CBSE Board Exam 2026: Detailed Sample Paper Of Class 12 Biology

The Central Board of Secondary Education (CBSE) has released the final date sheet for Class 10 and 12 board exams for the academic year 2025-26. The board exams for both the classes will begin on February 17, 2026. Providing students multiple opportunities to improve their performance, the board has decided to conduct two board exams for Class 10 this year.

To help students familiarise themselves with the new examination pattern, CBSE has released sample papers for all subjects. The board has advised students to carefully go through these papers to understand the types of questions, marking schemes, and paper formats.

Here is a detailed sample paper for Class 12 Biology.

Justify the following statements with suitable proof/examples: - 
A. ‘competition is not limited to closely related species' 
B. ‘competition is not always dependent on resources being limiting' 
C. ‘competitive exclusion occurs in nature' 
D. ‘competing species may evolve mechanisms for co-existence' 
E. ‘competition in nature comes from what is called ‘competitive release'' 
OR 
A. How does a simple food chain exemplify the First Law of Thermodynamics? 
B. The table below shows the number of species in different parts of the world.
Columbia- 1,400
India-1,200
Northern South America- 1,300
New York- 105
Denmark- 504
Identify the common factor in regions with a higher number of bird species and suggest at least two reasons for this greater diversity.

Some plant and animal pathogens serve as one of the tools of recombinant DNA (rDNA) technology.' A. Name one animal and one plant pathogen and discuss the pathogenic nature of both. State how they serve as a tool in rDNA technology. B. What are the enzymes needed for rDNA technology? C. A farmer owns a cotton farm land which is getting infested with coleopteran pests. He is not willing to use the microbes to protect his farm. i. Name an alternate method to introduce the gene of interest the pathogen would have otherwise delivered and discuss how the alternate method would deliver the gene. ii. State how this gene would control the pest.
OR
BamH1 is a restriction enzyme which recognizes the sequence- 5' - GGATCC - 3'. The restriction activity of this enzyme is between G and G. A. Construct the palindrome for the above sequence. B. Draw a labeled diagram to show the formation of recombinant DNA (rDNA) using BamH1. C. PBR322 is a plasmid that has a restriction site for this enzyme at the tetracycline resistant gene. If BamH1 were to be used, how will it impact the response of the transformant with rDNA to antibiotics ampicillin and tetracycline. Justify.

Why are both the strands not copied during transcription? B. How is transcription a more complex process in eukaryotic cells? Explain the additional processes that a precursor mRNA has to undergo in these organisms.

The antibody concentration in a young calf was studied. It was found that the antibodies derived from colostrum (passive immunity) decreased from day 1 to 14, while the antibodies derived from immune cells (active immunity) increased between day 1 to day 14 and remained steady thereafter. 
A. What do you think is the difference between passive and active immunity in this case? (1) 
B. What kind of immunity will be observed when a vaccine is administered to the calf and why?

Attempt either subpart C or D.
C. What kind of trend does passive immunity show and why? 
OR 
D. Why does active immunity start after 14 days as per the above graph?

Which of these fruits can be considered as parthenocarpic? Give a reason. (1) 
OR 
D. Which of the fruits P, Q, R or S is a true fruit with seeds? Give reason.

The population pyramids of Japan for the years 1950, 2007 and on the basis of the estimated value for 2050 have broad-based, inverted bell and urn shape, respectively. Answer the following questions: 
A. Comment upon the growth status of the population on the basis of shape of the age pyramids.
B. What insights can you gain about their population dynamics?

The Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment is reduced. Enlist the process of how this is achieved.

Expand ELISA. On what principle is the ELISA test based? List two ways by which an infection can be detected by this test.

The population pyramids of Japan for the years 1950, 2007 and on the basis of the estimated value for 2050 have broad-based, inverted bell and urn shape, respectively. Answer the following questions: 
A. Comment upon the growth status of the population on the basis of shape of the age pyramids.
B. What insights can you gain about their population dynamics?

In guinea pigs, black coat colour (G) dominates over white (g) and brown eyes (B) dominate over blue (b). The alleles for coat colour and eye colour are not linked. What will be the probability of the offspring having blue eyes and a white coat if both parents are heterozygous for eye and coat colour? Find the probability using a Punnett square

Suggest a suitable contraceptive device for the following cases with justification.
(i)    Mohini does not want to take the risk of conception and sexually transmitted infections (STIs).
(ii)    Lalita has two children and does not want any more children. 
(iii)     Geeta wants a contraceptive that she can take till she wants to avoid conception and can resume back to her fertile life without the intervention of the doctor. Also, it should have a lower failure rate.

Q (i) Compare the upright and inverted ecological pyramids of biomass and explain the situations in which this is possible. 
(ii) Construct an ideal pyramid of energy if 200,000 joules of sunlight is available.
OR
A tropical rainforest in South America is home to more than 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles and 1,25,000 insects, snails and worms. From the given data, calculate the total number of known vertebrate species in the rainforest.
(i) Give a reason to justify the huge difference in the number of plant and animal species.