Most Important MCQs for CBSE Class 12 Biology

(NCERT-Based | Exam-Focused | High-Weightage Questions with Detailed Explanations)

Section A: Reproduction (10 MCQs)

Q1. The hormone that triggers 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 a characteristic feature of:
A. Gymnosperms
B. Bryophytes
C. Angiosperms
D. Algae

Answer: C. Angiosperms
Explanation: In angiosperms, one male gamete fuses with the egg (syngamy) and the other with polar nuclei (triple fusion).

Q3. Which part of sperm contains mitochondria for energy?
A. Head
B. Acrosome
C. Neck
D. Middle piece

Answer: D. Middle piece
Explanation: The middle piece has a mitochondrial sheath supplying ATP for sperm motility.

Q4. The edible part of coconut is:
A. Embryo
B. Cotyledon
C. Endosperm
D. Pericarp

Answer: C. Endosperm
Explanation: Coconut water (liquid) and kernel (solid) both represent endosperm tissue.

Q5. Which hormone maintains pregnancy in humans?
A. Oxytocin
B. Estrogen
C. Progesterone
D. Prolactin

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

Q6. Apomixis results in:
A. Fruit without seeds
B. Seed without fertilization
C. Sterile hybrids
D. Polyembryony only

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

Q7. 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.

Q8. 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.

Q9. Which contraceptive method also prevents STDs?
A. Oral pills
B. Copper-T
C. Condom
D. Vasectomy

Answer: C. Condom
Explanation: Condoms act as barrier methods, preventing sperm entry and 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, removes wastes, supplies nutrients, and secretes hormones.

Section B: Genetics and Evolution (10 MCQs)

Q11. Mendel’s Law of Independent Assortment is derived from:
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 X-linked recessive?
A. Down syndrome
B. Sickle cell anemia
C. Hemophilia
D. Thalassemia

Answer: C. Hemophilia
Explanation: Hemophilia is inherited through the X chromosome and affects males more.

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

Answer: B. S phase
Explanation: DNA synthesis takes place during the 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. Community

Answer: C. Population
Explanation: Evolution involves changes in allele frequency within a population.

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

Answer: C. Divergent evolution
Explanation: Homologous organs have same origin but different functions.

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

Answer: C. Pachytene
Explanation: Genetic material is exchanged between homologous chromosomes.

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

Answer: B. Small populations
Explanation: Random changes affect small populations more intensely.

Q19. RNA polymerase is involved in:
A. Replication
B. Translation
C. Transcription
D. Mutation

Answer: C. Transcription
Explanation: RNA polymerase synthesizes RNA from DNA 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: Multiple species evolved from a common ancestor to occupy different niches.

Section C: Biology in Human Welfare (10 MCQs)

Q21. Curd formation involves the action of:
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. Bacteria
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. Minerals

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 the immune system.

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

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

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

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: Penicillium species produce penicillin.

Q29. Sewage treatment primarily uses:
A. Algae
B. Fungi
C. Bacteria
D. Protozoa

Answer: C. Bacteria
Explanation: Bacteria decompose organic matter in sewage.

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 also known as:
A. Molecular scissors
B. Molecular glue
C. Vectors
D. Markers

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

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

Answer: B. DNA amplification
Explanation: PCR makes millions of copies of a DNA segment.

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

Answer: B. Taq polymerase
Explanation: It withstands high temperatures during denaturation.

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 inside host cells.

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

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

Q37. Recombinant human 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 prevents expression of target genes.

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

Answer: C. Optimal growth conditions
Explanation: Controls temperature, pH, 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 main source of energy in an ecosystem is:
A. Producers
B. Consumers
C. Decomposers
D. Sun

Answer: D. Sun
Explanation: Solar energy drives all ecological processes.

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

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

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

Answer: C. Habitat loss
Explanation: Destruction of habitats leads to species 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: Species are conserved in their 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 concept of ecosystem.

✅ These most important, NCERT-aligned MCQs cover high-weightage concepts and are ideal for last-minute CBSE Class 12 Biology board exam revision.