CBSE Class 12 Biology MCQs for Boards & Competitive Exams

(NCERT-Based | Board + Competitive Exam Oriented | With Detailed 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) causes rupture of the mature Graafian follicle, leading to ovulation.

Q2. Double fertilization is unique to:
A. Gymnosperms
B. Bryophytes
C. Angiosperms
D. Pteridophytes

Answer: C. Angiosperms
Explanation: One male gamete fuses with the egg forming zygote, while the other fuses with polar nuclei forming endosperm.

Q3. The acrosome of sperm contains enzymes required for:
A. Energy production
B. Sperm motility
C. Penetration of ovum
D. Hormone secretion

Answer: C. Penetration of ovum
Explanation: Acrosomal enzymes help digest the zona pellucida during fertilization.

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

Answer: C. Progesterone
Explanation: Progesterone maintains the uterine lining and prevents premature contractions.

Q5. Apomixis results in:
A. Fruit without seeds
B. Seed without fertilization
C. Hybrid seeds only
D. Sterile plants

Answer: B. Seed without fertilization
Explanation: Apomixis is a form of asexual reproduction through seeds.

Q6. The site of fertilization in humans is:
A. Ovary
B. Uterus
C. Cervix
D. Fallopian tube

Answer: D. Fallopian tube
Explanation: Fertilization usually occurs in the ampullary region of the oviduct.

Q7. Menarche refers to:
A. First ovulation
B. First menstruation
C. Menopause
D. Ovulatory cycle

Answer: B. First menstruation
Explanation: Menarche marks the beginning of reproductive life in females.

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

Answer: C. Endosperm
Explanation: Coconut water and kernel are both forms of endosperm.

Q9. Which contraceptive method also protects against STDs?
A. IUD
B. Oral pills
C. Condom
D. Vasectomy

Answer: C. Condom
Explanation: Condoms act as barrier methods preventing infections.

Q10. Placenta functions as:
A. Respiratory organ
B. Endocrine organ
C. Excretory organ
D. All of the above

Answer: D. All of the above
Explanation: Placenta exchanges gases, nutrients, wastes and secretes hormones.

Section B: Genetics and Evolution (10 MCQs)

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

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

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

Answer: C. Hemophilia
Explanation: It mainly affects males due to inheritance 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 during 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. The unit of evolution is:
A. Individual
B. Species
C. Population
D. Ecosystem

Answer: C. Population
Explanation: Evolution involves changes in allele frequencies within populations.

Q16. Homologous organs indicate:
A. Convergent evolution
B. Parallel evolution
C. Divergent evolution
D. Co-evolution

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

Q17. Crossing over occurs during:
A. Leptotene
B. Zygotene
C. Pachytene
D. Diplotene

Answer: C. Pachytene
Explanation: Exchange of genetic material occurs between homologous chromosomes.

Q18. Genetic drift is most effective in:
A. Large populations
B. Stable populations
C. Small populations
D. Migrating populations

Answer: C. Small populations
Explanation: Random allele frequency changes are significant in small populations.

Q19. RNA polymerase is required for:
A. Replication
B. Translation
C. Transcription
D. Mutation

Answer: C. Transcription
Explanation: RNA polymerase synthesizes RNA using DNA as template.

Q20. Darwin’s finches are an example of:
A. Convergent evolution
B. Genetic drift
C. Adaptive radiation
D. Parallel evolution

Answer: C. Adaptive radiation
Explanation: Different species evolved from a common ancestor to occupy different niches.

Section C: Biology in Human Welfare (10 MCQs)

Q21. Curd formation is due to:
A. Yeast
B. Lactobacillus
C. Rhizobium
D. Penicillium

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

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

Answer: C. Protozoan
Explanation: Plasmodium species cause malaria.

Q23. Antibiotics are ineffective against:
A. Bacteria
B. Protozoa
C. Viruses
D. Fungi

Answer: C. Viruses
Explanation: Viruses lack metabolic pathways targeted by antibiotics.

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

Answer: B. Proteins
Explanation: Single Cell Protein provides high-quality protein.

