CBSE Class 12 2025 Biology 57-5-1 Question Paper Set-1 :Download Solutions with Answer Key

The histone core in a nucleosome of chromatin thread is a/an:

• (A) Pentamer
• (B) Hexamer
• (C) Heptamer
• (D) Octamer

Given below are few statements with reference to the uterus in the female reproductive system:

The myometrium exhibits strong contractions during the delivery of the baby.
The uterus opens into the cervix through a narrow opening called vagina.
The cavity of the cervix and the vagina forms the birth canal.
The outermost layer of uterus is a thin membranous perimetrium.
The uterus is supported by tendons attached to the pelvic wall.


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 (iv)

During the process of transcription, after binding to a promoter, RNA polymerase catalyses and makes the bases in the template strand of DNA available for base pairing, with the bases of:

• (A) Deoxyribonucleotide triphosphate
• (B) Deoxyribonucleoside triphosphate
• (C) Ribonucleotide triphosphate
• (D) Ribonucleoside triphosphate

Which of the following is not an example of aneuploidy?

• (A) Turner’s syndrome
• (B) Down’s syndrome
• (C) Phenylketonuria
• (D) Klinefelter’s syndrome

Colostrum secreted by the mother’s mammary glands in a human female during the initial days of lactation is rich in antibody:

• (A) IgE
• (B) IgD
• (C) IgA
• (D) IgG

Select the statements that are true for pollination mechanism in flowering plants from the given options:

In \textit{Vallisneria, the female flowers are pollinated by pollen grains inside the water.
In \textit{Zostera, pollen grains are released on the surface of water.
In most of the water-pollinated species, pollen grains are covered by a mucilaginous coating.
Pollination by water is quite rare and limited to about 30 genera.

Choose the correct answer:

• (A) (i) and (ii)
• (B) (ii) and (iii)
• (C) (iii) and (iv)
• (D) (i), (iii) and (iv)

Which of the following combinations is a correct example of convergent evolution in Australian marsupials and placental mammals?

 

Isolation of DNA from a fungal cell can be achieved by using:

• (A) Cellulase
• (B) Chitinase
• (C) Lysozyme
• (D) Protease

During a monohybrid cross involving a tall pea plant with a dwarf pea plant, the offspring populations were tall and dwarf in equal ratio. Find out the genotype of parent pea plants.

• (A) Tt × tt
• (B) TT × Tt
• (C) tt × tt
• (D) Tt × Tt

What would happen if a gene encoding a polypeptide of 50 amino acids, 25^th Codon (UAU) is mutated to “UAA”?

• (A) A polypeptide of 49 amino acids will be formed.
• (B) A polypeptide of 25 amino acids will be formed.
• (C) A polypeptide of 24 amino acids will be formed.
• (D) A polypeptide of 50 amino acids will be formed.

Large scale industrial production of Butyric acid for human welfare is done using the microbe:

• (A) Aspergillus sp.
• (B) Streptococcus sp.
• (C) Clostridium sp.
• (D) Trichoderma sp.

The correct depiction of the centrifugation step of the experiment conducted by Alfred Hershey and Martha Chase on using radioactive labelled phages to prove that DNA is the genetic material is:

Assertion (A): To generate only a part of the plant from a cell is totipotency.

Reason (R): Suitable special nutrient media and sterile conditions are required in \textit{‘in vitro’ conditions for the division of cells in explants.

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

Assertion (A): Biogas plants are more often built in rural areas.

Reason (R): The excreta or gobar of cattle is rich in \textit{Methanobacterium.

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

Assertion (A): Gene pairs present on the same chromosome may be tightly linked or loosely linked.

Reason (R): Frequency of recombination between gene pairs on different chromosomes as a measure of the distance between genes can be used for ‘mapping’ their position on the chromosomes.

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

Assertion (A): Cu-T, Cu-7 and LNG-20 are the most widely used copper-releasing IUDs.

Reason (R): Cu-ions in IUDs effectively suppress sperm motility and the fertilising capacity of sperms.

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

Student to attempt either option (A) or (B):

(A) Give an account of the generalised structure of an antibody molecule produced by B-lymphocytes in response to the pathogen.
OR
(B) Other than public awareness and counselling, enlist four measures taken up by NACO, WHO and other NGOs to prevent the spread of HIV infection in the society.

Given below are the diagrammatic representations of the replicating fork of DNA in E. coli. Study the diagrams and answer the questions that follow.




(a) Which one of the three diagrams (i), (ii) or (iii) is the correct representation of the replicating fork of DNA replication? Explain your answer.

(b) Name the enzyme used in \textit{E. coli to join the newly synthesised fragments of DNA.

Student to attempt either option (A) or (B):

(A) Explain what is meant by the term amniocentesis. How is this technique misused in India?
OR
(B) Name any two VDs which might occur in a human female. State any two complications in a female if it is left untreated.

