The Bihar Board Class 12 Biology Guess Paper 2025 has been prepared strictly as per the latest BSEB exam pattern. Biology plays a vital role for students aiming for careers in medical and life sciences. This model paper includes 35 objective questions, 5 short answer questions, and 3 long answer questions with answers, which help students revise important concepts before the board examination.

Bihar Board Class 12 Biology Guess Paper 2025

Section A – Objective Questions (35 × 1 = 35 Marks)

Q1. Who is known as the Father of Genetics?
(a) Darwin
(b) Mendel
(c) Morgan
(d) Watson
Answer: (b) Mendel

Q2. Which is the structural and functional unit of kidney?
(a) Nephron
(b) Neuron
(c) Alveoli
(d) Glomerulus
Answer: (a) Nephron

Q3. Which blood group is called Universal Donor?
(a) A
(b) AB
(c) O
(d) B
Answer: (c) O

Q4. DNA replication is:
(a) Conservative
(b) Semi-conservative
(c) Dispersive
(d) Random
Answer: (b) Semi-conservative

Q5. The powerhouse of the cell is:
(a) Nucleus
(b) Ribosome
(c) Mitochondria
(d) Golgi body
Answer: (c) Mitochondria

Q6. Which vitamin is produced in the skin in presence of sunlight?
(a) Vitamin A
(b) Vitamin D
(c) Vitamin K
(d) Vitamin C
Answer: (b) Vitamin D

Q7. Crossing over occurs in which stage of meiosis?
(a) Prophase I
(b) Metaphase I
(c) Anaphase II
(d) Telophase
Answer: (a) Prophase I

Q8. Which is the smallest functional unit of nervous system?
(a) Brain
(b) Neuron
(c) Spinal cord
(d) Nerve
Answer: (b) Neuron

Q9. The study of fossils is called:
(a) Ecology
(b) Palaeontology
(c) Taxonomy
(d) Embryology
Answer: (b) Palaeontology

Q10. Which hormone regulates blood sugar level?
(a) Insulin
(b) Thyroxine
(c) Adrenaline
(d) Estrogen
Answer: (a) Insulin

Q11. Which is a double membrane cell organelle?
(a) Lysosome
(b) Ribosome
(c) Chloroplast
(d) Centriole
Answer: (c) Chloroplast

Q12. Haemoglobin is present in:
(a) RBC
(b) WBC
(c) Platelets
(d) Plasma
Answer: (a) RBC

Q13. Tubectomy is a method of:
(a) Male sterilization
(b) Female sterilization
(c) Temporary contraception
(d) Hormonal method
Answer: (b) Female sterilization

Q14. Which is the site of protein synthesis?
(a) Lysosome
(b) Ribosome
(c) Nucleus
(d) Mitochondria
Answer: (b) Ribosome

Q15. Human eye lens is:
(a) Concave
(b) Convex
(c) Plane
(d) Cylindrical
Answer: (b) Convex

Q16. AIDS is caused by:
(a) Virus
(b) Bacteria
(c) Fungi
(d) Protozoa
Answer: (a) Virus

Q17. Green plants are called:
(a) Heterotrophs
(b) Autotrophs
(c) Parasites
(d) Saprophytes
Answer: (b) Autotrophs

Q18. Sickle cell anaemia is due to:
(a) Chromosome mutation
(b) Point mutation
(c) Deletion mutation
(d) Duplication mutation
Answer: (b) Point mutation

Q19. Which tissue transports water in plants?
(a) Phloem
(b) Xylem
(c) Cambium
(d) Cortex
Answer: (b) Xylem

Q20. Which kingdom includes bacteria?
(a) Protista
(b) Plantae
(c) Monera
(d) Fungi
Answer: (c) Monera

Q21. The functional unit of heredity is:
(a) Chromosome
(b) Gene
(c) DNA
(d) RNA
Answer: (b) Gene

Q22. Which blood cells help in clotting?
(a) RBC
(b) Platelets
(c) WBC
(d) Plasma
Answer: (b) Platelets

Q23. Which plant hormone is known as the stress hormone?
(a) Auxin
(b) Cytokinin
(c) ABA
(d) Gibberellin
Answer: (c) ABA

Q24. Who proposed the theory of natural selection?
(a) Lamarck
(b) Darwin
(c) Mendel
(d) Morgan
Answer: (b) Darwin

Q25. Endocrine glands are:
(a) Ductless glands
(b) With ducts
(c) Excretory glands
(d) Mixed glands
Answer: (a) Ductless glands

Q26. Which organ is affected by jaundice?
(a) Heart
(b) Liver
(c) Kidney
(d) Lungs
Answer: (b) Liver

Q27. The study of tissues is called:
(a) Histology
(b) Cytology
(c) Physiology
(d) Pathology

Answer: (a) Histology

Q28. Blood pressure is measured with:
(a) Stethoscope
(b) Spirometer
(c) Sphygmomanometer
(d) Thermometer
Answer: (c) Sphygmomanometer

Q29. Which vitamin is known as Ascorbic acid?
(a) Vitamin A
(b) Vitamin C
(c) Vitamin D
(d) Vitamin K
Answer: (b) Vitamin C

Q30. The largest gland in the human body is:
(a) Pancreas
(b) Liver
(c) Kidney
(d) Stomach
Answer: (b) Liver

Q31. Which part of brain controls balance of body?
(a) Cerebrum
(b) Cerebellum
(c) Medulla
(d) Thalamus
Answer: (b) Cerebellum