Q25. AIDS is caused by:
A. Bacterium
B. Fungus
C. Virus
D. Protozoan

Answer: C. Virus
Explanation: HIV attacks immune cells.

Q26. Biogas mainly contains:
A. CO₂
B. Methane
C. Nitrogen
D. Oxygen

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

Q27. Which organism acts as a biofertilizer?
A. Yeast
B. Azotobacter
C. Virus
D. Lactobacillus

Answer: B. Azotobacter
Explanation: It fixes atmospheric nitrogen in soil.

Q28. Penicillin is produced by:
A. Bacteria
B. Virus
C. Algae
D. Fungus

Answer: D. Fungus
Explanation: Produced by Penicillium species.

Q29. Sewage treatment plants mainly depend on:
A. Algae
B. Protozoa
C. Bacteria
D. Fungi

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

Q30. Rabies is transmitted through:
A. Water
B. Air
C. Animal bite
D. Food

Answer: C. Animal bite
Explanation: Virus spreads via saliva of infected animals.

Section D: Biotechnology (10 MCQs)

Q31. Restriction enzymes are known as:
A. Molecular glue
B. Molecular scissors
C. Vectors
D. Markers

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

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

Answer: A. DNA amplification
Explanation: PCR produces millions of copies of DNA.

Q33. Heat-stable enzyme used in PCR is:
A. DNA ligase
B. Taq polymerase
C. RNA polymerase
D. Primase

Answer: B. Taq polymerase
Explanation: It remains active at high temperatures.

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

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

Q35. A commonly used cloning vector is:
A. Ribosome
B. Chromosome
C. Plasmid
D. mRNA

Answer: C. Plasmid
Explanation: Plasmids replicate independently in host cells.

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

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

Q37. Recombinant insulin is produced using:
A. Yeast
B. Virus
C. E. coli
D. Algae

Answer: C. E. coli
Explanation: Genetically engineered bacteria synthesize insulin.

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

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

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

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

Q40. Selectable marker genes help in:
A. DNA cutting
B. Identifying recombinants
C. Replication
D. Transcription

Answer: B. Identifying recombinants
Explanation: They distinguish transformed cells.

Section E: Ecology and Environment (10 MCQs)

Q41. The ultimate source of energy in an ecosystem is:
A. Producers
B. Consumers
C. Decomposers
D. Sun

Answer: D. Sun
Explanation: Solar energy drives ecosystem processes.

Q42. Pyramid of energy is always:
A. Inverted
B. Upright
C. Spindle-shaped
D. Irregular

Answer: B. Upright
Explanation: Energy decreases at each trophic level.

Q43. Which biogeochemical cycle has no gaseous phase?
A. Carbon
B. Nitrogen
C. Water
D. Phosphorus

Answer: D. Phosphorus
Explanation: Phosphorus circulates through rocks and soil.

Q44. Lichens are indicators of:
A. Water pollution
B. Soil fertility
C. Air pollution
D. Radiation

Answer: C. Air pollution
Explanation: Lichens are sensitive to sulfur dioxide.

Q45. 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.

Q46. Biological magnification refers to:
A. Energy loss
B. Population increase
C. Accumulation of toxins
D. Nutrient cycling

Answer: C. Accumulation of toxins
Explanation: Toxins increase in concentration at higher trophic levels.

Q47. Eutrophication occurs due to excess:
A. Oxygen
B. Nutrients
C. Heat
D. Salts

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

Q48. In-situ conservation includes:
A. Zoo
B. Seed bank
C. Botanical garden
D. National park

Answer: D. National park
Explanation: Conservation within natural habitat.

Q49. Ex-situ conservation includes:
A. Wildlife sanctuary
B. Biosphere reserve
C. National park
D. Zoological park

Answer: D. Zoological park
Explanation: Conservation outside natural habitat.

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

Answer: D. Tansley
Explanation: A.G. Tansley introduced the ecosystem concept.

✅ These NCERT-aligned MCQs are ideal for CBSE Class 12 board exams as well as competitive exams like NEET.