QUESTION PAPER
2026 BOARD EXAM
CBSE Class 12 PCB Biology Board Paper 2026 — Set 2
2026
Biology
Class 12 PCB
CBSE EXAMINATION PAPER-2026
BIOLOGY
(Solved)
General Instructions :
Read the following instructions carefully and follow them :
- This question paper contains 39 questions. All questions are compulsory.
- This question paper is divided into 5 sections.
- Section A – questions number 1 to 2 are case based questions
- Section B – questions number 3 to 18 are multiple choice questions
- Section C – questions number 19 to 26 are very short answer
- Section D – questions number 27 to 33 are short answer
- Section E – questions number 34 to 39 are long answer
- There is no overall choice given in the question paper. However, an internal choice has been provided in few questions.
- Use of calculator is NOT allowed.
Section A
(1) Name one core technique of biotechnology that alters the genetic material.
[1 Mark](2) What is a plasmid ? Mention its importance in biotechnology.
[2 Marks](3) Which gene was isolated by Cohen and Boyer and from which bacteria
[1 Mark]
(1) Mention two abiotic components of a pond ecosystem
[1 Mark](2) Differentiate between the roles of producers and decomposers in such an ecosystem.
[2 Marks](3) Draw a simple food chain operating in such an ecosystem and label each trophic level.
[1 Mark]Section B
To separate repetitive DNA from bulk genomic DNA, which of the following method is used ?
Select the correct option
In a dihybrid cross, 2400 individuals are produced in F₂ generation. Approximately how many will be phenotypically similar to parents ?
What could be the reason of extinction of Abingdon Tortoise from Galapagos Islands?
What conclusion can be drawn if the forelimbs of an aquatic animal and a terrestrial animal have similar anatomical structure ?
How many of the following features are related to Nirodh – a popular brand of condoms?
(i) Prevention of sexually transmitted infections.
(ii) Phagocytosis of sperms
(iii) Male contraceptive device
(iv) Acts as chemical barrier
(v) Physiological changes in cervical mucus
A bacterium having radioactive thymidine in its DNA is allowed to multiply in a medium having non-radioactive thymidine for two generations. What percentage of bacteria will have radioactive thymidine in its DNA ?
What is the role of histamine released by mast cells ?
Which of the following is used to visualize DNA bands under UV light after gel electrophoresis ?
Genetically modified tobacco plants were produced using Agrobacterium vectors. Which property of Agrobacterium helps in carrying nematode specific genes into the host plant ?
Assertion (A) : Apomixis leads to production of genetically identical off springs.
Reason (R) : Apomixis involves fertilization between two genetically similar plants.
Assertion (A) : Microbes are used for commercial production of alcohol and beverages.
Reason (R) : Yeast converts glucose into ethanol and carbon dioxide during fermentation
Assertion (A) : IUCN Red List helps in identifying and protecting endangered species worldwide.
Reason (R) : The list includes the species facing risk of extinction.
Assertion (A) : DNA Ligase is used to join DNA fragments.
Reason (R) : It catalyses the formation of glycosidic bonds between nucleotides
Section C
The diagram below shows the sequence of amino acids in part of haemoglobin molecule.
(i) If the base T is substituted with A, in ‘CTT’ of DNA strand how would it affect the haemoglobin chain ? 1
(ii) Name the condition and the effects associated with the above substitution
DNA is considered a more stable genetic material than RNA. Justify this statement with suitable reasons.
How do scientists use microinjection and gene gun in biotechnology ?
After significant reduction of BOD during secondary treatment of sewage, what further processes are carried out ? Mention any one important outcome of these processes.
In some cases, measuring population density by counting individuals may not be feasible. Mention two other parameters that can be used and justify their use with suitable examples.
What factors contribute to the Amazonian rain forests in South America being the most biodiverse regions on Earth?
(i) Name the organ that forms a connection between foetus and the uterus of a pregnant human female.
(ii) How does it support both nutrition and hormonal regulation ?
Give reasons for :
(i) All copulations do not lead to pregnancy.
(ii) Meiosis I in spermatogenesis and oogenesis are markedly different.
Section D
There are limitations of traditional breeding techniques that led to promotion of micro-propagation.
(a) Mention two advantages of micropropagation.
(b) Give two examples where it is commercially adopted
(a) Give the scientific name of the organism used by Morgan to study sex-linked traits.
(b) Write any four reasons why this organism made it an ideal experimental model.
Draw a neat diagram of enlarged view of one microsporangium of a Young anther of an angiosperm. Label the different layers of the wall and write the functions of the outermost and innermost layer.
Study the diagram given below:
(a) Name and explain the procedure shown in the diagram. Mention one of its advantage and one disadvantage.
(b) How is ‘Saheli’ different from other oral pills in terms of its composition and advantage
S.L. Miller conducted an experiment in 1953 to simulate the conditions of early earth in a laboratory setup.
Answer the following questions based on the experiment
(a) What was the aim of his experiment ?
(b) Name the gases used and the source of energy
(a) What is a genetic code ?
(b) Why did scientists feel the need to propose a genetic code ?
(c) Genetic code is said to be ‘Universal’. Why
(a) A person inhales dust and pathogens but does not always fall sick. Explain how the body protects against such infections.
(b) Name and describe any two barriers involved in this protection
Section E
(i) Explain the role of stigma in pollen pistil interaction.
(ii) Describe the post pollination events leading to double fertilization in angiosperms starting with 2-celled pollen grain.
(i) Explain menstrual phase in the menstrual cycle of human female.
(ii) Why is follicular phase also called proliferative phase ?
(iii) Explain the events that occur in Graafian follicle at the time of ovulation and thereafter.
(iv) Draw a Graafian follicle and label – Antrum and secondary oocyte.
Observe the segment of mRNA given below and answers the questions given below:
(i)Explain and illustrate the steps involved to make fully processed hn RNA.
(ii) Gene encoding RNA polymerase I and RNA polymerase III have been affected by mutation.
Explain its impact on the synthesis of polypeptide giving reasons.
In a particular cattle, the coat colour red and white are controlled by single pair of alleles. A calf that receives allele for red coat from mother and allele for white coat from father shows equal number of red and white hairs on its coat.
(i) Is this an example of Co-dominance or incomplete dominance. Give a reason for your answer.
(ii) With the help of a genetic cross upto F₂ generation, explain
what will be the consequent phenotype of calf when
(1) Red is dominant over white.
(2) Red is incompletely dominant.
A 30 year old man was admitted to a hospital with recurrent infections, weight loss, prolonged fever. His blood report showed a decline in count of T-Lymphocytes thus affecting immune system.
(i) Identify the disease and its causative agent.
(ii) How did the pathogen affect the immune system once it entered the body ? Explain.
(iii) Mention two major modes of its transmission.
(i) Why are microbes considered effective biocontrol agents in sustainable agriculture
(ii) Explain the role of the following as biocontrol agents naming the pests or diseases they help to control :
(1) A Bacterium
(2) A Fungus
(3) Virus
Other Years — Biology