, mental health issues, etc. When addressed, these factors can effectively prevent the initiation of drug use and the progression to drug use disorders. Study the few key figures of drug use given below and answer the questions that follow.
(1) What do you infer from the figures in Table No. 1 about the people with drug use disorders, 2022 (in million) ? State any two of your observations.
(2) What do you infer from the figures in Table No. 1 about the people with drug use disorders, 2022 (in million) ? State any two of your observations.
(3) How are Hepatitis C and HIV related to drug use disorders by people, as shown in Table No. 2 ? State the correlation between the two.
(4) (i) Give the scientific name of (p) shown in Table
(5) (ii) Give the scientific name of (q) shown in Table
Section B
The process of splicing in eukaryotes represents the dominance of the :
Regulation of lac operon by repressor is referred to as :
SNPs in Human Genome Project refers to :
If a natural population with 50 individuals is in Hardy-Weinberg equilibrium for a gene with two alleles A and a, with the gene frequency of allele A of 0·6, the genotype frequency of Aa will be :
Given below are a few statements with respect to spermatogenesis in a human male. Choose the option with all true statements from the given options:
(i) Sperms are released from the seminiferous tubules by the process of spermiation.
(ii) Spermiogenesis involves the maturation of spermatids into sperms.
(iii) Spermatogonia produce spermatids by the process of spermiogenesis.
(iv) Meiosis II in secondary spermatocytes results in the formation of four equal haploid spermatids.
(v) Primary spermatocyte completes the first meiotic division forming two equal, diploid cells called secondary spermatocytes.
Study the pedigree chart of a family sharing the inheritance of sickle cell anemia.
The trait traced in the above pedigree chart is :
Which of the following do not follow the law of independent assortment ?
A characteristic property that distinguishes a malignant tumor from a benign tumor is :
The cloning site present in the tetracycline resistance gene of E. coli cloning vector pBR322 is :
Bottled fruit juices are clearer as compared to those made at home, as they are clarified by the use of :
In his observations of small black birds in the Galapagos Islands, Darwin found that all the finches arose from the original ancestor :
Assertion (A): In dihybrid crosses involving sex-linked genes in Drosophila, generation of non-parental gene combinations are observed. Reason (R): Two genes present on different chromosomes show linkage and recombination in Drosophila.
Assertion (A): A condom is used for avoiding chances of ovum and sperm meeting. Reason (R): It is made of thin rubber/latex sheath and is used to cover the penis before coitus.
Assertion (A): In humans, filariasis is characterized by inflammation in the lower limbs. Reason (R): Filarial worm usually lives in the lymphatic vessels of the lower limbs.
Section C
Arrange the given important steps of decomposition in their correct order of occurrence in the breakdown of complex organic matter and explain the fourth step in the process.
The basic scheme of the essential steps involved in the process of recombinant DNA technology is summarised below in the form of a flow diagram. Study the given flow diagram and answer the questions that follow.
(a)What is the technical term used for Step 4 in the above process ?
(b) Which of the given two combinations of restriction enzyme should
be used in Step 1 ? Justify your answer.
(i) EcoR I to cut the plasmid and Hind III to cut the alien DNA.
(ii) EcoR I to cut both the plasmid and alien DNA.
(a) (i) Explain why the milk produced by the mother during the initial days of lactation is considered to be very essential for the newborn infant.
(ii) What is the term used for the milk produced during the initial days of lactation ?
Many children in the metro cities are suffering from a very common exaggerated response of the immune system to certain weak antigens in air.
(i) What is the term used for the above mentioned disease ?
(ii) Name the main type of antibody produced by the immune system in response to this disease.
(iii) Which two main inflammation-causing chemicals are produced by the mast cells in such an immune response ?
Study the given molecular structure of double-stranded polynucleotide chain of DNA and answer the questions that follow.
(a) How many phosphodiester bonds are present in the given double-stranded polynucleotide chain ?
(b) How many base pairs are there in each helical turn of double helix structure of DNA ? Also write the distance between a base pair in a helix.
(c) In addition to H-bonds, what confers additional stability to the helical structure of DNA ?
Why are restrictions imposed on MTP in India ? Up to how many weeks or trimesters, is MTP considered relatively safe for a female, if necessary to perform, by a medical practitioner ?
How is the interaction between Ophrys and its specific bee
pollinator one of the best examples of co-evolution ? Explain.
Section D
Flowering plants with hermaphrodite flowers have developed many reproductive strategies to ensure cross-pollination. Study the given outbreeding devices adopted by certain flowering plants and answer the questions that follow
All plants belong to the same species.
- No pollen tube growth/inhibition of pollen germination on stigma.
- Pollen germination on stigma.
(a) Name and define the outbreeding device described in the above
table.
(b) Explain what would have been the disadvantage to the plant in the
absence of the given strategy.
(a) Alien species are highly invasive and are a threat to indigenous species. Substantiate this statement with the help of any two examples.
(b) State any two criteria for determining biodiversity hotspots
Answer the following questions with respect to the sex determining
mechanism observed in honey bee.
(a) Name the type of sex determination system observed in honey bee.
(b) Fill in the blanks (i), (ii) and (iii) in the given question.
(c) What will be the sex and chromosome number of the progeny formed from the unfertilised eggs of honey bee ?
Explain how the addition of lactose in the medium regulates the switching on of the lac operon in bacteria.
(a) Name and explain the role of inner and middle walls of the human female uterus.
(b) Write the location and function of fimbriae in human female
(a) What do you mean by activated sludge in an STP ?
(b) Explain the biological treatment of the major part of the sludge transferred from the large aeration tank into the anaerobic sludge digesters before its final release into the natural water bodies.
Explain the beneficial role of the following, produced as a result of the
processes of biotechnology, to mankind : 3
(a) Cow named Rosie
(b) -1-antitrypsin
Section E
(i) Explain how some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans but do not kill the Bacillus.
(ii) How is the above mechanism exploited for the production of Bt cotton plant by biotechnologists ?
(i) Explain how the amplification of gene of interest is done using PCR.
(ii) State two applications of the desired amplified fragment of DNA.
(i) Describe the Species-Area relationship as observed by Alexander von Humboldt, for a wide variety of taxa in nature.
(ii) Draw the graph showing Species-Area relationship for S = CAZ Species-Area relationship ?
(i) Describe the logistic population growth curve with the help of a suitable graphical representation.
(ii) Write the equation of Verhulst-Pearl logistic growth curve and explain wHat "K" and 'r' suggest in the given equation
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