Q32. DNA stands for:
(a) Deoxyribose nucleic acid
(b) Deoxyribonucleic acid
(c) Double nucleic acid
(d) None of these
Answer: (b) Deoxyribonucleic acid

Q33. Who discovered the double helix structure of DNA?
(a) Crick and Watson
(b) Lamarck
(c) Mendel
(d) Rosalind
Answer: (a) Crick and Watson

Q34. The SI unit of nervous impulse transmission is:
(a) Volt
(b) Hertz
(c) Millivolt
(d) Newton
Answer: (c) Millivolt

Q35. Photosynthesis occurs in:
(a) Mitochondria
(b) Ribosome
(c) Chloroplast
(d) Nucleus
Answer: (c) Chloroplast

Section B – Short Answer Questions (5 × 2 = 10 Marks)

Q1. Differentiate between mitosis and meiosis.
Answer: Mitosis produces two diploid identical daughter cells, while meiosis produces four haploid non-identical gametes.

Q2. Write two functions of the placenta.
Answer: Provides nutrients to embryo, and removes waste materials.

Q3. What is codominance? Give one example.
Answer: Expression of both alleles in heterozygote. Example: Blood group AB.

Q4. Define transpiration. Name its types.
Answer: Loss of water in vapour form from aerial parts of plants. Types: Stomatal, cuticular, lenticular.

Q5. Write two differences between aerobic and anaerobic respiration.
Answer: Aerobic requires oxygen, produces 38 ATP; Anaerobic occurs without oxygen, produces 2 ATP.

Section C – Long Answer Questions (3 × 5 = 15 Marks)

Q1. Explain Mendel’s Law of Independent Assortment with a dihybrid cross.

Answer:
Mendel’s Law of Independent Assortment states that:
“When two pairs of contrasting traits are considered together, the segregation of one pair of alleles is independent of the segregation of the other pair.”

Dihybrid Cross (Example: Seed Shape and Seed Colour in Pea Plant)

• Traits chosen:

  • Round (R) vs. Wrinkled (r) seeds

  • Yellow (Y) vs. Green (y) seed colour

• Parents: RRYY × rryy

• F₁ Generation: All RrYy (Round Yellow)

• F₂ Generation (Self-cross of RrYy):
  Gametes formed = RY, Ry, rY, ry

Punnett square shows 16 combinations:

• 9 Round Yellow

• 3 Round Green

• 3 Wrinkled Yellow

• 1 Wrinkled Green

Conclusion:

The ratio is 9:3:3:1, proving that seed shape and colour assort independently.

Q2. Describe the structure of human heart with diagram and explain its working.

Answer:

Structure:

• Human heart is a four-chambered muscular organ (~300 g).

• Chambers:

  • Right Atrium (receives deoxygenated blood from vena cava)

  • Right Ventricle (pumps blood to lungs via pulmonary artery)

  • Left Atrium (receives oxygenated blood from lungs via pulmonary veins)

  • Left Ventricle (pumps oxygenated blood to body via aorta)

• Valves present: Tricuspid valve, Bicuspid/Mitral valve, Pulmonary valve, and Aortic valve.

Working (Double Circulation):

1. Pulmonary Circulation:
   Deoxygenated blood from right ventricle → lungs (via pulmonary artery) → becomes oxygenated → returns to left atrium.

2. Systemic Circulation:
   Oxygenated blood from left ventricle → body tissues (via aorta) → delivers O₂ and nutrients → deoxygenated blood returns to right atrium.

Thus, human heart ensures continuous oxygen supply and removal of CO₂ through double circulation.

(Diagram is to be drawn in exam: Labelled heart showing 4 chambers, valves, arteries, veins

Q3. What is photosynthesis? Write light reaction and dark reaction in detail with balanced equation.

Answer:

Definition:

Photosynthesis is the process by which green plants prepare food (glucose) using CO₂, water, and sunlight in the presence of chlorophyll.

Overall Equation:

6CO2+12H2O→Light,ChlorophyllC6H12O6+6O2+6H2O6CO₂ + 12H₂O \xrightarrow{Light, Chlorophyll} C₆H₁₂O₆ + 6O₂ + 6H₂O6CO2​+12H2​OLight,Chlorophyll​C6​H12​O6​+6O2​+6H2​O

(A) Light Reaction (Occurs in thylakoid membranes):

• Absorption of light by chlorophyll → electrons get excited.

• Photolysis of water:

2H2O→4H++4e−+O2↑2H₂O → 4H⁺ + 4e⁻ + O₂↑2H2​O→4H++4e−+O2​↑

• Formation of ATP (Photophosphorylation) and NADPH.

Products: ATP, NADPH, O₂

(B) Dark Reaction (Calvin Cycle, occurs in stroma):

• Does not require light directly.

• CO₂ is fixed with the help of RuBisCO enzyme.

• Uses ATP and NADPH from light reaction.

• Series of steps lead to synthesis of glucose (C₆H₁₂O₆).

Conclusion:

Photosynthesis consists of two phases:

• Light reaction – energy capture and conversion into ATP & NADPH.

• Dark reaction – CO₂ fixation and carbohydrate synthesis.

  Bihar Board Class 12 Biology Guess Paper 2025

  we are Completed Bihar Board Class 12 Biology Guess Paper 2025

  Follow My Insta I’d 

  Bihar Board Class 12 Chemistry Guess Paper 2025 with Answers | BSEB