PSEB CLASS 12 BIOLOGY GUESS PAPER MARCH 2026

 

PUNJAB SCHOOL EDUCATION BOARD

GUESS PAPER / MODEL TEST PAPER

CLASS: 12th (BIOLOGY) | SESSION: 2025-26

Time: 3 Hours

Maximum Marks: 70

Note:

1. Question paper consists of four sections A, B, C and D with a total of 19 questions.
2. Section-A contains question number 1 having 20 parts of 1 mark each (12 MCQs, 4 Fill in the blanks, 4 True/False).
3. Section-B contains questions number 2 to 11 (10 short answer type questions of 2 marks each). Questions 4, 5, 9, 11 have internal choice.
4. Section-C contains questions number 12 to 16 (5 questions of 3 marks each). Questions 12 and 15 have internal choice.
5. Section-D consists of questions 17 to 19 (3 questions of 5 marks each). All questions have 100% internal choice.

SECTION A (20 Marks)

Q1. Multiple Choice Questions (I-XII):[12 × 1 = 12]

I. Double fertilization is unique to:

a. Gymnosperms b. Algae c. Angiosperms d. Bryophytes

II. The hormone responsible for ovulation (rupture of Graafian follicle) is:

a. FSH b. Estrogen c. LH d. Progesterone

III. "Saheli" is a:

a. Steroidal oral contraceptive pill b. Non-steroidal oral contraceptive pill c. Barrier method d. Surgical method

IV. The phenotypic ratio in a Mendelian dihybrid cross is:

a. 1:2:1 b. 3:1 c. 9:3:3:1 d. 1:1:1:1

V. The start codon for translation is:

a. UAA b. UAG c. AUG d. UGA

VI. Analogous organs are a result of:

a. Divergent evolution b. Convergent evolution c. Adaptive radiation d. Co-evolution

VII. Which antibody is most abundant in colostrum (first milk)?

a. IgG b. IgM c. IgA d. IgE

VIII. The antibiotic penicillin was discovered by:

a. Waksman b. Alexander Fleming c. Robert Koch d. Louis Pasteur

IX. The enzyme used to join DNA fragments (molecular glue) is:

a. DNA polymerase b. RNA polymerase c. DNA ligase d. Restriction endonuclease

X. Bt cotton is resistant to:

a. Aphids b. Bollworm c. Whitefly d. Nematodes

XI. The pyramid of energy in an ecosystem is always:

a. Inverted b. Spindle-shaped c. Upright d. Irregular

XII. Which of the following is a biodiversity hotspot in India?

a. Thar Desert b. Western Ghats c. Gangetic Plains d. Aravalli Hills

State True or False (XIII-XVI):[4 × 1 = 4]

XIII. Sporopollenin is resistant to high temperature and strong acids.
XIV. The genetic code is overlapping in nature.
XV. HIV primarily infects B-lymphocytes.
XVI. Insulin consists of two short polypeptide chains: Chain A and Chain B.

Fill in the Blanks (XVII-XX):[4 × 1 = 4]

XVII. The process of release of ovum from the ovary is called __________.
XVIII. __________ is the physical location of a gene on a chromosome.
XIX. __________ bacteria are responsible for methane production in biogas plants.
XX. The interaction where one species is benefited and the other is harmed is called __________.

SECTION B (20 Marks)

[2]Q2. What is apomixis? Explain its importance in hybrid seed industry.

[2]Q3. Write two major functions of the placenta in humans.

[2]Q4. What is amniocentesis? Why is there a statutory ban on it?

OR

Expand the following: a) GIFT, b) MTP

[2]Q5. Differentiate between Genotype and Phenotype.

OR

Explain the term 'Pleiotropy' with an example.

[2]Q6. State two differences between homologous and analogous organs.

[2]Q7. Differentiate between Active and Passive immunity.

[2]Q8. What is Biochemical Oxygen Demand (BOD)? What does a high BOD indicate in a water sample?

[2]Q9. State two functions of selectable marker genes in a cloning vector.

OR

Write two differences between Exonucleases and Endonucleases.

[2]Q10. What are Cry proteins? Name the organism that produces them.

[2]Q11. Distinguish between a Grazing Food Chain (GFC) and a Detritus Food Chain (DFC).

OR

What are 'Sacred Groves'? Mention their role in conservation.

SECTION C (15 Marks)

[3]Q12. Describe the experiment conducted by Meselson and Stahl to prove that DNA replication is semi-conservative.

OR

Explain the process of Translation (Initiation, Elongation, and Termination).

[3]Q13. Explain the mechanism of evolution by natural selection using the example of Industrial Melanism in peppered moths.

[3]Q14. Name the causative agent of Malaria. Describe its life cycle in the human host.

[3]Q15. Explain the role of Agrobacterium tumefaciens as a cloning vector in plants.

OR

What is RNA interference (RNAi)? How has it been used to develop nematode resistance in tobacco plants?

[3]Q16. Explain the following population interactions with one example each:
a) Mutualism
b) Commensalism

SECTION D (15 Marks)

[5]Q17. Describe the process of Spermatogenesis in humans with the help of a schematic representation. Mention the hormonal control of this process.

OR

With a neat labeled diagram, describe the structure of a typical Anatropous Ovule of an angiosperm.

[5]Q18. Explain the Inheritance of ABO blood groups in humans. What is Co-dominance?

OR

Describe the Lac Operon model of gene regulation in E. coli. Explain how it switches on and off in the presence and absence of lactose.

[5]Q19. Define Biodiversity. Explain the major causes of biodiversity loss (The Evil Quartet).

OR

Describe the Phosphorus Cycle in nature with the help of a schematic diagram. How does it differ from the Carbon Cycle?

--- End of Question Paper ---