CBSE Class 12 Biology Set 2 - (57/5/2) Question Paper 2026 with Solution PDF

In a human female, menstrual cycle of 28 days is represented by the diagram given below. Select the correct statement related with this diagram.

• (A) Primary follicle of ovary matures into Graafian follicle in phase II.
  
• (B) The hormone secreted in large amounts in phase III is also responsible for maintaining pregnancy in human females.
  
• (C) Corpus luteum secretes progesterone in phase I, however it degenerates completely in phase III.
  
• (D) Both (A) and (B).
  

The cells of endosperm have 24 chromosomes. What will be the number of chromosomes in the gametes?

• (A) 8
  
• (B) 16
  
• (C) 23
  
• (D) 32

During different phases of menstrual cycle, hormones are secreted. Choose the option showing the correct sequence of hormones.

• (A) FSH, Progesterone, Estrogen
  
• (B) Estrogen, FSH, Progesterone
  
• (C) FSH, Estrogen, Progesterone
  
• (D) Estrogen, Progesterone, FSH

A DNA molecule is 160 base pairs long. It has 30% Guanine. How many Adenine bases are present in this DNA molecule?

• (A) 48
  
• (B) 64
  
• (C) 96
  
• (D) 192
  

Arrange the following in the correct sequence of their evolution and select the correct option:
• [(i)] Seaweed
• [(ii)] Invertebrates
• [(iii)] Jawless fish

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

S is the stimulant of central nervous system and interferes with the transport of T, a neurotransmitter. Identify S and T and choose the correct option.

• (A) S – Cocaine, T – Dopamine
  
• (B) S – Heroin, T – Acetylcholine
  
• (C) S – Heroin, T – Dopamine
  
• (D) S – Cocaine, T – Acetylcholine

Select the odd option in the context of convergent evolution.

• (A) Eyes of Octopus and Mammals
  
• (B) Flippers of Penguins and Dolphins
  
• (C) Flying Squirrel and Flying Phalanger
  
• (D) Thorns of Bougainvillea and Tendrils of Cucurbita
  

Monascus purpureus is a yeast used commercially in the production of which one of the following?

• (A) Ethanol
  
• (B) Streptokinase
  
• (C) Citric acid
  
• (D) Statins
  

Given below is the restriction site of a restriction endonuclease Pst I and the cleavage sites on a DNA molecule.

• (A) 5' C – T – G C – A – G 3' and 3' G – A – C – G – T C 5'
  
• (B) 5' C – T G – C – A – G 3' and 3' G – A – C – G T – C 5'
  
• (C) 5' C – T – G – C A – G 3' and 3' G – A – C – G T – C 5'
  
• (D) 5' C – T – G – C – A G 3' and 3' G A – C – G – T – C 5'

Which of the following ecosystems is most productive in terms of net primary productivity?

• (A) Desert
  
• (B) Tropical rainforests
  
• (C) Oceans
  
• (D) Estuaries

Bt-toxin genes have been expressed in plants in order to provide resistance against:
• [(i)] lepidopterans and fungi
• [(ii)] animals and bacteria
• [(iii)] coleopterans and dipterans
• [(iv)] lepidopterans

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

According to IUCN, some of the extinctions include:
• [(i)] Dodo
• [(ii)] Indian gazelle
• [(iii)] Thylacine
• [(iv)] Steller’s Sea Cow

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

Assertion (A): Genetically modified microbes help in crop protection.
Reason (R): Bacillus thuringiensis (Bt) bacteria control insects by producing prototoxins.

• (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): Trichoderma species are free living fungi that are very common in the root ecosystems.
Reason (R): They are effective bio-control agents of several plant pathogens.

• (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): The endometrium undergoes cyclic changes during the menstrual cycle.
Reason (R): Perimetrium contracts strongly during delivery of the baby.

• (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): Repetitive sequences make up a very large portion of human genome.
Reason (R): Repetitive sequences do not have direct coding functions in the genome.

• (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.

Draw a labelled diagram of the embryonic stage that gets implanted in the human uterus. State the functions of two labelled parts.

Mention the functions of each of the following:
(i) Tassels of Corn Cob:
(ii) Scutellum:

Farmers prefer apomictic seeds over hybrid seeds. Give any two reasons.

Suggest how a virus-free healthy plant can be obtained from a diseased sugarcane plant.

In order to force bacteria to take up the recombinant DNA, they must be made competent. Explain how it can be achieved.

Differentiate between grazing food chain and detritus food chain.

Ecological pyramids are widely accepted but they still have some limitations. Write any two limitations.

One of the salient features of the genetic code is that it is nearly universal from bacteria to humans. Mention two exceptions to this rule. Why are some codes said to be degenerates?

(a) Draw a sectional view of seminiferous tubule of a human. Label the following cells in the seminiferous tubule: (i) Cells that divide by mitosis to increase their number, (ii) Cells that undergo meiosis I, (iii) Cells that undergo meiosis II, (iv) Cells that help in the process of spermiogenesis.
(b) Mention the role of Leydig cells.

Explain the polygenic inheritance pattern with the help of a suitable example.

Mention a product of human welfare obtained with the help of each one of the following:
(a) Saccharomyces cerevisiae
(b) Propionibacterium shermanii
(c) Aspergillus niger
(d) Trichoderma polysporum
(e) Acetobacter aceti
(f) Streptococcus

Study the given chart showing the evolution of plants. Answer the following questions:

Write the scientific name of the nematode that infects tobacco plants and identify the specific part of the plant that it targets and infects.

Explain how Agrobacterium vectors are used to protect tobacco plants from attacks by the root-knot nematode parasite.

Explain the level of biodiversity at genetic, species, and ecological levels with the help of one example each.

Explain Gause's 'Competitive Exclusion Principle' with the help of a suitable example.

Read the following passage and answer the questions that follow:

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow : 

Read the following passage and answer the questions that follow:
The process of copying genetic information from template strand of DNA into RNA is called transcription. It is mediated by RNA polymerase. Transcription takes place in the nucleus of eukaryotic cells. In transcription, only a segment of DNA and only one of the strands is copied into RNA.

(a) Why is the strand of DNA with \( 3^{\prime} \rightarrow 5^{\prime} \) polarity transcribed and not the other strand of \( 5^{\prime} \rightarrow 3^{\prime} \) polarity ?

(b) (i) Why is hnRNA required to undergo splicing ?

(b) (ii) Mention the two additional processes which hnRNA needs to undergo after splicing to become functional.

(c) Why is only one strand of the DNA transcribed ? Give two reasons.

Work out separate monohybrid crosses up to \(F_2\) generation between two pea plants and two Antirrhinum plants, both having contrasting traits with respect to the colour of the flower. Comment on the patterns of inheritance in the crosses carried out in such two cases.

Name the phenomenon that leads to situations like ‘XO’ abnormality in humans. Also name this genetic disorder. How are individuals with an XO chromosomal abnormality affected ? Write its symptoms as well as karyotype.

How does a chromosomal disorder differ from a Mendelian disorder ? Write one example for each.

Mention the source and the role of the following in providing defence against infection in the human body : (I) Histamine (II) Interferons

Draw the structure of an antibody molecule and label any four of its parts.

Differentiate between active and passive immunity. Write any three differences.

(I) Write the scientific names of the two species of filarial worms causing filariasis.
(II) How do they affect the body of infected persons ?
(III) How does the disease spread ?

Arrange the following hormones in sequence of their secretion in a pregnant woman : hCG; LH; FSH; Relaxin.

Briefly explain the events of fertilisation and implantation in an adult human female.

Mention the source and the functions of the following hormones :

hCG; LH; FSH; Relaxin.