Practice MCQs for CBSE Class 12 Biology Board Exams

(NCERT-Based | Exam-Focused | With Detailed Answers & Explanations)

Section A: Reproduction (10 MCQs)

Q1. The hormone responsible for ovulation in human females is:
A. FSH
B. Estrogen
C. LH
D. Progesterone

Answer: C. LH
Explanation: A sudden surge of Luteinizing Hormone (LH) triggers ovulation by causing rupture of the Graafian follicle.

Q2. Which part of the sperm provides energy for motility?
A. Head
B. Acrosome
C. Neck
D. Middle piece

Answer: D. Middle piece
Explanation: The middle piece contains mitochondria that generate ATP required for sperm movement.

Q3. Double fertilization is unique to:
A. Gymnosperms
B. Bryophytes
C. Pteridophytes
D. Angiosperms

Answer: D. Angiosperms
Explanation: One male gamete fuses with egg and the other with polar nuclei forming endosperm.

Q4. Which hormone maintains pregnancy in humans?
A. Oxytocin
B. Estrogen
C. Progesterone
D. Prolactin

Answer: C. Progesterone
Explanation: Progesterone maintains uterine endometrium for implantation and pregnancy.

Q5. Apomixis leads to formation of:
A. Fruits without seeds
B. Seeds without fertilization
C. Hybrid seeds
D. Sterile plants

Answer: B. Seeds without fertilization
Explanation: Apomixis is a form of asexual reproduction via seeds.

Q6. The placenta acts as:
A. Digestive organ
B. Respiratory organ
C. Endocrine organ
D. All of the above

Answer: D. All of the above
Explanation: Placenta helps in nutrition, gas exchange, waste removal and hormone secretion.

Q7. Which contraceptive method is hormone-based?
A. Condom
B. IUD
C. Oral pills
D. Vasectomy

Answer: C. Oral pills
Explanation: Oral contraceptives contain estrogen and progesterone.

Q8. The edible part of wheat grain is:
A. Embryo
B. Endosperm
C. Pericarp
D. Cotyledon

Answer: B. Endosperm
Explanation: Endosperm stores food in cereal grains.

Q9. Menstrual cycle normally lasts for:
A. 14 days
B. 21 days
C. 28 days
D. 35 days

Answer: C. 28 days
Explanation: Average menstrual cycle duration is 28 days.

Q10. Which method prevents ovulation?
A. Copper-T
B. Condom
C. Oral pills
D. Diaphragm

Answer: C. Oral pills
Explanation: Oral pills suppress ovulation hormonally.

Section B: Genetics and Evolution (10 MCQs)

Q11. Mendel’s Law of Independent Assortment is based on:
A. Monohybrid cross
B. Dihybrid cross
C. Back cross
D. Test cross

Answer: B. Dihybrid cross
Explanation: It explains independent segregation of two gene pairs.

Q12. Which genetic disorder is X-linked recessive?
A. Down syndrome
B. Sickle cell anemia
C. Hemophilia
D. Thalassemia

Answer: C. Hemophilia
Explanation: Hemophilia is inherited through X chromosome.

Q13. DNA replication takes place during:
A. G₁ phase
B. S phase
C. G₂ phase
D. M phase

Answer: B. S phase
Explanation: DNA synthesis occurs in S-phase of interphase.

Q14. The start codon for protein synthesis is:
A. UAA
B. UAG
C. AUG
D. UGA

Answer: C. AUG
Explanation: AUG codes for methionine and initiates translation.

Q15. Adaptive radiation is best seen in:
A. Darwin’s finches
B. Bacteria
C. Reptiles
D. Humans

Answer: A. Darwin’s finches
Explanation: Finches evolved into multiple species from a common ancestor.

Q16. The enzyme responsible for transcription is:
A. DNA polymerase
B. RNA polymerase
C. Ligase
D. Helicase

Answer: B. RNA polymerase
Explanation: RNA polymerase synthesizes RNA from DNA template.

Q17. Which mutation changes amino acid sequence?
A. Silent mutation
B. Missense mutation
C. Nonsense mutation
D. Neutral mutation

Answer: B. Missense mutation
Explanation: Missense mutation replaces one amino acid with another.

Q18. Genetic drift is also known as:
A. Founder effect
B. Bottle-neck effect
C. Random sampling effect
D. All of the above

Answer: D. All of the above
Explanation: Genetic drift involves random changes in allele frequency.

Q19. The unit of heredity is:
A. Chromosome
B. Gene
C. DNA
D. Allele

Answer: B. Gene
Explanation: Gene is the basic unit of inheritance.

Q20. Homologous organs support:
A. Convergent evolution
B. Divergent evolution
C. Parallel evolution
D. Co-evolution

Answer: B. Divergent evolution
Explanation: Same origin but different functions indicate divergence.

Section C: Biology in Human Welfare (10 MCQs)

Q21. Which microorganism is used in curd formation?
A. Yeast
B. Lactobacillus
C. Penicillium
D. Rhizobium

Answer: B. Lactobacillus
Explanation: It converts lactose into lactic acid.

Q22. Malaria is caused by:
A. Virus
B. Bacteria
C. Protozoan
D. Fungus

Answer: C. Protozoan
Explanation: Plasmodium is a protozoan parasite.

Q23. Which antibiotic is effective against gram-positive bacteria?
A. Penicillin
B. Streptomycin
C. Chloramphenicol
D. Tetracycline

Answer: A. Penicillin
Explanation: Penicillin inhibits cell wall synthesis.

Q24. SCP is rich in:
A. Carbohydrates
B. Proteins
C. Lipids
D. Vitamins

Answer: B. Proteins
Explanation: Single Cell Protein is a protein-rich food source.

