CBSE Class 12 PCB Biology Board Paper 2026 — Set 5

Identify the parts P, Q, R, S in the figure given below and select the option in the correct order.

The foetal ejection reflex in human triggers the release of ________hormone from __________. Fill in the blanks by choosing right option.

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

In Pisum sativum, the flower colour may be violet (V) or white (v). What proportion of the offspring in a cross of ‘VV’ × ‘vv’ would be expected to be violet ?

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

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

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

Choose a correct option that shows an interaction in which one species benefits while the other is neither harmed nor benefitted

Transgenic animals have their genetic material manipulated. Select the correct option in reference to transgenic animals

Select the odd option in the context of convergent evolution

Which of the following fish led to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in Lake Victoria of East Africa ?

Assertion (A) : The embryo with 8 to 16 blastomeres is called a morula.

Reason (R) : The morula continues to divide and transform into trophoblast

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.

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.

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.

Define the term ‘amniocentesis’. Why has the government imposed a statutory ban in spite of its importance in the medical field ?

Name the lymphoid organ that acts as a large reservoir of erythrocytes. Explain its role as a lymphoid organ

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

List any three outbreeding devices that flowering plants have developed for cross-pollination and explain how they help to encourage cross-pollination.

Draw a labelled diagram of a ‘replicating fork’ showing the polarity. Why does DNA replication occur within such ‘fork’ ?

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

(a) Identify the plant which acts as an immediate ancestor of both ferns and conifers.

(b) Name the nearest ancestors of flowering plants.

(c) Name the most primitive group of plants.

(d) Psilophyton provides common ancestry to which classes ?

(e) Name the common ancestor of psilophyton and seed ferns.

(f) Name the common ancestor of mosses and tracheophytes.

Mention a product of human welfare obtained with the help of each one of the following:

(a) Saccharomyces cerevisiae

(b) Propionibacterium shermanni

(c) Aspergillus niger

(d) Trichoderma polysporum

(e) Acetobacter aceti

(f) Streptococcus

Transgenic animals are produced by man. Explain any three ways in which such animals can be beneficial to humans.

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

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

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

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

(ii) Mention the source and the functions of the above mentioned hormones.

Work out separate monohybrid crosses up to F₂ 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.

Answer the following questions:

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

(ii) 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

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

(ii) Differentiate between active and passive immunity. Write any three differences

(i) (a) Write the scientific names of the two species of filarial worms causing filariasis.

(b) How do they affect the body of infected persons ?

(c) How does the disease spread ?

(ii) Mention the source and the role of the following in providing defence against infection in the human body :

(a) Histamine

(b) Interferons