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) Name the specific enzyme that might have been used to make the multiple copies of foreign DNA before undergoing Step-1 of the process.

(b) How does the use of restriction enzyme EcoR I in Step-1 facilitate the action of DNA ligase to form the recombinant DNA molecule? Explain.

(c) Name the most commonly used host in the above process.

Student to attempt either option (A) or (B):

(A) Explain how the interaction between a fig tree and its tight one-to-one relationship with the pollinator species of wasp is one of the best examples of mutualism.
OR
(B) Correctly depict (also indicate the trophic level) and describe the ecological pyramid of number with 32 birds dependent on 20 insects feeding on one banyan tree.

Explain the neuroendocrine mechanism involved in the process of parturition in a human female leading to the expulsion of the baby out of the uterus through the birth canal.

During a medical investigation, an infant was found to possess an extra copy of chromosome no. 21. Identify the disorder the child is suffering from. Describe the symptoms the child is likely to develop later in life.

(a) Write the full form of BOD.

(b) Define BOD. Explain how it is a measure of the organic matter present in the water body.

Enlist three advantages of genetically modified plants.

Study the diagram above and answer the following questions:
[label=(\alph*)]
How many alleles are involved in blood grouping?
A person having ‘AB’ blood group has both dominant alleles. What is this inheritance type called?
A man with ‘A’ blood group marries a woman with ‘B’ blood group. Can they have a child with ‘O’ blood group? Explain with the help of a cross.

Explain how the loss of habitat and fragmentation drives plants and animals to extinction with the help of an example of habitat loss in the Tropical Rain Forest. Also write the effect of fragmentation of a habitat on the population decline.

Many of the flowering plants producing hermaphrodite flowers have developed many devices to discourage self-pollination and to encourage cross-pollination. Given below is a picture of one such outbreeding device in a flowering plant. Study the picture and answer the questions that follow:





[label=(\alph*)]
Explain how the given type of pollination is advantageous to the plant.
Can this flowering plant show geitonogamy? Justify your answer.

Read the following passage and answer the questions that follow.

Highly conserved proteins such as Haemoglobin and Cytochrome-C provide the best biochemical evidences to trace evolutionary relationships between different groups. Cytochrome-C is formed of 104 amino acids. Cytochrome-C is the respiratory pigment present in all eukaryotic cells. It has evolved at a constant rate during evolution. In chimpanzees and humans, Cytochrome-C genes are identical. The given data shows the evolution of the Cytochrome-C gene in different mammals from kangaroos, cows, rodents to humans:

What do you infer about the type of evolution (convergent or divergent) for the given pair of groups and why?

[(i)] Human and Kangaroo
[(ii)] Human and Rodent
[(i)] Define convergent evolution.

OR
[(ii)] Define divergent evolution.

Read the following passage and answer the questions that follow.

In 2021, 5.3 percent of 15 to 16-year-olds worldwide (13.5 million individuals) had used \textit{Cannabis in the past year according to UNODC. The adolescent brain is still developing and drug use can have long-term negative effects. Early drug use initiation can lead to faster development of dependence than in adults and other problems in adulthood.

Parts of the Amazon Basin are at the intersection of multiple forms of organised crimes that are accelerating devastation, with severe implications for the security, health and well-being of the population across the region. The direct impact of coca cultivation on deforestation is minimal, but indirectly it acts as a catalyst for “Narco-deforestation”. The laundering of drug trafficking profits into land speculation etc. is posing a growing danger to the world’s largest rainforest.


Which age group or period of growth are people more vulnerable to drug abuse?

Explain the negative impact of coca cultivation on the world’s largest rainforest.

[(i)] From which part of the plant are cannabinoids mainly obtained? Mention any one negative effect of this drug on adolescents.

OR

[(ii)] State the scientific name of the plant from which coca alkaloids are derived and state one negative impact of use of excessive dosage of cocaine.

Define transgenic animals. Explain in detail any four areas where they can be used for human benefit.

OR

Describe the structure and working of a sparged stirred-tank bioreactor.

Describe the population growth curve applicable in a population of any species in nature that has unlimited resources at its disposal.
Explain the equation of this growth curve.
Name the growth curve and depict a graphical plot for this type of population growth.

OR
Explain the conclusion drawn by Alexander von Humboldt during his extensive explorations in the wilderness of South American jungles.
Give the equation of the Species-Area relationship.
Draw a graphical representation of the relation between species richness and area for a wide variety of taxa such as birds, bats, etc.

Explain the structure of a typical monocotyledonous embryo of a flowering plant.
How are multiple embryos formed in a citrus fruit? What is the mechanism known as?

OR
Name and explain the structural organisation of the male sex accessory ducts in the human male reproductive system.
Describe the role of gonadotropin FSH in the regulation of spermatogenesis.