Q25. Which disease is sexually transmitted?
A. Typhoid
B. AIDS
C. Malaria
D. Dengue

Answer: B. AIDS
Explanation: AIDS spreads through sexual contact and blood.

Q26. Biogas mainly consists of:
A. CO₂
B. Methane
C. Hydrogen
D. Nitrogen

Answer: B. Methane
Explanation: Methane is the main fuel component.

Q27. Which biofertilizer fixes nitrogen?
A. Lactobacillus
B. Azotobacter
C. Penicillium
D. Yeast

Answer: B. Azotobacter
Explanation: Azotobacter fixes atmospheric nitrogen.

Q28. Antibiotics are ineffective against:
A. Bacteria
B. Protozoa
C. Viruses
D. Fungi

Answer: C. Viruses
Explanation: Viruses lack metabolic machinery.

Q29. Which organism is used in sewage treatment?
A. Algae
B. Bacteria
C. Virus
D. Protozoa

Answer: B. Bacteria
Explanation: Bacteria decompose organic waste.

Q30. Rabies is caused by:
A. Bacteria
B. Fungus
C. Virus
D. Protozoa

Answer: C. Virus
Explanation: Rabies virus infects nervous system.

Section D: Biotechnology (10 MCQs)

Q31. Restriction enzymes are also called:
A. Molecular scissors
B. Molecular glue
C. Vectors
D. Markers

Answer: A. Molecular scissors
Explanation: They cut DNA at specific sites.

Q32. PCR technique is used for:
A. DNA sequencing
B. DNA amplification
C. Gene silencing
D. Protein synthesis

Answer: B. DNA amplification
Explanation: PCR makes multiple copies of DNA.

Q33. Which enzyme joins DNA fragments?
A. Ligase
B. Helicase
C. Polymerase
D. Primase

Answer: A. Ligase
Explanation: DNA ligase forms phosphodiester bonds.

Q34. Bt cotton is resistant to:
A. Fungi
B. Viruses
C. Insects
D. Weeds

Answer: C. Insects
Explanation: Bt toxin kills insect larvae.

Q35. Which vector is commonly used in cloning?
A. Virus
B. Plasmid
C. Chromosome
D. Ribosome

Answer: B. Plasmid
Explanation: Plasmids replicate independently.

Q36. ELISA is based on:
A. DNA hybridization
B. Antigen–antibody reaction
C. Protein synthesis
D. RNA transcription

Answer: B. Antigen–antibody reaction
Explanation: Used for disease diagnosis.

Q37. Which organism produces human insulin?
A. Yeast
B. Virus
C. E. coli
D. Algae

Answer: C. E. coli
Explanation: Recombinant bacteria produce insulin.

Q38. RNA interference is used to:
A. Clone genes
B. Silence genes
C. Amplify DNA
D. Mutate DNA

Answer: B. Silence genes
Explanation: RNAi blocks mRNA translation.

Q39. A bioreactor provides:
A. Genetic material
B. Sterile conditions only
C. Optimal growth conditions
D. Antibiotics

Answer: C. Optimal growth conditions
Explanation: Controls pH, temperature, oxygen.

Q40. Selectable marker helps in:
A. DNA cutting
B. Identifying recombinants
C. Protein synthesis
D. Transcription

Answer: B. Identifying recombinants
Explanation: Marker genes identify transformed cells.

Section E: Ecology and Environment (10 MCQs)

Q41. Pyramid of energy is always:
A. Inverted
B. Upright
C. Spindle-shaped
D. Irregular

Answer: B. Upright
Explanation: Energy decreases at higher trophic levels.

Q42. The major cause of biodiversity loss is:
A. Pollution
B. Climate change
C. Habitat loss
D. Overpopulation

Answer: C. Habitat loss
Explanation: Destruction of natural habitats leads to extinction.

Q43. Primary producers are:
A. Carnivores
B. Herbivores
C. Decomposers
D. Autotrophs

Answer: D. Autotrophs
Explanation: They synthesize food.

Q44. Ozone depletion is caused by:
A. CO₂
B. SO₂
C. CFCs
D. NO₂

Answer: C. CFCs
Explanation: Chlorine radicals destroy ozone.

Q45. Which cycle lacks gaseous phase?
A. Carbon
B. Nitrogen
C. Water
D. Phosphorus

Answer: D. Phosphorus
Explanation: Phosphorus cycle has no gaseous phase.

Q46. Lichens indicate:
A. Water pollution
B. Air pollution
C. Soil fertility
D. Radiation

Answer: B. Air pollution
Explanation: Lichens are sensitive to SO₂.

Q47. Eutrophication is caused by excess:
A. Oxygen
B. Nutrients
C. Pesticides
D. Salts

Answer: B. Nutrients
Explanation: Excess nitrates and phosphates cause algal bloom.

Q48. Biological magnification refers to:
A. Energy loss
B. Population increase
C. Toxin accumulation
D. Nutrient recycling

Answer: C. Toxin accumulation
Explanation: Toxins increase at higher trophic levels.

Q49. In-situ conservation includes:
A. Zoo
B. Seed bank
C. National park
D. Botanical garden

Answer: C. National park
Explanation: Species conserved in natural habitat.

Q50. The term ecosystem was given by:
A. Odum
B. Darwin
C. Tansley
D. Clements

Answer: C. Tansley
Explanation: A.G. Tansley coined the term ecosystem.

✅ This NCERT-aligned practice MCQ set is ideal for CBSE Class 12 Biology board exam revision and self-assessment.