CBSE Class 12 Biology Question Paper 2025 Set 2- 57/6/2 (Available) : Download Solution with Answer Key

Choose the correct option that indicates the enzyme, ribozyme in bacteria that acts as a catalyst.

• (A) 28S rRNA
• (B) 5.8S rRNA
• (C) 26S rRNA
• (D) 23S rRNA

When a pure tall pea plant (Pisum sativum) with green pod is crossed with a dwarf pea plant with yellow pod, how many dwarf pea plants, out of 16, will be produced in the F\textsubscript{2} generation?

• (A) 9
• (B) 3
• (C) 4
• (D) 1

Some of the important goals of HGP are given below. Choose the correct goal of HGP.

• (A) Identify approximately 20,000 - 30,000 genes in human DNA.
• (B) Determine the sequence of two billion chemical base pairs of human DNA.
• (C) Trace human history and disease associated sequences.
• (D) Address the ethical, legal and social issues that may arise from the project.

Inheritance of which of the following traits is shown in the cross given below?

Choose the correct option from the following:

• (A) Autosomal recessive trait
• (B) X-linked dominant trait
• (C) X-linked recessive trait
• (D) Autosomal dominant trait

Given below are few statements with reference to the human male reproductive system:

• (A) Paired seminal vesicles, prostate gland and bulbourethral gland constitute the male accessory glands.
• (B) Secretions of the male accessory glands constitute the seminal plasma.
• (C) Secretions of the bulbourethral glands help in the lubrication of the penis.
• (D) Enlarged end of the the penis is known as foreskin.
• (E) Seminal plasma is rich in fructose, calcium and certain enzymes.
• Choose the option with all true statements from the given options:
• (A) (i), (ii) and (iv)
• (B) (ii), (iii) and (v)
• (C) (ii), (iv) and (v)
• (D) (i), (iii) and (v)
• .

If a natural population of 60 individuals is in Hardy-Weinberg equilibrium for a gene with two alleles B and b, with the gene frequency of allele B of 0.7, the genotype frequency of Bb will be:

• (A) 0.21
• (B) 0.42
• (C) 0.49
• (D) 0.56

In a DNA, the percentage of thymine is 20. What is the percentage of guanine in it?

• (A) 20%
• (B) 40%
• (C) 30%
• (D) 60%

Select the statements that are true for the embryo of the flowering plants from the given options:

• (A) The zygote forms a proembryo and subsequently heart-shaped, globular and mature embryo.
• (B) Most zygotes divide to form embryo only after a certain amount of endosperm is formed.
• (C) The embryo develops at the micropylar end of the embryo sac.
• (D) A typical dicotyledonous embryo consists of an embryonal axis and a scutellum.
• Choose the correct option from the following:
• (A) (i) and (ii)
• (B) (ii) and (iii)
• (C) (iii) and (iv)
• (D) (i) and (iv)

Human Immunodeficiency Virus is a member of the group of viruses known as:

• (A) Adenovirus
• (B) Retrovirus
• (C) Rhinovirus
• (D) Nucleopolyhedrovirus

The animals that evolved into the first amphibians during evolutionary history were:

• (A) Archaeopteryx
• (B) Salamander
• (C) Coelacanth
• (D) Lobe fins

The cloning site present in the rop site of E. coli cloning vector pBR322 is:

• (A) Pvu II
• (B) Pst I
• (C) EcoR I
• (D) BamH I

Bacteria growing anaerobically on cellulosic material produce large amounts of which gases? Select the correct option.

• (A) CH₃, CO₂, H₂
• (B) H₂, NH₃, CH₄
• (C) H₂O, Cl₂, H₂S
• (D) CO₂, CH₄, H₂

Assertion (A): In humans, filariasis is characterized by inflammation of the lower limbs.
Reason (R): Filarial worm usually lives in the lymphatic vessels of the lower limbs.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): Isolated single cells can be fused to produce somatic hybrids.
Reason (R): Cells selected for somatic hybridisation have desirable characters.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

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.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): In some species of asteraceae and grasses, seeds are formed without fertilization.
Reason (R): Formation of fruit without fertilization is called parthenocarpy.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

17. Study the given molecular structure of a 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?

(a) 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?

(b) Expand PID. Name any two common viral infections transmitted through sexual contact in human females.

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

(b) 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.

• (A) EcoR I to cut the plasmid and Hind III to cut the alien DNA.
• (B) 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?

(b) Many children in the metro cities are suffering from a very common exaggerated response of the immune system to certain weak antigens in the 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?

(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.

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.


Note:

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 determination mechanism in birds:
(a) Name the type of heterogamety observed in most birds.

(b) If the birds have 18 pairs of autosomal chromosomes and a pair of sex chromosomes, fill in the blanks (i), (ii), (iii) and (iv) in the table given below. (Use symbols Z and W for sex chromosomes).

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.

Explain the beneficial role of the following, produced as a result of the processes of biotechnology, to mankind:

(a) Cow named Rosie

(b) (α) − 1 − antitrypsin

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.



(a) What do you infer from the figures in Table No. 1 about the people with drug use disorders, 2022 (in millions)? State any two of your observations.

(b) 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.

(c) (i) Give the scientific name of (p) shown in Table No. 1. OR (ii) Give the scientific name of (q) shown in Table No. 1.

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:  




(a) 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?

(b) Which one of the following holds true for the data provided in the above table?

• (A) Greater the evolutionary distance, greater are the differences in the nitrogenous bases.
• (B) Lesser the evolutionary distance, greater are the differences in the nitrogenous bases.
• (C) Greater the evolutionary distance, lesser are the differences in the nitrogenous bases.
• (D) Lesser the evolutionary distance, lesser are the differences in the nitrogenous bases.

(c) (i) To which category of evolution (divergent or convergent) does the following relationship belong to? Justify your answer. Human and Rhesus Monkey

OR
(c) (ii) Differentiate between Convergent and Divergent evolution.